A Landlock object enables to identify a kernel object (e.g. an inode). A Landlock rule is a set of access rights allowed on an object. Rules are grouped in rulesets that may be tied to a set of processes (i.e. subjects) to enforce a scoped access-control (i.e. a domain).

Because Landlock's goal is to empower any process (especially unprivileged ones) to sandbox themselves, we can't rely on a system-wide object identification such as file extended attributes. Indeed, we need innocuous, composable and modular access-controls.

The main challenge with these constraints is to identify kernel objects while this identification is useful (i.e. when a security policy makes use of this object). But this identification data should be freed once no policy is using it. This ephemeral tagging should not and may not be written in the filesystem. We then need to manage the lifetime of a rule according to the lifetime of its object. To avoid a global lock, this implementation make use of RCU and counters to safely reference objects.

A following commit uses this generic object management for inodes.

Signed-off-by: Mickaël Salaün mic@digikod.net Cc: Andy Lutomirski luto@amacapital.net Cc: James Morris jmorris@namei.org Cc: Kees Cook keescook@chromium.org Cc: Serge E. Hallyn serge@hallyn.com ---

Changes since v14: * Simplify the object, rule and ruleset management at the expense of a less aggressive memory freeing (contributed by Jann Horn, with additional modifications): - Remove object->list aggregating the rules tied to an object. - Remove landlock_get_object(), landlock_drop_object(), {get,put}_object_cleaner() and landlock_rule_is_disabled(). - Rewrite landlock_put_object() to use a more simple mechanism (no tricky RCU). - Replace enum landlock_object_type and landlock_release_object() with landlock_object_underops->release() - Adjust unions and Sparse annotations. Cf. https://lore.kernel.org/lkml/CAG48ez21bEn0wL1bbmTiiu8j9jP5iEWtHOwz4tURUJ+ki0... * Merge struct landlock_rule into landlock_ruleset_elem to simplify the rule management. * Constify variables. * Improve kernel documentation. * Cosmetic variable renames. * Remove the "default" in the Kconfig (suggested by Jann Horn). * Only use refcount_inc() through getter helpers. * Update Kconfig description.

Changes since v13: * New dedicated implementation, removing the need for eBPF.

Previous version: https://lore.kernel.org/lkml/20190721213116.23476-6-mic@digikod.net/ --- MAINTAINERS | 10 +++++ security/Kconfig | 1 + security/Makefile | 2 + security/landlock/Kconfig | 18 ++++++++ security/landlock/Makefile | 3 ++ security/landlock/object.c | 66 +++++++++++++++++++++++++++ security/landlock/object.h | 92 ++++++++++++++++++++++++++++++++++++++ 7 files changed, 192 insertions(+) create mode 100644 security/landlock/Kconfig create mode 100644 security/landlock/Makefile create mode 100644 security/landlock/object.c create mode 100644 security/landlock/object.h

diff --git a/MAINTAINERS b/MAINTAINERS index cc1d18cb5d18..440750cf4fbc 100644 --- a/MAINTAINERS +++ b/MAINTAINERS @@ -9358,6 +9358,16 @@ F: net/core/skmsg.c F: net/core/sock_map.c F: net/ipv4/tcp_bpf.c

+LANDLOCK SECURITY MODULE +M: Mickaël Salaün mic@digikod.net +L: linux-security-module@vger.kernel.org +W: https://landlock.io +T: git https://github.com/landlock-lsm/linux.git +S: Supported +F: security/landlock/ +K: landlock +K: LANDLOCK + LANTIQ / INTEL Ethernet drivers M: Hauke Mehrtens hauke@hauke-m.de L: netdev@vger.kernel.org diff --git a/security/Kconfig b/security/Kconfig index 2a1a2d396228..9d9981394fb0 100644 --- a/security/Kconfig +++ b/security/Kconfig @@ -238,6 +238,7 @@ source "security/loadpin/Kconfig" source "security/yama/Kconfig" source "security/safesetid/Kconfig" source "security/lockdown/Kconfig" +source "security/landlock/Kconfig"

source "security/integrity/Kconfig"

diff --git a/security/Makefile b/security/Makefile index 746438499029..2472ef96d40a 100644 --- a/security/Makefile +++ b/security/Makefile @@ -12,6 +12,7 @@ subdir-$(CONFIG_SECURITY_YAMA) += yama subdir-$(CONFIG_SECURITY_LOADPIN) += loadpin subdir-$(CONFIG_SECURITY_SAFESETID) += safesetid subdir-$(CONFIG_SECURITY_LOCKDOWN_LSM) += lockdown +subdir-$(CONFIG_SECURITY_LANDLOCK) += landlock

# always enable default capabilities obj-y += commoncap.o @@ -29,6 +30,7 @@ obj-$(CONFIG_SECURITY_YAMA) += yama/ obj-$(CONFIG_SECURITY_LOADPIN) += loadpin/ obj-$(CONFIG_SECURITY_SAFESETID) += safesetid/ obj-$(CONFIG_SECURITY_LOCKDOWN_LSM) += lockdown/ +obj-$(CONFIG_SECURITY_LANDLOCK) += landlock/ obj-$(CONFIG_CGROUP_DEVICE) += device_cgroup.o

# Object integrity file lists diff --git a/security/landlock/Kconfig b/security/landlock/Kconfig new file mode 100644 index 000000000000..9ec7593a534a --- /dev/null +++ b/security/landlock/Kconfig @@ -0,0 +1,18 @@ +# SPDX-License-Identifier: GPL-2.0-only + +config SECURITY_LANDLOCK + bool "Landlock support" + depends on SECURITY + select SECURITY_PATH + help + Landlock is a safe sandboxing mechanism which enables processes to + restrict themselves (and their future children) by gradually + enforcing tailored access control policies. A security policy is a + set of access rights (e.g. open a file in read-only, make a + directory) tied to a file hierarchy. The configuration can be set by + any processes, including unprivileged ones, thanks to the landlock() + system call. + + See Documentation/security/landlock/ for further information. + + If you are unsure how to answer this question, answer N. diff --git a/security/landlock/Makefile b/security/landlock/Makefile new file mode 100644 index 000000000000..cb6deefbf4c0 --- /dev/null +++ b/security/landlock/Makefile @@ -0,0 +1,3 @@ +obj-$(CONFIG_SECURITY_LANDLOCK) := landlock.o + +landlock-y := object.o diff --git a/security/landlock/object.c b/security/landlock/object.c new file mode 100644 index 000000000000..27da1ed45eaf --- /dev/null +++ b/security/landlock/object.c @@ -0,0 +1,66 @@ +// SPDX-License-Identifier: GPL-2.0-only +/* + * Landlock LSM - Object management + * + * Copyright © 2016-2020 Mickaël Salaün mic@digikod.net + * Copyright © 2018-2020 ANSSI + */ + +#include <linux/bug.h> +#include <linux/compiler_types.h> +#include <linux/kernel.h> +#include <linux/rcupdate.h> +#include <linux/refcount.h> +#include <linux/slab.h> +#include <linux/spinlock.h> + +#include "object.h" + +struct landlock_object *landlock_create_object( + const struct landlock_object_underops *underops, + void *const underobj) +{ + struct landlock_object *new_object; + + if (WARN_ON_ONCE(!underops || !underobj)) + return NULL; + new_object = kzalloc(sizeof(*new_object), GFP_KERNEL); + if (!new_object) + return NULL; + refcount_set(&new_object->usage, 1); + spin_lock_init(&new_object->lock); + new_object->underops = underops; + new_object->underobj = underobj; + return new_object; +} + +/* + * The caller must own the object (i.e. thanks to object->usage) to safely put + * it. + */ +void landlock_put_object(struct landlock_object *const object) +{ + /* + * The call to @object->underops->release(object) might sleep e.g., + * because of iput(). + */ + might_sleep(); + if (!object) + return; + + /* + * If the @object's refcount can't drop to zero, we can just decrement + * the refcount without holding a lock. Otherwise, the decrement must + * happen under @object->lock for synchronization with things like + * get_inode_object(). + */ + if (refcount_dec_and_lock(&object->usage, &object->lock)) { + __acquire(&object->lock); + /* + * With @object->lock initially held, remove the reference from + * @object->underobj to @object (if it still exists). + */ + object->underops->release(object); + kfree_rcu(object, rcu_free); + } +} diff --git a/security/landlock/object.h b/security/landlock/object.h new file mode 100644 index 000000000000..e61ce44c6a26 --- /dev/null +++ b/security/landlock/object.h @@ -0,0 +1,92 @@ +/* SPDX-License-Identifier: GPL-2.0-only */ +/* + * Landlock LSM - Object management + * + * Copyright © 2016-2020 Mickaël Salaün mic@digikod.net + * Copyright © 2018-2020 ANSSI + */ + +#ifndef _SECURITY_LANDLOCK_OBJECT_H +#define _SECURITY_LANDLOCK_OBJECT_H + +#include <linux/compiler_types.h> +#include <linux/refcount.h> +#include <linux/spinlock.h> + +struct landlock_object; + +/** + * struct landlock_object_underops - Operations on an underlying object + */ +struct landlock_object_underops { + /** + * @release: Releases the underlying object (e.g. iput() for an inode). + */ + void (*release)(struct landlock_object *const object) + __releases(object->lock); +}; + +/** + * struct landlock_object - Security blob tied to a kernel object + * + * The goal of this structure is to enable to tie a set of ephemeral access + * rights (pertaining to different domains) to a kernel object (e.g an inode) + * in a safe way. This imply to handle concurrent use and modification. + * + * The lifetime of a &struct landlock_object depends of the rules referring to + * it. + */ +struct landlock_object { + /** + * @usage: This counter is used to tie an object to the rules matching + * it or to keep it alive while adding a new rule. If this counter + * reaches zero, this struct must not be modified, but this counter can + * still be read from within an RCU read-side critical section. When + * adding a new rule to an object with a usage counter of zero, we must + * wait until the pointer to this object is set to NULL (or recycled). + */ + refcount_t usage; + /** + * @lock: Guards against concurrent modifications. This lock must be + * from the time @usage drops to zero until any weak references from + * @underobj to this object have been cleaned up. + * + * Lock ordering: + * - inode->i_lock nests inside this. + */ + spinlock_t lock; + /** + * @underobj: Used when cleaning up an object and to mark an object as + * tied to its underlying kernel structure. This pointer is protected + * by @lock. Cf. landlock_release_inodes() and release_inode(). + */ + void *underobj; + union { + /** + * @rcu_free: Enables lockless use of @usage, @lock and + * @underobj from within an RCU read-side critical section. + * @rcu_free and @underops are only used by + * landlock_put_object(). + */ + struct rcu_head rcu_free; + /** + * @underops: Enables landlock_put_object() to release the + * underlying object (e.g. inode). + */ + const struct landlock_object_underops *underops; + }; +}; + +struct landlock_object *landlock_create_object( + const struct landlock_object_underops *const underops, + void *const underojb); + +void landlock_put_object(struct landlock_object *const object); + +static inline void landlock_get_object(struct landlock_object *const object) +{ + if (object) + refcount_inc(&object->usage); +} + +#endif /* _SECURITY_LANDLOCK_OBJECT_H */

A process credentials point to a Landlock domain, which is underneath implemented with a ruleset. In the following commits, this domain is used to check and enforce the ptrace and filesystem security policies. A domain is inherited from a parent to its child the same way a thread inherits a seccomp policy.

Signed-off-by: Mickaël Salaün mic@digikod.net Cc: Andy Lutomirski luto@amacapital.net Cc: James Morris jmorris@namei.org Cc: Kees Cook keescook@chromium.org Cc: Serge E. Hallyn serge@hallyn.com ---

Changes since v14: * Uses pr_fmt from common.h . * Constify variables. * Remove useless NULL initialization.

Changes since v13: * totally get ride of the seccomp dependency * only keep credential management and LSM setup.

Previous version: https://lore.kernel.org/lkml/20191104172146.30797-4-mic@digikod.net/ --- security/Kconfig | 10 +++---- security/landlock/Makefile | 3 ++- security/landlock/common.h | 20 ++++++++++++++ security/landlock/cred.c | 46 +++++++++++++++++++++++++++++++ security/landlock/cred.h | 55 ++++++++++++++++++++++++++++++++++++++ security/landlock/setup.c | 31 +++++++++++++++++++++ security/landlock/setup.h | 16 +++++++++++ 7 files changed, 175 insertions(+), 6 deletions(-) create mode 100644 security/landlock/common.h create mode 100644 security/landlock/cred.c create mode 100644 security/landlock/cred.h create mode 100644 security/landlock/setup.c create mode 100644 security/landlock/setup.h

diff --git a/security/Kconfig b/security/Kconfig index 9d9981394fb0..76547b5c694d 100644 --- a/security/Kconfig +++ b/security/Kconfig @@ -278,11 +278,11 @@ endchoice

config LSM string "Ordered list of enabled LSMs" - default "lockdown,yama,loadpin,safesetid,integrity,smack,selinux,tomoyo,apparmor" if DEFAULT_SECURITY_SMACK - default "lockdown,yama,loadpin,safesetid,integrity,apparmor,selinux,smack,tomoyo" if DEFAULT_SECURITY_APPARMOR - default "lockdown,yama,loadpin,safesetid,integrity,tomoyo" if DEFAULT_SECURITY_TOMOYO - default "lockdown,yama,loadpin,safesetid,integrity" if DEFAULT_SECURITY_DAC - default "lockdown,yama,loadpin,safesetid,integrity,selinux,smack,tomoyo,apparmor" + default "landlock,lockdown,yama,loadpin,safesetid,integrity,smack,selinux,tomoyo,apparmor" if DEFAULT_SECURITY_SMACK + default "landlock,lockdown,yama,loadpin,safesetid,integrity,apparmor,selinux,smack,tomoyo" if DEFAULT_SECURITY_APPARMOR + default "landlock,lockdown,yama,loadpin,safesetid,integrity,tomoyo" if DEFAULT_SECURITY_TOMOYO + default "landlock,lockdown,yama,loadpin,safesetid,integrity" if DEFAULT_SECURITY_DAC + default "landlock,lockdown,yama,loadpin,safesetid,integrity,selinux,smack,tomoyo,apparmor" help A comma-separated list of LSMs, in initialization order. Any LSMs left off this list will be ignored. This can be diff --git a/security/landlock/Makefile b/security/landlock/Makefile index d846eba445bb..041ea242e627 100644 --- a/security/landlock/Makefile +++ b/security/landlock/Makefile @@ -1,3 +1,4 @@ obj-$(CONFIG_SECURITY_LANDLOCK) := landlock.o

-landlock-y := object.o ruleset.o +landlock-y := setup.o object.o ruleset.o \ + cred.o diff --git a/security/landlock/common.h b/security/landlock/common.h new file mode 100644 index 000000000000..5dc0fe15707d --- /dev/null +++ b/security/landlock/common.h @@ -0,0 +1,20 @@ +/* SPDX-License-Identifier: GPL-2.0-only */ +/* + * Landlock LSM - Common constants and helpers + * + * Copyright © 2016-2020 Mickaël Salaün mic@digikod.net + * Copyright © 2018-2020 ANSSI + */ + +#ifndef _SECURITY_LANDLOCK_COMMON_H +#define _SECURITY_LANDLOCK_COMMON_H + +#define LANDLOCK_NAME "landlock" + +#ifdef pr_fmt +#undef pr_fmt +#endif + +#define pr_fmt(fmt) LANDLOCK_NAME ": " fmt + +#endif /* _SECURITY_LANDLOCK_COMMON_H */ diff --git a/security/landlock/cred.c b/security/landlock/cred.c new file mode 100644 index 000000000000..84ecc78da800 --- /dev/null +++ b/security/landlock/cred.c @@ -0,0 +1,46 @@ +// SPDX-License-Identifier: GPL-2.0-only +/* + * Landlock LSM - Credential hooks + * + * Copyright © 2017-2019 Mickaël Salaün mic@digikod.net + * Copyright © 2018-2019 ANSSI + */ + +#include <linux/cred.h> +#include <linux/lsm_hooks.h> + +#include "common.h" +#include "cred.h" +#include "ruleset.h" +#include "setup.h" + +static int hook_cred_prepare(struct cred *const new, + const struct cred *const old, const gfp_t gfp) +{ + const struct landlock_cred_security *cred_old = landlock_cred(old); + struct landlock_cred_security *cred_new = landlock_cred(new); + struct landlock_ruleset *dom_old; + + dom_old = cred_old->domain; + if (dom_old) { + landlock_get_ruleset(dom_old); + cred_new->domain = dom_old; + } + return 0; +} + +static void hook_cred_free(struct cred *const cred) +{ + landlock_put_ruleset_deferred(landlock_cred(cred)->domain); +} + +static struct security_hook_list landlock_hooks[] __lsm_ro_after_init = { + LSM_HOOK_INIT(cred_prepare, hook_cred_prepare), + LSM_HOOK_INIT(cred_free, hook_cred_free), +}; + +__init void landlock_add_hooks_cred(void) +{ + security_add_hooks(landlock_hooks, ARRAY_SIZE(landlock_hooks), + LANDLOCK_NAME); +} diff --git a/security/landlock/cred.h b/security/landlock/cred.h new file mode 100644 index 000000000000..d3a8b1c2a4dd --- /dev/null +++ b/security/landlock/cred.h @@ -0,0 +1,55 @@ +/* SPDX-License-Identifier: GPL-2.0-only */ +/* + * Landlock LSM - Credential hooks + * + * Copyright © 2019 Mickaël Salaün mic@digikod.net + * Copyright © 2019 ANSSI + */ + +#ifndef _SECURITY_LANDLOCK_CRED_H +#define _SECURITY_LANDLOCK_CRED_H + +#include <linux/cred.h> +#include <linux/init.h> +#include <linux/rcupdate.h> + +#include "ruleset.h" +#include "setup.h" + +struct landlock_cred_security { + struct landlock_ruleset *domain; +}; + +static inline struct landlock_cred_security *landlock_cred( + const struct cred *cred) +{ + return cred->security + landlock_blob_sizes.lbs_cred; +} + +static inline struct landlock_ruleset *landlock_get_current_domain(void) +{ + return landlock_cred(current_cred())->domain; +} + +/* + * The call needs to come from an RCU read-side critical section. + */ +static inline struct landlock_ruleset *landlock_get_task_domain( + const struct task_struct *const task) +{ + return landlock_cred(__task_cred(task))->domain; +} + +static inline bool landlocked(const struct task_struct *const task) +{ + bool has_dom; + + rcu_read_lock(); + has_dom = !!landlock_get_task_domain(task); + rcu_read_unlock(); + return has_dom; +} + +__init void landlock_add_hooks_cred(void); + +#endif /* _SECURITY_LANDLOCK_CRED_H */ diff --git a/security/landlock/setup.c b/security/landlock/setup.c new file mode 100644 index 000000000000..00eb78275cd8 --- /dev/null +++ b/security/landlock/setup.c @@ -0,0 +1,31 @@ +// SPDX-License-Identifier: GPL-2.0-only +/* + * Landlock LSM - Security framework setup + * + * Copyright © 2016-2020 Mickaël Salaün mic@digikod.net + * Copyright © 2018-2020 ANSSI + */ + +#include <linux/init.h> +#include <linux/lsm_hooks.h> + +#include "common.h" +#include "cred.h" +#include "setup.h" + +struct lsm_blob_sizes landlock_blob_sizes __lsm_ro_after_init = { + .lbs_cred = sizeof(struct landlock_cred_security), +}; + +static int __init landlock_init(void) +{ + pr_info("Registering hooks.\n"); + landlock_add_hooks_cred(); + return 0; +} + +DEFINE_LSM(LANDLOCK_NAME) = { + .name = LANDLOCK_NAME, + .init = landlock_init, + .blobs = &landlock_blob_sizes, +}; diff --git a/security/landlock/setup.h b/security/landlock/setup.h new file mode 100644 index 000000000000..9fdbf33fcc33 --- /dev/null +++ b/security/landlock/setup.h @@ -0,0 +1,16 @@ +/* SPDX-License-Identifier: GPL-2.0-only */ +/* + * Landlock LSM - Security framework setup + * + * Copyright © 2016-2020 Mickaël Salaün mic@digikod.net + * Copyright © 2018-2020 ANSSI + */ + +#ifndef _SECURITY_LANDLOCK_SETUP_H +#define _SECURITY_LANDLOCK_SETUP_H + +#include <linux/lsm_hooks.h> + +extern struct lsm_blob_sizes landlock_blob_sizes; + +#endif /* _SECURITY_LANDLOCK_SETUP_H */

Thanks to the Landlock objects and ruleset, it is possible to identify inodes according to a process's domain. To enable an unprivileged process to express a file hierarchy, it first needs to open a directory (or a file) and pass this file descriptor to the kernel through landlock(2). When checking if a file access request is allowed, we walk from the requested dentry to the real root, following the different mount layers. The access to each "tagged" inodes are collected according to their rule layer level, and ANDed to create access to the requested file hierarchy. This makes possible to identify a lot of files without tagging every inodes nor modifying the filesystem, while still following the view and understanding the user has from the filesystem.

Signed-off-by: Mickaël Salaün mic@digikod.net Cc: Alexander Viro viro@zeniv.linux.org.uk Cc: Andy Lutomirski luto@amacapital.net Cc: James Morris jmorris@namei.org Cc: Kees Cook keescook@chromium.org Cc: Serge E. Hallyn serge@hallyn.com ---

Changes since v14: * Simplify the object, rule and ruleset management at the expense of a less aggressive memory freeing (contributed by Jann Horn, with additional modifications): - Rewrite release_inode() to use inode->sb->s_landlock_inode_refs. - Remove useless checks in landlock_release_inodes(), clean object pointer according to the new struct landlock_object and wait for all iput() to complete. - Rewrite get_inode_object() according to the new struct landlock_object. If there is a race-condition when cleaning up an object, we retry until the concurrent thread finished the object cleaning. Cf. https://lore.kernel.org/lkml/CAG48ez21bEn0wL1bbmTiiu8j9jP5iEWtHOwz4tURUJ+ki0... * Fix nested domains by implementing a notion of layer level and depth: - Check for matching level ranges when walking through a file path. - Only allow access if every layer granted the access request. * Handles files without mount points (e.g. pipes). * Hardens path walk by checking inode pointer values. * Prefetches d_parent when walking to the root directory. * Remove useless inode_alloc_security hook() (suggested by Jann Horn): already initialized by lsm_inode_alloc(). * Remove the inode_free_security hook. * Remove access checks that may be required for FD-only requests: truncate, getattr, lock, chmod, chown, chgrp, ioctl. This will be handle in a future evolution of Landlock, but right now the goal is to lighten the code to ease review. * Constify variables. * Move ABI checks into syscall.c . * Cosmetic variable renames.

Changes since v11: * Add back, revamp and make a fully working filesystem access-control based on paths and inodes. * Remove the eBPF dependency.

Previous version: https://lore.kernel.org/lkml/20190721213116.23476-6-mic@digikod.net/ --- MAINTAINERS | 1 + fs/super.c | 2 + include/linux/fs.h | 5 + include/linux/landlock.h | 22 ++ security/landlock/Makefile | 2 +- security/landlock/fs.c | 561 +++++++++++++++++++++++++++++++++++++ security/landlock/fs.h | 42 +++ security/landlock/setup.c | 6 + security/landlock/setup.h | 2 + 9 files changed, 642 insertions(+), 1 deletion(-) create mode 100644 include/linux/landlock.h create mode 100644 security/landlock/fs.c create mode 100644 security/landlock/fs.h

diff --git a/MAINTAINERS b/MAINTAINERS index f8fa29e0f550..3e917d9abce3 100644 --- a/MAINTAINERS +++ b/MAINTAINERS @@ -9364,6 +9364,7 @@ L: linux-security-module@vger.kernel.org W: https://landlock.io T: git https://github.com/landlock-lsm/linux.git S: Supported +F: include/linux/landlock.h F: include/uapi/linux/landlock.h F: security/landlock/ K: landlock diff --git a/fs/super.c b/fs/super.c index cd352530eca9..4ad6a64a1706 100644 --- a/fs/super.c +++ b/fs/super.c @@ -34,6 +34,7 @@ #include <linux/cleancache.h> #include <linux/fscrypt.h> #include <linux/fsnotify.h> +#include <linux/landlock.h> #include <linux/lockdep.h> #include <linux/user_namespace.h> #include <linux/fs_context.h> @@ -454,6 +455,7 @@ void generic_shutdown_super(struct super_block *sb) evict_inodes(sb); /* only nonzero refcount inodes can have marks */ fsnotify_sb_delete(sb); + landlock_release_inodes(sb);

if (sb->s_dio_done_wq) { destroy_workqueue(sb->s_dio_done_wq); diff --git a/include/linux/fs.h b/include/linux/fs.h index abedbffe2c9e..24e2e9b5a704 100644 --- a/include/linux/fs.h +++ b/include/linux/fs.h @@ -1512,6 +1512,11 @@ struct super_block { /* Pending fsnotify inode refs */ atomic_long_t s_fsnotify_inode_refs;

+#ifdef CONFIG_SECURITY_LANDLOCK + /* References to Landlock underlying objects */ + atomic_long_t s_landlock_inode_refs; +#endif + /* Being remounted read-only */ int s_readonly_remount;

diff --git a/include/linux/landlock.h b/include/linux/landlock.h new file mode 100644 index 000000000000..0fb16d130b0a --- /dev/null +++ b/include/linux/landlock.h @@ -0,0 +1,22 @@ +/* SPDX-License-Identifier: GPL-2.0 */ +/* + * Landlock LSM - public kernel headers + * + * Copyright © 2016-2019 Mickaël Salaün mic@digikod.net + * Copyright © 2018-2019 ANSSI + */ + +#ifndef _LINUX_LANDLOCK_H +#define _LINUX_LANDLOCK_H + +#include <linux/fs.h> + +#ifdef CONFIG_SECURITY_LANDLOCK +extern void landlock_release_inodes(struct super_block *sb); +#else +static inline void landlock_release_inodes(struct super_block *sb) +{ +} +#endif + +#endif /* _LINUX_LANDLOCK_H */ diff --git a/security/landlock/Makefile b/security/landlock/Makefile index f1d1eb72fa76..92e3d80ab8ed 100644 --- a/security/landlock/Makefile +++ b/security/landlock/Makefile @@ -1,4 +1,4 @@ obj-$(CONFIG_SECURITY_LANDLOCK) := landlock.o

landlock-y := setup.o object.o ruleset.o \ - cred.o ptrace.o + cred.o ptrace.o fs.o diff --git a/security/landlock/fs.c b/security/landlock/fs.c new file mode 100644 index 000000000000..9531e9c6664d --- /dev/null +++ b/security/landlock/fs.c @@ -0,0 +1,561 @@ +// SPDX-License-Identifier: GPL-2.0-only +/* + * Landlock LSM - Filesystem management and hooks + * + * Copyright © 2016-2020 Mickaël Salaün mic@digikod.net + * Copyright © 2018-2020 ANSSI + */ + +#include <linux/compiler_types.h> +#include <linux/dcache.h> +#include <linux/fs.h> +#include <linux/init.h> +#include <linux/kernel.h> +#include <linux/landlock.h> +#include <linux/list.h> +#include <linux/lsm_hooks.h> +#include <linux/mount.h> +#include <linux/namei.h> +#include <linux/path.h> +#include <linux/prefetch.h> +#include <linux/rcupdate.h> +#include <linux/spinlock.h> +#include <linux/stat.h> +#include <linux/types.h> +#include <linux/wait_bit.h> +#include <linux/workqueue.h> +#include <uapi/linux/landlock.h> + +#include "common.h" +#include "cred.h" +#include "fs.h" +#include "object.h" +#include "ruleset.h" +#include "setup.h" + +/* Underlying object management */ + +static void release_inode(struct landlock_object *const object) + __releases(object->lock) +{ + struct inode *const inode = object->underobj; + struct super_block *sb; + + if (!inode) { + spin_unlock(&object->lock); + return; + } + + spin_lock(&inode->i_lock); + /* + * Make sure that if the filesystem is concurrently unmounted, + * landlock_release_inodes() will wait for us to finish iput(). + */ + sb = inode->i_sb; + atomic_long_inc(&sb->s_landlock_inode_refs); + rcu_assign_pointer(inode_landlock(inode)->object, NULL); + spin_unlock(&inode->i_lock); + spin_unlock(&object->lock); + /* + * Now, new rules can safely be tied to @inode. + */ + + iput(inode); + if (atomic_long_dec_and_test(&sb->s_landlock_inode_refs)) + wake_up_var(&sb->s_landlock_inode_refs); +} + +static const struct landlock_object_underops landlock_fs_underops = { + .release = release_inode +}; + +/* + * Release the inodes used in a security policy. + * + * Cf. fsnotify_unmount_inodes() + */ +void landlock_release_inodes(struct super_block *const sb) +{ + struct inode *inode, *iput_inode = NULL; + + if (!landlock_initialized) + return; + + spin_lock(&sb->s_inode_list_lock); + list_for_each_entry(inode, &sb->s_inodes, i_sb_list) { + struct landlock_inode_security *inode_sec = + inode_landlock(inode); + struct landlock_object *object; + bool do_put = false; + + rcu_read_lock(); + object = rcu_dereference(inode_sec->object); + if (!object) { + rcu_read_unlock(); + continue; + } + + spin_lock(&object->lock); + if (object->underobj) { + object->underobj = NULL; + do_put = true; + spin_lock(&inode->i_lock); + rcu_assign_pointer(inode_sec->object, NULL); + spin_unlock(&inode->i_lock); + } + spin_unlock(&object->lock); + rcu_read_unlock(); + if (!do_put) + /* + * A concurrent iput() in release_inode() is ongoing + * and we will just wait for it to finish. + */ + continue; + + /* + * At this point, we own the ihold() reference that was + * originally set up by get_inode_object(). Therefore we can + * drop the list lock and know that the inode won't disappear + * from under us until the next loop walk. + */ + spin_unlock(&sb->s_inode_list_lock); + /* + * We can now actually put the previous inode, which is not + * needed anymore for the loop walk. + */ + if (iput_inode) + iput(iput_inode); + iput_inode = inode; + spin_lock(&sb->s_inode_list_lock); + } + spin_unlock(&sb->s_inode_list_lock); + if (iput_inode) + iput(iput_inode); + + /* + * Wait for pending iput() in release_inode(). + */ + wait_var_event(&sb->s_landlock_inode_refs, + !atomic_long_read(&sb->s_landlock_inode_refs)); +} + +/* Ruleset management */ + +static struct landlock_object *get_inode_object(struct inode *const inode) +{ + struct landlock_object *object, *new_object; + struct landlock_inode_security *inode_sec = inode_landlock(inode); + + rcu_read_lock(); +retry: + object = rcu_dereference(inode_sec->object); + if (object) { + if (likely(refcount_inc_not_zero(&object->usage))) { + rcu_read_unlock(); + return object; + } + /* + * We're racing with release_inode(), the object is going away. + * Wait for release_inode(), then retry. + */ + spin_lock(&object->lock); + spin_unlock(&object->lock); + goto retry; + } + rcu_read_unlock(); + + /* + * If there is no object tied to @inode, then create a new one (without + * holding any locks). + */ + new_object = landlock_create_object(&landlock_fs_underops, inode); + + spin_lock(&inode->i_lock); + object = rcu_dereference_protected(inode_sec->object, + lockdep_is_held(&inode->i_lock)); + if (unlikely(object)) { + /* Someone else just created the object, bail out and retry. */ + kfree(new_object); + spin_unlock(&inode->i_lock); + + rcu_read_lock(); + goto retry; + } else { + rcu_assign_pointer(inode_sec->object, new_object); + /* + * @inode will be released by landlock_release_inodes() on its + * super-block shutdown. + */ + ihold(inode); + spin_unlock(&inode->i_lock); + return new_object; + } +} + +/* + * @path: Should have been checked by get_path_from_fd(). + */ +int landlock_append_fs_rule(struct landlock_ruleset *const ruleset, + const struct path *const path, u32 access_hierarchy) +{ + int err; + struct landlock_rule rule = {}; + + /* Transforms relative access rights to absolute ones. */ + access_hierarchy |= _LANDLOCK_ACCESS_FS_MASK & + ~ruleset->fs_access_mask; + rule.access.self = access_hierarchy; + rule.access.beneath = access_hierarchy; + rule.object = get_inode_object(d_backing_inode(path->dentry)); + mutex_lock(&ruleset->lock); + err = landlock_insert_rule(ruleset, &rule, false); + mutex_unlock(&ruleset->lock); + /* + * No need to check for an error because landlock_insert_rule() + * increment the refcount for the new rule, if any. + */ + landlock_put_object(rule.object); + return err; +} + +/* Access-control management */ + +static bool check_access_path_continue( + const struct landlock_ruleset *const domain, + const struct path *const path, const u32 access_request, + const bool check_self, bool *const allow, + u32 *const layer_level) +{ + const struct landlock_rule *rule; + const struct inode *inode; + bool next = true; + + inode = d_backing_inode(path->dentry); + if (WARN_ON_ONCE(!inode)) { + /* + * Access denied when the absolute path contains a dentry + * without inode. + */ + *allow = false; + return false; + } + prefetch(path->dentry->d_parent); + rcu_read_lock(); + rule = landlock_find_rule(domain, + rcu_dereference(inode_landlock(inode)->object)); + rcu_read_unlock(); + + /* Checks for a matching layer level range. */ + if (rule && (rule->layer_level - rule->layer_depth) < *layer_level && + *layer_level <= rule->layer_level) { + *allow = ((check_self ? rule->access.self : + rule->access.beneath) & access_request) + == access_request; + if (*allow) { + *layer_level -= rule->layer_depth; + /* Stops when reaching the last layer. */ + next = (*layer_level > 0); + } else { + next = false; + } + } + return next; +} + +static int check_access_path(const struct landlock_ruleset *const domain, + const struct path *const path, u32 access_request) +{ + bool allow = false; + struct path walker_path; + u32 walker_layer_level = domain->top_layer_level; + + if (WARN_ON_ONCE(!path)) + return 0; + /* + * An access request which is not handled by the domain should be + * allowed. + */ + access_request &= domain->fs_access_mask; + if (access_request == 0) + return 0; + walker_path = *path; + path_get(&walker_path); + if (check_access_path_continue(domain, &walker_path, access_request, + true, &allow, &walker_layer_level)) { + /* + * We need to walk through all the hierarchy to not miss any + * relevant restriction. + */ + do { + struct dentry *parent_dentry; + +jump_up: + /* + * Does not work with orphaned/private mounts like + * overlayfs layers for now (cf. ovl_path_real() and + * ovl_path_open()). + */ + if (walker_path.dentry == walker_path.mnt->mnt_root) { + if (follow_up(&walker_path)) { + /* Ignores hidden mount points. */ + goto jump_up; + } else { + /* + * Stops at the real root. Denies + * access because not all layers have + * granted access. + */ + allow = false; + break; + } + } + if (IS_ROOT(walker_path.dentry)) { + /* + * Stops at directory without mount points + * (e.g. pipes). Denies access because not all + * layers have granted access. + */ + allow = false; + break; + } + parent_dentry = dget_parent(walker_path.dentry); + dput(walker_path.dentry); + walker_path.dentry = parent_dentry; + } while (check_access_path_continue(domain, &walker_path, + access_request, false, &allow, + &walker_layer_level)); + } + path_put(&walker_path); + return allow ? 0 : -EACCES; +} + +static inline int current_check_access_path(const struct path *const path, + const u32 access_request) +{ + struct landlock_ruleset *dom; + + dom = landlock_get_current_domain(); + if (!dom) + return 0; + return check_access_path(dom, path, access_request); +} + +/* Super-block hooks */ + +/* + * Because a Landlock security policy is defined according to the filesystem + * layout (i.e. the mount namespace), changing it may grant access to files not + * previously allowed. + * + * To make it simple, deny any filesystem layout modification by landlocked + * processes. Non-landlocked processes may still change the namespace of a + * landlocked process, but this kind of threat must be handled by a system-wide + * access-control security policy. + * + * This could be lifted in the future if Landlock can safely handle mount + * namespace updates requested by a landlocked process. Indeed, we could + * update the current domain (which is currently read-only) by taking into + * account the accesses of the source and the destination of a new mount point. + * However, it would also require to make all the child domains dynamically + * inherit these new constraints. Anyway, for backward compatibility reasons, + * a dedicated user space option would be required (e.g. as a ruleset command + * option). + */ +static int hook_sb_mount(const char *const dev_name, + const struct path *const path, const char *const type, + const unsigned long flags, void *const data) +{ + if (!landlock_get_current_domain()) + return 0; + return -EPERM; +} + +static int hook_move_mount(const struct path *const from_path, + const struct path *const to_path) +{ + if (!landlock_get_current_domain()) + return 0; + return -EPERM; +} + +/* + * Removing a mount point may reveal a previously hidden file hierarchy, which + * may then grant access to files, which may have previously been forbidden. + */ +static int hook_sb_umount(struct vfsmount *const mnt, const int flags) +{ + if (!landlock_get_current_domain()) + return 0; + return -EPERM; +} + +static int hook_sb_remount(struct super_block *const sb, void *const mnt_opts) +{ + if (!landlock_get_current_domain()) + return 0; + return -EPERM; +} + +/* + * pivot_root(2), like mount(2), changes the current mount namespace. It must + * then be forbidden for a landlocked process. + * + * However, chroot(2) may be allowed because it only changes the relative root + * directory of the current process. + */ +static int hook_sb_pivotroot(const struct path *const old_path, + const struct path *const new_path) +{ + if (!landlock_get_current_domain()) + return 0; + return -EPERM; +} + +/* Path hooks */ + +static int hook_path_link(struct dentry *const old_dentry, + const struct path *const new_dir, + struct dentry *const new_dentry) +{ + return current_check_access_path(new_dir, LANDLOCK_ACCESS_FS_LINK_TO); +} + +static int hook_path_mkdir(const struct path *const dir, + struct dentry *const dentry, const umode_t mode) +{ + return current_check_access_path(dir, LANDLOCK_ACCESS_FS_MAKE_DIR); +} + +static inline u32 get_mode_access(const umode_t mode) +{ + switch (mode & S_IFMT) { + case S_IFLNK: + return LANDLOCK_ACCESS_FS_MAKE_SYM; + case S_IFREG: + return LANDLOCK_ACCESS_FS_MAKE_REG; + case S_IFDIR: + return LANDLOCK_ACCESS_FS_MAKE_DIR; + case S_IFCHR: + return LANDLOCK_ACCESS_FS_MAKE_CHAR; + case S_IFBLK: + return LANDLOCK_ACCESS_FS_MAKE_BLOCK; + case S_IFIFO: + return LANDLOCK_ACCESS_FS_MAKE_FIFO; + case S_IFSOCK: + return LANDLOCK_ACCESS_FS_MAKE_SOCK; + default: + WARN_ON_ONCE(1); + return 0; + } +} + +static int hook_path_mknod(const struct path *const dir, + struct dentry *const dentry, const umode_t mode, + const unsigned int dev) +{ + return current_check_access_path(dir, get_mode_access(mode)); +} + +static int hook_path_symlink(const struct path *const dir, + struct dentry *const dentry, const char *const old_name) +{ + return current_check_access_path(dir, LANDLOCK_ACCESS_FS_MAKE_SYM); +} + +static int hook_path_unlink(const struct path *const dir, + struct dentry *const dentry) +{ + return current_check_access_path(dir, LANDLOCK_ACCESS_FS_UNLINK); +} + +static int hook_path_rmdir(const struct path *const dir, + struct dentry *const dentry) +{ + return current_check_access_path(dir, LANDLOCK_ACCESS_FS_RMDIR); +} + +static int hook_path_rename(const struct path *const old_dir, + struct dentry *const old_dentry, + const struct path *const new_dir, + struct dentry *const new_dentry) +{ + struct landlock_ruleset *dom; + int err; + + dom = landlock_get_current_domain(); + if (!dom) + return 0; + err = check_access_path(dom, old_dir, LANDLOCK_ACCESS_FS_RENAME_FROM); + if (err) + return err; + return check_access_path(dom, new_dir, LANDLOCK_ACCESS_FS_RENAME_TO); +} + +static int hook_path_chroot(const struct path *const path) +{ + return current_check_access_path(path, LANDLOCK_ACCESS_FS_CHROOT); +} + +/* File hooks */ + +static inline u32 get_file_access(const struct file *const file) +{ + u32 access = 0; + + if (file->f_mode & FMODE_READ) { + /* A directory can only be opened in read mode. */ + if (S_ISDIR(file_inode(file)->i_mode)) + access |= LANDLOCK_ACCESS_FS_READ_DIR; + else + access |= LANDLOCK_ACCESS_FS_READ_FILE; + } + /* + * A LANDLOCK_ACCESS_FS_APPEND could be added be we also need to check + * fcntl(2). + */ + if (file->f_mode & FMODE_WRITE) + access |= LANDLOCK_ACCESS_FS_WRITE_FILE; + /* __FMODE_EXEC is indeed part of f_flags, not f_mode. */ + if (file->f_flags & __FMODE_EXEC) + access |= LANDLOCK_ACCESS_FS_EXECUTE; + return access; +} + +static int hook_file_open(struct file *const file) +{ + if (WARN_ON_ONCE(!file)) + return 0; + if (!file_inode(file)) + return -ENOENT; + /* + * Because a file may be opened with O_PATH, get_file_access() may + * return 0. This case will be handled with a future Landlock + * evolution. + */ + return current_check_access_path(&file->f_path, get_file_access(file)); +} + +static struct security_hook_list landlock_hooks[] __lsm_ro_after_init = { + LSM_HOOK_INIT(sb_mount, hook_sb_mount), + LSM_HOOK_INIT(move_mount, hook_move_mount), + LSM_HOOK_INIT(sb_umount, hook_sb_umount), + LSM_HOOK_INIT(sb_remount, hook_sb_remount), + LSM_HOOK_INIT(sb_pivotroot, hook_sb_pivotroot), + + LSM_HOOK_INIT(path_link, hook_path_link), + LSM_HOOK_INIT(path_mkdir, hook_path_mkdir), + LSM_HOOK_INIT(path_mknod, hook_path_mknod), + LSM_HOOK_INIT(path_symlink, hook_path_symlink), + LSM_HOOK_INIT(path_unlink, hook_path_unlink), + LSM_HOOK_INIT(path_rmdir, hook_path_rmdir), + LSM_HOOK_INIT(path_rename, hook_path_rename), + LSM_HOOK_INIT(path_chroot, hook_path_chroot), + + LSM_HOOK_INIT(file_open, hook_file_open), +}; + +__init void landlock_add_hooks_fs(void) +{ + security_add_hooks(landlock_hooks, ARRAY_SIZE(landlock_hooks), + LANDLOCK_NAME); +} diff --git a/security/landlock/fs.h b/security/landlock/fs.h new file mode 100644 index 000000000000..2cf55ed1e800 --- /dev/null +++ b/security/landlock/fs.h @@ -0,0 +1,42 @@ +/* SPDX-License-Identifier: GPL-2.0-only */ +/* + * Landlock LSM - Filesystem management and hooks + * + * Copyright © 2017-2020 Mickaël Salaün mic@digikod.net + * Copyright © 2018-2020 ANSSI + */ + +#ifndef _SECURITY_LANDLOCK_FS_H +#define _SECURITY_LANDLOCK_FS_H + +#include <linux/fs.h> +#include <linux/init.h> +#include <linux/rcupdate.h> + +#include "ruleset.h" +#include "setup.h" + +struct landlock_inode_security { + /* + * @object: Weak pointer to an allocated object. All writes (i.e. + * creating a new object or removing one) are protected by the + * underlying inode->i_lock. Disassociating @object from the inode is + * additionally protected by @object->lock, from the time @object's + * usage refcount drops to zero to the time this pointer is nulled out. + * Cf. release_inode(). + */ + struct landlock_object __rcu *object; +}; + +static inline struct landlock_inode_security *inode_landlock( + const struct inode *const inode) +{ + return inode->i_security + landlock_blob_sizes.lbs_inode; +} + +__init void landlock_add_hooks_fs(void); + +int landlock_append_fs_rule(struct landlock_ruleset *const ruleset, + const struct path *const path, u32 access_hierarchy); + +#endif /* _SECURITY_LANDLOCK_FS_H */ diff --git a/security/landlock/setup.c b/security/landlock/setup.c index a40822135d13..f77fc7749f49 100644 --- a/security/landlock/setup.c +++ b/security/landlock/setup.c @@ -11,11 +11,15 @@

#include "common.h" #include "cred.h" +#include "fs.h" #include "ptrace.h" #include "setup.h"

+bool landlock_initialized __lsm_ro_after_init = false; + struct lsm_blob_sizes landlock_blob_sizes __lsm_ro_after_init = { .lbs_cred = sizeof(struct landlock_cred_security), + .lbs_inode = sizeof(struct landlock_inode_security), };

static int __init landlock_init(void) @@ -23,6 +27,8 @@ static int __init landlock_init(void) pr_info("Registering hooks.\n"); landlock_add_hooks_cred(); landlock_add_hooks_ptrace(); + landlock_add_hooks_fs(); + landlock_initialized = true; return 0; }

diff --git a/security/landlock/setup.h b/security/landlock/setup.h index 9fdbf33fcc33..1daffab1ab4b 100644 --- a/security/landlock/setup.h +++ b/security/landlock/setup.h @@ -11,6 +11,8 @@

#include <linux/lsm_hooks.h>

+extern bool landlock_initialized; + extern struct lsm_blob_sizes landlock_blob_sizes;

#endif /* _SECURITY_LANDLOCK_SETUP_H */

This system call, inspired from seccomp(2) and bpf(2), is designed to be used by unprivileged processes to sandbox themselves. It has the same usage restrictions as seccomp(2): the caller must have the no_new_privs attribute set or have CAP_SYS_ADMIN in the current user namespace.

Here are the motivations for this new syscall: * A sandboxed process may not have access to file systems, including /dev, /sys or /proc, but it should still be able to add more restrictions to itself. * Neither prctl(2) nor seccomp(2) (which was used in a previous version) fit well with the current definition of a Landlock security policy. * It is quite easy to whitelist this syscall with seccomp-bpf to enable all processes to use it. It is also easy to filter specific commands or options to restrict a process to a subset of Landlock features.

There is currently four commands: * LANDLOCK_CMD_GET_FEATURES: Gets the supported features (required for backward compatibility and best-effort security). * LANDLOCK_CMD_CREATE_RULESET: Creates a ruleset and returns its file descriptor. * LANDLOCK_CMD_ADD_RULE: Adds a rule (e.g. file hierarchy access) to a ruleset, identified by the dedicated file descriptor. * LANDLOCK_CMD_ENFORCE_RULESET: Enforces a ruleset on the current thread and its future children (similar to seccomp).

See the user and code documentation for more details (provided by a following commit): Documentation/security/landlock/

Signed-off-by: Mickaël Salaün mic@digikod.net Cc: Andy Lutomirski luto@amacapital.net Cc: Arnd Bergmann arnd@arndb.de Cc: James Morris jmorris@namei.org Cc: Kees Cook keescook@chromium.org Cc: Serge E. Hallyn serge@hallyn.com ---

Changes since v14: * Remove the security_file_open() check in get_path_from_fd(): an opened FD should not be restricted here, and even less with this hook. As a result, it is now allowed to add a path to a ruleset even if the access to this path is not allowed (without O_PATH). This doesn't change the fact that enforcing a ruleset can't grant any right, only remove some rights. The new layer levels add more consistent restrictions. * Check minimal landlock_attr_* size/content. This fix the case when no data was provided and e.g., FD 0 was interpreted as ruleset_fd. Now this leads to a returned -EINVAL. * Fix credential double-free error case. * Complete struct landlock_attr_size with size_attr_enforce. * Fix undefined reference to syscall when Landlock is not selected. * Remove f.file->f_path.mnt check (suggested by Al Viro). * Add build-time checks. * Move ABI checks from fs.c . * Constify variables. * Fix spelling. * Add comments.

Changes since v13: * New implementation, replacing the dependency on seccomp(2) and bpf(2). --- include/linux/syscalls.h | 3 + include/uapi/linux/landlock.h | 218 ++++++++++++++ kernel/sys_ni.c | 3 + security/landlock/Makefile | 2 +- security/landlock/syscall.c | 521 ++++++++++++++++++++++++++++++++++ 5 files changed, 746 insertions(+), 1 deletion(-) create mode 100644 security/landlock/syscall.c

diff --git a/include/linux/syscalls.h b/include/linux/syscalls.h index 1815065d52f3..beaadcf4ef77 100644 --- a/include/linux/syscalls.h +++ b/include/linux/syscalls.h @@ -1003,6 +1003,9 @@ asmlinkage long sys_pidfd_send_signal(int pidfd, int sig, siginfo_t __user *info, unsigned int flags); asmlinkage long sys_pidfd_getfd(int pidfd, int fd, unsigned int flags); +asmlinkage long sys_landlock(unsigned int command, unsigned int options, + size_t attr1_size, void __user *attr1_ptr, + size_t attr2_size, void __user *attr2_ptr);

/* * Architecture-specific system calls diff --git a/include/uapi/linux/landlock.h b/include/uapi/linux/landlock.h index 32003e8b845a..3f60d0e148b8 100644 --- a/include/uapi/linux/landlock.h +++ b/include/uapi/linux/landlock.h @@ -9,6 +9,224 @@ #ifndef _UAPI__LINUX_LANDLOCK_H__ #define _UAPI__LINUX_LANDLOCK_H__

+#include <linux/types.h> + +/** + * enum landlock_cmd - Landlock commands + * + * First argument of sys_landlock(). + */ +enum landlock_cmd { + /** + * @LANDLOCK_CMD_GET_FEATURES: Asks the kernel for supported Landlock + * features. The option argument must contains + * %LANDLOCK_OPT_GET_FEATURES. This commands fills the &struct + * landlock_attr_features provided as first attribute. + */ + LANDLOCK_CMD_GET_FEATURES = 1, + /** + * @LANDLOCK_CMD_CREATE_RULESET: Creates a new ruleset and return its + * file descriptor on success. The option argument must contains + * %LANDLOCK_OPT_CREATE_RULESET. The ruleset is defined by the &struct + * landlock_attr_ruleset provided as first attribute. + */ + LANDLOCK_CMD_CREATE_RULESET, + /** + * @LANDLOCK_CMD_ADD_RULE: Adds a rule to a ruleset. The option + * argument must contains %LANDLOCK_OPT_ADD_RULE_PATH_BENEATH. The + * ruleset and the rule are both defined by the &struct + * landlock_attr_path_beneath provided as first attribute. + */ + LANDLOCK_CMD_ADD_RULE, + /** + * @LANDLOCK_CMD_ENFORCE_RULESET: Enforces a ruleset on the current + * process. The option argument must contains + * %LANDLOCK_OPT_ENFORCE_RULESET. The ruleset is defined by the + * &struct landlock_attr_enforce provided as first attribute. + */ + LANDLOCK_CMD_ENFORCE_RULESET, +}; + +/** + * DOC: options_intro + * + * These options may be used as second argument of sys_landlock(). Each + * command have a dedicated set of options, represented as bitmasks. For two + * different commands, their options may overlap. Each command have at least + * one option defining the used attribute type. This also enables to always + * have a usable &struct landlock_attr_features (i.e. filled with bits). + */ + +/** + * DOC: options_get_features + * + * Options for ``LANDLOCK_CMD_GET_FEATURES`` + * ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ + * + * - %LANDLOCK_OPT_GET_FEATURES: the attr type is `struct + * landlock_attr_features`. + */ +#define LANDLOCK_OPT_GET_FEATURES (1ULL << 0) + +/** + * DOC: options_create_ruleset + * + * Options for ``LANDLOCK_CMD_CREATE_RULESET`` + * ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ + * + * - %LANDLOCK_OPT_CREATE_RULESET: the attr type is `struct + * landlock_attr_ruleset`. + */ +#define LANDLOCK_OPT_CREATE_RULESET (1ULL << 0) + +/** + * DOC: options_add_rule + * + * Options for ``LANDLOCK_CMD_ADD_RULE`` + * ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ + * + * - %LANDLOCK_OPT_ADD_RULE_PATH_BENEATH: the attr type is `struct + * landlock_attr_path_beneath`. + */ +#define LANDLOCK_OPT_ADD_RULE_PATH_BENEATH (1ULL << 0) + +/** + * DOC: options_enforce_ruleset + * + * Options for ``LANDLOCK_CMD_ENFORCE_RULESET`` + * ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ + * + * - %LANDLOCK_OPT_ENFORCE_RULESET: the attr type is `struct + * landlock_attr_enforce`. + */ +#define LANDLOCK_OPT_ENFORCE_RULESET (1ULL << 0) + +/** + * struct landlock_attr_features - Receives the supported features + * + * This struct should be allocated by user space but it will be filled by the + * kernel to indicate the subset of Landlock features effectively handled by + * the running kernel. This enables backward compatibility for applications + * which are developed on a newer kernel than the one running the application. + * This helps avoid hard errors that may entirely disable the use of Landlock + * features because some of them may not be supported. Indeed, because + * Landlock is a security feature, even if the kernel doesn't support all the + * requested features, user space applications should still use the subset + * which is supported by the running kernel. Indeed, a partial security policy + * can still improve the security of the application and better protect the + * user (i.e. best-effort approach). The %LANDLOCK_CMD_GET_FEATURES command + * and &struct landlock_attr_features are future-proof because the future + * unknown fields requested by user space (i.e. a larger &struct + * landlock_attr_features) can still be filled with zeros. + * + * The Landlock commands will fail if an unsupported option or access is + * requested. By firstly requesting the supported options and accesses, it is + * quite easy for the developer to binary AND these returned bitmasks with the + * used options and accesses from the attribute structs (e.g. &struct + * landlock_attr_ruleset), and even infer the supported Landlock commands. + * Indeed, because each command must support at least one option, the options_* + * fields are always filled if the related commands are supported. The + * supported attributes are also discoverable thanks to the size_* fields. All + * this data enable to create applications doing their best to sandbox + * themselves regardless of the running kernel. + */ +struct landlock_attr_features { + /** + * @options_get_features: Options supported by the + * %LANDLOCK_CMD_GET_FEATURES command. Cf. `Options`_. + */ + __aligned_u64 options_get_features; + /** + * @options_create_ruleset: Options supported by the + * %LANDLOCK_CMD_CREATE_RULESET command. Cf. `Options`_. + */ + __aligned_u64 options_create_ruleset; + /** + * @options_add_rule: Options supported by the %LANDLOCK_CMD_ADD_RULE + * command. Cf. `Options`_. + */ + __aligned_u64 options_add_rule; + /** + * @options_enforce_ruleset: Options supported by the + * %LANDLOCK_CMD_ENFORCE_RULESET command. Cf. `Options`_. + */ + __aligned_u64 options_enforce_ruleset; + /** + * @access_fs: Subset of file system access supported by the running + * kernel, used in &struct landlock_attr_ruleset and &struct + * landlock_attr_path_beneath. Cf. `Filesystem flags`_. + */ + __aligned_u64 access_fs; + /** + * @size_attr_ruleset: Size of the &struct landlock_attr_ruleset as + * known by the kernel (i.e. ``sizeof(struct + * landlock_attr_ruleset)``). + */ + __aligned_u64 size_attr_ruleset; + /** + * @size_attr_path_beneath: Size of the &struct + * landlock_attr_path_beneath as known by the kernel (i.e. + * ``sizeof(struct landlock_path_beneath)``). + */ + __aligned_u64 size_attr_path_beneath; + /** + * @size_attr_enforce: Size of the &struct landlock_attr_enforce as + * known by the kernel (i.e. ``sizeof(struct landlock_enforce)``). + */ + __aligned_u64 size_attr_enforce; +}; + +/** + * struct landlock_attr_ruleset- Defines a new ruleset + * + * Used as first attribute for the %LANDLOCK_CMD_CREATE_RULESET command and + * with the %LANDLOCK_OPT_CREATE_RULESET option. + */ +struct landlock_attr_ruleset { + /** + * @handled_access_fs: Bitmask of actions (cf. `Filesystem flags`_) + * that is handled by this ruleset and should then be forbidden if no + * rule explicitly allow them. This is needed for backward + * compatibility reasons. The user space code should check the + * effectively supported actions thanks to %LANDLOCK_CMD_GET_SUPPORTED + * and &struct landlock_attr_features, and then adjust the arguments of + * the next calls to sys_landlock() accordingly. + */ + __aligned_u64 handled_access_fs; +}; + +/** + * struct landlock_attr_path_beneath - Defines a path hierarchy + */ +struct landlock_attr_path_beneath { + /** + * @ruleset_fd: File descriptor tied to the ruleset which should be + * extended with this new access. + */ + __aligned_u64 ruleset_fd; + /** + * @parent_fd: File descriptor, open with ``O_PATH``, which identify + * the parent directory of a file hierarchy, or just a file. + */ + __aligned_u64 parent_fd; + /** + * @allowed_access: Bitmask of allowed actions for this file hierarchy + * (cf. `Filesystem flags`_). + */ + __aligned_u64 allowed_access; +}; + +/** + * struct landlock_attr_enforce - Describes the enforcement + */ +struct landlock_attr_enforce { + /** + * @ruleset_fd: File descriptor tied to the ruleset to merge with the + * current domain. + */ + __aligned_u64 ruleset_fd; +}; + /** * DOC: fs_access * diff --git a/kernel/sys_ni.c b/kernel/sys_ni.c index 3b69a560a7ac..70cea36eb7ce 100644 --- a/kernel/sys_ni.c +++ b/kernel/sys_ni.c @@ -264,6 +264,9 @@ COND_SYSCALL(request_key); COND_SYSCALL(keyctl); COND_SYSCALL_COMPAT(keyctl);

+/* security/landlock/syscall.c */ +COND_SYSCALL(landlock); + /* arch/example/kernel/sys_example.c */

/* mm/fadvise.c */ diff --git a/security/landlock/Makefile b/security/landlock/Makefile index 92e3d80ab8ed..4388494779ec 100644 --- a/security/landlock/Makefile +++ b/security/landlock/Makefile @@ -1,4 +1,4 @@ obj-$(CONFIG_SECURITY_LANDLOCK) := landlock.o

-landlock-y := setup.o object.o ruleset.o \ +landlock-y := setup.o syscall.o object.o ruleset.o \ cred.o ptrace.o fs.o diff --git a/security/landlock/syscall.c b/security/landlock/syscall.c new file mode 100644 index 000000000000..2afa28b5f587 --- /dev/null +++ b/security/landlock/syscall.c @@ -0,0 +1,521 @@ +// SPDX-License-Identifier: GPL-2.0-only +/* + * Landlock LSM - System call and user space interfaces + * + * Copyright © 2016-2020 Mickaël Salaün mic@digikod.net + * Copyright © 2018-2020 ANSSI + */ + +#include <asm/current.h> +#include <linux/anon_inodes.h> +#include <linux/build_bug.h> +#include <linux/capability.h> +#include <linux/compiler_types.h> +#include <linux/dcache.h> +#include <linux/err.h> +#include <linux/errno.h> +#include <linux/fs.h> +#include <linux/landlock.h> +#include <linux/limits.h> +#include <linux/path.h> +#include <linux/sched.h> +#include <linux/security.h> +#include <linux/stddef.h> +#include <linux/syscalls.h> +#include <linux/types.h> +#include <linux/uaccess.h> +#include <uapi/linux/landlock.h> + +#include "cred.h" +#include "fs.h" +#include "ruleset.h" +#include "setup.h" + +/** + * copy_struct_if_any_from_user - Safe future-proof argument copying + * + * Extend copy_struct_from_user() to handle NULL @src, which allows for future + * use of @src even if it is not used right now. + * + * @dst: Kernel space pointer or NULL. + * @ksize: Actual size of the data pointed to by @dst. + * @ksize_min: Minimal required size to be copied. + * @src: User space pointer or NULL. + * @usize: (Alleged) size of the data pointed to by @src. + */ +static int copy_struct_if_any_from_user(void *const dst, const size_t ksize, + const size_t ksize_min, const void __user *const src, + const size_t usize) +{ + int ret; + + /* Checks kernel buffer size inconsistencies. */ + if (dst) { + if (WARN_ON_ONCE(ksize == 0)) + return -EFAULT; + } else { + if (WARN_ON_ONCE(ksize != 0)) + return -EFAULT; + } + + /* Checks minimal size. */ + if (WARN_ON_ONCE(ksize < ksize_min)) + return -EFAULT; + if (usize < ksize_min) + return -EINVAL; + + /* Handles empty user buffer. */ + if (!src) { + if (usize != 0) + return -EFAULT; + if (dst) + memset(dst, 0, ksize); + return 0; + } + + /* Checks user buffer size inconsistency and limit. */ + if (usize == 0) + return -ENODATA; + if (usize > PAGE_SIZE) + return -E2BIG; + + /* Copies user buffer and fills with zeros. */ + if (dst) + return copy_struct_from_user(dst, ksize, src, usize); + + /* Checks unknown user data. */ + ret = check_zeroed_user(src, usize); + if (ret <= 0) + return ret ?: -E2BIG; + return 0; +} + +/* Features */ + +#define _LANDLOCK_OPT_GET_FEATURES_LAST LANDLOCK_OPT_GET_FEATURES +#define _LANDLOCK_OPT_GET_FEATURES_MASK ((_LANDLOCK_OPT_GET_FEATURES_LAST << 1) - 1) + +#define _LANDLOCK_OPT_CREATE_RULESET_LAST LANDLOCK_OPT_CREATE_RULESET +#define _LANDLOCK_OPT_CREATE_RULESET_MASK ((_LANDLOCK_OPT_CREATE_RULESET_LAST << 1) - 1) + +#define _LANDLOCK_OPT_ADD_RULE_LAST LANDLOCK_OPT_ADD_RULE_PATH_BENEATH +#define _LANDLOCK_OPT_ADD_RULE_MASK ((_LANDLOCK_OPT_ADD_RULE_LAST << 1) - 1) + +#define _LANDLOCK_OPT_ENFORCE_RULESET_LAST LANDLOCK_OPT_ENFORCE_RULESET +#define _LANDLOCK_OPT_ENFORCE_RULESET_MASK ((_LANDLOCK_OPT_ENFORCE_RULESET_LAST << 1) - 1) + +static int syscall_get_features(const size_t attr_size, + void __user *const attr_ptr) +{ + size_t data_size, fill_size; + const struct landlock_attr_features supported = { + .options_get_features = _LANDLOCK_OPT_GET_FEATURES_MASK, + .options_create_ruleset = _LANDLOCK_OPT_CREATE_RULESET_MASK, + .options_add_rule = _LANDLOCK_OPT_ADD_RULE_MASK, + .options_enforce_ruleset = _LANDLOCK_OPT_ENFORCE_RULESET_MASK, + .access_fs = _LANDLOCK_ACCESS_FS_MASK, + .size_attr_ruleset = sizeof(struct landlock_attr_ruleset), + .size_attr_path_beneath = sizeof(struct + landlock_attr_path_beneath), + .size_attr_enforce = sizeof(struct landlock_attr_enforce), + }; + + BUILD_BUG_ON(!__same_type(supported.access_fs, + ((struct landlock_attr_ruleset *)NULL)->handled_access_fs)); + BUILD_BUG_ON(!__same_type(supported.access_fs, + ((struct landlock_attr_path_beneath *)NULL)->allowed_access)); + + /* Checks attribute consistency. */ + if (attr_size == 0) + return -ENODATA; + if (attr_size > PAGE_SIZE) + return -E2BIG; + + /* Copy features to user space. */ + data_size = min(sizeof(supported), attr_size); + if (copy_to_user(attr_ptr, &supported, data_size)) + return -EFAULT; + + /* Fills with zeros. */ + fill_size = attr_size - data_size; + if (fill_size > 0 && clear_user(attr_ptr + data_size, fill_size)) + return -EFAULT; + return 0; +} + +/* Ruleset handling */ + +#ifdef CONFIG_PROC_FS +static void fop_ruleset_show_fdinfo(struct seq_file *const m, + struct file *const filp) +{ + const struct landlock_ruleset *ruleset = filp->private_data; + + seq_printf(m, "handled_access_fs:\t%x\n", ruleset->fs_access_mask); + seq_printf(m, "nb_rules:\t%d\n", atomic_read(&ruleset->nb_rules)); +} +#endif + +static int fop_ruleset_release(struct inode *const inode, + struct file *const filp) +{ + struct landlock_ruleset *ruleset = filp->private_data; + + landlock_put_ruleset(ruleset); + return 0; +} + +static ssize_t fop_dummy_read(struct file *const filp, char __user *const buf, + const size_t size, loff_t *const ppos) +{ + /* Dummy handler to enable FMODE_CAN_READ. */ + return -EINVAL; +} + +static ssize_t fop_dummy_write(struct file *const filp, + const char __user *const buf, const size_t size, + loff_t *const ppos) +{ + /* Dummy handler to enable FMODE_CAN_WRITE. */ + return -EINVAL; +} + +/* + * A ruleset file descriptor enables to build a ruleset by adding (i.e. + * writing) rule after rule, without relying on the task's context. This + * reentrant design is also used in a read way to enforce the ruleset on the + * current task. + */ +static const struct file_operations ruleset_fops = { +#ifdef CONFIG_PROC_FS + .show_fdinfo = fop_ruleset_show_fdinfo, +#endif + .release = fop_ruleset_release, + .read = fop_dummy_read, + .write = fop_dummy_write, +}; + +static int syscall_create_ruleset(const size_t attr_size, + const void __user *const attr_ptr) +{ + struct landlock_attr_ruleset attr_ruleset; + struct landlock_ruleset *ruleset; + int err, ruleset_fd; + + /* Copies raw user space buffer. */ + err = copy_struct_if_any_from_user(&attr_ruleset, sizeof(attr_ruleset), + offsetofend(typeof(attr_ruleset), handled_access_fs), + attr_ptr, attr_size); + if (err) + return err; + + /* Checks content (and 32-bits cast). */ + if ((attr_ruleset.handled_access_fs | _LANDLOCK_ACCESS_FS_MASK) != + _LANDLOCK_ACCESS_FS_MASK) + return -EINVAL; + + /* Checks arguments and transforms to kernel struct. */ + ruleset = landlock_create_ruleset(attr_ruleset.handled_access_fs); + if (IS_ERR(ruleset)) + return PTR_ERR(ruleset); + + /* Creates anonymous FD referring to the ruleset. */ + ruleset_fd = anon_inode_getfd("landlock-ruleset", &ruleset_fops, + ruleset, O_RDWR | O_CLOEXEC); + if (ruleset_fd < 0) + landlock_put_ruleset(ruleset); + return ruleset_fd; +} + +/* + * Returns an owned ruleset from a FD. It is thus needed to call + * landlock_put_ruleset() on the return value. + */ +static struct landlock_ruleset *get_ruleset_from_fd(const u64 fd, + const fmode_t mode) +{ + struct fd ruleset_f; + struct landlock_ruleset *ruleset; + int err; + + BUILD_BUG_ON(!__same_type(fd, + ((struct landlock_attr_path_beneath *)NULL)->ruleset_fd)); + BUILD_BUG_ON(!__same_type(fd, + ((struct landlock_attr_enforce *)NULL)->ruleset_fd)); + + /* Checks 32-bits overflow. fdget() checks for INT_MAX/FD. */ + if (fd > U32_MAX) + return ERR_PTR(-EINVAL); + ruleset_f = fdget(fd); + if (!ruleset_f.file) + return ERR_PTR(-EBADF); + + /* Checks FD type and access right. */ + err = 0; + if (ruleset_f.file->f_op != &ruleset_fops) + err = -EBADR; + else if (!(ruleset_f.file->f_mode & mode)) + err = -EPERM; + if (!err) { + ruleset = ruleset_f.file->private_data; + landlock_get_ruleset(ruleset); + } + fdput(ruleset_f); + return err ? ERR_PTR(err) : ruleset; +} + +/* Path handling */ + +static inline bool is_user_mountable(const struct dentry *const dentry) +{ + /* + * Checks pseudo-filesystems that will never be mountable (e.g. sockfs, + * pipefs, bdev), cf. fs/libfs.c:init_pseudo(). + */ + return d_is_positive(dentry) && + !IS_PRIVATE(dentry->d_inode) && + !(dentry->d_sb->s_flags & SB_NOUSER); +} + +/* + * @path: Must call put_path(@path) after the call if it succeeded. + */ +static int get_path_from_fd(const u64 fd, struct path *const path) +{ + struct fd f; + int err = 0; + + BUILD_BUG_ON(!__same_type(fd, + ((struct landlock_attr_path_beneath *)NULL)->parent_fd)); + + /* Checks 32-bits overflow. fdget_raw() checks for INT_MAX/FD. */ + if (fd > U32_MAX) + return -EINVAL; + + /* Handles O_PATH. */ + f = fdget_raw(fd); + if (!f.file) + return -EBADF; + + /* + * Only allows O_PATH FD: enables to restrict ambient (FS) accesses + * without requiring to open and risk leaking or misusing a FD. Accept + * removed, but still open directory (S_DEAD). + */ + if (!(f.file->f_mode & FMODE_PATH) || + !is_user_mountable(f.file->f_path.dentry)) { + err = -EBADR; + goto out_fdput; + } + path->mnt = f.file->f_path.mnt; + path->dentry = f.file->f_path.dentry; + path_get(path); + +out_fdput: + fdput(f); + return err; +} + +static int syscall_add_rule_path_beneath(const size_t attr_size, + const void __user *const attr_ptr) +{ + struct landlock_attr_path_beneath attr_path_beneath; + struct path path; + struct landlock_ruleset *ruleset; + int err; + + /* Copies raw user space buffer. */ + err = copy_struct_if_any_from_user(&attr_path_beneath, + sizeof(attr_path_beneath), + offsetofend(typeof(attr_path_beneath), allowed_access), + attr_ptr, attr_size); + if (err) + return err; + + /* Gets and checks the ruleset. */ + ruleset = get_ruleset_from_fd(attr_path_beneath.ruleset_fd, + FMODE_CAN_WRITE); + if (IS_ERR(ruleset)) + return PTR_ERR(ruleset); + + /* + * Checks that allowed_access matches the @ruleset constraints + * (ruleset->fs_access_mask is automatically upgraded to 64-bits). + * Allows empty allowed_access i.e., deny @ruleset->fs_access_mask . + */ + if ((attr_path_beneath.allowed_access | ruleset->fs_access_mask) != + ruleset->fs_access_mask) { + err = -EINVAL; + goto out_put_ruleset; + } + + /* Gets and checks the new rule. */ + err = get_path_from_fd(attr_path_beneath.parent_fd, &path); + if (err) + goto out_put_ruleset; + + /* Imports the new rule. */ + err = landlock_append_fs_rule(ruleset, &path, + attr_path_beneath.allowed_access); + path_put(&path); + +out_put_ruleset: + landlock_put_ruleset(ruleset); + return err; +} + +/* Enforcement */ + +static int syscall_enforce_ruleset(const size_t attr_size, + const void __user *const attr_ptr) +{ + struct landlock_ruleset *new_dom, *ruleset; + struct cred *new_cred; + struct landlock_cred_security *new_llcred; + struct landlock_attr_enforce attr_enforce; + int err; + + /* + * Enforcing a Landlock ruleset requires that the task has + * CAP_SYS_ADMIN in its namespace or be running with no_new_privs. + * This avoids scenarios where unprivileged tasks can affect the + * behavior of privileged children. These are similar checks as for + * seccomp(2), except that an -EPERM may be returned. + */ + if (!task_no_new_privs(current)) { + err = security_capable(current_cred(), current_user_ns(), + CAP_SYS_ADMIN, CAP_OPT_NOAUDIT); + if (err) + return err; + } + + /* Copies raw user space buffer. */ + err = copy_struct_if_any_from_user(&attr_enforce, sizeof(attr_enforce), + offsetofend(typeof(attr_enforce), ruleset_fd), + attr_ptr, attr_size); + if (err) + return err; + + /* Gets and checks the ruleset. */ + ruleset = get_ruleset_from_fd(attr_enforce.ruleset_fd, FMODE_CAN_READ); + if (IS_ERR(ruleset)) + return PTR_ERR(ruleset); + + /* Informs about useless ruleset. */ + if (!atomic_read(&ruleset->nb_rules)) { + err = -ENOMSG; + goto out_put_ruleset; + } + + /* Prepares new credentials. */ + new_cred = prepare_creds(); + if (!new_cred) { + err = -ENOMEM; + goto out_put_ruleset; + } + new_llcred = landlock_cred(new_cred); + + /* + * There is no possible race condition while copying and manipulating + * the current credentials because they are dedicated per thread. + */ + new_dom = landlock_merge_ruleset(new_llcred->domain, ruleset); + if (IS_ERR(new_dom)) { + err = PTR_ERR(new_dom); + goto out_put_creds; + } + + /* Replaces the old (prepared) domain. */ + landlock_put_ruleset(new_llcred->domain); + new_llcred->domain = new_dom; + + landlock_put_ruleset(ruleset); + return commit_creds(new_cred); + +out_put_creds: + abort_creds(new_cred); + return err; + +out_put_ruleset: + landlock_put_ruleset(ruleset); + return err; +} + +/** + * landlock - System call to enable a process to safely sandbox itself + * + * @command: Landlock command to perform miscellaneous, but safe, actions. Cf. + * `Commands`_. + * @options: Bitmask of options dedicated to one command. Cf. `Options`_. + * @attr1_size: First attribute size (i.e. size of the struct). + * @attr1_ptr: Pointer to the first attribute. Cf. `Attributes`_. + * @attr2_size: Unused for now. + * @attr2_ptr: Unused for now. + * + * The @command and @options arguments enable a seccomp-bpf policy to control + * the requested actions. However, it should be noted that Landlock is + * designed from the ground to enable unprivileged process to drop privileges + * and accesses in a way that can not harm other processes. This syscall and + * all its arguments should then be allowed for any process, which will then + * enable applications to strengthen the security of the whole system. + * + * @attr2_size and @attr2_ptr describe a second attribute which could be used + * in the future to compose with the first attribute (e.g. a + * landlock_attr_path_beneath with a landlock_attr_ioctl). + * + * The order of return errors begins with ENOPKG (disabled Landlock), + * EOPNOTSUPP (unknown command or option) and then EINVAL (invalid attribute). + * The other error codes may be specific to each command. + */ +SYSCALL_DEFINE6(landlock, const unsigned int, command, + const unsigned int, options, + const size_t, attr1_size, void __user *const, attr1_ptr, + const size_t, attr2_size, void __user *const, attr2_ptr) +{ + /* + * Enables user space to identify if Landlock is disabled, thanks to a + * specific error code. + */ + if (!landlock_initialized) + return -ENOPKG; + + switch ((enum landlock_cmd)command) { + case LANDLOCK_CMD_GET_FEATURES: + if (options == LANDLOCK_OPT_GET_FEATURES) { + if (attr2_size || attr2_ptr) + return -EINVAL; + return syscall_get_features(attr1_size, attr1_ptr); + } + return -EOPNOTSUPP; + + case LANDLOCK_CMD_CREATE_RULESET: + if (options == LANDLOCK_OPT_CREATE_RULESET) { + if (attr2_size || attr2_ptr) + return -EINVAL; + return syscall_create_ruleset(attr1_size, attr1_ptr); + } + return -EOPNOTSUPP; + + case LANDLOCK_CMD_ADD_RULE: + /* + * A future extension could add a + * LANDLOCK_OPT_ADD_RULE_PATH_RANGE. + */ + if (options == LANDLOCK_OPT_ADD_RULE_PATH_BENEATH) { + if (attr2_size || attr2_ptr) + return -EINVAL; + return syscall_add_rule_path_beneath(attr1_size, + attr1_ptr); + } + return -EOPNOTSUPP; + + case LANDLOCK_CMD_ENFORCE_RULESET: + if (options == LANDLOCK_OPT_ENFORCE_RULESET) { + if (attr2_size || attr2_ptr) + return -EINVAL; + return syscall_enforce_ruleset(attr1_size, attr1_ptr); + } + return -EOPNOTSUPP; + } + return -EOPNOTSUPP; +}

Test landlock syscall, ptrace hooks semantic and filesystem access-control.

Signed-off-by: Mickaël Salaün mic@digikod.net Reviewed-by: Vincent Dagonneau vincent.dagonneau@ssi.gouv.fr Cc: Andy Lutomirski luto@amacapital.net Cc: James Morris jmorris@namei.org Cc: Kees Cook keescook@chromium.org Cc: Serge E. Hallyn serge@hallyn.com Cc: Shuah Khan shuah@kernel.org ---

Changes since v14: * Add new tests: - Compatibility: empty_attr_{ruleset,path_beneath,enforce} to check minimal attr size. - Access types: link_to, rename_from, rename_to, rmdir, unlink, make_char, make_block, make_reg, make_sock, make_fifo, make_sym, make_dir, chroot, execute. - Test privilege escalation prevention by enforcing a nested rule, on a parent directory, with less restrictions than one on a child directory. - Test for empty and more than 32-bits allowed_access * Merge the two test mount hierarchies. * Complete relative path tests by combining chdir and chroot. * Adjust tests: - Remove the layout1/extend_ruleset_with_denied_path test. - Extend layout1/whitelist test with checks on file. - Add and use create_dir_and_file(). * Only use read/write checks but not stat(2) for tests. * Rename test.h to common.h and improve it. * Rename path name to make them more consistent, easy to understand and make them in a common directory. * Make create_ruleset() more generic. * Constify variables. * Re-add static global variables. * Remove useless openat(2). * Fix and complete kernel config. * Set umask and clean up file modes. * Clean up open flags. * Improve Makefile. * Fix spelling. * Improve comments and error messages.

Changes since v13: * Add back the filesystem tests (from v10) and extend them. * Add tests for the new syscall.

Previous version: https://lore.kernel.org/lkml/20191104172146.30797-7-mic@digikod.net/ --- tools/testing/selftests/Makefile | 1 + tools/testing/selftests/landlock/.gitignore | 4 + tools/testing/selftests/landlock/Makefile | 26 + tools/testing/selftests/landlock/common.h | 42 + tools/testing/selftests/landlock/config | 5 + tools/testing/selftests/landlock/test_base.c | 113 ++ tools/testing/selftests/landlock/test_fs.c | 1249 +++++++++++++++++ .../testing/selftests/landlock/test_ptrace.c | 294 ++++ tools/testing/selftests/landlock/true.c | 5 + 9 files changed, 1739 insertions(+) create mode 100644 tools/testing/selftests/landlock/.gitignore create mode 100644 tools/testing/selftests/landlock/Makefile create mode 100644 tools/testing/selftests/landlock/common.h create mode 100644 tools/testing/selftests/landlock/config create mode 100644 tools/testing/selftests/landlock/test_base.c create mode 100644 tools/testing/selftests/landlock/test_fs.c create mode 100644 tools/testing/selftests/landlock/test_ptrace.c create mode 100644 tools/testing/selftests/landlock/true.c

diff --git a/tools/testing/selftests/Makefile b/tools/testing/selftests/Makefile index 6ec503912bea..5183f269c244 100644 --- a/tools/testing/selftests/Makefile +++ b/tools/testing/selftests/Makefile @@ -24,6 +24,7 @@ TARGETS += ir TARGETS += kcmp TARGETS += kexec TARGETS += kvm +TARGETS += landlock TARGETS += lib TARGETS += livepatch TARGETS += lkdtm diff --git a/tools/testing/selftests/landlock/.gitignore b/tools/testing/selftests/landlock/.gitignore new file mode 100644 index 000000000000..fd081d6ef7c0 --- /dev/null +++ b/tools/testing/selftests/landlock/.gitignore @@ -0,0 +1,4 @@ +/test_base +/test_fs +/test_ptrace +/true diff --git a/tools/testing/selftests/landlock/Makefile b/tools/testing/selftests/landlock/Makefile new file mode 100644 index 000000000000..96ec5863c156 --- /dev/null +++ b/tools/testing/selftests/landlock/Makefile @@ -0,0 +1,26 @@ +# SPDX-License-Identifier: GPL-2.0 + +test_src := $(wildcard test_*.c) + +TEST_GEN_PROGS := $(test_src:.c=) + +TEST_GEN_PROGS_EXTENDED := true + +KSFT_KHDR_INSTALL := 1 +include ../lib.mk + +# Cf. tools/testing/selftests/arm64/Makefile +ifeq ($(KBUILD_OUTPUT),) +khdr_dir = $(top_srcdir)/usr/include +else +khdr_dir = $(KBUILD_OUTPUT)/kselftest/usr/include +endif + +CFLAGS += -Wall -O2 -I$(khdr_dir) + +$(khdr_dir)/linux/landlock.h: khdr + +$(TEST_GEN_PROGS): $(khdr_dir)/linux/landlock.h ../kselftest_harness.h common.h + +$(OUTPUT)/true: true.c + $(CC) -Os -static -o $@ $< diff --git a/tools/testing/selftests/landlock/common.h b/tools/testing/selftests/landlock/common.h new file mode 100644 index 000000000000..3e0d56a4363a --- /dev/null +++ b/tools/testing/selftests/landlock/common.h @@ -0,0 +1,42 @@ +/* SPDX-License-Identifier: GPL-2.0 */ +/* + * Landlock test helpers + * + * Copyright © 2017-2020 Mickaël Salaün mic@digikod.net + * Copyright © 2019-2020 ANSSI + */ + +#include <errno.h> +#include <linux/landlock.h> +#include <sys/syscall.h> + +#include "../kselftest_harness.h" + +#ifndef landlock +static inline int landlock(const unsigned int command, + const unsigned int options, + const size_t attr_size, void *const attr_ptr) +{ + errno = 0; + return syscall(__NR_landlock, command, options, attr_size, attr_ptr, 0, + NULL); +} +#endif + +FIXTURE(ruleset_rw) { + struct landlock_attr_ruleset attr_ruleset; + int ruleset_fd; +}; + +FIXTURE_SETUP(ruleset_rw) { + self->attr_ruleset.handled_access_fs = LANDLOCK_ACCESS_FS_READ_FILE | + LANDLOCK_ACCESS_FS_WRITE_FILE; + self->ruleset_fd = landlock(LANDLOCK_CMD_CREATE_RULESET, + LANDLOCK_OPT_CREATE_RULESET, + sizeof(self->attr_ruleset), &self->attr_ruleset); + ASSERT_LE(0, self->ruleset_fd); +} + +FIXTURE_TEARDOWN(ruleset_rw) { + ASSERT_EQ(0, close(self->ruleset_fd)); +} diff --git a/tools/testing/selftests/landlock/config b/tools/testing/selftests/landlock/config new file mode 100644 index 000000000000..042298105821 --- /dev/null +++ b/tools/testing/selftests/landlock/config @@ -0,0 +1,5 @@ +CONFIG_SECURITY_LANDLOCK=y +CONFIG_SECURITY_PATH=y +CONFIG_SECURITY=y +CONFIG_SHMEM=y +CONFIG_TMPFS=y diff --git a/tools/testing/selftests/landlock/test_base.c b/tools/testing/selftests/landlock/test_base.c new file mode 100644 index 000000000000..effc419593ce --- /dev/null +++ b/tools/testing/selftests/landlock/test_base.c @@ -0,0 +1,113 @@ +// SPDX-License-Identifier: GPL-2.0 +/* + * Landlock tests - common resources + * + * Copyright © 2017-2020 Mickaël Salaün mic@digikod.net + * Copyright © 2019-2020 ANSSI + */ + +#define _GNU_SOURCE +#include <errno.h> +#include <fcntl.h> +#include <linux/landlock.h> +#include <sys/prctl.h> + +#include "common.h" + +#define FDINFO_TEMPLATE "/proc/self/fdinfo/%d" +#define FDINFO_SIZE 128 + +#ifndef O_PATH +#define O_PATH 010000000 +#endif + +TEST_F(ruleset_rw, fdinfo) +{ + int fdinfo_fd, fdinfo_path_size, fdinfo_buf_size; + char fdinfo_path[sizeof(FDINFO_TEMPLATE) + 2]; + char fdinfo_buf[FDINFO_SIZE]; + + fdinfo_path_size = snprintf(fdinfo_path, sizeof(fdinfo_path), + FDINFO_TEMPLATE, self->ruleset_fd); + ASSERT_LE(fdinfo_path_size, sizeof(fdinfo_path)); + + fdinfo_fd = open(fdinfo_path, O_RDONLY | O_CLOEXEC); + ASSERT_GE(fdinfo_fd, 0); + + fdinfo_buf_size = read(fdinfo_fd, fdinfo_buf, sizeof(fdinfo_buf)); + ASSERT_LE(fdinfo_buf_size, sizeof(fdinfo_buf) - 1); + + /* + * fdinfo_buf: pos: 0 + * flags: 02000002 + * mnt_id: 13 + * handled_access_fs: 804000 + */ + EXPECT_EQ(0, close(fdinfo_fd)); +} + +TEST(features) +{ + struct landlock_attr_features attr_features = { + .options_get_features = ~0ULL, + .options_create_ruleset = ~0ULL, + .options_add_rule = ~0ULL, + .options_enforce_ruleset = ~0ULL, + .access_fs = ~0ULL, + .size_attr_ruleset = ~0ULL, + .size_attr_path_beneath = ~0ULL, + .size_attr_enforce = ~0ULL, + }; + + ASSERT_EQ(0, landlock(LANDLOCK_CMD_GET_FEATURES, + LANDLOCK_OPT_GET_FEATURES, + sizeof(attr_features), &attr_features)); + ASSERT_EQ(((LANDLOCK_OPT_GET_FEATURES << 1) - 1), + attr_features.options_get_features); + ASSERT_EQ(((LANDLOCK_OPT_CREATE_RULESET << 1) - 1), + attr_features.options_create_ruleset); + ASSERT_EQ(((LANDLOCK_OPT_ADD_RULE_PATH_BENEATH << 1) - 1), + attr_features.options_add_rule); + ASSERT_EQ(((LANDLOCK_OPT_ENFORCE_RULESET << 1) - 1), + attr_features.options_enforce_ruleset); + ASSERT_EQ(((LANDLOCK_ACCESS_FS_CHROOT << 1) - 1), + attr_features.access_fs); + ASSERT_EQ(sizeof(struct landlock_attr_ruleset), + attr_features.size_attr_ruleset); + ASSERT_EQ(sizeof(struct landlock_attr_path_beneath), + attr_features.size_attr_path_beneath); + ASSERT_EQ(sizeof(struct landlock_attr_enforce), + attr_features.size_attr_enforce); +} + +TEST(empty_attr_ruleset) { + int err; + + /* Similar to struct landlock_attr_create.handled_access_fs = 0 */ + err = landlock(LANDLOCK_CMD_CREATE_RULESET, + LANDLOCK_OPT_CREATE_RULESET, 0, NULL); + ASSERT_EQ(errno, EINVAL); + ASSERT_EQ(err, -1); +} + +TEST(empty_attr_path_beneath) { + int err; + + /* Similar to struct landlock_attr_path_beneath.*_fd = 0 */ + err = landlock(LANDLOCK_CMD_ADD_RULE, + LANDLOCK_OPT_ADD_RULE_PATH_BENEATH, 0, NULL); + ASSERT_EQ(errno, EINVAL); + ASSERT_EQ(err, -1); +} + +TEST(empty_attr_enforce) { + int err; + + /* Similar to struct landlock_attr_enforce.ruleset_fd = 0 */ + err = landlock(LANDLOCK_CMD_ENFORCE_RULESET, + LANDLOCK_OPT_ENFORCE_RULESET, 0, NULL); + ASSERT_EQ(errno, EINVAL); + ASSERT_EQ(err, -1); +} + +TEST_HARNESS_MAIN diff --git a/tools/testing/selftests/landlock/test_fs.c b/tools/testing/selftests/landlock/test_fs.c new file mode 100644 index 000000000000..747f2cf7a59f --- /dev/null +++ b/tools/testing/selftests/landlock/test_fs.c @@ -0,0 +1,1249 @@ +// SPDX-License-Identifier: GPL-2.0 +/* + * Landlock tests - filesystem + * + * Copyright © 2017-2020 Mickaël Salaün mic@digikod.net + * Copyright © 2020 ANSSI + */ + +#define _GNU_SOURCE +#include <fcntl.h> +#include <linux/landlock.h> +#include <sched.h> +#include <string.h> +#include <sys/mount.h> +#include <sys/prctl.h> +#include <sys/sendfile.h> +#include <sys/stat.h> +#include <sys/sysmacros.h> +#include <unistd.h> + +#include "common.h" + +#define TMP_DIR "tmp/" +#define FILE_NAME "file" +#define BINARY_PATH "./true" + +/* Paths (sibling number and depth) */ +static const char dir_s1d1[] = TMP_DIR "s1d1"; +static const char file_s1d1[] = TMP_DIR "s1d1/" FILE_NAME; +static const char dir_s1d2[] = TMP_DIR "s1d1/s1d2"; +static const char file_s1d2[] = TMP_DIR "s1d1/s1d2/" FILE_NAME; +static const char dir_s1d3[] = TMP_DIR "s1d1/s1d2/s1d3"; +static const char file_s1d3[] = TMP_DIR "s1d1/s1d2/s1d3/" FILE_NAME; + +static const char dir_s2d1[] = TMP_DIR "s2d1"; +static const char file_s2d1[] = TMP_DIR "s2d1/" FILE_NAME; +static const char dir_s2d2[] = TMP_DIR "s2d1/s2d2"; +static const char file_s2d2[] = TMP_DIR "s2d1/s2d2/" FILE_NAME; +static const char dir_s2d3[] = TMP_DIR "s2d1/s2d2/s2d3"; +static const char file_s2d3[] = TMP_DIR "s2d1/s2d2/s2d3/" FILE_NAME; + +static const char dir_s3d1[] = TMP_DIR "s3d1"; +/* dir_s3d2 is a mount point. */ +static const char dir_s3d2[] = TMP_DIR "s3d1/s3d2"; +static const char dir_s3d3[] = TMP_DIR "s3d1/s3d2/s3d3"; + +static void create_dir_and_file(struct __test_metadata *const _metadata, + const char *const dir_path) +{ + int file_fd; + const size_t file_name_len = sizeof(FILE_NAME); + char *const file_path = alloca(strlen(dir_path) + file_name_len + 2); + + strcpy(file_path, dir_path); + strcat(file_path, "/"); + strcat(file_path, FILE_NAME); + + ASSERT_EQ(0, mkdir(dir_path, 0700)) { + TH_LOG("Failed to create directory "%s": %s\n", dir_path, + strerror(errno)); + } + file_fd = open(file_path, O_CREAT | O_EXCL | O_WRONLY | O_CLOEXEC, + 0700); + ASSERT_LE(0, file_fd); + ASSERT_EQ(0, close(file_fd)); +} + +static void delete_dir_and_file(const char *const dir_path) +{ + char *const file_path = alloca(strlen(dir_path) + + sizeof(FILE_NAME) + 2); + + strcpy(file_path, dir_path); + strcat(file_path, "/"); + strcat(file_path, FILE_NAME); + + unlink(file_path); + /* file_path may be a directory, cf. layout1/make_directory. */ + rmdir(file_path); + rmdir(dir_path); +} + +static void cleanup_layout1(void) +{ + delete_dir_and_file(dir_s1d3); + delete_dir_and_file(dir_s1d2); + delete_dir_and_file(dir_s1d1); + + delete_dir_and_file(dir_s2d3); + delete_dir_and_file(dir_s2d2); + delete_dir_and_file(dir_s2d1); + + delete_dir_and_file(dir_s3d3); + umount(dir_s3d2); + delete_dir_and_file(dir_s3d2); + delete_dir_and_file(dir_s3d1); + + delete_dir_and_file(TMP_DIR); +} + +FIXTURE(layout1) { +}; + +FIXTURE_SETUP(layout1) +{ + cleanup_layout1(); + + /* Do not pollute the rest of the system. */ + ASSERT_NE(-1, unshare(CLONE_NEWNS)); + umask(0077); + create_dir_and_file(_metadata, TMP_DIR); + + create_dir_and_file(_metadata, dir_s1d1); + create_dir_and_file(_metadata, dir_s1d2); + create_dir_and_file(_metadata, dir_s1d3); + + create_dir_and_file(_metadata, dir_s2d1); + create_dir_and_file(_metadata, dir_s2d2); + create_dir_and_file(_metadata, dir_s2d3); + + create_dir_and_file(_metadata, dir_s3d1); + create_dir_and_file(_metadata, dir_s3d2); + ASSERT_EQ(0, mount("tmp", dir_s3d2, "tmpfs", 0, "size=4m,mode=700")); + create_dir_and_file(_metadata, dir_s3d3); +} + +FIXTURE_TEARDOWN(layout1) +{ + /* + * cleanup_layout1() would be denied here, use TEST(cleanup) instead. + */ +} + +static void test_path_rel(struct __test_metadata *const _metadata, + const int dirfd, const char *const path, const int ret) +{ + int fd; + + /* Works with file and directories. */ + fd = openat(dirfd, path, O_RDONLY | O_CLOEXEC); + if (ret) { + ASSERT_EQ(-1, fd) { + TH_LOG("Successfully opened "%s": %s\n", path, + strerror(errno)); + } + ASSERT_EQ(EACCES, errno) { + TH_LOG("Wrong error code to open "%s": %s\n", path, + strerror(errno)); + } + } else { + ASSERT_NE(-1, fd) { + TH_LOG("Failed to open "%s": %s\n", path, + strerror(errno)); + } + EXPECT_EQ(0, close(fd)); + } +} + +static void test_path(struct __test_metadata *const _metadata, + const char *const path, const int ret) +{ + return test_path_rel(_metadata, AT_FDCWD, path, ret); +} + +TEST_F(layout1, no_restriction) +{ + test_path(_metadata, dir_s1d1, 0); + test_path(_metadata, file_s1d1, 0); + test_path(_metadata, dir_s1d2, 0); + test_path(_metadata, file_s1d2, 0); + test_path(_metadata, dir_s1d3, 0); + test_path(_metadata, file_s1d3, 0); + + test_path(_metadata, dir_s2d1, 0); + test_path(_metadata, file_s2d1, 0); + test_path(_metadata, dir_s2d2, 0); + test_path(_metadata, file_s2d2, 0); + test_path(_metadata, dir_s2d3, 0); + test_path(_metadata, file_s2d3, 0); + + test_path(_metadata, dir_s3d1, 0); + test_path(_metadata, dir_s3d2, 0); + test_path(_metadata, dir_s3d3, 0); +} + +TEST_F(ruleset_rw, inval) +{ + int err; + struct landlock_attr_path_beneath path_beneath = { + .allowed_access = LANDLOCK_ACCESS_FS_READ_FILE | + LANDLOCK_ACCESS_FS_WRITE_FILE, + .parent_fd = -1, + }; + struct landlock_attr_enforce attr_enforce; + + path_beneath.ruleset_fd = self->ruleset_fd; + path_beneath.parent_fd = open(dir_s1d2, O_PATH | O_DIRECTORY | + O_CLOEXEC); + ASSERT_GE(path_beneath.parent_fd, 0); + err = landlock(LANDLOCK_CMD_ADD_RULE, + LANDLOCK_OPT_ADD_RULE_PATH_BENEATH, + sizeof(path_beneath), &path_beneath); + ASSERT_EQ(errno, 0); + ASSERT_EQ(err, 0); + ASSERT_EQ(0, close(path_beneath.parent_fd)); + + /* Tests without O_PATH. */ + path_beneath.parent_fd = open(dir_s1d2, O_DIRECTORY | + O_CLOEXEC); + ASSERT_GE(path_beneath.parent_fd, 0); + err = landlock(LANDLOCK_CMD_ADD_RULE, + LANDLOCK_OPT_ADD_RULE_PATH_BENEATH, + sizeof(path_beneath), &path_beneath); + ASSERT_EQ(err, -1); + ASSERT_EQ(errno, EBADR); + errno = 0; + ASSERT_EQ(0, close(path_beneath.parent_fd)); + + /* Checks unhandled allowed_access. */ + path_beneath.parent_fd = open(dir_s1d2, O_PATH | O_DIRECTORY | + O_CLOEXEC); + ASSERT_GE(path_beneath.parent_fd, 0); + + /* Test with legitimate values. */ + path_beneath.allowed_access |= LANDLOCK_ACCESS_FS_EXECUTE; + err = landlock(LANDLOCK_CMD_ADD_RULE, + LANDLOCK_OPT_ADD_RULE_PATH_BENEATH, + sizeof(path_beneath), &path_beneath); + path_beneath.allowed_access &= ~LANDLOCK_ACCESS_FS_EXECUTE; + ASSERT_EQ(errno, EINVAL); + errno = 0; + ASSERT_EQ(err, -1); + + /* Test with unknown (64-bits) value. */ + path_beneath.allowed_access |= (1ULL << 60); + err = landlock(LANDLOCK_CMD_ADD_RULE, + LANDLOCK_OPT_ADD_RULE_PATH_BENEATH, + sizeof(path_beneath), &path_beneath); + path_beneath.allowed_access &= ~(1ULL << 60); + ASSERT_EQ(errno, EINVAL); + errno = 0; + ASSERT_EQ(err, -1); + + /* Test with no access. */ + path_beneath.allowed_access = 0; + err = landlock(LANDLOCK_CMD_ADD_RULE, + LANDLOCK_OPT_ADD_RULE_PATH_BENEATH, + sizeof(path_beneath), &path_beneath); + path_beneath.allowed_access &= ~(1ULL << 60); + ASSERT_EQ(err, 0); + + ASSERT_EQ(0, close(path_beneath.parent_fd)); + + err = prctl(PR_SET_NO_NEW_PRIVS, 1, 0, 0, 0); + ASSERT_EQ(errno, 0); + ASSERT_EQ(err, 0); + + attr_enforce.ruleset_fd = self->ruleset_fd; + err = landlock(LANDLOCK_CMD_ENFORCE_RULESET, + LANDLOCK_OPT_ENFORCE_RULESET, sizeof(attr_enforce), + &attr_enforce); + ASSERT_EQ(errno, 0); + ASSERT_EQ(err, 0); +} + +TEST_F(ruleset_rw, nsfs) +{ + struct landlock_attr_path_beneath path_beneath = { + .allowed_access = LANDLOCK_ACCESS_FS_READ_FILE | + LANDLOCK_ACCESS_FS_WRITE_FILE, + .ruleset_fd = self->ruleset_fd, + }; + int err; + + path_beneath.parent_fd = open("/proc/self/ns/mnt", O_PATH | O_CLOEXEC); + ASSERT_GE(path_beneath.parent_fd, 0); + err = landlock(LANDLOCK_CMD_ADD_RULE, + LANDLOCK_OPT_ADD_RULE_PATH_BENEATH, + sizeof(path_beneath), &path_beneath); + ASSERT_EQ(errno, 0); + ASSERT_EQ(err, 0); + ASSERT_EQ(0, close(path_beneath.parent_fd)); +} + +static void add_path_beneath(struct __test_metadata *const _metadata, + const int ruleset_fd, const __u64 allowed_access, + const char *const path) +{ + int err; + struct landlock_attr_path_beneath path_beneath = { + .ruleset_fd = ruleset_fd, + .allowed_access = allowed_access, + }; + + path_beneath.parent_fd = open(path, O_PATH | O_CLOEXEC); + ASSERT_GE(path_beneath.parent_fd, 0) { + TH_LOG("Failed to open directory "%s": %s\n", path, + strerror(errno)); + } + err = landlock(LANDLOCK_CMD_ADD_RULE, + LANDLOCK_OPT_ADD_RULE_PATH_BENEATH, + sizeof(path_beneath), &path_beneath); + ASSERT_EQ(err, 0) { + TH_LOG("Failed to update the ruleset with "%s": %s\n", path, + strerror(errno)); + } + ASSERT_EQ(errno, 0); + ASSERT_EQ(0, close(path_beneath.parent_fd)); +} + +struct rule { + const char *path; + __u64 access; +}; + +#define ACCESS_RO ( \ + LANDLOCK_ACCESS_FS_READ_FILE | \ + LANDLOCK_ACCESS_FS_READ_DIR) + +#define ACCESS_RW ( \ + ACCESS_RO | \ + LANDLOCK_ACCESS_FS_WRITE_FILE) + +static int create_ruleset(struct __test_metadata *const _metadata, + const __u64 handled_access_fs, const struct rule rules[]) +{ + int ruleset_fd, i; + struct landlock_attr_features attr_features; + struct landlock_attr_ruleset attr_ruleset = { + .handled_access_fs = handled_access_fs, + }; + + ASSERT_NE(NULL, rules) { + TH_LOG("No rule list\n"); + } + ASSERT_NE(NULL, rules[0].path) { + TH_LOG("Empty rule list\n"); + } + + ASSERT_EQ(0, landlock(LANDLOCK_CMD_GET_FEATURES, + LANDLOCK_OPT_GET_FEATURES, + sizeof(attr_features), &attr_features)); + /* Only for test, use a binary AND for real application instead. */ + ASSERT_EQ(attr_ruleset.handled_access_fs, + attr_ruleset.handled_access_fs & + attr_features.access_fs); + ruleset_fd = landlock(LANDLOCK_CMD_CREATE_RULESET, + LANDLOCK_OPT_CREATE_RULESET, sizeof(attr_ruleset), + &attr_ruleset); + ASSERT_GE(ruleset_fd, 0) { + TH_LOG("Failed to create a ruleset: %s\n", strerror(errno)); + } + + for (i = 0; rules[i].path; i++) { + ASSERT_EQ(rules[i].access, rules[i].access & + attr_features.access_fs); + add_path_beneath(_metadata, ruleset_fd, rules[i].access, + rules[i].path); + } + return ruleset_fd; +} + +static void enforce_ruleset(struct __test_metadata *const _metadata, + const int ruleset_fd) +{ + struct landlock_attr_enforce attr_enforce = { + .ruleset_fd = ruleset_fd, + }; + int err; + + err = prctl(PR_SET_NO_NEW_PRIVS, 1, 0, 0, 0); + ASSERT_EQ(errno, 0); + ASSERT_EQ(err, 0); + + err = landlock(LANDLOCK_CMD_ENFORCE_RULESET, + LANDLOCK_OPT_ENFORCE_RULESET, sizeof(attr_enforce), + &attr_enforce); + ASSERT_EQ(err, 0) { + TH_LOG("Failed to enforce ruleset: %s\n", strerror(errno)); + } + ASSERT_EQ(errno, 0); +} + +TEST_F(layout1, whitelist) +{ + const struct rule rules[] = { + { + .path = dir_s1d2, + .access = ACCESS_RO, + }, + { + .path = file_s2d2, + .access = ACCESS_RO, + }, + {}, + }; + const int ruleset_fd = create_ruleset(_metadata, ACCESS_RW, rules); + + ASSERT_NE(-1, ruleset_fd); + enforce_ruleset(_metadata, ruleset_fd); + EXPECT_EQ(0, close(ruleset_fd)); + + /* Tests on a directory. */ + test_path(_metadata, "/", -1); + test_path(_metadata, dir_s1d1, -1); + test_path(_metadata, file_s1d1, -1); + test_path(_metadata, dir_s1d2, 0); + test_path(_metadata, file_s1d2, 0); + test_path(_metadata, dir_s1d3, 0); + test_path(_metadata, file_s1d3, 0); + + /* Tests on a file. */ + test_path(_metadata, dir_s2d2, -1); + test_path(_metadata, file_s2d2, 0); +} + +TEST_F(layout1, unhandled_access) +{ + const struct rule rules[] = { + { + .path = dir_s1d2, + .access = ACCESS_RO, + }, + {}, + }; + const int ruleset_fd = create_ruleset(_metadata, ACCESS_RW, rules); + + ASSERT_NE(-1, ruleset_fd); + enforce_ruleset(_metadata, ruleset_fd); + EXPECT_EQ(0, close(ruleset_fd)); + + /* + * Because the policy does not handle LANDLOCK_ACCESS_FS_CHROOT, + * chroot(2) should be allowed. + */ + ASSERT_EQ(0, chroot(dir_s1d1)); + ASSERT_EQ(0, chroot(dir_s1d2)); + ASSERT_EQ(0, chroot(dir_s1d3)); +} + +TEST_F(layout1, ruleset_overlap) +{ + const struct rule rules[] = { + /* These rules should be ORed among them. */ + { + .path = dir_s1d2, + .access = LANDLOCK_ACCESS_FS_WRITE_FILE, + }, + { + .path = dir_s1d2, + .access = LANDLOCK_ACCESS_FS_READ_DIR, + }, + {}, + }; + int open_fd; + const int ruleset_fd = create_ruleset(_metadata, ACCESS_RW, rules); + + ASSERT_NE(-1, ruleset_fd); + enforce_ruleset(_metadata, ruleset_fd); + EXPECT_EQ(0, close(ruleset_fd)); + + ASSERT_EQ(-1, open(file_s1d1, O_WRONLY | O_CLOEXEC)); + ASSERT_EQ(EACCES, errno); + ASSERT_EQ(-1, open(dir_s1d1, O_RDONLY | O_DIRECTORY | O_CLOEXEC)); + ASSERT_EQ(EACCES, errno); + + open_fd = open(file_s1d2, O_WRONLY | O_CLOEXEC); + ASSERT_NE(-1, open_fd); + EXPECT_EQ(0, close(open_fd)); + open_fd = open(dir_s1d2, O_RDONLY | O_DIRECTORY | O_CLOEXEC); + ASSERT_NE(-1, open_fd); + EXPECT_EQ(0, close(open_fd)); + + open_fd = open(file_s1d3, O_WRONLY | O_CLOEXEC); + ASSERT_NE(-1, open_fd); + EXPECT_EQ(0, close(open_fd)); + open_fd = open(dir_s1d3, O_RDONLY | O_DIRECTORY | O_CLOEXEC); + ASSERT_NE(-1, open_fd); + EXPECT_EQ(0, close(open_fd)); +} + +TEST_F(layout1, inherit_superset) +{ + const struct rule rules[] = { + { + .path = dir_s1d2, + .access = LANDLOCK_ACCESS_FS_READ_FILE | + LANDLOCK_ACCESS_FS_READ_DIR, + }, + {}, + }; + int open_fd; + const int ruleset_fd = create_ruleset(_metadata, ACCESS_RW, rules); + + ASSERT_NE(-1, ruleset_fd); + enforce_ruleset(_metadata, ruleset_fd); + + ASSERT_EQ(-1, open(file_s1d1, O_WRONLY | O_CLOEXEC)); + ASSERT_EQ(EACCES, errno); + ASSERT_EQ(-1, open(dir_s1d1, O_RDONLY | O_DIRECTORY | O_CLOEXEC)); + ASSERT_EQ(EACCES, errno); + + /* Write access is forbidden. */ + ASSERT_EQ(-1, open(file_s1d2, O_WRONLY | O_CLOEXEC)); + ASSERT_EQ(EACCES, errno); + /* Readdir access is allowed. */ + open_fd = open(dir_s1d2, O_RDONLY | O_DIRECTORY | O_CLOEXEC); + ASSERT_NE(-1, open_fd); + ASSERT_EQ(0, close(open_fd)); + + /* Write access is forbidden. */ + ASSERT_EQ(-1, open(file_s1d3, O_WRONLY | O_CLOEXEC)); + ASSERT_EQ(EACCES, errno); + /* Readdir access is allowed. */ + open_fd = open(dir_s1d3, O_RDONLY | O_DIRECTORY | O_CLOEXEC); + ASSERT_NE(-1, open_fd); + ASSERT_EQ(0, close(open_fd)); + + /* + * Tests shared rule extension: the following rules should not grant + * any new access, only remove some. Once enforced, these rules are + * ANDed with the previous ones. + */ + add_path_beneath(_metadata, ruleset_fd, LANDLOCK_ACCESS_FS_WRITE_FILE, + dir_s1d2); + /* + * According to ruleset_fd, dir_s1d2 should now have the + * LANDLOCK_ACCESS_FS_READ_FILE and LANDLOCK_ACCESS_FS_WRITE_FILE + * access rights (even if this directory is opened a second time). + * However, when enforcing this updated ruleset, the ruleset tied to + * the current process (i.e. its domain) will still only have the + * dir_s1d2 with LANDLOCK_ACCESS_FS_READ_FILE and + * LANDLOCK_ACCESS_FS_READ_DIR accesses, but + * LANDLOCK_ACCESS_FS_WRITE_FILE must not be allowed because it would + * be a privilege escalation. + */ + enforce_ruleset(_metadata, ruleset_fd); + + /* Same tests and results as above. */ + ASSERT_EQ(-1, open(file_s1d1, O_WRONLY | O_CLOEXEC)); + ASSERT_EQ(EACCES, errno); + ASSERT_EQ(-1, open(dir_s1d1, O_RDONLY | O_DIRECTORY | O_CLOEXEC)); + ASSERT_EQ(EACCES, errno); + + /* It is still forbidden to write in file_s1d2. */ + ASSERT_EQ(-1, open(file_s1d2, O_WRONLY | O_CLOEXEC)); + ASSERT_EQ(EACCES, errno); + /* Readdir access is still allowed. */ + open_fd = open(dir_s1d2, O_RDONLY | O_DIRECTORY | O_CLOEXEC); + ASSERT_NE(-1, open_fd); + ASSERT_EQ(0, close(open_fd)); + + /* It is still forbidden to write in file_s1d3. */ + ASSERT_EQ(-1, open(file_s1d3, O_WRONLY | O_CLOEXEC)); + ASSERT_EQ(EACCES, errno); + /* Readdir access is still allowed. */ + open_fd = open(dir_s1d3, O_RDONLY | O_DIRECTORY | O_CLOEXEC); + ASSERT_NE(-1, open_fd); + ASSERT_EQ(0, close(open_fd)); + + /* + * Try to get more privileges by adding new access rights to the parent + * directory: dir_s1d1. + */ + add_path_beneath(_metadata, ruleset_fd, ACCESS_RW, dir_s1d1); + enforce_ruleset(_metadata, ruleset_fd); + + /* Same tests and results as above. */ + ASSERT_EQ(-1, open(file_s1d1, O_WRONLY | O_CLOEXEC)); + ASSERT_EQ(EACCES, errno); + ASSERT_EQ(-1, open(dir_s1d1, O_RDONLY | O_DIRECTORY | O_CLOEXEC)); + ASSERT_EQ(EACCES, errno); + + /* It is still forbidden to write in file_s1d2. */ + ASSERT_EQ(-1, open(file_s1d2, O_WRONLY | O_CLOEXEC)); + ASSERT_EQ(EACCES, errno); + /* Readdir access is still allowed. */ + open_fd = open(dir_s1d2, O_RDONLY | O_DIRECTORY | O_CLOEXEC); + ASSERT_NE(-1, open_fd); + ASSERT_EQ(0, close(open_fd)); + + /* It is still forbidden to write in file_s1d3. */ + ASSERT_EQ(-1, open(file_s1d3, O_WRONLY | O_CLOEXEC)); + ASSERT_EQ(EACCES, errno); + /* Readdir access is still allowed. */ + open_fd = open(dir_s1d3, O_RDONLY | O_DIRECTORY | O_CLOEXEC); + ASSERT_NE(-1, open_fd); + ASSERT_EQ(0, close(open_fd)); + + /* + * Now, dir_s1d3 get a new rule tied to it, only allowing + * LANDLOCK_ACCESS_FS_WRITE_FILE. The (kernel internal) difference is + * that there was no rule tied to it before. + */ + add_path_beneath(_metadata, ruleset_fd, LANDLOCK_ACCESS_FS_WRITE_FILE, + dir_s1d3); + enforce_ruleset(_metadata, ruleset_fd); + EXPECT_EQ(0, close(ruleset_fd)); + + /* + * Same tests and results as above, except for open(dir_s1d3) which is + * now denied because the new rule mask the rule previously inherited + * from dir_s1d2. + */ + + /* Same tests and results as above. */ + ASSERT_EQ(-1, open(file_s1d1, O_WRONLY | O_CLOEXEC)); + ASSERT_EQ(EACCES, errno); + ASSERT_EQ(-1, open(dir_s1d1, O_RDONLY | O_DIRECTORY | O_CLOEXEC)); + ASSERT_EQ(EACCES, errno); + + /* It is still forbidden to write in file_s1d2. */ + ASSERT_EQ(-1, open(file_s1d2, O_WRONLY | O_CLOEXEC)); + /* Readdir access is still allowed. */ + open_fd = open(dir_s1d2, O_RDONLY | O_DIRECTORY | O_CLOEXEC); + ASSERT_NE(-1, open_fd); + ASSERT_EQ(0, close(open_fd)); + + /* It is still forbidden to write in file_s1d3. */ + ASSERT_EQ(-1, open(file_s1d3, O_WRONLY | O_CLOEXEC)); + open_fd = open(dir_s1d3, O_RDONLY | O_DIRECTORY | O_CLOEXEC); + /* Readdir of dir_s1d3 is now forbidden too. */ + ASSERT_EQ(-1, open_fd); + ASSERT_EQ(EACCES, errno); +} + +TEST_F(layout1, rule_on_mountpoint) +{ + const struct rule rules[] = { + { + .path = dir_s1d1, + .access = ACCESS_RO, + }, + { + /* dir_s3d2 is a mount point. */ + .path = dir_s3d2, + .access = ACCESS_RO, + }, + {}, + }; + const int ruleset_fd = create_ruleset(_metadata, ACCESS_RW, rules); + + ASSERT_NE(-1, ruleset_fd); + enforce_ruleset(_metadata, ruleset_fd); + EXPECT_EQ(0, close(ruleset_fd)); + + test_path(_metadata, dir_s1d1, 0); + + test_path(_metadata, dir_s2d1, -1); + + test_path(_metadata, dir_s3d1, -1); + test_path(_metadata, dir_s3d2, 0); + test_path(_metadata, dir_s3d3, 0); +} + +TEST_F(layout1, rule_over_mountpoint) +{ + const struct rule rules[] = { + { + .path = dir_s1d1, + .access = ACCESS_RO, + }, + { + /* dir_s3d2 is a mount point. */ + .path = dir_s3d1, + .access = ACCESS_RO, + }, + {}, + }; + const int ruleset_fd = create_ruleset(_metadata, ACCESS_RW, rules); + + ASSERT_NE(-1, ruleset_fd); + enforce_ruleset(_metadata, ruleset_fd); + EXPECT_EQ(0, close(ruleset_fd)); + + test_path(_metadata, dir_s1d1, 0); + + test_path(_metadata, dir_s2d1, -1); + + test_path(_metadata, dir_s3d1, 0); + test_path(_metadata, dir_s3d2, 0); + test_path(_metadata, dir_s3d3, 0); +} + +/* + * This test verifies that we can apply a landlock rule on the root (/), it + * might require special handling. + */ +TEST_F(layout1, rule_over_root) +{ + const struct rule rules[] = { + { + .path = "/", + .access = ACCESS_RO, + }, + {}, + }; + const int ruleset_fd = create_ruleset(_metadata, ACCESS_RW, rules); + + ASSERT_NE(-1, ruleset_fd); + enforce_ruleset(_metadata, ruleset_fd); + EXPECT_EQ(0, close(ruleset_fd)); + + test_path(_metadata, "/", 0); + test_path(_metadata, dir_s1d1, 0); +} + +TEST_F(layout1, rule_inside_mount_ns) +{ + const struct rule rules[] = { + { + .path = "s3d3", + .access = ACCESS_RO, + }, + {}, + }; + int ruleset_fd; + + ASSERT_NE(-1, mount(NULL, "/", NULL, MS_PRIVATE | MS_REC, NULL)); + ASSERT_NE(-1, syscall(SYS_pivot_root, dir_s3d2, dir_s3d3)) { + TH_LOG("Failed to pivot_root into "%s": %s\n", dir_s3d2, + strerror(errno)); + }; + ASSERT_NE(-1, chdir("/")); + + ruleset_fd = create_ruleset(_metadata, ACCESS_RW, rules); + ASSERT_NE(-1, ruleset_fd); + enforce_ruleset(_metadata, ruleset_fd); + EXPECT_EQ(0, close(ruleset_fd)); + + test_path(_metadata, "s3d3", 0); + test_path(_metadata, "/", -1); +} + +TEST_F(layout1, mount_and_pivot) +{ + const struct rule rules[] = { + { + .path = dir_s3d2, + .access = ACCESS_RO, + }, + {}, + }; + const int ruleset_fd = create_ruleset(_metadata, ACCESS_RW, rules); + + ASSERT_NE(-1, ruleset_fd); + enforce_ruleset(_metadata, ruleset_fd); + EXPECT_EQ(0, close(ruleset_fd)); + + ASSERT_EQ(-1, mount(NULL, "/", NULL, MS_PRIVATE | MS_REC, NULL)); + ASSERT_EQ(-1, syscall(SYS_pivot_root, dir_s3d2, dir_s3d3)); +} + +enum relative_access { + REL_OPEN, + REL_CHDIR, + REL_CHROOT_ONLY, + REL_CHROOT_CHDIR, +}; + +static void test_relative_path(struct __test_metadata *const _metadata, + const enum relative_access rel) +{ + const struct rule rules[] = { + { + .path = dir_s1d2, + .access = ACCESS_RO, + }, + { + .path = dir_s2d2, + .access = ACCESS_RO, + }, + {}, + }; + int dirfd; + const int ruleset_fd = create_ruleset(_metadata, ACCESS_RW, rules); + + ASSERT_NE(-1, ruleset_fd); + switch (rel) { + case REL_OPEN: + case REL_CHDIR: + break; + case REL_CHROOT_ONLY: + ASSERT_EQ(0, chdir(dir_s2d2)); + break; + case REL_CHROOT_CHDIR: + ASSERT_EQ(0, chdir(dir_s1d2)); + break; + default: + ASSERT_TRUE(false); + return; + } + enforce_ruleset(_metadata, ruleset_fd); + + switch (rel) { + case REL_OPEN: + dirfd = open(dir_s1d2, O_DIRECTORY); + ASSERT_NE(-1, dirfd); + break; + case REL_CHDIR: + ASSERT_NE(-1, chdir(dir_s1d2)); + dirfd = AT_FDCWD; + break; + case REL_CHROOT_ONLY: + /* Do chroot into dir_s1d2 (relative to dir_s2d2). */ + ASSERT_NE(-1, chroot("../../s1d1/s1d2")) { + TH_LOG("Failed to chroot: %s\n", strerror(errno)); + } + dirfd = AT_FDCWD; + break; + case REL_CHROOT_CHDIR: + /* Do chroot into dir_s1d2. */ + ASSERT_NE(-1, chroot(".")) { + TH_LOG("Failed to chroot: %s\n", strerror(errno)); + } + dirfd = AT_FDCWD; + break; + } + + test_path_rel(_metadata, dirfd, "..", + (rel == REL_CHROOT_CHDIR) ? 0 : -1); + test_path_rel(_metadata, dirfd, ".", 0); + + if (rel == REL_CHROOT_ONLY) + /* The current directory is dir_s2d2. */ + test_path_rel(_metadata, dirfd, "./s2d3", 0); + else + /* The current directory is dir_s1d2. */ + test_path_rel(_metadata, dirfd, "./s1d3", 0); + + if (rel != REL_CHROOT_CHDIR) { + test_path_rel(_metadata, dirfd, "../../s1d1", -1); + test_path_rel(_metadata, dirfd, "../../s1d1/s1d2", 0); + test_path_rel(_metadata, dirfd, "../../s1d1/s1d2/s1d3", 0); + + test_path_rel(_metadata, dirfd, "../../s2d1", -1); + test_path_rel(_metadata, dirfd, "../../s2d1/s2d2", 0); + test_path_rel(_metadata, dirfd, "../../s2d1/s2d2/s2d3", 0); + } + + if (rel == REL_OPEN) + EXPECT_EQ(0, close(dirfd)); + EXPECT_EQ(0, close(ruleset_fd)); +} + +TEST_F(layout1, relative_open) +{ + test_relative_path(_metadata, REL_OPEN); +} + +TEST_F(layout1, relative_chdir) +{ + test_relative_path(_metadata, REL_CHDIR); +} + +TEST_F(layout1, relative_chroot_only) +{ + test_relative_path(_metadata, REL_CHROOT_ONLY); +} + +TEST_F(layout1, relative_chroot_chdir) +{ + test_relative_path(_metadata, REL_CHROOT_CHDIR); +} + +TEST_F(layout1, chroot) +{ + const struct rule rules[] = { + { + .path = dir_s1d2, + .access = LANDLOCK_ACCESS_FS_CHROOT, + }, + {}, + }; + const int ruleset_fd = create_ruleset(_metadata, + LANDLOCK_ACCESS_FS_CHROOT, rules); + + ASSERT_NE(-1, ruleset_fd); + + enforce_ruleset(_metadata, ruleset_fd); + EXPECT_EQ(0, close(ruleset_fd)); + + ASSERT_EQ(-1, chroot(dir_s1d1)); + ASSERT_EQ(EACCES, errno); + ASSERT_EQ(0, chroot(dir_s1d2)) { + TH_LOG("Failed to chroot into "%s": %s\n", file_s1d2, + strerror(errno)); + }; + /* This chroot still works because we didn't chdir(dir_s1d2). */ + ASSERT_EQ(0, chroot(dir_s1d3)); +} + +static void copy_binary(struct __test_metadata *const _metadata, + const char *const dst_path) +{ + int dst_fd, src_fd; + struct stat statbuf; + + dst_fd = open(dst_path, O_WRONLY | O_TRUNC | O_CLOEXEC); + ASSERT_LE(0, dst_fd) { + TH_LOG("Failed to open "%s": %s\n", dst_path, + strerror(errno)); + } + src_fd = open(BINARY_PATH, O_RDONLY | O_CLOEXEC); + ASSERT_LE(0, src_fd) { + TH_LOG("Failed to open "" BINARY_PATH "": %s\n", + strerror(errno)); + } + ASSERT_EQ(0, fstat(src_fd, &statbuf)); + ASSERT_LE(0, sendfile(dst_fd, src_fd, 0, statbuf.st_size)); + ASSERT_EQ(0, close(src_fd)); + ASSERT_EQ(0, close(dst_fd)); +} + +static void test_execute(struct __test_metadata *const _metadata, + const char *const path, const int ret) +{ + int status; + char *const argv[] = {(char *)path, NULL}; + const pid_t child = fork(); + + ASSERT_LE(0, child); + if (child == 0) { + ASSERT_EQ(ret, execve(path, argv, NULL)) { + TH_LOG("Failed to execute "%s": %s\n", path, + strerror(errno)); + }; + ASSERT_EQ(EACCES, errno); + _exit(_metadata->passed ? EXIT_SUCCESS : EXIT_FAILURE); + return; + } + ASSERT_EQ(child, waitpid(child, &status, 0)); + ASSERT_EQ(1, WIFEXITED(status)); + ASSERT_EQ(0, WEXITSTATUS(status)) { + TH_LOG("Unexpected return code for "%s": %s\n", path, + strerror(errno)); + }; +} + +TEST_F(layout1, execute) +{ + const struct rule rules[] = { + { + .path = dir_s1d1, + .access = LANDLOCK_ACCESS_FS_EXECUTE, + }, + {}, + }; + const int ruleset_fd = create_ruleset(_metadata, + LANDLOCK_ACCESS_FS_EXECUTE, rules); + + ASSERT_NE(-1, ruleset_fd); + copy_binary(_metadata, file_s1d1); + copy_binary(_metadata, file_s1d2); + copy_binary(_metadata, file_s1d3); + + enforce_ruleset(_metadata, ruleset_fd); + EXPECT_EQ(0, close(ruleset_fd)); + + test_execute(_metadata, file_s1d1, -1); + test_execute(_metadata, file_s1d2, 0); + test_execute(_metadata, file_s1d3, 0); +} + +TEST_F(layout1, link_to) +{ + const struct rule rules[] = { + { + .path = dir_s1d2, + .access = LANDLOCK_ACCESS_FS_LINK_TO, + }, + {}, + }; + const int ruleset_fd = create_ruleset(_metadata, + LANDLOCK_ACCESS_FS_LINK_TO, rules); + + ASSERT_NE(-1, ruleset_fd); + + ASSERT_EQ(0, unlink(file_s1d1)); + ASSERT_EQ(0, unlink(file_s1d2)); + ASSERT_EQ(0, unlink(file_s1d3)); + + enforce_ruleset(_metadata, ruleset_fd); + EXPECT_EQ(0, close(ruleset_fd)); + + ASSERT_EQ(-1, link(file_s2d1, file_s1d1)); + ASSERT_EQ(EACCES, errno); + ASSERT_EQ(0, link(file_s2d1, file_s1d2)) { + TH_LOG("Failed to link file to "%s": %s\n", file_s1d2, + strerror(errno)); + }; + ASSERT_EQ(0, link(file_s2d1, file_s1d3)); +} + +static void test_rename(struct __test_metadata *const _metadata) +{ + /* Renames files. */ + ASSERT_EQ(-1, rename(file_s2d1, file_s1d1)); + ASSERT_EQ(EACCES, errno); + ASSERT_EQ(0, rename(file_s2d2, file_s1d2)) { + TH_LOG("Failed to rename file "%s": %s\n", file_s2d3, + strerror(errno)); + }; + ASSERT_EQ(0, rename(file_s2d3, file_s1d3)); + + /* Renames directories (reverse order). */ + ASSERT_EQ(0, unlink(file_s1d3)); + ASSERT_EQ(0, rename(dir_s2d3, dir_s1d3)) { + TH_LOG("Failed to rename directory "%s": %s\n", dir_s2d3, + strerror(errno)); + }; + + ASSERT_EQ(0, rmdir(dir_s1d3)); + ASSERT_EQ(0, unlink(file_s1d2)); + ASSERT_EQ(-1, rename(dir_s2d2, dir_s1d2)); + ASSERT_EQ(EACCES, errno); + + ASSERT_EQ(0, rmdir(dir_s1d2)); + ASSERT_EQ(0, unlink(file_s1d1)); + ASSERT_EQ(-1, rename(dir_s2d1, dir_s1d1)); + ASSERT_EQ(EACCES, errno); +} + +TEST_F(layout1, rename_from) +{ + const struct rule rules[] = { + { + .path = dir_s2d2, + .access = LANDLOCK_ACCESS_FS_RENAME_FROM, + }, + {}, + }; + const int ruleset_fd = create_ruleset(_metadata, + LANDLOCK_ACCESS_FS_RENAME_FROM, rules); + + ASSERT_NE(-1, ruleset_fd); + + enforce_ruleset(_metadata, ruleset_fd); + EXPECT_EQ(0, close(ruleset_fd)); + + test_rename(_metadata); +} + +TEST_F(layout1, rename_to) +{ + /* + * Same tests as layout1/rename_from, except the rename_from access + * rule is on dir_s1d2. + */ + const struct rule rules[] = { + { + .path = dir_s1d2, + .access = LANDLOCK_ACCESS_FS_RENAME_TO, + }, + {}, + }; + const int ruleset_fd = create_ruleset(_metadata, + LANDLOCK_ACCESS_FS_RENAME_TO, rules); + + ASSERT_NE(-1, ruleset_fd); + + enforce_ruleset(_metadata, ruleset_fd); + EXPECT_EQ(0, close(ruleset_fd)); + + test_rename(_metadata); +} + +TEST_F(layout1, rmdir) +{ + const struct rule rules[] = { + { + .path = dir_s1d2, + .access = LANDLOCK_ACCESS_FS_RMDIR, + }, + {}, + }; + const int ruleset_fd = create_ruleset(_metadata, + LANDLOCK_ACCESS_FS_RMDIR, rules); + + ASSERT_NE(-1, ruleset_fd); + + ASSERT_EQ(0, unlink(file_s1d1)); + ASSERT_EQ(0, unlink(file_s1d2)); + ASSERT_EQ(0, unlink(file_s1d3)); + + enforce_ruleset(_metadata, ruleset_fd); + EXPECT_EQ(0, close(ruleset_fd)); + + ASSERT_EQ(0, rmdir(dir_s1d3)) { + TH_LOG("Failed to remove directory "%s": %s\n", file_s1d2, + strerror(errno)); + } + ASSERT_EQ(-1, rmdir(dir_s1d2)); + ASSERT_EQ(EACCES, errno); + ASSERT_EQ(-1, rmdir(dir_s1d1)); + ASSERT_EQ(EACCES, errno); +} + +TEST_F(layout1, unlink) +{ + const struct rule rules[] = { + { + .path = dir_s1d2, + .access = LANDLOCK_ACCESS_FS_UNLINK, + }, + {}, + }; + const int ruleset_fd = create_ruleset(_metadata, + LANDLOCK_ACCESS_FS_UNLINK, rules); + + ASSERT_NE(-1, ruleset_fd); + enforce_ruleset(_metadata, ruleset_fd); + EXPECT_EQ(0, close(ruleset_fd)); + + ASSERT_EQ(-1, unlink(file_s1d1)); + ASSERT_EQ(EACCES, errno); + ASSERT_EQ(0, unlink(file_s1d2)) { + TH_LOG("Failed to unlink file "%s": %s\n", file_s1d2, + strerror(errno)); + }; + ASSERT_EQ(0, unlink(file_s1d3)); +} + +static void test_make_file(struct __test_metadata *const _metadata, + const __u64 access, const mode_t mode, const dev_t dev) +{ + const struct rule rules[] = { + { + .path = dir_s1d2, + .access = access, + }, + {}, + }; + const int ruleset_fd = create_ruleset(_metadata, access, rules); + + ASSERT_NE(-1, ruleset_fd); + + ASSERT_EQ(0, unlink(file_s1d1)); + ASSERT_EQ(0, unlink(file_s1d2)); + ASSERT_EQ(0, unlink(file_s1d3)); + + enforce_ruleset(_metadata, ruleset_fd); + EXPECT_EQ(0, close(ruleset_fd)); + + ASSERT_EQ(-1, mknod(file_s1d1, mode | 0400, dev)); + ASSERT_EQ(EACCES, errno); + ASSERT_EQ(0, mknod(file_s1d2, mode | 0400, dev)) { + TH_LOG("Failed to make file "%s": %s\n", + file_s1d2, strerror(errno)); + }; + ASSERT_EQ(0, mknod(file_s1d3, mode | 0400, dev)); +} + +TEST_F(layout1, make_char) +{ + /* Creates a /dev/null device. */ + test_make_file(_metadata, LANDLOCK_ACCESS_FS_MAKE_CHAR, S_IFCHR, + major(1) | minor(3)); +} + +TEST_F(layout1, make_block) +{ + /* Creates a /dev/loop0 device. */ + test_make_file(_metadata, LANDLOCK_ACCESS_FS_MAKE_BLOCK, S_IFBLK, + major(7) | minor(0)); +} + +TEST_F(layout1, make_reg) +{ + test_make_file(_metadata, LANDLOCK_ACCESS_FS_MAKE_REG, S_IFREG, 0); +} + +TEST_F(layout1, make_sock) +{ + test_make_file(_metadata, LANDLOCK_ACCESS_FS_MAKE_SOCK, S_IFSOCK, 0); +} + +TEST_F(layout1, make_fifo) +{ + test_make_file(_metadata, LANDLOCK_ACCESS_FS_MAKE_FIFO, S_IFIFO, 0); +} + +TEST_F(layout1, make_sym) +{ + const struct rule rules[] = { + { + .path = dir_s1d2, + .access = LANDLOCK_ACCESS_FS_MAKE_SYM, + }, + {}, + }; + const int ruleset_fd = create_ruleset(_metadata, + LANDLOCK_ACCESS_FS_MAKE_SYM, rules); + + ASSERT_NE(-1, ruleset_fd); + + ASSERT_EQ(0, unlink(file_s1d1)); + ASSERT_EQ(0, unlink(file_s1d2)); + ASSERT_EQ(0, unlink(file_s1d3)); + + enforce_ruleset(_metadata, ruleset_fd); + EXPECT_EQ(0, close(ruleset_fd)); + + ASSERT_EQ(-1, symlink("none", file_s1d1)); + ASSERT_EQ(EACCES, errno); + ASSERT_EQ(0, symlink("none", file_s1d2)) { + TH_LOG("Failed to make symlink "%s": %s\n", + file_s1d2, strerror(errno)); + }; + ASSERT_EQ(0, symlink("none", file_s1d3)); +} + +TEST_F(layout1, make_dir) +{ + const struct rule rules[] = { + { + .path = dir_s1d2, + .access = LANDLOCK_ACCESS_FS_MAKE_DIR, + }, + {}, + }; + const int ruleset_fd = create_ruleset(_metadata, + LANDLOCK_ACCESS_FS_MAKE_DIR, rules); + + ASSERT_NE(-1, ruleset_fd); + + ASSERT_EQ(0, unlink(file_s1d1)); + ASSERT_EQ(0, unlink(file_s1d2)); + ASSERT_EQ(0, unlink(file_s1d3)); + + enforce_ruleset(_metadata, ruleset_fd); + EXPECT_EQ(0, close(ruleset_fd)); + + /* Uses file_* as directory names. */ + ASSERT_EQ(-1, mkdir(file_s1d1, 0700)); + ASSERT_EQ(EACCES, errno); + ASSERT_EQ(0, mkdir(file_s1d2, 0700)) { + TH_LOG("Failed to make directory "%s": %s\n", + file_s1d2, strerror(errno)); + }; + ASSERT_EQ(0, mkdir(file_s1d3, 0700)); +} + +TEST(cleanup) +{ + cleanup_layout1(); +} + +TEST_HARNESS_MAIN diff --git a/tools/testing/selftests/landlock/test_ptrace.c b/tools/testing/selftests/landlock/test_ptrace.c new file mode 100644 index 000000000000..407cc99e5340 --- /dev/null +++ b/tools/testing/selftests/landlock/test_ptrace.c @@ -0,0 +1,294 @@ +// SPDX-License-Identifier: GPL-2.0 +/* + * Landlock tests - ptrace + * + * Copyright © 2017-2020 Mickaël Salaün mic@digikod.net + * Copyright © 2019-2020 ANSSI + */ + +#define _GNU_SOURCE +#include <errno.h> +#include <fcntl.h> +#include <linux/landlock.h> +#include <signal.h> +#include <sys/prctl.h> +#include <sys/ptrace.h> +#include <sys/types.h> +#include <sys/wait.h> +#include <unistd.h> + +#include "common.h" + +static void create_domain(struct __test_metadata *const _metadata) +{ + int ruleset_fd, err; + struct landlock_attr_features attr_features; + struct landlock_attr_enforce attr_enforce; + struct landlock_attr_ruleset attr_ruleset = { + .handled_access_fs = LANDLOCK_ACCESS_FS_READ_FILE, + }; + struct landlock_attr_path_beneath path_beneath = { + .allowed_access = LANDLOCK_ACCESS_FS_READ_FILE, + }; + + ASSERT_EQ(0, landlock(LANDLOCK_CMD_GET_FEATURES, + LANDLOCK_OPT_GET_FEATURES, + sizeof(attr_features), &attr_features)); + /* Only for test, use a binary AND for real application instead. */ + ASSERT_EQ(attr_ruleset.handled_access_fs, + attr_ruleset.handled_access_fs & + attr_features.access_fs); + ruleset_fd = landlock(LANDLOCK_CMD_CREATE_RULESET, + LANDLOCK_OPT_CREATE_RULESET, sizeof(attr_ruleset), + &attr_ruleset); + ASSERT_GE(ruleset_fd, 0) { + TH_LOG("Failed to create a ruleset: %s\n", strerror(errno)); + } + path_beneath.ruleset_fd = ruleset_fd; + path_beneath.parent_fd = open("/tmp", O_PATH | O_NOFOLLOW | O_DIRECTORY + | O_CLOEXEC); + ASSERT_GE(path_beneath.parent_fd, 0); + err = landlock(LANDLOCK_CMD_ADD_RULE, + LANDLOCK_OPT_ADD_RULE_PATH_BENEATH, + sizeof(path_beneath), &path_beneath); + ASSERT_EQ(err, 0); + ASSERT_EQ(errno, 0); + ASSERT_EQ(0, close(path_beneath.parent_fd)); + + err = prctl(PR_SET_NO_NEW_PRIVS, 1, 0, 0, 0); + ASSERT_EQ(errno, 0); + ASSERT_EQ(err, 0); + + attr_enforce.ruleset_fd = ruleset_fd; + err = landlock(LANDLOCK_CMD_ENFORCE_RULESET, + LANDLOCK_OPT_ENFORCE_RULESET, sizeof(attr_enforce), + &attr_enforce); + ASSERT_EQ(err, 0); + ASSERT_EQ(errno, 0); + + ASSERT_EQ(0, close(ruleset_fd)); +} + +/* test PTRACE_TRACEME and PTRACE_ATTACH for parent and child */ +static void check_ptrace(struct __test_metadata *const _metadata, + const bool domain_both, const bool domain_parent, + const bool domain_child) +{ + pid_t child, parent; + int status; + int pipe_child[2], pipe_parent[2]; + char buf_parent; + + parent = getpid(); + ASSERT_EQ(0, pipe(pipe_child)); + ASSERT_EQ(0, pipe(pipe_parent)); + if (domain_both) + create_domain(_metadata); + + child = fork(); + ASSERT_LE(0, child); + if (child == 0) { + char buf_child; + + EXPECT_EQ(0, close(pipe_parent[1])); + EXPECT_EQ(0, close(pipe_child[0])); + if (domain_child) + create_domain(_metadata); + + /* sync #1 */ + ASSERT_EQ(1, read(pipe_parent[0], &buf_child, 1)) { + TH_LOG("Failed to read() sync #1 from parent"); + } + ASSERT_EQ('.', buf_child); + + /* Tests the parent protection. */ + ASSERT_EQ(domain_child ? -1 : 0, + ptrace(PTRACE_ATTACH, parent, NULL, 0)); + if (domain_child) { + ASSERT_EQ(EPERM, errno); + } else { + ASSERT_EQ(parent, waitpid(parent, &status, 0)); + ASSERT_EQ(1, WIFSTOPPED(status)); + ASSERT_EQ(0, ptrace(PTRACE_DETACH, parent, NULL, 0)); + } + + /* sync #2 */ + ASSERT_EQ(1, write(pipe_child[1], ".", 1)) { + TH_LOG("Failed to write() sync #2 to parent"); + } + + /* Tests traceme. */ + ASSERT_EQ(domain_parent ? -1 : 0, ptrace(PTRACE_TRACEME)); + if (domain_parent) { + ASSERT_EQ(EPERM, errno); + } else { + ASSERT_EQ(0, raise(SIGSTOP)); + } + + /* sync #3 */ + ASSERT_EQ(1, read(pipe_parent[0], &buf_child, 1)) { + TH_LOG("Failed to read() sync #3 from parent"); + } + ASSERT_EQ('.', buf_child); + _exit(_metadata->passed ? EXIT_SUCCESS : EXIT_FAILURE); + } + + EXPECT_EQ(0, close(pipe_child[1])); + EXPECT_EQ(0, close(pipe_parent[0])); + if (domain_parent) + create_domain(_metadata); + + /* sync #1 */ + ASSERT_EQ(1, write(pipe_parent[1], ".", 1)) { + TH_LOG("Failed to write() sync #1 to child"); + } + + /* Tests the parent protection. */ + /* sync #2 */ + ASSERT_EQ(1, read(pipe_child[0], &buf_parent, 1)) { + TH_LOG("Failed to read() sync #2 from child"); + } + ASSERT_EQ('.', buf_parent); + + /* Tests traceme. */ + if (!domain_parent) { + ASSERT_EQ(child, waitpid(child, &status, 0)); + ASSERT_EQ(1, WIFSTOPPED(status)); + ASSERT_EQ(0, ptrace(PTRACE_DETACH, child, NULL, 0)); + } + /* Tests attach. */ + ASSERT_EQ(domain_parent ? -1 : 0, + ptrace(PTRACE_ATTACH, child, NULL, 0)); + if (domain_parent) { + ASSERT_EQ(EPERM, errno); + } else { + ASSERT_EQ(child, waitpid(child, &status, 0)); + ASSERT_EQ(1, WIFSTOPPED(status)); + ASSERT_EQ(0, ptrace(PTRACE_DETACH, child, NULL, 0)); + } + + /* sync #3 */ + ASSERT_EQ(1, write(pipe_parent[1], ".", 1)) { + TH_LOG("Failed to write() sync #3 to child"); + } + ASSERT_EQ(child, waitpid(child, &status, 0)); + if (WIFSIGNALED(status) || WEXITSTATUS(status)) + _metadata->passed = 0; +} + +/* + * Test multiple tracing combinations between a parent process P1 and a child + * process P2. + * + * Yama's scoped ptrace is presumed disabled. If enabled, this optional + * restriction is enforced in addition to any Landlock check, which means that + * all P2 requests to trace P1 would be denied. + */ + +/* + * No domain + * + * P1-. P1 -> P2 : allow + * \ P2 -> P1 : allow + * 'P2 + */ +TEST(allow_without_domain) { + check_ptrace(_metadata, false, false, false); +} + +/* + * Child domain + * + * P1--. P1 -> P2 : allow + * \ P2 -> P1 : deny + * .'-----. + * | P2 | + * '------' + */ +TEST(allow_with_one_domain) { + check_ptrace(_metadata, false, false, true); +} + +/* + * Parent domain + * .------. + * | P1 --. P1 -> P2 : deny + * '------' \ P2 -> P1 : allow + * ' + * P2 + */ +TEST(deny_with_parent_domain) { + check_ptrace(_metadata, false, true, false); +} + +/* + * Parent + child domain (siblings) + * .------. + * | P1 ---. P1 -> P2 : deny + * '------' \ P2 -> P1 : deny + * .---'--. + * | P2 | + * '------' + */ +TEST(deny_with_sibling_domain) { + check_ptrace(_metadata, false, true, true); +} + +/* + * Same domain (inherited) + * .-------------. + * | P1----. | P1 -> P2 : allow + * | \ | P2 -> P1 : allow + * | ' | + * | P2 | + * '-------------' + */ +TEST(allow_sibling_domain) { + check_ptrace(_metadata, true, false, false); +} + +/* + * Inherited + child domain + * .-----------------. + * | P1----. | P1 -> P2 : allow + * | \ | P2 -> P1 : deny + * | .-'----. | + * | | P2 | | + * | '------' | + * '-----------------' + */ +TEST(allow_with_nested_domain) { + check_ptrace(_metadata, true, false, true); +} + +/* + * Inherited + parent domain + * .-----------------. + * |.------. | P1 -> P2 : deny + * || P1 ----. | P2 -> P1 : allow + * |'------' \ | + * | ' | + * | P2 | + * '-----------------' + */ +TEST(deny_with_nested_and_parent_domain) { + check_ptrace(_metadata, true, true, false); +} + +/* + * Inherited + parent and child domain (siblings) + * .-----------------. + * | .------. | P1 -> P2 : deny + * | | P1 . | P2 -> P1 : deny + * | '------'\ | + * | \ | + * | .--'---. | + * | | P2 | | + * | '------' | + * '-----------------' + */ +TEST(deny_with_forked_domain) { + check_ptrace(_metadata, true, true, true); +} + +TEST_HARNESS_MAIN diff --git a/tools/testing/selftests/landlock/true.c b/tools/testing/selftests/landlock/true.c new file mode 100644 index 000000000000..3f9ccbf52783 --- /dev/null +++ b/tools/testing/selftests/landlock/true.c @@ -0,0 +1,5 @@ +// SPDX-License-Identifier: GPL-2.0 +int main(void) +{ + return 0; +}

This documentation can be built with the Sphinx framework.

Signed-off-by: Mickaël Salaün mic@digikod.net Reviewed-by: Vincent Dagonneau vincent.dagonneau@ssi.gouv.fr Cc: Andy Lutomirski luto@amacapital.net Cc: James Morris jmorris@namei.org Cc: Kees Cook keescook@chromium.org Cc: Serge E. Hallyn serge@hallyn.com ---

Changes since v14: * Fix spelling (contributed by Randy Dunlap). * Extend documentation about inheritance and explain layer levels. * Remove the use of now-removed access rights. * Use GitHub links. * Improve kernel documentation. * Add section for tests. * Update example.

Changes since v13: * Rewrote the documentation according to the major revamp.

Previous version: https://lore.kernel.org/lkml/20191104172146.30797-8-mic@digikod.net/ --- Documentation/security/index.rst | 1 + Documentation/security/landlock/index.rst | 18 ++ Documentation/security/landlock/kernel.rst | 69 +++++++ Documentation/security/landlock/user.rst | 227 +++++++++++++++++++++ 4 files changed, 315 insertions(+) create mode 100644 Documentation/security/landlock/index.rst create mode 100644 Documentation/security/landlock/kernel.rst create mode 100644 Documentation/security/landlock/user.rst

diff --git a/Documentation/security/index.rst b/Documentation/security/index.rst index fc503dd689a7..4d213e76ddf4 100644 --- a/Documentation/security/index.rst +++ b/Documentation/security/index.rst @@ -15,3 +15,4 @@ Security Documentation self-protection siphash tpm/index + landlock/index diff --git a/Documentation/security/landlock/index.rst b/Documentation/security/landlock/index.rst new file mode 100644 index 000000000000..2520f8f33f5e --- /dev/null +++ b/Documentation/security/landlock/index.rst @@ -0,0 +1,18 @@ +========================================= +Landlock LSM: unprivileged access control +========================================= + +:Author: Mickaël Salaün + +The goal of Landlock is to enable to restrict ambient rights (e.g. global +filesystem access) for a set of processes. Because Landlock is a stackable +LSM, it makes possible to create safe security sandboxes as new security layers +in addition to the existing system-wide access-controls. This kind of sandbox +is expected to help mitigate the security impact of bugs or +unexpected/malicious behaviors in user-space applications. Landlock empowers +any process, including unprivileged ones, to securely restrict themselves. + +.. toctree:: + + user + kernel diff --git a/Documentation/security/landlock/kernel.rst b/Documentation/security/landlock/kernel.rst new file mode 100644 index 000000000000..0211ef5df06f --- /dev/null +++ b/Documentation/security/landlock/kernel.rst @@ -0,0 +1,69 @@ +============================== +Landlock: kernel documentation +============================== + +Landlock's goal is to create scoped access-control (i.e. sandboxing). To +harden a whole system, this feature should be available to any process, +including unprivileged ones. Because such process may be compromised or +backdoored (i.e. untrusted), Landlock's features must be safe to use from the +kernel and other processes point of view. Landlock's interface must therefore +expose a minimal attack surface. + +Landlock is designed to be usable by unprivileged processes while following the +system security policy enforced by other access control mechanisms (e.g. DAC, +LSM). Indeed, a Landlock rule shall not interfere with other access-controls +enforced on the system, only add more restrictions. + +Any user can enforce Landlock rulesets on their processes. They are merged and +evaluated according to the inherited ones in a way that ensures that only more +constraints can be added. + +Guiding principles for safe access controls +=========================================== + +* A Landlock rule shall be focused on access control on kernel objects instead + of syscall filtering (i.e. syscall arguments), which is the purpose of + seccomp-bpf. +* To avoid multiple kinds of side-channel attacks (e.g. leak of security + policies, CPU-based attacks), Landlock rules shall not be able to + programmatically communicate with user space. +* Kernel access check shall not slow down access request from unsandboxed + processes. +* Computation related to Landlock operations (e.g. enforce a ruleset) shall + only impact the processes requesting them. + +Tests +===== + +Userspace tests for backward compatibility, ptrace restrictions and filesystem +support can be found here: `tools/testing/selftests/landlock/`_. + +Kernel structures +================= + +Object +------ + +.. kernel-doc:: security/landlock/object.h + :identifiers: + +Ruleset and domain +------------------ + +A domain is a read-only ruleset tied to a set of subjects (i.e. tasks' +credentials). Each time a ruleset is enforced on a task, the current domain is +duplicated and the ruleset is imported as a new layer of rules in the new +domain. Indeed, once in a domain, each rule is tied to a layer level. To +grant access to an object, at least one rule of each layer must allow the +requested action on the object. A task can then only transit to a new domain +which is the intersection of the constraints from the current domain and those +of a ruleset provided by the task. + +The definition of a subject is implicit for a task sandboxing itself, which +makes the reasoning much easier and helps avoid pitfalls. + +.. kernel-doc:: security/landlock/ruleset.h + :identifiers: + +.. Links +.. _tools/testing/selftests/landlock/: https://github.com/landlock-lsm/linux/tree/landlock-v15/tools/testing/selfte... diff --git a/Documentation/security/landlock/user.rst b/Documentation/security/landlock/user.rst new file mode 100644 index 000000000000..8f34d1cf1e03 --- /dev/null +++ b/Documentation/security/landlock/user.rst @@ -0,0 +1,227 @@ +================================= +Landlock: userspace documentation +================================= + +Landlock rules +============== + +A Landlock rule enables to describe an action on an object. An object is +currently a file hierarchy, and the related filesystem actions are defined in +`Access rights`_. A set of rules is aggregated in a ruleset, which can then +restrict the thread enforcing it, and its future children. + +Defining and enforcing a security policy +---------------------------------------- + +Before defining a security policy, an application should first probe for the +features supported by the running kernel, which is important to be compatible +with older kernels. This can be done thanks to the `landlock` syscall (cf. +:ref:`syscall`). + +.. code-block:: c + + struct landlock_attr_features attr_features; + + if (landlock(LANDLOCK_CMD_GET_FEATURES, LANDLOCK_OPT_GET_FEATURES, + sizeof(attr_features), &attr_features)) { + perror("Failed to probe the Landlock supported features"); + return 1; + } + +Then, we need to create the ruleset that will contain our rules. For this +example, the ruleset will contain rules which only allow read actions, but +write actions will be denied. The ruleset then needs to handle both of these +kind of actions. To have a backward compatibility, these actions should be +ANDed with the supported ones. + +.. code-block:: c + + int ruleset_fd; + struct landlock_attr_ruleset ruleset = { + .handled_access_fs = + LANDLOCK_ACCESS_FS_EXECUTE | + LANDLOCK_ACCESS_FS_WRITE_FILE | + LANDLOCK_ACCESS_FS_READ_FILE | + LANDLOCK_ACCESS_FS_READ_DIR | + LANDLOCK_ACCESS_FS_LINK_TO | + LANDLOCK_ACCESS_FS_RENAME_FROM | + LANDLOCK_ACCESS_FS_RENAME_TO | + LANDLOCK_ACCESS_FS_RMDIR | + LANDLOCK_ACCESS_FS_UNLINK | + LANDLOCK_ACCESS_FS_MAKE_CHAR | + LANDLOCK_ACCESS_FS_MAKE_DIR | + LANDLOCK_ACCESS_FS_MAKE_REG | + LANDLOCK_ACCESS_FS_MAKE_SOCK | + LANDLOCK_ACCESS_FS_MAKE_FIFO | + LANDLOCK_ACCESS_FS_MAKE_BLOCK | + LANDLOCK_ACCESS_FS_MAKE_SYM, + }; + + ruleset.handled_access_fs &= attr_features.access_fs; + ruleset_fd = landlock(LANDLOCK_CMD_CREATE_RULESET, + LANDLOCK_OPT_CREATE_RULESET, sizeof(ruleset), &ruleset); + if (ruleset_fd < 0) { + perror("Failed to create a ruleset"); + return 1; + } + +We can now add a new rule to this ruleset thanks to the returned file +descriptor referring to this ruleset. The rule will only enable to read the +file hierarchy ``/usr``. Without another rule, write actions would then be +denied by the ruleset. To add ``/usr`` to the ruleset, we open it with the +``O_PATH`` flag and fill the &struct landlock_attr_path_beneath with this file +descriptor. + +.. code-block:: c + + int err; + struct landlock_attr_path_beneath path_beneath = { + .ruleset_fd = ruleset_fd, + .allowed_access = + LANDLOCK_ACCESS_FS_EXECUTE | + LANDLOCK_ACCESS_FS_READ_FILE | + LANDLOCK_ACCESS_FS_READ_DIR, + }; + + path_beneath.allowed_access &= attr_features.access_fs; + path_beneath.parent_fd = open("/usr", O_PATH | O_CLOEXEC); + if (path_beneath.parent_fd < 0) { + perror("Failed to open file"); + close(ruleset_fd); + return 1; + } + err = landlock(LANDLOCK_CMD_ADD_RULE, LANDLOCK_OPT_ADD_RULE_PATH_BENEATH, + sizeof(path_beneath), &path_beneath); + close(path_beneath.parent_fd); + if (err) { + perror("Failed to update ruleset"); + close(ruleset_fd); + return 1; + } + +We now have a ruleset with one rule allowing read access to ``/usr`` while +denying all accesses featured in ``attr_features.access_fs`` to everything else +on the filesystem. The next step is to restrict the current thread from +gaining more privileges (e.g. thanks to a SUID binary). + +.. code-block:: c + + if (prctl(PR_SET_NO_NEW_PRIVS, 1, 0, 0, 0)) { + perror("Failed to restrict privileges"); + close(ruleset_fd); + return 1; + } + +The current thread is now ready to sandbox itself with the ruleset. + +.. code-block:: c + + struct landlock_attr_enforce attr_enforce = { + .ruleset_fd = ruleset_fd, + }; + + if (landlock(LANDLOCK_CMD_ENFORCE_RULESET, LANDLOCK_OPT_ENFORCE_RULESET, + sizeof(attr_enforce), &attr_enforce)) { + perror("Failed to enforce ruleset"); + close(ruleset_fd); + return 1; + } + close(ruleset_fd); + +If the last `landlock` system call succeeds, the current thread is now +restricted and this policy will be enforced on all its subsequently created +children as well. Once a thread is landlocked, there is no way to remove its +security policy; only adding more restrictions is allowed. These threads are +now in a new Landlock domain, merge of their parent one (if any) with the new +ruleset. + +Full working code can be found in `samples/landlock/sandboxer.c`_. + +Inheritance +----------- + +Every new thread resulting from a :manpage:`clone(2)` inherits Landlock domain +restrictions from its parent. This is similar to the seccomp inheritance (cf. +:doc:`/userspace-api/seccomp_filter`) or any other LSM dealing with task's +:manpage:`credentials(7)`. For instance, one process's thread may apply +Landlock rules to itself, but they will not be automatically applied to other +sibling threads (unlike POSIX thread credential changes, cf. +:manpage:`nptl(7)`). + +When a thread sandbox itself, we have the grantee that the related security +policy will stay enforced on all this thread's descendants. This enables to +create standalone and modular security policies per application, which will +automatically be composed between themselves according to their runtime parent +policies. + +Ptrace restrictions +------------------- + +A sandboxed process has less privileges than a non-sandboxed process and must +then be subject to additional restrictions when manipulating another process. +To be allowed to use :manpage:`ptrace(2)` and related syscalls on a target +process, a sandboxed process should have a subset of the target process rules, +which means the tracee must be in a sub-domain of the tracer. + +.. _syscall: + +The `landlock` syscall and its arguments +======================================== + +.. kernel-doc:: security/landlock/syscall.c + :identifiers: sys_landlock + +Commands +-------- + +.. kernel-doc:: include/uapi/linux/landlock.h + :identifiers: landlock_cmd + +Options +------- + +.. kernel-doc:: include/uapi/linux/landlock.h + :identifiers: options_intro + options_get_features options_create_ruleset + options_add_rule options_enforce_ruleset + +Attributes +---------- + +.. kernel-doc:: include/uapi/linux/landlock.h + :identifiers: landlock_attr_features landlock_attr_ruleset + landlock_attr_path_beneath landlock_attr_enforce + +Access rights +------------- + +.. kernel-doc:: include/uapi/linux/landlock.h + :identifiers: fs_access + +Questions and answers +===================== + +What about user space sandbox managers? +--------------------------------------- + +Using user space process to enforce restrictions on kernel resources can lead +to race conditions or inconsistent evaluations (i.e. `Incorrect mirroring of +the OS code and state +https://www.ndss-symposium.org/ndss2003/traps-and-pitfalls-practical-problems-system-call-interposition-based-security-tools/`_). + +What about namespaces and containers? +------------------------------------- + +Namespaces can help create sandboxes but they are not designed for +access-control and then miss useful features for such use case (e.g. no +fine-grained restrictions). Moreover, their complexity can lead to security +issues, especially when untrusted processes can manipulate them (cf. +`Controlling access to user namespaces https://lwn.net/Articles/673597/`_). + +Additional documentation +======================== + +See https://landlock.io + +.. Links +.. _samples/landlock/sandboxer.c: https://github.com/landlock-lsm/linux/tree/landlock-v15/samples/landlock/san...