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; +}