Using ptrace(2) and related debug features on a target process can lead to a privilege escalation. Indeed, ptrace(2) can be used by an attacker to impersonate another task and to remain undetected while performing malicious activities. Thanks to ptrace_may_access(), various part of the kernel can check if a tracer is more privileged than a tracee.
A landlocked process has fewer privileges than a non-landlocked process and must then be subject to additional restrictions when manipulating processes. To be allowed to use ptrace(2) and related syscalls on a target process, a landlocked process must have a subset of the target process' rules (i.e. the tracee must be in a sub-domain of the tracer).
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: * Constify variables.
Changes since v13: * Make the ptrace restriction mandatory, like in the v10. * Remove the eBPF dependency.
Previous version: https://lore.kernel.org/lkml/20191104172146.30797-5-mic@digikod.net/ --- security/landlock/Makefile | 2 +- security/landlock/ptrace.c | 120 +++++++++++++++++++++++++++++++++++++ security/landlock/ptrace.h | 14 +++++ security/landlock/setup.c | 2 + 4 files changed, 137 insertions(+), 1 deletion(-) create mode 100644 security/landlock/ptrace.c create mode 100644 security/landlock/ptrace.h
diff --git a/security/landlock/Makefile b/security/landlock/Makefile index 041ea242e627..f1d1eb72fa76 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 + cred.o ptrace.o diff --git a/security/landlock/ptrace.c b/security/landlock/ptrace.c new file mode 100644 index 000000000000..61df38b13f5c --- /dev/null +++ b/security/landlock/ptrace.c @@ -0,0 +1,120 @@ +// SPDX-License-Identifier: GPL-2.0-only +/* + * Landlock LSM - Ptrace hooks + * + * Copyright © 2017-2020 Mickaël Salaün mic@digikod.net + * Copyright © 2020 ANSSI + */ + +#include <asm/current.h> +#include <linux/cred.h> +#include <linux/errno.h> +#include <linux/kernel.h> +#include <linux/lsm_hooks.h> +#include <linux/rcupdate.h> +#include <linux/sched.h> + +#include "common.h" +#include "cred.h" +#include "ptrace.h" +#include "ruleset.h" +#include "setup.h" + +/** + * domain_scope_le - Checks domain ordering for scoped ptrace + * + * @parent: Parent domain. + * @child: Potential child of @parent. + * + * Checks if the @parent domain is less or equal to (i.e. an ancestor, which + * means a subset of) the @child domain. + */ +static bool domain_scope_le(const struct landlock_ruleset *const parent, + const struct landlock_ruleset *const child) +{ + const struct landlock_hierarchy *walker; + + if (!parent) + return true; + if (!child) + return false; + for (walker = child->hierarchy; walker; walker = walker->parent) { + if (walker == parent->hierarchy) + /* @parent is in the scoped hierarchy of @child. */ + return true; + } + /* There is no relationship between @parent and @child. */ + return false; +} + +static bool task_is_scoped(const struct task_struct *const parent, + const struct task_struct *const child) +{ + bool is_scoped; + const struct landlock_ruleset *dom_parent, *dom_child; + + rcu_read_lock(); + dom_parent = landlock_get_task_domain(parent); + dom_child = landlock_get_task_domain(child); + is_scoped = domain_scope_le(dom_parent, dom_child); + rcu_read_unlock(); + return is_scoped; +} + +static int task_ptrace(const struct task_struct *const parent, + const struct task_struct *const child) +{ + /* Quick return for non-landlocked tasks. */ + if (!landlocked(parent)) + return 0; + if (task_is_scoped(parent, child)) + return 0; + return -EPERM; +} + +/** + * hook_ptrace_access_check - Determines whether the current process may access + * another + * + * @child: Process to be accessed. + * @mode: Mode of attachment. + * + * If the current task has Landlock rules, then the child must have at least + * the same rules. Else denied. + * + * Determines whether a process may access another, returning 0 if permission + * granted, -errno if denied. + */ +static int hook_ptrace_access_check(struct task_struct *const child, + const unsigned int mode) +{ + return task_ptrace(current, child); +} + +/** + * hook_ptrace_traceme - Determines whether another process may trace the + * current one + * + * @parent: Task proposed to be the tracer. + * + * If the parent has Landlock rules, then the current task must have the same + * or more rules. Else denied. + * + * Determines whether the nominated task is permitted to trace the current + * process, returning 0 if permission is granted, -errno if denied. + */ +static int hook_ptrace_traceme(struct task_struct *const parent) +{ + return task_ptrace(parent, current); +} + +static struct security_hook_list landlock_hooks[] __lsm_ro_after_init = { + LSM_HOOK_INIT(ptrace_access_check, hook_ptrace_access_check), + LSM_HOOK_INIT(ptrace_traceme, hook_ptrace_traceme), +}; + +__init void landlock_add_hooks_ptrace(void) +{ + security_add_hooks(landlock_hooks, ARRAY_SIZE(landlock_hooks), + LANDLOCK_NAME); +} diff --git a/security/landlock/ptrace.h b/security/landlock/ptrace.h new file mode 100644 index 000000000000..6740c6a723de --- /dev/null +++ b/security/landlock/ptrace.h @@ -0,0 +1,14 @@ +/* SPDX-License-Identifier: GPL-2.0-only */ +/* + * Landlock LSM - Ptrace hooks + * + * Copyright © 2017-2019 Mickaël Salaün mic@digikod.net + * Copyright © 2019 ANSSI + */ + +#ifndef _SECURITY_LANDLOCK_PTRACE_H +#define _SECURITY_LANDLOCK_PTRACE_H + +__init void landlock_add_hooks_ptrace(void); + +#endif /* _SECURITY_LANDLOCK_PTRACE_H */ diff --git a/security/landlock/setup.c b/security/landlock/setup.c index 00eb78275cd8..a40822135d13 100644 --- a/security/landlock/setup.c +++ b/security/landlock/setup.c @@ -11,6 +11,7 @@
#include "common.h" #include "cred.h" +#include "ptrace.h" #include "setup.h"
struct lsm_blob_sizes landlock_blob_sizes __lsm_ro_after_init = { @@ -21,6 +22,7 @@ static int __init landlock_init(void) { pr_info("Registering hooks.\n"); landlock_add_hooks_cred(); + landlock_add_hooks_ptrace(); return 0; }