Commit afe81f75 authored by Mickaël Salaün's avatar Mickaël Salaün Committed by James Morris

landlock: Add ptrace restrictions

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's rules (i.e. the tracee must be in a sub-domain of the tracer).

Cc: James Morris <jmorris@namei.org>
Signed-off-by: default avatarMickaël Salaün <mic@linux.microsoft.com>
Reviewed-by: default avatarJann Horn <jannh@google.com>
Acked-by: default avatarSerge Hallyn <serge@hallyn.com>
Reviewed-by: default avatarKees Cook <keescook@chromium.org>
Link: https://lore.kernel.org/r/20210422154123.13086-5-mic@digikod.netSigned-off-by: default avatarJames Morris <jamorris@linux.microsoft.com>
parent 385975dc
obj-$(CONFIG_SECURITY_LANDLOCK) := landlock.o
landlock-y := setup.o object.o ruleset.o \
cred.o
cred.o ptrace.o
// SPDX-License-Identifier: GPL-2.0-only
/*
* Landlock LSM - Ptrace hooks
*
* Copyright © 2017-2020 Mickaël Salaün <mic@digikod.net>
* Copyright © 2019-2020 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_ptrace_hooks(void)
{
security_add_hooks(landlock_hooks, ARRAY_SIZE(landlock_hooks),
LANDLOCK_NAME);
}
/* 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_ptrace_hooks(void);
#endif /* _SECURITY_LANDLOCK_PTRACE_H */
......@@ -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 = {
......@@ -20,6 +21,7 @@ struct lsm_blob_sizes landlock_blob_sizes __lsm_ro_after_init = {
static int __init landlock_init(void)
{
landlock_add_cred_hooks();
landlock_add_ptrace_hooks();
pr_info("Up and running.\n");
return 0;
}
......
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