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// 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 "ruleset.h"
#include "setup.h"
#include "task.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[] __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_task_hooks(void)
{
security_add_hooks(landlock_hooks, ARRAY_SIZE(landlock_hooks),
&landlock_lsmid);
}
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