Unverified Commit 33e65b0d authored by Mickaël Salaün's avatar Mickaël Salaün
Browse files

landlock: Add AUDIT_LANDLOCK_ACCESS and log ptrace denials 



Add a new AUDIT_LANDLOCK_ACCESS record type dedicated to an access
request denied by a Landlock domain.  AUDIT_LANDLOCK_ACCESS indicates
that something unexpected happened.

For now, only denied access are logged, which means that any
AUDIT_LANDLOCK_ACCESS record is always followed by a SYSCALL record with
"success=no".  However, log parsers should check this syscall property
because this is the only sign that a request was denied.  Indeed, we
could have "success=yes" if Landlock would support a "permissive" mode.
We could also add a new field to AUDIT_LANDLOCK_DOMAIN for this mode
(see following commit).

By default, the only logged access requests are those coming from the
same executed program that enforced the Landlock restriction on itself.
In other words, no audit record are created for a task after it called
execve(2).  This is required to avoid log spam because programs may only
be aware of their own restrictions, but not the inherited ones.

Following commits will allow to conditionally generate
AUDIT_LANDLOCK_ACCESS records according to dedicated
landlock_restrict_self(2)'s flags.

The AUDIT_LANDLOCK_ACCESS message contains:
- the "domain" ID restricting the action on an object,
- the "blockers" that are missing to allow the requested access,
- a set of fields identifying the related object (e.g. task identified
  with "opid" and "ocomm").

The blockers are implicit restrictions (e.g. ptrace), or explicit access
rights (e.g. filesystem), or explicit scopes (e.g. signal).  This field
contains a list of at least one element, each separated with a comma.

The initial blocker is "ptrace", which describe all implicit Landlock
restrictions related to ptrace (e.g. deny tracing of tasks outside a
sandbox).

Add audit support to ptrace_access_check and ptrace_traceme hooks.  For
the ptrace_access_check case, we log the current/parent domain and the
child task.  For the ptrace_traceme case, we log the parent domain and
the current/child task.  Indeed, the requester and the target are the
current task, but the action would be performed by the parent task.

Audit event sample:

  type=LANDLOCK_ACCESS msg=audit(1729738800.349:44): domain=195ba459b blockers=ptrace opid=1 ocomm="systemd"
  type=SYSCALL msg=audit(1729738800.349:44): arch=c000003e syscall=101 success=no [...] pid=300 auid=0

A following commit adds user documentation.

Add KUnit tests to check reading of domain ID relative to layer level.

The quick return for non-landlocked tasks is moved from task_ptrace() to
each LSM hooks.

It is not useful to inline the audit_enabled check because other
computation are performed by landlock_log_denial().

Use scoped guards for RCU read-side critical sections.

Cc: Günther Noack <gnoack@google.com>
Acked-by: default avatarPaul Moore <paul@paul-moore.com>
Link: https://lore.kernel.org/r/20250320190717.2287696-10-mic@digikod.net


Signed-off-by: default avatarMickaël Salaün <mic@digikod.net>
parent 14f6c14e

include/uapi/linux/audit.h

+2 −1
Original line number Diff line number Diff line
@@ -33,7 +33,7 @@ 
 * 1100 - 1199 user space trusted application messages

 * 1200 - 1299 messages internal to the audit daemon

 * 1300 - 1399 audit event messages

 * 1400 - 1499 SE Linux use

 * 1400 - 1499 access control messages

 * 1500 - 1599 kernel LSPP events

 * 1600 - 1699 kernel crypto events

 * 1700 - 1799 kernel anomaly records
@@ -146,6 +146,7 @@ 
#define AUDIT_IPE_ACCESS	1420	/* IPE denial or grant */

#define AUDIT_IPE_CONFIG_CHANGE	1421	/* IPE config change */

#define AUDIT_IPE_POLICY_LOAD	1422	/* IPE policy load */

#define AUDIT_LANDLOCK_ACCESS	1423	/* Landlock denial */



#define AUDIT_FIRST_KERN_ANOM_MSG   1700

#define AUDIT_LAST_KERN_ANOM_MSG    1799

security/landlock/Makefile

+4 −1
Original line number Diff line number Diff line
@@ -5,4 +5,7 @@ landlock-y := setup.o syscalls.o object.o ruleset.o \ 


landlock-$(CONFIG_INET) += net.o



landlock-$(CONFIG_AUDIT) += id.o
 
landlock-$(CONFIG_AUDIT) += \

	id.o \

	audit.o \

	domain.o

security/landlock/audit.c

0 → 100644
+151 −0
Original line number Diff line number Diff line 
// SPDX-License-Identifier: GPL-2.0-only

/*

 * Landlock - Audit helpers

 *

 * Copyright © 2023-2025 Microsoft Corporation

 */



#include <kunit/test.h>

#include <linux/audit.h>

#include <linux/lsm_audit.h>



#include "audit.h"

#include "cred.h"

#include "domain.h"

#include "limits.h"

#include "ruleset.h"



static const char *get_blocker(const enum landlock_request_type type)

{

	switch (type) {

	case LANDLOCK_REQUEST_PTRACE:

		return "ptrace";

	}



	WARN_ON_ONCE(1);

	return "unknown";

}



static void log_blockers(struct audit_buffer *const ab,

			 const enum landlock_request_type type)

{

	audit_log_format(ab, "%s", get_blocker(type));

}



static struct landlock_hierarchy *

get_hierarchy(const struct landlock_ruleset *const domain, const size_t layer)

{

	struct landlock_hierarchy *hierarchy = domain->hierarchy;

	ssize_t i;



	if (WARN_ON_ONCE(layer >= domain->num_layers))

		return hierarchy;



	for (i = domain->num_layers - 1; i > layer; i--) {

		if (WARN_ON_ONCE(!hierarchy->parent))

			break;



		hierarchy = hierarchy->parent;

	}



	return hierarchy;

}



#ifdef CONFIG_SECURITY_LANDLOCK_KUNIT_TEST



static void test_get_hierarchy(struct kunit *const test)

{

	struct landlock_hierarchy dom0_hierarchy = {

		.id = 10,

	};

	struct landlock_hierarchy dom1_hierarchy = {

		.parent = &dom0_hierarchy,

		.id = 20,

	};

	struct landlock_hierarchy dom2_hierarchy = {

		.parent = &dom1_hierarchy,

		.id = 30,

	};

	struct landlock_ruleset dom2 = {

		.hierarchy = &dom2_hierarchy,

		.num_layers = 3,

	};



	KUNIT_EXPECT_EQ(test, 10, get_hierarchy(&dom2, 0)->id);

	KUNIT_EXPECT_EQ(test, 20, get_hierarchy(&dom2, 1)->id);

	KUNIT_EXPECT_EQ(test, 30, get_hierarchy(&dom2, 2)->id);

	KUNIT_EXPECT_EQ(test, 30, get_hierarchy(&dom2, -1)->id);

}



#endif /* CONFIG_SECURITY_LANDLOCK_KUNIT_TEST */



static bool is_valid_request(const struct landlock_request *const request)

{

	if (WARN_ON_ONCE(request->layer_plus_one > LANDLOCK_MAX_NUM_LAYERS))

		return false;



	if (WARN_ON_ONCE(!request->layer_plus_one))

		return false;



	return true;

}



/**

 * landlock_log_denial - Create audit records related to a denial

 *

 * @subject: The Landlock subject's credential denying an action.

 * @request: Detail of the user space request.

 */

void landlock_log_denial(const struct landlock_cred_security *const subject,

			 const struct landlock_request *const request)

{

	struct audit_buffer *ab;

	struct landlock_hierarchy *youngest_denied;

	size_t youngest_layer;



	if (WARN_ON_ONCE(!subject || !subject->domain ||

			 !subject->domain->hierarchy || !request))

		return;



	if (!is_valid_request(request))

		return;



	if (!audit_enabled)

		return;



	youngest_layer = request->layer_plus_one - 1;

	youngest_denied = get_hierarchy(subject->domain, youngest_layer);



	/* Ignores denials after an execution. */

	if (!(subject->domain_exec & (1 << youngest_layer)))

		return;



	/* Uses consistent allocation flags wrt common_lsm_audit(). */

	ab = audit_log_start(audit_context(), GFP_ATOMIC | __GFP_NOWARN,

			     AUDIT_LANDLOCK_ACCESS);

	if (!ab)

		return;



	audit_log_format(ab, "domain=%llx blockers=", youngest_denied->id);

	log_blockers(ab, request->type);

	audit_log_lsm_data(ab, &request->audit);

	audit_log_end(ab);

}



#ifdef CONFIG_SECURITY_LANDLOCK_KUNIT_TEST



static struct kunit_case test_cases[] = {

	/* clang-format off */

	KUNIT_CASE(test_get_hierarchy),

	{}

	/* clang-format on */

};



static struct kunit_suite test_suite = {

	.name = "landlock_audit",

	.test_cases = test_cases,

};



kunit_test_suite(test_suite);



#endif /* CONFIG_SECURITY_LANDLOCK_KUNIT_TEST */

security/landlock/audit.h

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+52 −0
Original line number Diff line number Diff line 
/* SPDX-License-Identifier: GPL-2.0-only */

/*

 * Landlock - Audit helpers

 *

 * Copyright © 2023-2025 Microsoft Corporation

 */



#ifndef _SECURITY_LANDLOCK_AUDIT_H

#define _SECURITY_LANDLOCK_AUDIT_H



#include <linux/audit.h>

#include <linux/lsm_audit.h>



#include "cred.h"



enum landlock_request_type {

	LANDLOCK_REQUEST_PTRACE = 1,

};



/*

 * We should be careful to only use a variable of this type for

 * landlock_log_denial().  This way, the compiler can remove it entirely if

 * CONFIG_AUDIT is not set.

 */

struct landlock_request {

	/* Mandatory fields. */

	enum landlock_request_type type;

	struct common_audit_data audit;



	/**

	 * layer_plus_one: First layer level that denies the request + 1.  The

	 * extra one is useful to detect uninitialized field.

	 */

	size_t layer_plus_one;

};



#ifdef CONFIG_AUDIT



void landlock_log_denial(const struct landlock_cred_security *const subject,

			 const struct landlock_request *const request);



#else /* CONFIG_AUDIT */



static inline void

landlock_log_denial(const struct landlock_cred_security *const subject,

		    const struct landlock_request *const request)

{

}



#endif /* CONFIG_AUDIT */



#endif /* _SECURITY_LANDLOCK_AUDIT_H */

security/landlock/domain.c

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+28 −0
Original line number Diff line number Diff line 
// SPDX-License-Identifier: GPL-2.0-only

/*

 * Landlock - Domain management

 *

 * Copyright © 2016-2020 Mickaël Salaün <mic@digikod.net>

 * Copyright © 2018-2020 ANSSI

 * Copyright © 2024-2025 Microsoft Corporation

 */



#include "domain.h"

#include "id.h"



#ifdef CONFIG_AUDIT



/**

 * landlock_init_hierarchy_log - Partially initialize landlock_hierarchy

 *

 * @hierarchy: The hierarchy to initialize.

 *

 * @hierarchy->parent and @hierarchy->usage should already be set.

 */

int landlock_init_hierarchy_log(struct landlock_hierarchy *const hierarchy)

{

	hierarchy->id = landlock_get_id_range(1);

	return 0;

}



#endif /* CONFIG_AUDIT */