[PATCH v5 23/24] selftests/landlock: Add audit tests for ptrace

[Mickaël Salaün]

Add tests for all ptrace actions.  This improves all the ptrace tests by
making sure that the restrictions comes from Landlock, and with the
expected objects.  These extended tests are like enhanced errno checks
that make sure Landlock enforcement is consistent.

Test coverage for security/landlock is 93.4% of 1619 lines according to
gcc/gcov-14.

Cc: Günther Noack <gnoack at google.com>
Cc: Paul Moore <paul at paul-moore.com>
Signed-off-by: Mickaël Salaün <mic at digikod.net>
Link: https://lore.kernel.org/r/20250131163059.1139617-24-mic@digikod.net
---

Changes since v3:
- Update test coverage.

Changes since v2:
- New patch.
---
 .../testing/selftests/landlock/ptrace_test.c  | 67 +++++++++++++++++--
 1 file changed, 63 insertions(+), 4 deletions(-)

diff --git a/tools/testing/selftests/landlock/ptrace_test.c b/tools/testing/selftests/landlock/ptrace_test.c
index 8f31b673ff2d..6f1551290450 100644
--- a/tools/testing/selftests/landlock/ptrace_test.c
+++ b/tools/testing/selftests/landlock/ptrace_test.c
@@ -4,6 +4,7 @@
  *
  * Copyright © 2017-2020 Mickaël Salaün <mic at digikod.net>
  * Copyright © 2019-2020 ANSSI
+ * Copyright © 2024-2025 Microsoft Corporation
  */
 
 #define _GNU_SOURCE
@@ -17,6 +18,7 @@
 #include <sys/wait.h>
 #include <unistd.h>
 
+#include "audit.h"
 #include "common.h"
 
 /* Copied from security/yama/yama_lsm.c */
@@ -83,9 +85,27 @@ static int get_yama_ptrace_scope(void)
 	return ret;
 }
 
-/* clang-format off */
-FIXTURE(hierarchy) {};
-/* clang-format on */
+static int matches_log_ptrace(struct __test_metadata *const _metadata,
+			      int audit_fd, const pid_t opid)
+{
+	static const char log_template[] = REGEX_LANDLOCK_PREFIX
+		" blockers=ptrace opid=%d ocomm=\"ptrace_test\"$";
+	char log_match[sizeof(log_template) + 10];
+	int log_match_len;
+
+	log_match_len =
+		snprintf(log_match, sizeof(log_match), log_template, opid);
+	if (log_match_len > sizeof(log_match))
+		return -E2BIG;
+
+	return audit_match_record(audit_fd, AUDIT_LANDLOCK_ACCESS, log_match);
+}
+
+FIXTURE(hierarchy)
+{
+	struct audit_filter audit_filter;
+	int audit_fd;
+};
 
 FIXTURE_VARIANT(hierarchy)
 {
@@ -243,10 +263,16 @@ FIXTURE_VARIANT_ADD(hierarchy, deny_with_forked_domain) {
 
 FIXTURE_SETUP(hierarchy)
 {
+	disable_caps(_metadata);
+	set_cap(_metadata, CAP_AUDIT_CONTROL);
+	self->audit_fd = audit_init_with_exe_filter(&self->audit_filter);
+	EXPECT_LE(0, self->audit_fd);
+	clear_cap(_metadata, CAP_AUDIT_CONTROL);
 }
 
-FIXTURE_TEARDOWN(hierarchy)
+FIXTURE_TEARDOWN_PARENT(hierarchy)
 {
+	EXPECT_EQ(0, audit_cleanup(-1, NULL));
 }
 
 /* Test PTRACE_TRACEME and PTRACE_ATTACH for parent and child. */
@@ -259,6 +285,7 @@ TEST_F(hierarchy, trace)
 	char buf_parent;
 	long ret;
 	bool can_read_child, can_trace_child, can_read_parent, can_trace_parent;
+	struct audit_records records;
 
 	yama_ptrace_scope = get_yama_ptrace_scope();
 	ASSERT_LE(0, yama_ptrace_scope);
@@ -334,17 +361,29 @@ TEST_F(hierarchy, trace)
 		err_proc_read = test_ptrace_read(parent);
 		if (can_read_parent) {
 			EXPECT_EQ(0, err_proc_read);
+			EXPECT_EQ(-EAGAIN,
+				  matches_log_ptrace(_metadata, self->audit_fd,
+						     parent));
 		} else {
 			EXPECT_EQ(EACCES, err_proc_read);
+			EXPECT_EQ(0,
+				  matches_log_ptrace(_metadata, self->audit_fd,
+						     parent));
 		}
 
 		/* Tests PTRACE_ATTACH on the parent. */
 		ret = ptrace(PTRACE_ATTACH, parent, NULL, 0);
 		if (can_trace_parent) {
 			EXPECT_EQ(0, ret);
+			EXPECT_EQ(-EAGAIN,
+				  matches_log_ptrace(_metadata, self->audit_fd,
+						     parent));
 		} else {
 			EXPECT_EQ(-1, ret);
 			EXPECT_EQ(EPERM, errno);
+			EXPECT_EQ(can_read_parent ? -EAGAIN : 0,
+				  matches_log_ptrace(_metadata, self->audit_fd,
+						     parent));
 		}
 		if (ret == 0) {
 			ASSERT_EQ(parent, waitpid(parent, &status, 0));
@@ -356,9 +395,16 @@ TEST_F(hierarchy, trace)
 		ret = ptrace(PTRACE_TRACEME);
 		if (can_trace_child) {
 			EXPECT_EQ(0, ret);
+			EXPECT_EQ(-EAGAIN,
+				  matches_log_ptrace(_metadata, self->audit_fd,
+						     parent));
 		} else {
 			EXPECT_EQ(-1, ret);
 			EXPECT_EQ(EPERM, errno);
+			/* We should indeed see the parent process. */
+			EXPECT_EQ(can_read_child ? -EAGAIN : 0,
+				  matches_log_ptrace(_metadata, self->audit_fd,
+						     parent));
 		}
 
 		/*
@@ -406,17 +452,25 @@ TEST_F(hierarchy, trace)
 	err_proc_read = test_ptrace_read(child);
 	if (can_read_child) {
 		EXPECT_EQ(0, err_proc_read);
+		EXPECT_EQ(-EAGAIN,
+			  matches_log_ptrace(_metadata, self->audit_fd, child));
 	} else {
 		EXPECT_EQ(EACCES, err_proc_read);
+		EXPECT_EQ(0,
+			  matches_log_ptrace(_metadata, self->audit_fd, child));
 	}
 
 	/* Tests PTRACE_ATTACH on the child. */
 	ret = ptrace(PTRACE_ATTACH, child, NULL, 0);
 	if (can_trace_child) {
 		EXPECT_EQ(0, ret);
+		EXPECT_EQ(-EAGAIN,
+			  matches_log_ptrace(_metadata, self->audit_fd, child));
 	} else {
 		EXPECT_EQ(-1, ret);
 		EXPECT_EQ(EPERM, errno);
+		EXPECT_EQ(can_read_child ? -EAGAIN : 0,
+			  matches_log_ptrace(_metadata, self->audit_fd, child));
 	}
 
 	if (ret == 0) {
@@ -432,6 +486,11 @@ TEST_F(hierarchy, trace)
 	if (WIFSIGNALED(status) || !WIFEXITED(status) ||
 	    WEXITSTATUS(status) != EXIT_SUCCESS)
 		_metadata->exit_code = KSFT_FAIL;
+
+	/* Makes sure there is no superfluous logged records. */
+	audit_count_records(self->audit_fd, &records);
+	EXPECT_EQ(0, records.access);
+	EXPECT_EQ(0, records.domain);
 }
 
 TEST_HARNESS_MAIN
-- 
2.48.1