[PATCH v2 2/2] landlock: selftests for LANDLOCK_RESTRICT_SELF_TSYNC

["Günther Noack" <gnoack@google.com>]

Exercise various scenarios where Landlock domains are enforced across
all of a processes' threads.

Cc: Mickaël Salaün <mic@digikod.net>
Cc: Paul Moore <paul@paul-moore.com>
Cc: linux-security-module@vger.kernel.org
Signed-off-by: Günther Noack <gnoack@google.com>
---
 tools/testing/selftests/landlock/base_test.c  |  6 +-
 tools/testing/selftests/landlock/tsync_test.c | 99 +++++++++++++++++++
 2 files changed, 102 insertions(+), 3 deletions(-)
 create mode 100644 tools/testing/selftests/landlock/tsync_test.c

diff --git a/tools/testing/selftests/landlock/base_test.c b/tools/testing/selftests/landlock/base_test.c
index 7b69002239d7..b9be6dcb7e8c 100644
--- a/tools/testing/selftests/landlock/base_test.c
+++ b/tools/testing/selftests/landlock/base_test.c
@@ -288,7 +288,7 @@ TEST(restrict_self_fd)
 	EXPECT_EQ(EBADFD, errno);
 }
 
-TEST(restrict_self_fd_flags)
+TEST(restrict_self_fd_logging_flags)
 {
 	int fd;
 
@@ -304,9 +304,9 @@ TEST(restrict_self_fd_flags)
 	EXPECT_EQ(EBADFD, errno);
 }
 
-TEST(restrict_self_flags)
+TEST(restrict_self_logging_flags)
 {
-	const __u32 last_flag = LANDLOCK_RESTRICT_SELF_LOG_SUBDOMAINS_OFF;
+	const __u32 last_flag = LANDLOCK_RESTRICT_SELF_TSYNC;
 
 	/* Tests invalid flag combinations. */
 
diff --git a/tools/testing/selftests/landlock/tsync_test.c b/tools/testing/selftests/landlock/tsync_test.c
new file mode 100644
index 000000000000..356e20de352f
--- /dev/null
+++ b/tools/testing/selftests/landlock/tsync_test.c
@@ -0,0 +1,99 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Landlock tests - Enforcing the same restrictions across multiple threads
+ *
+ * Copyright © 2025 Günther Noack <gnoack3000@gmail.com>
+ */
+
+#define _GNU_SOURCE
+#include <pthread.h>
+#include <sys/prctl.h>
+#include <linux/landlock.h>
+
+#include "common.h"
+
+/* create_ruleset - Create a simple ruleset FD common to all tests */
+static int create_ruleset(struct __test_metadata *const _metadata)
+{
+	struct landlock_ruleset_attr ruleset_attr = {
+		.handled_access_fs = (LANDLOCK_ACCESS_FS_WRITE_FILE |
+				      LANDLOCK_ACCESS_FS_TRUNCATE),
+	};
+	const int ruleset_fd =
+		landlock_create_ruleset(&ruleset_attr, sizeof(ruleset_attr), 0);
+
+	ASSERT_LE(0, ruleset_fd);
+	return ruleset_fd;
+}
+
+TEST(single_threaded_success)
+{
+	const int ruleset_fd = create_ruleset(_metadata);
+
+	disable_caps(_metadata);
+
+	ASSERT_EQ(0, prctl(PR_SET_NO_NEW_PRIVS, 1, 0, 0, 0));
+	ASSERT_EQ(0, landlock_restrict_self(ruleset_fd,
+					    LANDLOCK_RESTRICT_SELF_TSYNC));
+
+	ASSERT_EQ(0, close(ruleset_fd));
+}
+
+void *idle(void *data)
+{
+	while (true)
+		sleep(1);
+}
+
+TEST(multi_threaded_success)
+{
+	pthread_t t1, t2;
+	const int ruleset_fd = create_ruleset(_metadata);
+
+	disable_caps(_metadata);
+
+	ASSERT_EQ(0, prctl(PR_SET_NO_NEW_PRIVS, 1, 0, 0, 0));
+
+	ASSERT_EQ(0, pthread_create(&t1, NULL, idle, NULL));
+	ASSERT_EQ(0, pthread_create(&t2, NULL, idle, NULL));
+
+	EXPECT_EQ(0, landlock_restrict_self(ruleset_fd,
+					    LANDLOCK_RESTRICT_SELF_TSYNC));
+
+	ASSERT_EQ(0, pthread_cancel(t1));
+	ASSERT_EQ(0, pthread_cancel(t2));
+	ASSERT_EQ(0, pthread_join(t1, NULL));
+	ASSERT_EQ(0, pthread_join(t2, NULL));
+	ASSERT_EQ(0, close(ruleset_fd));
+}
+
+TEST(multi_threaded_success_despite_diverging_domains)
+{
+	pthread_t t1, t2;
+	const int ruleset_fd = create_ruleset(_metadata);
+
+	disable_caps(_metadata);
+
+	ASSERT_EQ(0, prctl(PR_SET_NO_NEW_PRIVS, 1, 0, 0, 0));
+
+	ASSERT_EQ(0, pthread_create(&t1, NULL, idle, NULL));
+	ASSERT_EQ(0, pthread_create(&t2, NULL, idle, NULL));
+
+	/*
+	 * The main thread enforces a ruleset,
+	 * thereby bringing the threads' Landlock domains out of sync.
+	 */
+	EXPECT_EQ(0, landlock_restrict_self(ruleset_fd, 0));
+
+	/* Still, TSYNC succeeds, bringing the threads in sync again. */
+	EXPECT_EQ(0, landlock_restrict_self(ruleset_fd,
+					    LANDLOCK_RESTRICT_SELF_TSYNC));
+
+	ASSERT_EQ(0, pthread_cancel(t1));
+	ASSERT_EQ(0, pthread_cancel(t2));
+	ASSERT_EQ(0, pthread_join(t1, NULL));
+	ASSERT_EQ(0, pthread_join(t2, NULL));
+	ASSERT_EQ(0, close(ruleset_fd));
+}
+
+TEST_HARNESS_MAIN
-- 
2.51.0.618.g983fd99d29-goog