Merge tag 'landlock-7.0-rc6' of git://git.kernel.org/pub/scm/linux/kernel/git/mic/linux

Pull Landlock fixes from Mickaël Salaün:
 "This mainly fixes Landlock TSYNC issues related to interrupts and
  unexpected task exit.

  Other fixes touch documentation and sample, and a new test extends
  coverage"

* tag 'landlock-7.0-rc6' of git://git.kernel.org/pub/scm/linux/kernel/git/mic/linux:
  landlock: Expand restrict flags example for ABI version 8
  selftests/landlock: Test tsync interruption and cancellation paths
  landlock: Clean up interrupted thread logic in TSYNC
  landlock: Serialize TSYNC thread restriction
  samples/landlock: Bump ABI version to 8
  landlock: Improve TSYNC types
  landlock: Fully release unused TSYNC work entries
  landlock: Fix formatting

1 files changed, 90 insertions, 1 deletions

diff --git a/tools/testing/selftests/landlock/tsync_test.c b/tools/testing/selftests/landlock/tsync_test.c
index 37ef0d2270db..2b9ad4f154f4 100644
--- a/tools/testing/selftests/landlock/tsync_test.c
+++ b/tools/testing/selftests/landlock/tsync_test.c
@@ -6,9 +6,10 @@
  */
 
 #define _GNU_SOURCE
+#include <linux/landlock.h>
 #include <pthread.h>
+#include <signal.h>
 #include <sys/prctl.h>
-#include <linux/landlock.h>
 
 #include "common.h"
 
@@ -158,4 +159,92 @@ TEST(competing_enablement)
 	EXPECT_EQ(0, close(ruleset_fd));
 }
 
+static void signal_nop_handler(int sig)
+{
+}
+
+struct signaler_data {
+	pthread_t target;
+	volatile bool stop;
+};
+
+static void *signaler_thread(void *data)
+{
+	struct signaler_data *sd = data;
+
+	while (!sd->stop)
+		pthread_kill(sd->target, SIGUSR1);
+
+	return NULL;
+}
+
+/*
+ * Number of idle sibling threads.  This must be large enough that even on
+ * machines with many cores, the sibling threads cannot all complete their
+ * credential preparation in a single parallel wave, otherwise the signaler
+ * thread has no window to interrupt wait_for_completion_interruptible().
+ * 200 threads on a 64-core machine yields ~3 serialized waves, giving the
+ * tight signal loop enough time to land an interruption.
+ */
+#define NUM_IDLE_THREADS 200
+
+/*
+ * Exercises the tsync interruption and cancellation paths in tsync.c.
+ *
+ * When a signal interrupts the calling thread while it waits for sibling
+ * threads to finish their credential preparation
+ * (wait_for_completion_interruptible in landlock_restrict_sibling_threads),
+ * the kernel sets ERESTARTNOINTR, cancels queued task works that have not
+ * started yet (cancel_tsync_works), then waits for the remaining works to
+ * finish.  On the error return, syscalls.c aborts the prepared credentials.
+ * The kernel automatically restarts the syscall, so userspace sees success.
+ */
+TEST(tsync_interrupt)
+{
+	size_t i;
+	pthread_t threads[NUM_IDLE_THREADS];
+	pthread_t signaler;
+	struct signaler_data sd;
+	struct sigaction sa = {};
+	const int ruleset_fd = create_ruleset(_metadata);
+
+	disable_caps(_metadata);
+
+	/* Install a no-op SIGUSR1 handler so the signal does not kill us. */
+	sa.sa_handler = signal_nop_handler;
+	sigemptyset(&sa.sa_mask);
+	ASSERT_EQ(0, sigaction(SIGUSR1, &sa, NULL));
+
+	ASSERT_EQ(0, prctl(PR_SET_NO_NEW_PRIVS, 1, 0, 0, 0));
+
+	for (i = 0; i < NUM_IDLE_THREADS; i++)
+		ASSERT_EQ(0, pthread_create(&threads[i], NULL, idle, NULL));
+
+	/*
+	 * Start a signaler thread that continuously sends SIGUSR1 to the
+	 * calling thread.  This maximizes the chance of interrupting
+	 * wait_for_completion_interruptible() in the kernel's tsync path.
+	 */
+	sd.target = pthread_self();
+	sd.stop = false;
+	ASSERT_EQ(0, pthread_create(&signaler, NULL, signaler_thread, &sd));
+
+	/*
+	 * The syscall may be interrupted and transparently restarted by the
+	 * kernel (ERESTARTNOINTR).  From userspace, it should always succeed.
+	 */
+	EXPECT_EQ(0, landlock_restrict_self(ruleset_fd,
+					    LANDLOCK_RESTRICT_SELF_TSYNC));
+
+	sd.stop = true;
+	ASSERT_EQ(0, pthread_join(signaler, NULL));
+
+	for (i = 0; i < NUM_IDLE_THREADS; i++) {
+		ASSERT_EQ(0, pthread_cancel(threads[i]));
+		ASSERT_EQ(0, pthread_join(threads[i], NULL));
+	}
+
+	EXPECT_EQ(0, close(ruleset_fd));
+}
+
 TEST_HARNESS_MAIN