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

3 files changed, 78 insertions, 26 deletions

diff --git a/security/landlock/domain.c b/security/landlock/domain.c
index f5b78d4766cd..f0d83f43afa1 100644
--- a/security/landlock/domain.c
+++ b/security/landlock/domain.c
@@ -94,8 +94,7 @@ static struct landlock_details *get_current_details(void)
 	 * allocate with GFP_KERNEL_ACCOUNT because it is independent from the
 	 * caller.
 	 */
-	details =
-		kzalloc_flex(*details, exe_path, path_size);
+	details = kzalloc_flex(*details, exe_path, path_size);
 	if (!details)
 		return ERR_PTR(-ENOMEM);
 
diff --git a/security/landlock/ruleset.c b/security/landlock/ruleset.c
index 319873586385..73018dc8d6c7 100644
--- a/security/landlock/ruleset.c
+++ b/security/landlock/ruleset.c
@@ -32,9 +32,8 @@ static struct landlock_ruleset *create_ruleset(const u32 num_layers)
 {
 	struct landlock_ruleset *new_ruleset;
 
-	new_ruleset =
-		kzalloc_flex(*new_ruleset, access_masks, num_layers,
-			     GFP_KERNEL_ACCOUNT);
+	new_ruleset = kzalloc_flex(*new_ruleset, access_masks, num_layers,
+				   GFP_KERNEL_ACCOUNT);
 	if (!new_ruleset)
 		return ERR_PTR(-ENOMEM);
 	refcount_set(&new_ruleset->usage, 1);
@@ -559,8 +558,8 @@ landlock_merge_ruleset(struct landlock_ruleset *const parent,
 	if (IS_ERR(new_dom))
 		return new_dom;
 
-	new_dom->hierarchy = kzalloc_obj(*new_dom->hierarchy,
-					 GFP_KERNEL_ACCOUNT);
+	new_dom->hierarchy =
+		kzalloc_obj(*new_dom->hierarchy, GFP_KERNEL_ACCOUNT);
 	if (!new_dom->hierarchy)
 		return ERR_PTR(-ENOMEM);
 
diff --git a/security/landlock/tsync.c b/security/landlock/tsync.c
index de01aa899751..4d4427ba8d93 100644
--- a/security/landlock/tsync.c
+++ b/security/landlock/tsync.c
@@ -203,6 +203,40 @@ static struct tsync_work *tsync_works_provide(struct tsync_works *s,
 	return ctx;
 }
 
+/**
+ * tsync_works_trim - Put the last tsync_work element
+ *
+ * @s: TSYNC works to trim.
+ *
+ * Put the last task and decrement the size of @s.
+ *
+ * This helper does not cancel a running task, but just reset the last element
+ * to zero.
+ */
+static void tsync_works_trim(struct tsync_works *s)
+{
+	struct tsync_work *ctx;
+
+	if (WARN_ON_ONCE(s->size <= 0))
+		return;
+
+	ctx = s->works[s->size - 1];
+
+	/*
+	 * For consistency, remove the task from ctx so that it does not look like
+	 * we handed it a task_work.
+	 */
+	put_task_struct(ctx->task);
+	*ctx = (typeof(*ctx)){};
+
+	/*
+	 * Cancel the tsync_works_provide() change to recycle the reserved memory
+	 * for the next thread, if any.  This also ensures that cancel_tsync_works()
+	 * and tsync_works_release() do not see any NULL task pointers.
+	 */
+	s->size--;
+}
+
 /*
  * tsync_works_grow_by - preallocates space for n more contexts in s
  *
@@ -256,13 +290,14 @@ static int tsync_works_grow_by(struct tsync_works *s, size_t n, gfp_t flags)
  * tsync_works_contains - checks for presence of task in s
  */
 static bool tsync_works_contains_task(const struct tsync_works *s,
-				      struct task_struct *task)
+				      const struct task_struct *task)
 {
 	size_t i;
 
 	for (i = 0; i < s->size; i++)
 		if (s->works[i]->task == task)
 			return true;
+
 	return false;
 }
 
@@ -276,7 +311,7 @@ static void tsync_works_release(struct tsync_works *s)
 	size_t i;
 
 	for (i = 0; i < s->size; i++) {
-		if (!s->works[i]->task)
+		if (WARN_ON_ONCE(!s->works[i]->task))
 			continue;
 
 		put_task_struct(s->works[i]->task);
@@ -284,6 +319,7 @@ static void tsync_works_release(struct tsync_works *s)
 
 	for (i = 0; i < s->capacity; i++)
 		kfree(s->works[i]);
+
 	kfree(s->works);
 	s->works = NULL;
 	s->size = 0;
@@ -295,7 +331,7 @@ static void tsync_works_release(struct tsync_works *s)
  */
 static size_t count_additional_threads(const struct tsync_works *works)
 {
-	struct task_struct *thread, *caller;
+	const struct task_struct *caller, *thread;
 	size_t n = 0;
 
 	caller = current;
@@ -334,7 +370,8 @@ static bool schedule_task_work(struct tsync_works *works,
 			       struct tsync_shared_context *shared_ctx)
 {
 	int err;
-	struct task_struct *thread, *caller;
+	const struct task_struct *caller;
+	struct task_struct *thread;
 	struct tsync_work *ctx;
 	bool found_more_threads = false;
 
@@ -379,16 +416,14 @@ static bool schedule_task_work(struct tsync_works *works,
 
 		init_task_work(&ctx->work, restrict_one_thread_callback);
 		err = task_work_add(thread, &ctx->work, TWA_SIGNAL);
-		if (err) {
+		if (unlikely(err)) {
 			/*
 			 * task_work_add() only fails if the task is about to exit.  We
 			 * checked that earlier, but it can happen as a race.  Resume
 			 * without setting an error, as the task is probably gone in the
-			 * next loop iteration.  For consistency, remove the task from ctx
-			 * so that it does not look like we handed it a task_work.
+			 * next loop iteration.
 			 */
-			put_task_struct(ctx->task);
-			ctx->task = NULL;
+			tsync_works_trim(works);
 
 			atomic_dec(&shared_ctx->num_preparing);
 			atomic_dec(&shared_ctx->num_unfinished);
@@ -406,12 +441,15 @@ static bool schedule_task_work(struct tsync_works *works,
  * shared_ctx->num_preparing and shared_ctx->num_unfished and mark the two
  * completions if needed, as if the task was never scheduled.
  */
-static void cancel_tsync_works(struct tsync_works *works,
+static void cancel_tsync_works(const struct tsync_works *works,
 			       struct tsync_shared_context *shared_ctx)
 {
-	int i;
+	size_t i;
 
 	for (i = 0; i < works->size; i++) {
+		if (WARN_ON_ONCE(!works->works[i]->task))
+			continue;
+
 		if (!task_work_cancel(works->works[i]->task,
 				      &works->works[i]->work))
 			continue;
@@ -448,6 +486,16 @@ int landlock_restrict_sibling_threads(const struct cred *old_cred,
 	shared_ctx.set_no_new_privs = task_no_new_privs(current);
 
 	/*
+	 * Serialize concurrent TSYNC operations to prevent deadlocks when
+	 * multiple threads call landlock_restrict_self() simultaneously.
+	 * If the lock is already held, we gracefully yield by restarting the
+	 * syscall. This allows the current thread to process pending
+	 * task_works before retrying.
+	 */
+	if (!down_write_trylock(&current->signal->exec_update_lock))
+		return restart_syscall();
+
+	/*
 	 * We schedule a pseudo-signal task_work for each of the calling task's
 	 * sibling threads.  In the task work, each thread:
 	 *
@@ -527,24 +575,30 @@ int landlock_restrict_sibling_threads(const struct cred *old_cred,
 					   -ERESTARTNOINTR);
 
 				/*
-				 * Cancel task works for tasks that did not start running yet,
-				 * and decrement all_prepared and num_unfinished accordingly.
+				 * Opportunistic improvement: try to cancel task
+				 * works for tasks that did not start running
+				 * yet. We do not have a guarantee that it
+				 * cancels any of the enqueued task works
+				 * because task_work_run() might already have
+				 * dequeued them.
 				 */
 				cancel_tsync_works(&works, &shared_ctx);
 
 				/*
-				 * The remaining task works have started running, so waiting for
-				 * their completion will finish.
+				 * Break the loop with error. The cleanup code
+				 * after the loop unblocks the remaining
+				 * task_works.
 				 */
-				wait_for_completion(&shared_ctx.all_prepared);
+				break;
 			}
 		}
 	} while (found_more_threads &&
 		 !atomic_read(&shared_ctx.preparation_error));
 
 	/*
-	 * We now have all sibling threads blocking and in "prepared" state in the
-	 * task work. Ask all threads to commit.
+	 * We now have either (a) all sibling threads blocking and in "prepared"
+	 * state in the task work, or (b) the preparation error is set. Ask all
+	 * threads to commit (or abort).
 	 */
 	complete_all(&shared_ctx.ready_to_commit);
 
@@ -556,6 +610,6 @@ int landlock_restrict_sibling_threads(const struct cred *old_cred,
 		wait_for_completion(&shared_ctx.all_finished);
 
 	tsync_works_release(&works);
-
+	up_write(&current->signal->exec_update_lock);
 	return atomic_read(&shared_ctx.preparation_error);
 }