Merge tag 'locking-urgent-2025-02-08' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

Pull locking fix from Ingo Molnar:
 "Fix a dangling pointer bug in the futex code used by the uring code.

  It isn't causing problems at the moment due to uring ABI limitations
  leaving it essentially unused in current usages, but is a good idea to
  fix nevertheless"

* tag 'locking-urgent-2025-02-08' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  futex: Pass in task to futex_queue()

4 files changed, 14 insertions, 8 deletions

diff --git a/kernel/futex/core.c b/kernel/futex/core.c
index ebdd76b4ecbb..3db8567f5a44 100644
--- a/kernel/futex/core.c
+++ b/kernel/futex/core.c
@@ -532,7 +532,8 @@ void futex_q_unlock(struct futex_hash_bucket *hb)
 	futex_hb_waiters_dec(hb);
 }
 
-void __futex_queue(struct futex_q *q, struct futex_hash_bucket *hb)
+void __futex_queue(struct futex_q *q, struct futex_hash_bucket *hb,
+		   struct task_struct *task)
 {
 	int prio;
 
@@ -548,7 +549,7 @@ void __futex_queue(struct futex_q *q, struct futex_hash_bucket *hb)
 
 	plist_node_init(&q->list, prio);
 	plist_add(&q->list, &hb->chain);
-	q->task = current;
+	q->task = task;
 }
 
 /**
diff --git a/kernel/futex/futex.h b/kernel/futex/futex.h
index 99b32e728c4a..6b2f4c7eb720 100644
--- a/kernel/futex/futex.h
+++ b/kernel/futex/futex.h
@@ -285,13 +285,15 @@ static inline int futex_get_value_locked(u32 *dest, u32 __user *from)
 }
 
 extern void __futex_unqueue(struct futex_q *q);
-extern void __futex_queue(struct futex_q *q, struct futex_hash_bucket *hb);
+extern void __futex_queue(struct futex_q *q, struct futex_hash_bucket *hb,
+				struct task_struct *task);
 extern int futex_unqueue(struct futex_q *q);
 
 /**
  * futex_queue() - Enqueue the futex_q on the futex_hash_bucket
  * @q:	The futex_q to enqueue
  * @hb:	The destination hash bucket
+ * @task: Task queueing this futex
  *
  * The hb->lock must be held by the caller, and is released here. A call to
  * futex_queue() is typically paired with exactly one call to futex_unqueue().  The
@@ -299,11 +301,14 @@ extern int futex_unqueue(struct futex_q *q);
  * or nothing if the unqueue is done as part of the wake process and the unqueue
  * state is implicit in the state of woken task (see futex_wait_requeue_pi() for
  * an example).
+ *
+ * Note that @task may be NULL, for async usage of futexes.
  */
-static inline void futex_queue(struct futex_q *q, struct futex_hash_bucket *hb)
+static inline void futex_queue(struct futex_q *q, struct futex_hash_bucket *hb,
+			       struct task_struct *task)
 	__releases(&hb->lock)
 {
-	__futex_queue(q, hb);
+	__futex_queue(q, hb, task);
 	spin_unlock(&hb->lock);
 }
 
diff --git a/kernel/futex/pi.c b/kernel/futex/pi.c
index daea650b16f5..7a941845f7ee 100644
--- a/kernel/futex/pi.c
+++ b/kernel/futex/pi.c
@@ -982,7 +982,7 @@ retry_private:
 	/*
 	 * Only actually queue now that the atomic ops are done:
 	 */
-	__futex_queue(&q, hb);
+	__futex_queue(&q, hb, current);
 
 	if (trylock) {
 		ret = rt_mutex_futex_trylock(&q.pi_state->pi_mutex);
diff --git a/kernel/futex/waitwake.c b/kernel/futex/waitwake.c
index eb86a7ade06a..25877d4f2f8f 100644
--- a/kernel/futex/waitwake.c
+++ b/kernel/futex/waitwake.c
@@ -349,7 +349,7 @@ void futex_wait_queue(struct futex_hash_bucket *hb, struct futex_q *q,
 	 * access to the hash list and forcing another memory barrier.
 	 */
 	set_current_state(TASK_INTERRUPTIBLE|TASK_FREEZABLE);
-	futex_queue(q, hb);
+	futex_queue(q, hb, current);
 
 	/* Arm the timer */
 	if (timeout)
@@ -460,7 +460,7 @@ retry:
 			 * next futex. Queue each futex at this moment so hb can
 			 * be unlocked.
 			 */
-			futex_queue(q, hb);
+			futex_queue(q, hb, current);
 			continue;
 		}