snd_pcm_drain() uses init_waitqueue_entry which does not clear
entry.prev/next, and add_wait_queue with a conditional
remove_wait_queue that is skipped when to_check is no longer
in the group after concurrent UNLINK.  The orphaned wait entry
remains on the unlinked substream sleep queue.  On the next
drain iteration, add_wait_queue adds the entry to a new queue
while still linked on the old one, corrupting both lists.  A
subsequent wake_up dereferences NULL at the func pointer
(mapped from the spinlock at offset 0 of the misinterpreted
wait_queue_head_t), causing a kernel panic.

Replace init_waitqueue_entry/add_wait_queue/conditional
remove_wait_queue with init_wait_entry/prepare_to_wait/
finish_wait.  init_wait_entry clears prev/next via
INIT_LIST_HEAD on each iteration and sets
autoremove_wake_function which auto-removes the entry on
wake-up.  finish_wait safely handles both the already-removed
and still-queued cases.

Fixes: 9b1dbd69ba6f ("ALSA: pcm: fix use-after-free on linked stream runtime in snd_pcm_drain")
Signed-off-by: Ji'an Zhou <eilaimemedsnaimel@gmail.com>
---
 sound/core/pcm_native.c | 7 +++----
 1 file changed, 3 insertions(+), 4 deletions(-)

diff --git a/sound/core/pcm_native.c b/sound/core/pcm_native.c
index a541bb235cfa..302643c1c192 100644
--- a/sound/core/pcm_native.c
+++ b/sound/core/pcm_native.c
@@ -2199,9 +2199,8 @@ static int snd_pcm_drain(struct snd_pcm_substream *substream,
 		drain_no_period_wakeup = to_check->no_period_wakeup;
 		drain_rate = to_check->rate;
 		drain_bufsz = to_check->buffer_size;
-		init_waitqueue_entry(&wait, current);
-		set_current_state(TASK_INTERRUPTIBLE);
-		add_wait_queue(&to_check->sleep, &wait);
+		init_wait_entry(&wait, 0);
+		prepare_to_wait(&to_check->sleep, &wait, TASK_INTERRUPTIBLE);
 		snd_pcm_stream_unlock_irq(substream);
 		if (drain_no_period_wakeup)
 			tout = MAX_SCHEDULE_TIMEOUT;
@@ -2219,7 +2218,7 @@ static int snd_pcm_drain(struct snd_pcm_substream *substream,
 		group = snd_pcm_stream_group_ref(substream);
 		snd_pcm_group_for_each_entry(s, substream) {
 			if (s->runtime == to_check) {
-				remove_wait_queue(&to_check->sleep, &wait);
+				finish_wait(&to_check->sleep, &wait);
 				break;
 			}
 		}
-- 
2.43.0

On Thu, 04 Jun 2026 16:25:59 +0200,
Ji'an Zhou wrote:
> 
> snd_pcm_drain() uses init_waitqueue_entry which does not clear
> entry.prev/next, and add_wait_queue with a conditional
> remove_wait_queue that is skipped when to_check is no longer
> in the group after concurrent UNLINK.  The orphaned wait entry
> remains on the unlinked substream sleep queue.  On the next
> drain iteration, add_wait_queue adds the entry to a new queue
> while still linked on the old one, corrupting both lists.  A
> subsequent wake_up dereferences NULL at the func pointer
> (mapped from the spinlock at offset 0 of the misinterpreted
> wait_queue_head_t), causing a kernel panic.
> 
> Replace init_waitqueue_entry/add_wait_queue/conditional
> remove_wait_queue with init_wait_entry/prepare_to_wait/
> finish_wait.  init_wait_entry clears prev/next via
> INIT_LIST_HEAD on each iteration and sets
> autoremove_wake_function which auto-removes the entry on
> wake-up.  finish_wait safely handles both the already-removed
> and still-queued cases.
> 
> Fixes: 9b1dbd69ba6f ("ALSA: pcm: fix use-after-free on linked stream runtime in snd_pcm_drain")
> Signed-off-by: Ji'an Zhou <eilaimemedsnaimel@gmail.com>

Applied now.  Thanks.


Takashi