From: Takashi Iwai tiwai@suse.de
[ Upstream commit e3cd33ab17c33bd8f1a9df66ec83a15dd8f7afbb ]
snd_seq_poll() calls snd_seq_write_pool_allocated() that reads out a field in client->pool object, while it can be updated concurrently via ioctls, as reported by syzbot. The data race itself is harmless, as it's merely a poll() call, and the state is volatile. OTOH, the read out of poll object info from the caller side is fragile, and we can leave it better in snd_seq_pool_poll_wait() alone.
A similar pattern is seen in snd_seq_kernel_client_write_poll(), too, which is called from the OSS sequencer.
This patch drops the pool checks from the caller side and add the pool->lock in snd_seq_pool_poll_wait() for better data consistency.
Reported-by: syzbot+2d373c9936c00d7e120c@syzkaller.appspotmail.com Closes: https://lore.kernel.org/67c88903.050a0220.15b4b9.0028.GAE@google.com Link: https://patch.msgid.link/20250307084246.29271-1-tiwai@suse.de Signed-off-by: Takashi Iwai tiwai@suse.de Signed-off-by: Sasha Levin sashal@kernel.org --- sound/core/seq/seq_clientmgr.c | 5 +---- sound/core/seq/seq_memory.c | 1 + 2 files changed, 2 insertions(+), 4 deletions(-)
diff --git a/sound/core/seq/seq_clientmgr.c b/sound/core/seq/seq_clientmgr.c index 706f53e39b53c..7f03e1ec92355 100644 --- a/sound/core/seq/seq_clientmgr.c +++ b/sound/core/seq/seq_clientmgr.c @@ -1150,8 +1150,7 @@ static __poll_t snd_seq_poll(struct file *file, poll_table * wait) if (snd_seq_file_flags(file) & SNDRV_SEQ_LFLG_OUTPUT) {
/* check if data is available in the pool */ - if (!snd_seq_write_pool_allocated(client) || - snd_seq_pool_poll_wait(client->pool, file, wait)) + if (snd_seq_pool_poll_wait(client->pool, file, wait)) mask |= EPOLLOUT | EPOLLWRNORM; }
@@ -2586,8 +2585,6 @@ int snd_seq_kernel_client_write_poll(int clientid, struct file *file, poll_table if (client == NULL) return -ENXIO;
- if (! snd_seq_write_pool_allocated(client)) - return 1; if (snd_seq_pool_poll_wait(client->pool, file, wait)) return 1; return 0; diff --git a/sound/core/seq/seq_memory.c b/sound/core/seq/seq_memory.c index 20155e3e87c6a..ccde0ca3d2082 100644 --- a/sound/core/seq/seq_memory.c +++ b/sound/core/seq/seq_memory.c @@ -427,6 +427,7 @@ int snd_seq_pool_poll_wait(struct snd_seq_pool *pool, struct file *file, poll_table *wait) { poll_wait(file, &pool->output_sleep, wait); + guard(spinlock_irq)(&pool->lock); return snd_seq_output_ok(pool); }