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Subject[PATCH 4.9 014/199] ALSA: pcm: Fix stream lock usage in snd_pcm_period_elapsed()
Date
From: paulhsia <paulhsia@chromium.org>

[ Upstream commit f5cdc9d4003a2f66ea57b3edd3e04acc2b1a4439 ]

If the nullity check for `substream->runtime` is outside of the lock
region, it is possible to have a null runtime in the critical section
if snd_pcm_detach_substream is called right before the lock.

Signed-off-by: paulhsia <paulhsia@chromium.org>
Link: https://lore.kernel.org/r/20191112171715.128727-2-paulhsia@chromium.org
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
sound/core/pcm_lib.c | 8 ++++++--
1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/sound/core/pcm_lib.c b/sound/core/pcm_lib.c
index 3acb373674c37..f09ae7efc6957 100644
--- a/sound/core/pcm_lib.c
+++ b/sound/core/pcm_lib.c
@@ -1877,11 +1877,14 @@ void snd_pcm_period_elapsed(struct snd_pcm_substream *substream)
struct snd_pcm_runtime *runtime;
unsigned long flags;

- if (PCM_RUNTIME_CHECK(substream))
+ if (snd_BUG_ON(!substream))
return;
- runtime = substream->runtime;

snd_pcm_stream_lock_irqsave(substream, flags);
+ if (PCM_RUNTIME_CHECK(substream))
+ goto _unlock;
+ runtime = substream->runtime;
+
if (!snd_pcm_running(substream) ||
snd_pcm_update_hw_ptr0(substream, 1) < 0)
goto _end;
@@ -1892,6 +1895,7 @@ void snd_pcm_period_elapsed(struct snd_pcm_substream *substream)
#endif
_end:
kill_fasync(&runtime->fasync, SIGIO, POLL_IN);
+ _unlock:
snd_pcm_stream_unlock_irqrestore(substream, flags);
}

--
2.20.1


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