[PATCH 4.19 021/243] ALSA: pcm: Fix stream lock usage in snd_pcm_period_elapsed()

[Greg Kroah-Hartman]

From: paulhsia <paulhsia@xxxxxxxxxxxx>

[ 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@xxxxxxxxxxxx>
Link: https://lore.kernel.org/r/20191112171715.128727-2-paulhsia@xxxxxxxxxxxx
Signed-off-by: Takashi Iwai <tiwai@xxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
 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 4e6110d778bd2..ad52126d3d22e 100644
--- a/sound/core/pcm_lib.c
+++ b/sound/core/pcm_lib.c
@@ -1797,11 +1797,14 @@ 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;
@@ -1812,6 +1815,7 @@ 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);
 }
 EXPORT_SYMBOL(snd_pcm_period_elapsed);
-- 
2.20.1