[PATCH] ALSA: pcm: Check for null pointer of pointer substream before dereferencing it

[Colin Ian King <colin.i.king@gmail.com>]

Pointer substream is being dereferenced on the assignment of pointer card
before substream is being null checked with the macro PCM_RUNTIME_CHECK.
Although PCM_RUNTIME_CHECK calls BUG_ON, it still is useful to perform the
the pointer check before card is assigned.

Fixes: commit d4cfb30fce03 ("ALSA: pcm: Set per-card upper limit of PCM buffer allocations")

Signed-off-by: Colin Ian King <colin.i.king@gmail.com>
---
 sound/core/pcm_memory.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/sound/core/pcm_memory.c b/sound/core/pcm_memory.c
index 8848d2f3160d..b8296b6eb2c1 100644
--- a/sound/core/pcm_memory.c
+++ b/sound/core/pcm_memory.c
@@ -453,7 +453,6 @@ EXPORT_SYMBOL(snd_pcm_lib_malloc_pages);
  */
 int snd_pcm_lib_free_pages(struct snd_pcm_substream *substream)
 {
-	struct snd_card *card = substream->pcm->card;
 	struct snd_pcm_runtime *runtime;
 
 	if (PCM_RUNTIME_CHECK(substream))
@@ -462,6 +461,8 @@ int snd_pcm_lib_free_pages(struct snd_pcm_substream *substream)
 	if (runtime->dma_area == NULL)
 		return 0;
 	if (runtime->dma_buffer_p != &substream->dma_buffer) {
+		struct snd_card *card = substream->pcm->card;
+
 		/* it's a newly allocated buffer.  release it now. */
 		do_free_pages(card, runtime->dma_buffer_p);
 		kfree(runtime->dma_buffer_p);
-- 
2.35.1