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

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Date:   Sun, 24 Apr 2022 21:59:45 +0100
From:   Colin Ian King <colin.i.king@...il.com>
To:     Takashi Iwai <tiwai@...e.com>, alsa-devel@...a-project.org
Cc:     kernel-janitors@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [PATCH] ALSA: pcm: Check for null pointer of pointer substream before dereferencing it

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@...il.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