[PATCH] ALSA: pcm: Test for "silence" field in struct "pcm_format_data"

["Fabio M. De Francesco" <fmdefrancesco@gmail.com>]

Syzbot reports "KASAN: null-ptr-deref Write in
snd_pcm_format_set_silence".[1]

It is due to missing validation of the "silence" field of struct
"pcm_format_data" in "pcm_formats" array.

Add a test for valid "pat" and, if it is not so, return -EINVAL.

[1] https://lore.kernel.org/lkml/000000000000d188ef05dc2c7279@google.com/

Reported-and-tested-by: syzbot+205eb15961852c2c5974@syzkaller.appspotmail.com
Signed-off-by: Fabio M. De Francesco <fmdefrancesco@gmail.com>
---

I wasn't able to figure out the commit for the "Fixes:" tag. If this patch
is good, can someone please help with providing this missing information?

 sound/core/pcm_misc.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/sound/core/pcm_misc.c b/sound/core/pcm_misc.c
index 4866aed97aac..5588b6a1ee8b 100644
--- a/sound/core/pcm_misc.c
+++ b/sound/core/pcm_misc.c
@@ -433,7 +433,7 @@ int snd_pcm_format_set_silence(snd_pcm_format_t format, void *data, unsigned int
 		return 0;
 	width = pcm_formats[(INT)format].phys; /* physical width */
 	pat = pcm_formats[(INT)format].silence;
-	if (! width)
+	if (!width || !pat)
 		return -EINVAL;
 	/* signed or 1 byte data */
 	if (pcm_formats[(INT)format].signd == 1 || width <= 8) {
-- 
2.34.1