On martedì 14 giugno 2022 11:58:51 CEST Eugeniu Rosca wrote:
Hello Fabio, hello All,
On Sa, Apr 09, 2022 at 03:26:55 +0200, Fabio M. De Francesco wrote:
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.
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) {
JFYI, PVS-Studio 7.19 reports:
sound/core/pcm_misc.c 409 warn V560 A part of
conditional expression is always false: !pat.
Sorry, I assumed (wrongly!) that when we have
static const struct pcm_format_data pcm_formats[(INT)SNDRV_PCM_FORMAT_LAST+1] = { [SNDRV_PCM_FORMAT_S8] = { .width = 8, .phys = 8, .le = -1, .signd = 1, .silence = {}, }, [snip] /* FIXME: the following two formats are not defined properly yet */ [SNDRV_PCM_FORMAT_MPEG] = { .le = -1, .signd = -1, }, [SNDRV_PCM_FORMAT_GSM] = { .le = -1, .signd = -1, },
pointer "silence", and then "pat", must be NULL.
I'd better read again how fields of global struct variables are initialized :-(
Thanks for this finding,
Fabio
I haven't fully validated the finding, but it appears to be legit, since the pointer variable (as opposed to the contents behind the pointer) is always non-null, hence !pat always evaluating to false.
If the above is true, then the patch likely hasn't introduced any regression, but also likely hasn't fixed the original KASAN problem.
Or are there alternative views?
BR, Eugeniu.