On Tue, 14 Jun 2022 11:58:51 +0200, 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.
[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) {
JFYI, PVS-Studio 7.19 reports:
sound/core/pcm_misc.c 409 warn V560 A part of conditional expression is always false: !pat.
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?
Indeed the fix looks bogus, and maybe better to revert.
Looking at the original syzkaller report again, it points rather to the *write* at the address 1, and it means not the source (silence[]) but the target pointer (data) is invalid; i.e. it's a problem in the caller side, likely some race between the OSS temporary buffer removal and other operation.
Thanks for checking this.
Takashi