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. > > > > [1] https://lore.kernel.org/lkml/ 000000000000d188ef05dc2c7279@xxxxxxxxxx/ > > > > Reported-and-tested-by: syzbot+205eb15961852c2c5974@xxxxxxxxxxxxxxxxxxxxxxxxx > > Signed-off-by: Fabio M. De Francesco <fmdefrancesco@xxxxxxxxx> > > --- > > > > 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. >
