On Tue, 14 Jun 2022 13:30:13 +0200, Fabio M. De Francesco wrote: > > On martedì 14 giugno 2022 12:49:38 CEST Takashi Iwai wrote: > > On Tue, 14 Jun 2022 12:43:16 +0200, > > Fabio M. De Francesco wrote: > > > > > > 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. > > > > Oh right, those are missing ones. I haven't realized that those > > formats are allowed by PCM OSS layer. > > > > Practically seen, those formats have never been used in reality, and > > we may consider dropping them completely to plug such holes... > > > Does it imply that my argument is correct or my "fix" can't yet catch those > missing ones? Your fix should catch the case with a NULL pat pointer, I guess. PCM OSS layer allows this format, so this could be hit. However, whether it's really a fix for the given syzkaller code path, it's doubtful. Nevertheless, your check is still worth to keep. > Besides the question above, I want to notice that we have one more /* FIXME > */ entry... > > /* FIXME: the following format is not defined properly yet */ > [SNDRV_PCM_FORMAT_SPECIAL] = { > .le = -1, .signd = -1, > }, > > If you want I can get rid of those three entries if you confirm they can > safely be deleted. In a second patch I can also remove that unnecessary > check for valid "pat". Well, you can't "delete" those entries so easiy. The formats themselves are still allowed for user-space, hence every caller needs to check. If any, we need to add the check in valid_format() for such unsupported formats, then drop the rest checks and entries. thanks, Takashi
