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From:   "Fabio M. De Francesco" <fmdefrancesco@gmail.com>
To:     Takashi Iwai <tiwai@suse.de>
Cc:     Eugeniu Rosca <erosca@de.adit-jv.com>,
        Jaroslav Kysela <perex@perex.cz>,
        Takashi Iwai <tiwai@suse.com>, Mark Brown <broonie@kernel.org>,
        alsa-devel@alsa-project.org, linux-kernel@vger.kernel.org,
        syzbot+205eb15961852c2c5974@syzkaller.appspotmail.com,
        naveenkumar.sunkari@in.bosch.com,
        Eugeniu Rosca <roscaeugeniu@gmail.com>
Subject: Re: [PATCH] ALSA: pcm: Test for "silence" field in struct "pcm_format_data"
Date:   Tue, 14 Jun 2022 13:30:13 +0200
Message-ID: <8079585.T7Z3S40VBb@opensuse>
In-Reply-To: <87y1xzplj1.wl-tiwai@suse.de>
References: <20220409012655.9399-1-fmdefrancesco@gmail.com> <2245197.ElGaqSPkdT@opensuse> <87y1xzplj1.wl-tiwai@suse.de>
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On marted=C3=AC 14 giugno 2022 12:49:38 CEST Takashi Iwai wrote:
> On Tue, 14 Jun 2022 12:43:16 +0200,
> Fabio M. De Francesco wrote:
> >=20
> > On marted=C3=AC 14 giugno 2022 11:58:51 CEST Eugeniu Rosca wrote:
> > > Hello Fabio, hello All,
> > >=20
> > > 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]
> > > >=20
> > > > It is due to missing validation of the "silence" field of struct
> > > > "pcm_format_data" in "pcm_formats" array.
> > > >=20
> > > > Add a test for valid "pat" and, if it is not so, return -EINVAL.
> > > >=20
> > > > [1] https://lore.kernel.org/lkml/
> > 000000000000d188ef05dc2c7279@google.com/
> > > >=20
> > > > Reported-and-tested-by:=20
> > syzbot+205eb15961852c2c5974@syzkaller.appspotmail.com
> > > > Signed-off-by: Fabio M. De Francesco <fmdefrancesco@gmail.com>
> > > > ---
> > > >=20
> > > > I wasn't able to figure out the commit for the "Fixes:" tag. If=20
this=20
> > patch
> > > > is good, can someone please help with providing this missing=20
> > information?
> > > >=20
> > > >  sound/core/pcm_misc.c | 2 +-
> > > >  1 file changed, 1 insertion(+), 1 deletion(-)
> > > >=20
> > > > 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=
=20
> > format, void *data, unsigned int
> > > >  		return 0;
> > > >  	width =3D pcm_formats[(INT)format].phys; /* physical width */
> > > >  	pat =3D pcm_formats[(INT)format].silence;
> > > > -	if (! width)
> > > > +	if (!width || !pat)
> > > >  		return -EINVAL;
> > > >  	/* signed or 1 byte data */
> > > >  	if (pcm_formats[(INT)format].signd =3D=3D 1 || width <=3D 8) {
> > >=20
> > > JFYI, PVS-Studio 7.19 reports:
> > >=20
> > > sound/core/pcm_misc.c	409	warn	V560 A part of=20
> > conditional expression is always false: !pat.
> >=20
> > Sorry, I assumed (wrongly!) that when we have
> >=20
> > static const struct pcm_format_data=20
> > pcm_formats[(INT)SNDRV_PCM_FORMAT_LAST+1] =3D {
> > 	[SNDRV_PCM_FORMAT_S8] =3D {
> > 		.width =3D 8, .phys =3D 8, .le =3D -1, .signd =3D 1,
> > 		.silence =3D {},
> > 	},
> > 	[snip]
> > 	/* FIXME: the following two formats are not defined properly yet=20
> > */
> > 	[SNDRV_PCM_FORMAT_MPEG] =3D {
> > 		.le =3D -1, .signd =3D -1,
> > 	},
> > 	[SNDRV_PCM_FORMAT_GSM] =3D {
> > 		.le =3D -1, .signd =3D -1,
> > 	},
> >=20
> > pointer "silence", and then "pat", must be NULL.
>=20
> Oh right, those are missing ones.  I haven't realized that those
> formats are allowed by PCM OSS layer.
>=20
> Practically seen, those formats have never been used in reality, and
> we may consider dropping them completely to plug such holes...
>=20
Does it imply that my argument is correct or my "fix" can't yet catch those=
=20
missing ones?

Besides the question above, I want to notice that we have one more /* FIXME=
=20
*/ entry...

/* FIXME: the following format is not defined properly yet */
	[SNDRV_PCM_FORMAT_SPECIAL] =3D {
		.le =3D -1, .signd =3D -1,
	},

If you want I can get rid of those three entries if you confirm they can=20
safely be deleted. In a second patch I can also remove that unnecessary=20
check for valid "pat".

Please let me know.

Thanks,

=46abio