[FFmpeg-devel] [PATCH 4/5] avcodec/alac: Check for bps of 0

[Paul B Mahol]

On Sun, Aug 25, 2019 at 9:33 AM Michael Niedermayer <michael at niedermayer.cc>
wrote:

> On Fri, Aug 23, 2019 at 11:20:48AM -0300, James Almer wrote:
> > On 8/8/2019 8:23 PM, Michael Niedermayer wrote:
> > > Fixes: shift exponent 32 is too large for 32-bit type 'unsigned int'
> > > Fixes:
> 15764/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_ALAC_fuzzer-5102101203517440
> > >
> > > Found-by: continuous fuzzing process
> https://github.com/google/oss-fuzz/tree/master/projects/ffmpeg
> > > Signed-off-by: Michael Niedermayer <michael at niedermayer.cc>
> > > ---
> > >  libavcodec/alac.c | 2 +-
> > >  1 file changed, 1 insertion(+), 1 deletion(-)
> > >
> > > diff --git a/libavcodec/alac.c b/libavcodec/alac.c
> > > index 6086e2caa8..1196925aa7 100644
> > > --- a/libavcodec/alac.c
> > > +++ b/libavcodec/alac.c
> > > @@ -250,7 +250,7 @@ static int decode_element(AVCodecContext *avctx,
> AVFrame *frame, int ch_index,
> > >
> > >      alac->extra_bits = get_bits(&alac->gb, 2) << 3;
> > >      bps = alac->sample_size - alac->extra_bits + channels - 1;
> > > -    if (bps > 32U) {
> > > +    if (bps > 32 || bps < 1) {
> > >          avpriv_report_missing_feature(avctx, "bps %d", bps);
> > >          return AVERROR_PATCHWELCOME;
> >
> > bps 0 (or negative) is obviously a broken file,
>
> id say very likely a broken file, yes
>
>
> > so asking for a sample
> > is pointless. Just return invalid data in those cases, and leave this
> > check for > 32.
>
> thats a few lines more code, for an error code and different/no message
> its a bit difficult to guess where people prefer the extra code to be
> correct and where they prefer somewhat incorrect solutions to minimize
> fuzzer found bugfixes.
>

If you dislike what people prefer when reviewing, perhaps you should stop
sending patches :-)


>
> but yes, will post a new patch for this.
>
> thx
>
>
> [...]
> --
> Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB
>
> Any man who breaks a law that conscience tells him is unjust and willingly
> accepts the penalty by staying in jail in order to arouse the conscience
> of
> the community on the injustice of the law is at that moment expressing the
> very highest respect for law. - Martin Luther King Jr
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