Re: [FFmpeg-devel] [PATCH] avcodec/vvc_mp4toannexb: check the return of bytestream2_get_buffer

[Nuo Mi <nuomi2021@gmail.com>]

On Thu, Feb 8, 2024 at 11:50 PM Andreas Rheinhardt <
andreas.rheinhardt@outlook.com> wrote:

> Nuo Mi:
> > Fixes: fuzzer timeout
> > Fixes:
> 65253/clusterfuzz-testcase-minimized-ffmpeg_BSF_VVC_MP4TOANNEXB_fuzzer-4972412487467008
> >
> > Found-by: continuous fuzzing process
> https://github.com/google/oss-fuzz/tree/master/projects/ffmpeg
> > Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>
> > ---
> >  libavcodec/bsf/vvc_mp4toannexb.c | 12 ++++++++----
> >  1 file changed, 8 insertions(+), 4 deletions(-)
> >
> > diff --git a/libavcodec/bsf/vvc_mp4toannexb.c
> b/libavcodec/bsf/vvc_mp4toannexb.c
> > index 25c3726918..a15c1eef5b 100644
> > --- a/libavcodec/bsf/vvc_mp4toannexb.c
> > +++ b/libavcodec/bsf/vvc_mp4toannexb.c
> > @@ -168,8 +168,10 @@ static int vvc_extradata_to_annexb(AVBSFContext
> *ctx)
> >                  goto fail;
> >
> >              AV_WB32(new_extradata + new_extradata_size, 1); // add the
> startcode
> > -            bytestream2_get_buffer(&gb, new_extradata +
> new_extradata_size + 4,
> > -                                   nalu_len);
> > +            if (bytestream2_get_buffer(&gb, new_extradata +
> new_extradata_size + 4, nalu_len) != nalu_len) {
> > +                ret = AVERROR_INVALIDDATA;
> > +                goto fail;
> > +            }
> >              new_extradata_size += 4 + nalu_len;
> >              memset(new_extradata + new_extradata_size, 0,
> >                     AV_INPUT_BUFFER_PADDING_SIZE);
> > @@ -298,8 +300,10 @@ static int vvc_mp4toannexb_filter(AVBSFContext
> *ctx, AVPacket *out)
> >          if (extra_size)
> >              memcpy(out->data + prev_size, ctx->par_out->extradata,
> extra_size);
> >          AV_WB32(out->data + prev_size + extra_size, 1);
> > -        bytestream2_get_buffer(&gb, out->data + prev_size + 4 +
> extra_size,
> > -                               nalu_size);
> > +        if (bytestream2_get_buffer(&gb, out->data + prev_size + 4 +
> extra_size, nalu_size) != nalu_size) {
> > +            ret = AVERROR_INVALIDDATA;
> > +            goto fail;
> > +        }
> >      }
> >
> >      ret = av_packet_copy_props(out, in);
>
> It is better to check that there is enough input before growing the
> packet/the extradata. This also allows to use unchecked reads lateron.
>
Good idea, fixed in v2.

>
> - Andreas
>
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