Re: [FFmpeg-devel] [PATCH 1/4] avcodec/vp9_superframe_split_bsf: Check in size

From: Michael Niedermayer <michael@niedermayer.cc>
To: FFmpeg development discussions and patches <ffmpeg-devel@ffmpeg.org>
Subject: Re: [FFmpeg-devel] [PATCH 1/4] avcodec/vp9_superframe_split_bsf: Check in size
Date: Mon, 21 Mar 2022 19:59:21 +0100
Message-ID: <20220321185921.GL2829255@pb2> (raw)
In-Reply-To: <a3ea1212-c123-10d6-5954-0ce8cc2af281@gmail.com>

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On Sun, Mar 13, 2022 at 04:03:42PM -0300, James Almer wrote:
> 
> 
> On 3/12/2022 8:52 PM, Michael Niedermayer wrote:
> > Fixes: Out of array read
> > Fixes: 45137/clusterfuzz-testcase-minimized-ffmpeg_BSF_VP9_SUPERFRAME_SPLIT_fuzzer-4984270639202304
> > 
> > Found-by: continuous fuzzing process https://github.com/google/oss-fuzz/tree/master/projects/ffmpeg
> > Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>
> > ---
> >   libavcodec/vp9_superframe_split_bsf.c | 5 +++++
> >   1 file changed, 5 insertions(+)
> > 
> > diff --git a/libavcodec/vp9_superframe_split_bsf.c b/libavcodec/vp9_superframe_split_bsf.c
> > index ed0444561a..6af555c078 100644
> > --- a/libavcodec/vp9_superframe_split_bsf.c
> > +++ b/libavcodec/vp9_superframe_split_bsf.c
> > @@ -51,6 +51,11 @@ static int vp9_superframe_split_filter(AVBSFContext *ctx, AVPacket *out)
> >               return ret;
> >           in = s->buffer_pkt;
> > +        if (in->size == 0) {
> 
> !in->size
> 
> > +            ret = AVERROR_INVALIDDATA;
> > +            goto fail;
> > +        }
> > +
> >           marker = in->data[in->size - 1];
> 
> Do we want to abort on in->data && !in->size, or just pass the packet
> through?
> I'm partial to the latter, so it would mean initializing marker to 0 and
> check instead for in->size before setting marker, so the check below fails
> and the packet is just passed through.
> 
> Not sure what others think about it.

I have no opinion on this. I just want the bug fixed. As both andreas
and ossfuzz noticed this affects other filters too.
not sure the passthough makes sense for all them, i will just dumbly
post a passthrough based patch for the other one ossfuzz found too
but maybe erroring out as in andreas patch makes more sense

thx

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