Re: [FFmpeg-devel] [PATCH 4/6] avformat/cafdec: saturate start + size into 64bit

From: Michael Niedermayer <michael@niedermayer.cc>
To: FFmpeg development discussions and patches <ffmpeg-devel@ffmpeg.org>
Subject: Re: [FFmpeg-devel] [PATCH 4/6] avformat/cafdec: saturate start + size into 64bit
Date: Sat, 30 Sep 2023 18:32:07 +0200
Message-ID: <20230930163207.GM3543730@pb2> (raw)
In-Reply-To: <ab85ee6f-e46c-4b5f-aeb1-5f273475391e@gmail.com>

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On Fri, Sep 29, 2023 at 08:41:23PM -0300, James Almer wrote:
> On 9/29/2023 8:19 PM, Michael Niedermayer wrote:
> > Fixes: signed integer overflow: 64 + 9223372036854775803 cannot be represented in type 'long long'
> > Fixes: 51896/clusterfuzz-testcase-minimized-ffmpeg_dem_CAF_fuzzer-6536881135550464
> > 
> > Found-by: continuous fuzzing process https://github.com/google/oss-fuzz/tree/master/projects/ffmpeg
> > Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>
> > ---
> >   libavformat/cafdec.c | 2 +-
> >   1 file changed, 1 insertion(+), 1 deletion(-)
> > 
> > diff --git a/libavformat/cafdec.c b/libavformat/cafdec.c
> > index e92e3279fc6..0e50a3cfe68 100644
> > --- a/libavformat/cafdec.c
> > +++ b/libavformat/cafdec.c
> > @@ -435,7 +435,7 @@ static int read_packet(AVFormatContext *s, AVPacket *pkt)
> >       /* don't read past end of data chunk */
> >       if (caf->data_size > 0) {
> > -        left = (caf->data_start + caf->data_size) - avio_tell(pb);
> > +        left = av_sat_add64(caf->data_start, caf->data_size) - avio_tell(pb);
> 
> avio_tell(pb) here is guaranteed to be bigger than caf->data_start, which is
> the offset where the DATA chunk starts, so the result of this calculation
> will be <= INT64_MAX even if you don't saturate it and instead cast it to
> uint64_t. Nonetheless, if the DATA chunk ends at an offset that would not
> fit in an int64_t, then we can't parse it to begin with due to AVIOContext
> API limitations.
> 

> Maybe we should just abort in read_header() if data_start + data_size >
> INT64_MAX, instead of pretending we can parse the file, invalid or not, by
> saturating values.

yes ill try that

thx

[...]
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Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

If you think the mosad wants you dead since a long time then you are either
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