[FFmpeg-devel] [PATCH 1/6] avformat/avidec: support huge durations

[Michael Niedermayer]

On Sat, Sep 30, 2023 at 11:35:19AM +0200, Marton Balint wrote:
> 
> 
> On Sat, 30 Sep 2023, Michael Niedermayer wrote:
> 
> > Fixes: signed integer overflow: 109817402400 * 301990077 cannot be represented in type 'long long'
> > Fixes: 51896/clusterfuzz-testcase-minimized-ffmpeg_dem_AVI_fuzzer-6706191715139584
> > 
> > Found-by: continuous fuzzing process https://github.com/google/oss-fuzz/tree/master/projects/ffmpeg
> > Signed-off-by: Michael Niedermayer <michael at niedermayer.cc>
> > ---
> > libavformat/avidec.c | 12 ++++++++++--
> > 1 file changed, 10 insertions(+), 2 deletions(-)
> > 
> > diff --git a/libavformat/avidec.c b/libavformat/avidec.c
> > index 00bd7a98a9d..cfc693842b7 100644
> > --- a/libavformat/avidec.c
> > +++ b/libavformat/avidec.c
> > @@ -27,6 +27,7 @@
> > #include "libavutil/avstring.h"
> > #include "libavutil/opt.h"
> > #include "libavutil/dict.h"
> > +#include "libavutil/integer.h"
> > #include "libavutil/internal.h"
> > #include "libavutil/intreadwrite.h"
> > #include "libavutil/mathematics.h"
> > @@ -476,7 +477,7 @@ static int calculate_bitrate(AVFormatContext *s)
> >         AVStream *st = s->streams[i];
> >         FFStream *const sti = ffstream(st);
> >         int64_t duration;
> > -        int64_t bitrate;
> > +        int64_t bitrate = 0;
> > 
> >         for (j = 0; j < sti->nb_index_entries; j++)
> >             len += sti->index_entries[j].size;
> > @@ -484,7 +485,14 @@ static int calculate_bitrate(AVFormatContext *s)
> >         if (sti->nb_index_entries < 2 || st->codecpar->bit_rate > 0)
> >             continue;
> >         duration = sti->index_entries[j-1].timestamp - sti->index_entries[0].timestamp;
> > -        bitrate = av_rescale(8*len, st->time_base.den, duration * st->time_base.num);
> > +        if (INT64_MAX / duration >= st->time_base.num) {
> > +            bitrate = av_rescale(8*len, st->time_base.den, duration * st->time_base.num);
> 
> Why not always use the AVInteger version? This is not performance sensitive
> as far as I see.

We can, i will have to fix the rounding though so it matches av_rescale()

[...]

-- 
Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

Let us carefully observe those good qualities wherein our enemies excel us
and endeavor to excel them, by avoiding what is faulty, and imitating what
is excellent in them. -- Plutarch
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