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

[Marton Balint <cus@passwd.hu>]

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@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.

Regards,
Marton

> +        } else {
> +            AVInteger bitrate_i = av_div_i(av_mul_i(av_int2i(8*len), av_int2i(st->time_base.den)),
> +                                           av_mul_i(av_int2i(duration), av_int2i(st->time_base.num)));
> +            if (av_cmp_i(bitrate_i, av_int2i(INT64_MAX)) <= 0)
> +                bitrate = av_i2int(bitrate_i);
> +        }
>         if (bitrate > 0) {
>             st->codecpar->bit_rate = bitrate;
>         }
> -- 
> 2.17.1
>
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