[FFmpeg-devel] [FFmpeg-cvslog] lavc/h264_levels: Avoid integer overflow in bitrate

[Carl Eugen Hoyos]

2018-09-27 0:15 GMT+02:00, Mark Thompson <sw at jkqxz.net>:
> On 26/09/18 22:43, Carl Eugen Hoyos wrote:
>> 2018-09-25 0:16 GMT+02:00, Mark Thompson <git at videolan.org>:
>>> ffmpeg | branch: master | Mark Thompson <sw at jkqxz.net> | Mon Sep 24
>>> 23:03:32
>>> 2018 +0100| [581b4125aa187f2cf848d7a27e6128573c80dc64] | committer: Mark
>>> Thompson
>>>
>>> lavc/h264_levels: Avoid integer overflow in bitrate
>>>
>>> Fixes CID #1439656.
>>>
>>>> http://git.videolan.org/gitweb.cgi/ffmpeg.git/?a=commit;h=581b4125aa187f2cf848d7a27e6128573c80dc64
>>> ---
>>>
>>>  libavcodec/h264_levels.c | 2 +-
>>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>>
>>> diff --git a/libavcodec/h264_levels.c b/libavcodec/h264_levels.c
>>> index 6b4e18a914..737b7dcf06 100644
>>> --- a/libavcodec/h264_levels.c
>>> +++ b/libavcodec/h264_levels.c
>>> @@ -105,7 +105,7 @@ const H264LevelDescriptor *ff_h264_guess_level(int
>>> profile_idc,
>>>          if (level->constraint_set3_flag && no_cs3f)
>>>              continue;
>>>
>>> -        if (bitrate > level->max_br * h264_get_br_factor(profile_idc))
>>> +        if (bitrate > (int64_t)level->max_br *
>>> h264_get_br_factor(profile_idc))
>>
>> If the overflow is possible at all (I doubt it), wouldn't it be cleaner
>> to change the type of cpb_br_nal_factor to uint32_t?
>
> Some of the largest cases overflow 32-bit signed int - e.g. level 6.2 in
> High 10 allows up to 800000 * 3600 = 2880000000 bps.  (High profile or lower
> doesn't have a cpbBrNalFactor large enough to hit this case.)

But max_br is already unsigned, what's wrong with making cpb_br_nal_factor
also unsigned?

> I used int64_t because that's the type of bitrate, on the other side of the
> comparison.

Does that simplify things for the compiler?

Thank you for explaining, Carl Eugen