[FFmpeg-devel] [PATCH] avformat/utils: fix undefined behaviour

[Andreas Rheinhardt]

James Almer:
> On 2/14/2021 6:09 PM, Paul B Mahol wrote:
>> Fixes following report:
>> libavformat/utils.c:1429:14: runtime error: applying zero offset to
>> null pointer
> 
> How is data NULL here? That's the input packet's data pointer, and this
> loop is accessed only if size is > 0. data == NULL and size != 0 doesn't
> sound valid. Or am i missing something?

Flushing.

> 
> Try compiling with assert level set to 1, see if you get an assertion
> failure on avpacket helpers.
> 
>> SUMMARY: UndefinedBehaviorSanitizer: undefined-behavior
>> libavformat/utils.c:1429:14
>>
>> Signed-off-by: Paul B Mahol <onemda at gmail.com>
>> ---
>>   libavformat/utils.c | 6 ++++--
>>   1 file changed, 4 insertions(+), 2 deletions(-)
>>
>> diff --git a/libavformat/utils.c b/libavformat/utils.c
>> index 3e955b85bc..e4f100fda2 100644
>> --- a/libavformat/utils.c
>> +++ b/libavformat/utils.c
>> @@ -1426,8 +1426,10 @@ static int parse_packet(AVFormatContext *s,
>> AVPacket *pkt,
>>           pkt->pts = pkt->dts = AV_NOPTS_VALUE;
>>           pkt->pos = -1;
>>           /* increment read pointer */
>> -        data += len;
>> -        size -= len;
>> +        if (len > 0) {
>> +            data += len;
>> +            size -= len;
>> +        }
>>             got_output = !!out_pkt.size;
>>  
> 
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