[FFmpeg-devel] [PATCH] avformat/aviobuf: Delay buffer downsizing until asserts are met

[Andreas Rheinhardt]

Michael Niedermayer:
> On Mon, Jun 17, 2019 at 11:12:00PM +0000, Andreas Rheinhardt wrote:
>> Michael Niedermayer:
>>> Fixes: Assertion failure
>>> Fixes: 15151/clusterfuzz-testcase-minimized-ffmpeg_DEMUXER_fuzzer-5757079496687616
>>>
>>> Signed-off-by: Michael Niedermayer <michael at niedermayer.cc>
>>> ---
>>>  libavformat/aviobuf.c | 3 +--
>>>  1 file changed, 1 insertion(+), 2 deletions(-)
>>>
>>> diff --git a/libavformat/aviobuf.c b/libavformat/aviobuf.c
>>> index 5a33f82950..6a5cd97b0a 100644
>>> --- a/libavformat/aviobuf.c
>>> +++ b/libavformat/aviobuf.c
>>> @@ -570,7 +570,7 @@ static void fill_buffer(AVIOContext *s)
>>>      }
>>>  
>>>      /* make buffer smaller in case it ended up large after probing */
>>> -    if (s->read_packet && s->orig_buffer_size && s->buffer_size > s->orig_buffer_size) {
>>> +    if (s->read_packet && s->orig_buffer_size && s->buffer_size > s->orig_buffer_size && len >= s->orig_buffer_size) {
>>>          if (dst == s->buffer && s->buf_ptr != dst) {
>>>              int ret = ffio_set_buf_size(s, s->orig_buffer_size);
>>>              if (ret < 0)
>>> @@ -578,7 +578,6 @@ static void fill_buffer(AVIOContext *s)
>>>  
>>>              s->checksum_ptr = dst = s->buffer;
>>>          }
>>> -        av_assert0(len >= s->orig_buffer_size);
>>>          len = s->orig_buffer_size;
>>>      }
>>>  
>>>
>> I just noticed that ticket #7094 is about this assert. Could you test
>> whether everything works fine with your fix applied (and then mention
>> said this ticket in the commit message)?
> 
> The ticket does not contain a full testcase, just a code snippet,
> and the person reporting the issue has not yet replied
> I suggest we apply this fix with a "May fix Ticket7094"
> 
> 
Agreed.

- Andreas