[FFmpeg-devel] [PATCH 3/3] avformat/mov: Check for EOF in mov_read_meta()

[James Almer]

On 8/31/2019 5:47 AM, Michael Niedermayer wrote:
> On Fri, Aug 30, 2019 at 08:57:29PM -0300, James Almer wrote:
>> On 8/30/2019 8:25 PM, Michael Niedermayer wrote:
>>> Fixes: Timeout (195sec -> 2ms)
>>> Fixes: 16735/clusterfuzz-testcase-minimized-ffmpeg_DEMUXER_fuzzer-5090676403863552
>>>
>>> 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/mov.c | 5 ++++-
>>>  1 file changed, 4 insertions(+), 1 deletion(-)
>>>
>>> diff --git a/libavformat/mov.c b/libavformat/mov.c
>>> index 675b915906..46c544b61f 100644
>>> --- a/libavformat/mov.c
>>> +++ b/libavformat/mov.c
>>> @@ -4419,7 +4419,10 @@ static int mov_read_custom(MOVContext *c, AVIOContext *pb, MOVAtom atom)
>>>  static int mov_read_meta(MOVContext *c, AVIOContext *pb, MOVAtom atom)
>>>  {
>>>      while (atom.size > 8) {
>>> -        uint32_t tag = avio_rl32(pb);
>>> +        uint32_t tag;
>>> +        if (avio_feof(pb))
>>> +            return AVERROR_EOF;
>>> +        tag = avio_rl32(pb);
>>>          atom.size -= 4;
>>>          if (tag == MKTAG('h','d','l','r')) {
>>>              avio_seek(pb, -8, SEEK_CUR);
>>
>> Maybe do something like "while (atom.size > 8 && !avio_feof(pb))"
>> instead, which is similar to the loop in mov_read_default.
> 
> Can do but why ?
> the code in the patch returns an error if the atom is truncated
> the change suggested does not return an error if the atom is truncated
> on its own this doesnt sound better
> 
> Thanks

There's Marton's "avformat/utils: return pending IO error on EOF in
av_read_frame()" patch to check in generic code if avio_feof() != 0 is
an actual EOF or an IO error, so if you make this code here simply break
the loop, same as it's done in mov_read_default(), then said generic
code would be triggered and return the proper error code once the
current packet is done processing.