[FFmpeg-devel] [PATCH 3/5] avcodec/decode: Check progress before dereferencing

[Andreas Rheinhardt]

Michael Niedermayer:
> On Sat, Apr 27, 2024 at 01:13:54PM +0200, Andreas Rheinhardt wrote:
>> Michael Niedermayer:
>>> Fixes: NULL pointer dereference
>>> Fixes: 68192/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_VP8_fuzzer-6180311026171904
>>>
>>> Found-by: continuous fuzzing process https://github.com/google/oss-fuzz/tree/master/projects/ffmpeg
>>> Signed-off-by: Michael Niedermayer <michael at niedermayer.cc>
>>> ---
>>>  libavcodec/decode.c | 2 ++
>>>  1 file changed, 2 insertions(+)
>>>
>>> diff --git a/libavcodec/decode.c b/libavcodec/decode.c
>>> index d031b1ca176..a6131941f43 100644
>>> --- a/libavcodec/decode.c
>>> +++ b/libavcodec/decode.c
>>> @@ -1744,6 +1744,8 @@ void ff_progress_frame_report(ProgressFrame *f, int n)
>>>  
>>>  void ff_progress_frame_await(const ProgressFrame *f, int n)
>>>  {
>>> +    if (!f->progress)
>>> +        return;
>>>      ff_thread_progress_await(&f->progress->progress, n);
>>>  }
>>>  
>>
>> Can I get the sample? I see two places in VP8 where the VP8Frame
>> pointers are set before the actual frame inside it is properly allocated.
>>
>> (Actually, it was intended for this API to not support waiting on
>> non-existent frames (i.e. let the caller check for this; in most
>> instances, it is already guaranteed that the frame one waits one exists,
>> so this is unnecessary for them).)
> 
> did you receive the sample i sent you in april ?
> 
> any update on this ?
> its still crashing without this patch
> 
> Running: 68192/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_VP8_fuzzer-6180311026171904
> libavcodec/decode.c:1766:44: runtime error: member access within null pointer of type 'struct ProgressInternal'
> SUMMARY: UndefinedBehaviorSanitizer: undefined-behavior libavcodec/decode.c:1766:44 in
> libavcodec/threadprogress.c:72:36: runtime error: member access within null pointer of type 'ThreadProgress' (aka 'struct ThreadProgress')
> SUMMARY: UndefinedBehaviorSanitizer: undefined-behavior libavcodec/threadprogress.c:72:36 in
> 

Totally forgot about this. Will look into it. Thanks for the reminder.

- Andreas