Michael Niedermayer: > On Thu, Oct 22, 2020 at 07:55:31AM +0200, Andreas Rheinhardt wrote: >> Michael Niedermayer: >>> Fixes: SEGV on unknown address 0x000000000000 >>> Fixes: >>> 26482/clusterfuzz-testcase-minimized-ffmpeg_dem_VIVIDAS_fuzzer-4905102324006912 >>> >>> Found-by: continuous fuzzing process >>> https://github.com/google/oss-fuzz/tree/master/projects/ffmpeg >>> Signed-off-by: Michael Niedermayer <mich...@niedermayer.cc> >>> --- >>> libavformat/vividas.c | 4 ++-- >>> 1 file changed, 2 insertions(+), 2 deletions(-) >>> >>> diff --git a/libavformat/vividas.c b/libavformat/vividas.c >>> index 999c4a5d1c..6e93d96aef 100644 >>> --- a/libavformat/vividas.c >>> +++ b/libavformat/vividas.c >>> @@ -682,7 +682,7 @@ static int viv_read_packet(AVFormatContext *s, >>> return AVERROR_INVALIDDATA; >>> >>> ffio_read_varlen(pb); >>> - if (v_size > INT_MAX) >>> + if (v_size > INT_MAX || !v_size) >>> return AVERROR_INVALIDDATA; >>> ret = av_get_packet(pb, pkt, v_size); >>> if (ret < 0) >>> @@ -711,7 +711,7 @@ static int viv_read_packet(AVFormatContext *s, >>> } else { >>> uint64_t v_size = ffio_read_varlen(pb); >>> >>> - if (v_size > INT_MAX) >>> + if (v_size > INT_MAX || !v_size) >>> return AVERROR_INVALIDDATA; >>> ret = av_get_packet(pb, pkt, v_size); >>> if (ret < 0) >>> >> av_get_packet(pb, pkt, 0) should get a packet with pkt->data pointing to >> a zeroed buffer of size AV_INPUT_BUFFER_PADDING_SIZE. So accessing >> pkt->data[0] for the flags should not segfault (but it would set the >> wrong result: that it is a keyframe). So where is the segfault? > > I tried to simulate this in a different demuxer: > (different to make sure its not the file or demuxer that somehow affects this) > --- a/libavformat/avidec.c > +++ b/libavformat/avidec.c > @@ -1446,9 +1446,10 @@ resync: > if (size > ast->remaining) > size = ast->remaining; > avi->last_pkt_pos = avio_tell(pb); > - err = av_get_packet(pb, pkt, size); > + err = av_get_packet(pb, pkt, 0); > if (err < 0) > return err; > + av_log(0,0, "P %p\n", pkt->data); > size = err; > > if (ast->has_pal && pkt->size < (unsigned)INT_MAX / 2) { > > what is printed is: > P (nil) > My bad: append_packet_chunked() unrefs the packet if pkt->size is zero before returning (without returning an error). So your patch seems to be the way to go.
- Andreas _______________________________________________ ffmpeg-devel mailing list ffmpeg-devel@ffmpeg.org https://ffmpeg.org/mailman/listinfo/ffmpeg-devel To unsubscribe, visit link above, or email ffmpeg-devel-requ...@ffmpeg.org with subject "unsubscribe".
