On Thu, Jul 27, 2023 at 4:38 AM Steven Liu <l...@chinaffmpeg.org> wrote:
>
> fix segfaults:
> READ of size 1 at 0x6100000003b7 thread T0
> #0 0x7f928d in flv_same_video_codec ffmpeg/libavformat/flvdec.c:317:29
> #1 0x7f928d in flv_read_packet ffmpeg/libavformat/flvdec.c:1177
> #2 0x6ff32f in ff_read_packet ffmpeg/libavformat/demux.c:575:15
> #3 0x70a2fd in read_frame_internal ffmpeg/libavformat/demux.c:1263:15
> #4 0x71d158 in avformat_find_stream_info
> ffmpeg/libavformat/demux.c:2634:15
> #5 0x4c821b in LLVMFuzzerTestOneInput
> ffmpeg/tools/target_dem_fuzzer.c:206:11
>
> Signed-off-by: Steven Liu <l...@chinaffmpeg.org>
> ---
> libavformat/flvdec.c | 5 +++--
> 1 file changed, 3 insertions(+), 2 deletions(-)
>
> diff --git a/libavformat/flvdec.c b/libavformat/flvdec.c
> index 3fe21622f7..003e4d7691 100644
> --- a/libavformat/flvdec.c
> +++ b/libavformat/flvdec.c
> @@ -313,8 +313,9 @@ static int flv_same_video_codec(AVFormatContext *s,
> AVCodecParameters *vpar, int
> return 1;
>
> if (flv->exheader) {
> - uint8_t *codec_id_str = (uint8_t *)s->pb->buf_ptr;
> - uint32_t codec_id = codec_id_str[3] | codec_id_str[2] << 8 |
> codec_id_str[1] << 16 | codec_id_str[0] << 24;
> + int64_t pos = avio_tell(s->pb);
> + uint32_t codec_id = avio_rb32(s->pb);
> + avio_seek(s->pb, pos, SEEK_SET);
> switch(codec_id) {
> case MKBETAG('h', 'v', 'c', '1'):
> return vpar->codec_id == AV_CODEC_ID_HEVC;
You don't need to store the position, just do a relative seek
backwards by 4 bytes.
I would also recommend to include a call to ffio_ensure_seekback so it
works with streams.
eg. something like this:
ffio_ensure_seekback(s->pb, 4);
avio_rb32(s->pb);
avio_seek(s->pb, -4, SEEK_CUR);
Add appropriate error checking, in particular for ffio_ensure_seekback, etc.
- Hendrik
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