On Thu, Apr 13, 2023 at 05:44:37PM +0800, Steven Liu wrote:
> Signed-off-by: Steven Liu <lq@chinaffmpeg.org>
> ---
>  libavformat/flvdec.c | 58 ++++++++++++++++++++++++++++++++++++++------
>  1 file changed, 50 insertions(+), 8 deletions(-)
> 
> diff --git a/libavformat/flvdec.c b/libavformat/flvdec.c
> index d83edff727..6a1e6e7ff0 100644
> --- a/libavformat/flvdec.c
> +++ b/libavformat/flvdec.c
> @@ -79,6 +79,8 @@ typedef struct FLVContext {
>      int64_t last_ts;
>      int64_t time_offset;
>      int64_t time_pos;
> +
> +    uint8_t exheader;
>  } FLVContext;
>  
>  /* AMF date type */
> @@ -302,13 +304,25 @@ static void flv_set_audio_codec(AVFormatContext *s, AVStream *astream,
>      }
>  }
>  
> -static int flv_same_video_codec(AVCodecParameters *vpar, int flags)
> +static int flv_same_video_codec(AVFormatContext *s, AVCodecParameters *vpar, int flags)
>  {
>      int flv_codecid = flags & FLV_VIDEO_CODECID_MASK;
> +    FLVContext *flv = s->priv_data;
>  
>      if (!vpar->codec_id && !vpar->codec_tag)
>          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;

pb->buf_ptr is in general not supposed to be directly accessed

In this case here it 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

can you remove pb->buf_ptr use ?
I can fix it too but i have no testcase and fate doesnt cover this so my fix would
be untested ...

thx

[...]
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Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

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