[FFmpeg-devel] [PATCH] avcodec/parser: Check next against buffer index

[Andreas Rheinhardt]

Michael Niedermayer:
> Fixes: out of array access
> Fixes: crash-0d640731c7da52415670eb47a2af701cbe2e1a3b
> 
> Found-by: Catena cyber <contact at catenacyber.fr>
> Signed-off-by: Michael Niedermayer <michael at niedermayer.cc>
> ---
>  libavcodec/parser.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/libavcodec/parser.c b/libavcodec/parser.c
> index efc28b8918..db39e698ab 100644
> --- a/libavcodec/parser.c
> +++ b/libavcodec/parser.c
> @@ -214,7 +214,7 @@ int ff_combine_frame(ParseContext *pc, int next,
>      for (; pc->overread > 0; pc->overread--)
>          pc->buffer[pc->index++] = pc->buffer[pc->overread_index++];
>  
> -    if (next > *buf_size)
> +    if (next > *buf_size || (next < -pc->index && next != END_NOT_FOUND))
>          return AVERROR(EINVAL);
>  
>      /* flush remaining if EOF */

Could you provide more details about this? E.g. which parser is this
about at all? And how can we actually come in this situation at all?
(Whenever I looked at ff_combine_frame() I do not really understand what
its invariants are supposed to be.)

- Andreas