[FFmpeg-devel] [PATCH 2/5] av1_parser: do not check buf_size if we have size in obu header

[Xu, Guangxin]

Hi James,
Thanks for the review.
How about we add a new function in av1dec.c like this:

static inline int read_obu_header_with_size_flag(const uint8_t *buf, int buf_size,
                                   int64_t *obu_size, int *type);
then we can remove first two patches and check has_size_flag in the function. 

I guess "out of array reads" will not happen in low overhead obu, since it always prepare enough data the obu.


> -----Original Message-----
> From: ffmpeg-devel <ffmpeg-devel-bounces at ffmpeg.org> On Behalf Of James
> Almer
> Sent: Thursday, August 6, 2020 10:03 PM
> To: ffmpeg-devel at ffmpeg.org
> Subject: Re: [FFmpeg-devel] [PATCH 2/5] av1_parser: do not check buf_size if
> we have size in obu header
> 
> On 8/6/2020 5:04 AM, Xu Guangxin wrote:
> > for low overhead obu, we can't forsee the obu size. we can only get it
> > when we parsed the obu header.
> > ---
> >  libavcodec/av1_parse.h | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/libavcodec/av1_parse.h b/libavcodec/av1_parse.h index
> > a3b39f039c..823bdedd5e 100644
> > --- a/libavcodec/av1_parse.h
> > +++ b/libavcodec/av1_parse.h
> > @@ -135,7 +135,7 @@ static inline int parse_obu_header(const uint8_t
> > *buf, int buf_size,
> >
> >      size = *obu_size + *start_pos;
> >
> > -    if (size > buf_size)
> > +    if (!*has_size_flag && size > buf_size)
> 
> This check was added in c27c7b49dc to fix out of array reads, so this change will
> surely reintroduce the issue.
> 
> Also, when has_size_flag is 0, size will never be bigger than buf_size because it
> will be derived from it, meaning this change is the same as removing the check
> altogether.
> 
> >          return AVERROR_INVALIDDATA;
> >
> >      return size;
> >
> 
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