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

[Michael Niedermayer <michael@niedermayer.cc>]

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On Sat, Jun 24, 2023 at 09:14:53PM +0200, Andreas Rheinhardt wrote:
> Michael Niedermayer:
> > Fixes: out of array access
> > Fixes: crash-0d640731c7da52415670eb47a2af701cbe2e1a3b
> > 
> > Found-by: Catena cyber <contact@catenacyber.fr>
> > Signed-off-by: Michael Niedermayer <michael@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.)

truehd with a malloc() failure
and i dont think it should happen but, it felt like a good idea to check

also *buf_size should probably be reset to 0, there was a patch about that
from reimar (in CC)

thx

[...]
-- 
Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

Frequently ignored answer#1 FFmpeg bugs should be sent to our bugtracker. User
questions about the command line tools should be sent to the ffmpeg-user ML.
And questions about how to use libav* should be sent to the libav-user ML.

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