[FFmpeg-devel] [PATCH] ff_split_xiph_headers returns broken header_len < 0

[Michael Niedermayer]

On Tue, Apr 15, 2008 at 07:44:49PM +0200, Reimar D?ffinger wrote:
> On Tue, Apr 15, 2008 at 07:38:57PM +0200, Reimar D?ffinger wrote:
> > On Tue, Apr 15, 2008 at 07:11:12PM +0200, Michael Niedermayer wrote:
> > > On Tue, Apr 15, 2008 at 06:54:45PM +0200, Reimar D?ffinger wrote:
> > > > when trying to play http://wdz5.xs4all.nl/~hendrik/mmw-deadzy.ogg with
> > > > MPlayer (ffplay untested), the vorbis decoder crashes.
> > > > The reason is that ff_split_xiph_headers does not fail but returns an
> > > > invalid (negative) header_len[2].
> > > > Attached patch is one possible fix. Maybe doing a return -1 if this case
> > > > happens is the better solution, I just like to default to solutions that
> > > > have a higher chance of still working with broken files (though at least
> > > > in this case it does not help anyway, the files till does not play).
> > > 
> > > I prefer a return -1 (unless doing something else helps some existing file)
> > > Also your check is insufficient header_len 0/1 still can reach arbitrary
> > > values, i think this should be fixed more generically. That is checking
> > > that all are within extradata.
> > 
> > I misread one of the existing checks, I think attached patch should
> > actually work.
> 
> With better aligning.

> Index: libavcodec/xiph.c
> ===================================================================
> --- libavcodec/xiph.c	(revision 12807)
> +++ libavcodec/xiph.c	(working copy)
> @@ -34,17 +34,24 @@
>              extradata += header_len[i];
>          }
>      } else if (extradata[0] == 2) {

> +        int overall_len = 0;
>          for (i=0,j=1; i<2; i++,j++) {
>              header_len[i] = 0;
>              for (; j<extradata_size && extradata[j]==0xff; j++) {
> +                if (overall_len > extradata_size - (0xff + 1))
> +                    return -1;
> +                overall_len   += 0xff + 1;
>                  header_len[i] += 0xff;
>              }
>              if (j >= extradata_size)
>                  return -1;
>  
> +            if (overall_len > extradata_size - (extradata[j] + 1))
> +                return -1;
> +            overall_len   += extradata[j] + 1;
>              header_len[i] += extradata[j];

int overall_len = 1;
for (i=0,j=1; i<2; i++,j++) {
    header_len[i] = 0;
    for (; overall_len <= extradata_size && extradata[j]==0xff; j++) {
        overall_len   += 0xff + 1;
        header_len[i] += 0xff;
    }
    overall_len   += extradata[j];
    header_len[i] += extradata[j];

    if (overall_len > extradata_size)
        return -1;

and feel free to commit if above works


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

Its not that you shouldnt use gotos but rather that you should write
readable code and code with gotos often but not always is less readable
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