[FFmpeg-devel] [PATCH 1/4] avformat/asfdec_f: Fix overflow check in get_tag()

[Michael Niedermayer]

On Mon, Mar 16, 2020 at 10:45:21AM +0100, Anton Khirnov wrote:
> Quoting Michael Niedermayer (2020-03-15 22:20:55)
> > Fixes: signed integer overflow: 2 * 1210064928 cannot be represented in type 'int'
> > Fixes: 20873/clusterfuzz-testcase-minimized-ffmpeg_DEMUXER_fuzzer-5761116909338624
> > 
> > Found-by: continuous fuzzing process https://github.com/google/oss-fuzz/tree/master/projects/ffmpeg
> > Signed-off-by: Michael Niedermayer <michael at niedermayer.cc>
> > ---
> >  libavformat/asfdec_f.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> > 
> > diff --git a/libavformat/asfdec_f.c b/libavformat/asfdec_f.c
> > index 57dc3b09b9..3f19747d78 100644
> > --- a/libavformat/asfdec_f.c
> > +++ b/libavformat/asfdec_f.c
> > @@ -321,7 +321,7 @@ static void get_tag(AVFormatContext *s, const char *key, int type, int len, int
> >      int64_t off = avio_tell(s->pb);
> >  #define LEN 22
> >  
> > -    if ((unsigned)len >= (UINT_MAX - LEN) / 2)
> > +    if ((unsigned)len >= (INT_MAX - LEN) / 2)
> 
> Is the cast still necessary then?

it only makes a difference for negative len. And negative len looks invalid
and would cause problems. So some check for negative len is needed, the
(unsigned) achievs this but i can replace it by an explicit len < 0 
if people prefer ?

thx

[...]
-- 
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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