On Sat, Jan 23, 2021 at 03:29:38PM +0100, Anton Khirnov wrote: > Quoting Michael Niedermayer (2021-01-22 15:09:47) > > Fixes: Timeout (too long -> 241ms) > > Fixes: > > 29083/clusterfuzz-testcase-minimized-ffmpeg_dem_SWF_fuzzer-6273684478230528 > > > > Found-by: continuous fuzzing process > > https://github.com/google/oss-fuzz/tree/master/projects/ffmpeg > > Signed-off-by: Michael Niedermayer <mich...@niedermayer.cc> > > --- > > libavformat/swfdec.c | 3 +++ > > 1 file changed, 3 insertions(+) > > > > diff --git a/libavformat/swfdec.c b/libavformat/swfdec.c > > index 1463f0ad4d..aa4be88f91 100644 > > --- a/libavformat/swfdec.c > > +++ b/libavformat/swfdec.c > > @@ -367,6 +367,9 @@ static int swf_read_packet(AVFormatContext *s, AVPacket > > *pkt) > > ff_dlog(s, "bitmap: ch=%d fmt=%d %dx%d (linesize=%d) > > len=%d->%ld pal=%d\n", > > ch_id, bmp_fmt, width, height, linesize, len, out_len, > > colormapsize); > > > > + if (len * 17373LL < out_len) > > Where does the magic number come from?
A very quick simulation of the best case compression for "compress"
below is not nice written code as i did not expect I or anyone else
would ever see it again
I would have preferred some nicer expression or course, but thats
what it seems to be asymptotically. For smaller amounts of data a
tighter bound is possible but i saw no nice way to consider that
and it seems also overkill to try to do it more fine grained for
just this
main(){
int64_t bits = 0;
int bank = 256;
int bitbank = 8;
for(unsigned i = 0; i<1024*1024*1024*4U-100000;) {
int word_size = bank-255;
i += word_size;
bits += bitbank;
if (!(bank & (bank-1)))
bitbank ++;
bank++;
if (bitbank > 16) {
printf("BEST %f \n", 8.0 * i / bits );
bank = 256;
bitbank = 8;
}
}
}
above assumes i remembered correctly how the algorithm works but the
value was close to what actual compession of zeros gave
[...]
--
Michael GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB
The misfortune of the wise is better than the prosperity of the fool.
-- Epicurus
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