ffmpeg | branch: master | Michael Niedermayer <mich...@niedermayer.cc> | Fri
Jan 22 00:39:19 2021 +0100| [1957095e808b80cbe607347a6f23207d6318a48d] |
committer: Michael Niedermayer
avformat/swfdec: Check outlen before allocation
Fixes: Timeout (too long -> 241ms)
Fixes:
29083/clusterfuzz-testcase-minimized-ffmpeg_dem_SWF_fuzzer-6273684478230528
The source of the magic number is
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
Found-by: continuous fuzzing process
https://github.com/google/oss-fuzz/tree/master/projects/ffmpeg
Signed-off-by: Michael Niedermayer <mich...@niedermayer.cc>
> http://git.videolan.org/gitweb.cgi/ffmpeg.git/?a=commit;h=1957095e808b80cbe607347a6f23207d6318a48d
---
libavformat/swfdec.c | 3 +++
1 file changed, 3 insertions(+)
diff --git a/libavformat/swfdec.c b/libavformat/swfdec.c
index 9416187803..f9a164b33f 100644
--- a/libavformat/swfdec.c
+++ b/libavformat/swfdec.c
@@ -377,6 +377,9 @@ 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)
+ goto bitmap_end_skip;
+
zbuf = av_malloc(len);
if (!zbuf) {
res = AVERROR(ENOMEM);
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