Quoting Michael Niedermayer (2022-11-25 14:38:46) > t On Fri, Nov 25, 2022 at 05:45:29PM +1100, Peter Ross wrote: > > On Tue, Nov 22, 2022 at 11:56:51PM +0100, Michael Niedermayer wrote: > > > Fixes: Timeout > > > Fixes: > > > 53438/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_PICTOR_fuzzer-5458939919859712 > > > > > > Found-by: continuous fuzzing process > > > https://github.com/google/oss-fuzz/tree/master/projects/ffmpe > > > Signed-off-by: Michael Niedermayer <mich...@niedermayer.cc> > > > --- > > > libavcodec/pictordec.c | 3 +++ > > > 1 file changed, 3 insertions(+) > > > > > > diff --git a/libavcodec/pictordec.c b/libavcodec/pictordec.c > > > index 71bad40a0a..09229b94fd 100644 > > > --- a/libavcodec/pictordec.c > > > +++ b/libavcodec/pictordec.c > > > @@ -162,6 +162,9 @@ static int decode_frame(AVCodecContext *avctx, > > > AVFrame *frame, > > > > > > if (av_image_check_size(s->width, s->height, 0, avctx) < 0) > > > return -1; > > > + if (bytestream2_get_bytes_left(&s->g) < s->width * s->height / 65536 > > > * 5) > > > + return AVERROR_INVALIDDATA; > > > > how did you arrive at this formula? > > There are 2 coding modes, RLE and RAW > I assume usable raw images will need around W*H and thus more than RLE > RLE codes the most compressed runs by > 1 byte for val (=marker) > 1 byte run (=0) > 2 bytes run > 1 byte val > thats 5 bytes and the maximum run we can code is 65535 > > The RLE decoder loop exits before applying the last RLE run and then > there is a seperate piece of code after it that fills the last color to > the end. Iam not sure why its done like that way but if i remove that > mid exit the seperate code piece becomes unused for all images i have > so it seems all RLE images are always fully coded with no special case > at the end. > Based on this iam guesing that my formula is correct for undamaged images > but of course i could find one tomorrow that exploits the special end > handling and breaks this formula > and of course its very possible that i missed some other thing that changes > this limit
This should be written in a comment above the code then, otherwise all future readers will be completely clueless. -- Anton Khirnov _______________________________________________ ffmpeg-devel mailing list ffmpeg-devel@ffmpeg.org https://ffmpeg.org/mailman/listinfo/ffmpeg-devel To unsubscribe, visit link above, or email ffmpeg-devel-requ...@ffmpeg.org with subject "unsubscribe".
