On Wed, Apr 07, 2021 at 12:42:50AM +0200, Andreas Rheinhardt wrote: > Michael Niedermayer: > > Fixes: out of array read > > Fixes: > > 32968/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_MSP2_fuzzer-5315296027082752 > > > > Found-by: continuous fuzzing process > > https://github.com/google/oss-fuzz/tree/master/projects/ffmpeg > > Signed-off-by: Michael Niedermayer <mich...@niedermayer.cc> > > --- > > libavcodec/msp2dec.c | 3 ++- > > 1 file changed, 2 insertions(+), 1 deletion(-) > > > > diff --git a/libavcodec/msp2dec.c b/libavcodec/msp2dec.c > > index cc548d218a..87057fb5e2 100644 > > --- a/libavcodec/msp2dec.c > > +++ b/libavcodec/msp2dec.c > > @@ -68,9 +68,10 @@ static int msp2_decode_frame(AVCodecContext *avctx, > > > > bytestream2_init(&gb, buf, pkt_size); > > x = 0; > > - while (bytestream2_get_bytes_left(&gb) && x < width) { > > + while (bytestream2_get_bytes_left(&gb) > 0 && x < width) { > > This decoder uses the checked bytestream2 API, so != 0 and > 0 should be > equivalent for bytestream2_get_bytes_left(&gb).
I changed it to "> 0" because it felt clearer&more robust
i will drop that as its not needed for the bugfix
>
> > int size = bytestream2_get_byte(&gb);
> > if (size) {
> > + size = FFMIN(size, bytestream2_get_bytes_left(&gb));
> > memcpy(p->data[0] + y * p->linesize[0] + x, gb.buffer,
> > FFMIN(size, width - x));
>
> width can include seven bytes of the packet's padding, but it stays
> within the padding, so I wonder where the out of array read comes from.
> The only fishy thing in this decoder I see is that 2 * avctx->height
> might overflow.
size is a value read from the bytestream, theres no guarntee that
the amount that byte calls for is not beyond the end of the bytestream
and its not checked by memcpy
bytestream2_get_buffer() would check it and it can maybe be used instead
thx
[...]
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