On 4/7/2021 11:59 AM, Michael Niedermayer wrote:
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
If you knew about it, why didn't you use it? This code here basically
duplicates the three lines in bytestream2_get_buffer().
thx
[...]
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