avcodec/mjpegdec: Check escape sequence validity

Fixes assertion failure
Fixes: asan_heap-oob_1c1a4ea_1242_cov_2274415971_TESTcmyk.jpg

Found-by: Mateusz "j00ru" Jurczyk and Gynvael Coldwind
Signed-off-by: Michael Niedermayer <[email protected]>
(cherry picked from commit afa92907f3c6a0c3bdad766ec8d938ee17ee1c9e)

Signed-off-by: Michael Niedermayer <[email protected]>

1 files changed, 4 insertions, 0 deletions

diff --git a/libavcodec/mjpegdec.c b/libavcodec/mjpegdec.c
index 95a066f3d6..e8bbf6080a 100644
--- a/libavcodec/mjpegdec.c
+++ b/libavcodec/mjpegdec.c
@@ -1877,6 +1877,10 @@ int ff_mjpeg_find_marker(MJpegDecodeContext *s,
             put_bits(&pb, 8, x);
             if (x == 0xFF) {
                 x = src[b++];
+                if (x & 0x80) {
+                    av_log(s->avctx, AV_LOG_WARNING, "Invalid escape sequence\n");
+                    x &= 0x7f;
+                }
                 put_bits(&pb, 7, x);
                 bit_count--;
             }