[FFmpeg-cvslog] avcodec/hevcdec: Check s->ref in the md5 path similar to hwaccel

[Michael Niedermayer]

ffmpeg | branch: release/4.1 | Michael Niedermayer <michael at niedermayer.cc> | Sun Aug 14 23:39:56 2022 +0200| [ec9af84dc5445d272092e91452fa67d796729e1f] | committer: Michael Niedermayer

avcodec/hevcdec: Check s->ref in the md5 path similar to hwaccel

This is somewhat redundant with the is_decoded check. Maybe
there is a nicer solution

Fixes: Null pointer dereference
Fixes: 49584/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_HEVC_fuzzer-5297367351427072

Found-by: continuous fuzzing process https://github.com/google/oss-fuzz/tree/master/projects/ffmpeg
Signed-off-by: Michael Niedermayer <michael at niedermayer.cc>
(cherry picked from commit 3b51e1992289383aa9f083c88e153e34b6412c89)
Signed-off-by: Michael Niedermayer <michael at niedermayer.cc>

> http://git.videolan.org/gitweb.cgi/ffmpeg.git/?a=commit;h=ec9af84dc5445d272092e91452fa67d796729e1f
---

 libavcodec/hevcdec.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/libavcodec/hevcdec.c b/libavcodec/hevcdec.c
index 97f9def809..1960c6a202 100644
--- a/libavcodec/hevcdec.c
+++ b/libavcodec/hevcdec.c
@@ -3221,7 +3221,7 @@ static int hevc_decode_frame(AVCodecContext *avctx, void *data, int *got_output,
         }
     } else {
         /* verify the SEI checksum */
-        if (avctx->err_recognition & AV_EF_CRCCHECK && s->is_decoded &&
+        if (avctx->err_recognition & AV_EF_CRCCHECK && s->ref && s->is_decoded &&
             s->sei.picture_hash.is_md5) {
             ret = verify_md5(s, s->ref->frame);
             if (ret < 0 && avctx->err_recognition & AV_EF_EXPLODE) {