[FFmpeg-cvslog] avcodec/assdec: undefined use of memcpy()

[Michael Niedermayer]

ffmpeg | branch: release/4.2 | Michael Niedermayer <michael at niedermayer.cc> | Wed Jul 24 22:55:15 2019 +0200| [8d2e23508f20e0221418b9804fa9af4c90e73e3e] | committer: Michael Niedermayer

avcodec/assdec: undefined use of memcpy()

Fixes: null pointer passed as argument 2, which is declared to never be null
Fixes: 16008/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_SSA_fuzzer-5650582821404672 (this is a separate issue found in this testcase)

Found-by: continuous fuzzing process https://github.com/google/oss-fuzz/tree/master/projects/ffmpeg
Reviewed-by: Paul B Mahol <onemda at gmail.com>
Signed-off-by: Michael Niedermayer <michael at niedermayer.cc>
(cherry picked from commit 47b6ca0b022a413e392707464f2423795aa89bfb)
Signed-off-by: Michael Niedermayer <michael at niedermayer.cc>

> http://git.videolan.org/gitweb.cgi/ffmpeg.git/?a=commit;h=8d2e23508f20e0221418b9804fa9af4c90e73e3e
---

 libavcodec/assdec.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/libavcodec/assdec.c b/libavcodec/assdec.c
index 3178f2953c..f0b1069cd2 100644
--- a/libavcodec/assdec.c
+++ b/libavcodec/assdec.c
@@ -31,7 +31,8 @@ static av_cold int ass_decode_init(AVCodecContext *avctx)
     avctx->subtitle_header = av_malloc(avctx->extradata_size + 1);
     if (!avctx->subtitle_header)
         return AVERROR(ENOMEM);
-    memcpy(avctx->subtitle_header, avctx->extradata, avctx->extradata_size);
+    if (avctx->extradata_size)
+        memcpy(avctx->subtitle_header, avctx->extradata, avctx->extradata_size);
     avctx->subtitle_header[avctx->extradata_size] = 0;
     avctx->subtitle_header_size = avctx->extradata_size;
     return 0;