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@gmail.com>
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

diff --git a/libavcodec/assdec.c b/libavcodec/assdec.c
index 3178f2953ca6a73a8a641aca7995ab400af40b53..f0b1069cd255407cf697851e312697cc6d066558 100644 (file)
--- 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;