[FFmpeg-cvslog] avcodec/prosumer: Only memset(0) what is needed.

[Michael Niedermayer]

ffmpeg | branch: master | Michael Niedermayer <michael at niedermayer.cc> | Wed May  1 19:43:40 2019 +0200| [17f91c07ef4c04b80d5b09dc3baa64dec161e307] | committer: Michael Niedermayer

avcodec/prosumer: Only memset(0) what is needed.

Fixes: Timeout (11sec -> 0.08sec)
Fixes: 14406/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_PROSUMER_fuzzer-5151210148986880

Found-by: continuous fuzzing process https://github.com/google/oss-fuzz/tree/master/projects/ffmpeg
Signed-off-by: Michael Niedermayer <michael at niedermayer.cc>

> http://git.videolan.org/gitweb.cgi/ffmpeg.git/?a=commit;h=17f91c07ef4c04b80d5b09dc3baa64dec161e307
---

 libavcodec/prosumer.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/libavcodec/prosumer.c b/libavcodec/prosumer.c
index f064f7bad7..9950519604 100644
--- a/libavcodec/prosumer.c
+++ b/libavcodec/prosumer.c
@@ -153,7 +153,6 @@ static int decode_frame(AVCodecContext *avctx, void *data,
     if (avpkt->size <= 32)
         return AVERROR_INVALIDDATA;
 
-    memset(s->decbuffer, 0, s->size);
     bytestream2_init(&s->gb, avpkt->data, avpkt->size);
     bytestream2_init_writer(&s->pb, s->decbuffer, s->size);
     ret = decompress(&s->gb, AV_RL32(avpkt->data + 28) >> 1, &s->pb, s->lut);
@@ -161,6 +160,10 @@ static int decode_frame(AVCodecContext *avctx, void *data,
         return ret;
     if (bytestream2_get_bytes_left_p(&s->pb) > s->size * (int64_t)avctx->discard_damaged_percentage / 100)
         return AVERROR_INVALIDDATA;
+
+    av_assert0(s->size >= bytestream2_get_bytes_left_p(&s->pb));
+    memset(s->decbuffer + bytestream2_tell_p(&s->pb), 0, bytestream2_get_bytes_left_p(&s->pb));
+
     vertical_predict((uint32_t *)s->decbuffer, 0, (uint32_t *)s->initial_line, s->stride, 1);
     vertical_predict((uint32_t *)s->decbuffer, s->stride, (uint32_t *)s->decbuffer, s->stride, avctx->height - 1);