[FFmpeg-cvslog] avformat/vividas: check for tiny blocks using alignment

[Michael Niedermayer]

ffmpeg | branch: release/4.2 | Michael Niedermayer <michael at niedermayer.cc> | Sat Aug 31 23:20:01 2019 +0200| [5a1e0cae2f78b10cc7ab6cd41d6908c4ae89276f] | committer: Michael Niedermayer

avformat/vividas: check for tiny blocks using alignment

Ask for a sample for these
Fixes: out of array access
Fixes: 16624/clusterfuzz-testcase-minimized-ffmpeg_DEMUXER_fuzzer-5762455661182976

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 55d4e22d71ca75223ee61f7d2535fdc6e9991026)
Signed-off-by: Michael Niedermayer <michael at niedermayer.cc>

> http://git.videolan.org/gitweb.cgi/ffmpeg.git/?a=commit;h=5a1e0cae2f78b10cc7ab6cd41d6908c4ae89276f
---

 libavformat/vividas.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/libavformat/vividas.c b/libavformat/vividas.c
index 645e322b6e..1ac86a107e 100644
--- a/libavformat/vividas.c
+++ b/libavformat/vividas.c
@@ -153,6 +153,10 @@ static void decode_block(uint8_t *src, uint8_t *dest, unsigned size,
 
     if (align) {
         uint32_t tmpkey = *key_ptr - key;
+        if (a2 > s) {
+            a2 = s;
+            avpriv_request_sample(NULL, "tiny aligned block\n");
+        }
         memcpy(tmp + align, src, a2);
         xor_block(tmp, tmp, 4, key, &tmpkey);
         memcpy(dest, tmp + align, a2);