[FFmpeg-cvslog] xxan: don't read before start of buffer in av_memcpy_backptr().

[Ronald S. Bultje]

ffmpeg | branch: master | Ronald S. Bultje <rsbultje at gmail.com> | Thu Mar  8 16:32:46 2012 -0800| [f1279e286b00e99f343adb51e251f036a3df6f32] | committer: Ronald S. Bultje

xxan: don't read before start of buffer in av_memcpy_backptr().

Found-by: Mateusz "j00ru" Jurczyk and Gynvael Coldwind
CC: libav-stable at libav.org

> http://git.videolan.org/gitweb.cgi/ffmpeg.git/?a=commit;h=f1279e286b00e99f343adb51e251f036a3df6f32
---

 libavcodec/xxan.c |    3 ++-
 1 files changed, 2 insertions(+), 1 deletions(-)

diff --git a/libavcodec/xxan.c b/libavcodec/xxan.c
index 4659d34..8147bad 100644
--- a/libavcodec/xxan.c
+++ b/libavcodec/xxan.c
@@ -129,7 +129,8 @@ static int xan_unpack(uint8_t *dest, const int dest_len,
                 if (size + size2 > dest_end - dest)
                     break;
             }
-            if (src + size > src_end || dest + size + size2 > dest_end)
+            if (src + size > src_end || dest + size + size2 > dest_end ||
+                dest - orig_dest + size < back)
                 return -1;
             bytestream_get_buffer(&src, dest, size);
             dest += size;