[FFmpeg-cvslog] rv34: fix invalid memory access for small video dimensions

[John Brooks]

ffmpeg | branch: release/0.9 | John Brooks <john.brooks at bluecherry.net> | Tue Jan  3 23:27:35 2012 -0700| [fc9c5ad9ea70479d09a5d37c800665746ff4710d] | committer: Michael Niedermayer

rv34: fix invalid memory access for small video dimensions

For small video dimensions calculations of the upper bound for pixel
access may result in negative value. Using an unsigned comparison
works only if the greater operand is non-negative. This is fixed by
doing edge emulation explicitly for such conditions.

Signed-off-by: Kostya Shishkov <kostya.shishkov at gmail.com>
(cherry picked from commit aacf6b3a2fd8bc8603e3deaa6e612ea03cf08707)

Signed-off-by: Michael Niedermayer <michaelni at gmx.at>

> http://git.videolan.org/gitweb.cgi/ffmpeg.git/?a=commit;h=fc9c5ad9ea70479d09a5d37c800665746ff4710d
---

 libavcodec/rv34.c |    5 +++--
 1 files changed, 3 insertions(+), 2 deletions(-)

diff --git a/libavcodec/rv34.c b/libavcodec/rv34.c
index 15a5c54..1e05906 100644
--- a/libavcodec/rv34.c
+++ b/libavcodec/rv34.c
@@ -690,8 +690,9 @@ static inline void rv34_mc(RV34DecContext *r, const int block_type,
     srcY += src_y * s->linesize + src_x;
     srcU += uvsrc_y * s->uvlinesize + uvsrc_x;
     srcV += uvsrc_y * s->uvlinesize + uvsrc_x;
-    if(   (unsigned)(src_x - !!lx*2) > s->h_edge_pos - !!lx*2 - (width <<3) - 4
-       || (unsigned)(src_y - !!ly*2) > s->v_edge_pos - !!ly*2 - (height<<3) - 4){
+    if(s->h_edge_pos - (width << 3) < 6 || s->v_edge_pos - (height << 3) < 6 ||
+       (unsigned)(src_x - !!lx*2) > s->h_edge_pos - !!lx*2 - (width <<3) - 4 ||
+       (unsigned)(src_y - !!ly*2) > s->v_edge_pos - !!ly*2 - (height<<3) - 4) {
         uint8_t *uvbuf = s->edge_emu_buffer + 22 * s->linesize;
 
         srcY -= 2 + 2*s->linesize;