eamad: check for out of bound reads when doing MC

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

libavcodec/eamad.c

@@ -85,15 +85,21 @@ static inline void comp_block(MadContext *t, int mb_x, int mb_y,
 {
     MpegEncContext *s = &t->s;
     if (j < 4) {
+        unsigned offset = (mb_y*16 + ((j&2)<<2) + mv_y)*t->last_frame.linesize[0] + mb_x*16 + ((j&1)<<3) + mv_x;
+        if (offset >= (s->height - 7) * t->last_frame.linesize[0] - 7)
+            return;
         comp(t->frame.data[0] + (mb_y*16 + ((j&2)<<2))*t->frame.linesize[0] + mb_x*16 + ((j&1)<<3),
              t->frame.linesize[0],
-             t->last_frame.data[0] + (mb_y*16 + ((j&2)<<2) + mv_y)*t->last_frame.linesize[0] + mb_x*16 + ((j&1)<<3) + mv_x,
+             t->last_frame.data[0] + offset,
              t->last_frame.linesize[0], add);
     } else if (!(s->avctx->flags & CODEC_FLAG_GRAY)) {
         int index = j - 3;
+        unsigned offset = (mb_y * 8 + (mv_y/2))*t->last_frame.linesize[index] + mb_x * 8 + (mv_x/2);
+        if (offset >= (s->height/2 - 7) * t->last_frame.linesize[index] - 7)
+            return;
         comp(t->frame.data[index] + (mb_y*8)*t->frame.linesize[index] + mb_x * 8,
              t->frame.linesize[index],
-             t->last_frame.data[index] + (mb_y * 8 + (mv_y/2))*t->last_frame.linesize[index] + mb_x * 8 + (mv_x/2),
+             t->last_frame.data[index] + offset,
              t->last_frame.linesize[index], add);
     }
 }