vc1: check the source buffer in vc1_mc functions

Reported-by: Mateusz "j00ru" Jurczyk and Gynvael Coldwind
CC: libav-stable@libav.org
(cherry picked from commit 090cd0631140ac1a3a795d2adfac5dbf5e381aa2)
Signed-off-by: Luca Barbato <lu_zero@gentoo.org>

Conflicts:
	libavcodec/vc1dec.c

1 files changed, 15 insertions, 0 deletions

diff --git a/libavcodec/vc1dec.c b/libavcodec/vc1dec.c
index c29f91ce11..e24a15380e 100644
--- a/libavcodec/vc1dec.c
+++ b/libavcodec/vc1dec.c
@@ -394,6 +394,11 @@ static void vc1_mc_1mv(VC1Context *v, int dir)
         }
     }
 
+    if (!srcY || !srcU) {
+        av_log(v->s.avctx, AV_LOG_ERROR, "Referenced frame missing.\n");
+        return;
+    }
+
     src_x   = s->mb_x * 16 + (mx   >> 2);
     src_y   = s->mb_y * 16 + (my   >> 2);
     uvsrc_x = s->mb_x *  8 + (uvmx >> 2);
@@ -569,6 +574,11 @@ static void vc1_mc_4mv_luma(VC1Context *v, int n, int dir)
     } else
         srcY = s->next_picture.f.data[0];
 
+    if (!srcY) {
+        av_log(v->s.avctx, AV_LOG_ERROR, "Referenced frame missing.\n");
+        return;
+    }
+
     if (v->field_mode) {
         if (v->cur_field_type != v->ref_field_type[dir])
             my = my - 2 + 4 * v->cur_field_type;
@@ -856,6 +866,11 @@ static void vc1_mc_4mv_chroma(VC1Context *v, int dir)
         srcV = s->next_picture.f.data[2] + uvsrc_y * s->uvlinesize + uvsrc_x;
     }
 
+    if (!srcU) {
+        av_log(v->s.avctx, AV_LOG_ERROR, "Referenced frame missing.\n");
+        return;
+    }
+
     if (v->field_mode) {
         if (chroma_ref_type) {
             srcU += s->current_picture_ptr->f.linesize[1];