kvmc: Fix out of reference frame reads.

Found-by: Mateusz "j00ru" Jurczyk and Gynvael Coldwind
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavcodec/kmvc.c

@@ -106,6 +106,10 @@ static int kmvc_decode_intra_8x8(KmvcContext * ctx, int w, int h)
                             val = bytestream2_get_byte(&ctx->g);
                             mx = val & 0xF;
                             my = val >> 4;
+                            if ((l0x-mx) + 320*(l0y-my) < 0 || (l0x-mx) + 320*(l0y-my) > 316*196) {
+                                av_log(ctx->avctx, AV_LOG_ERROR, "Invalid MV\n");
+                                return AVERROR_INVALIDDATA;
+                            }
                             for (j = 0; j < 16; j++)
                                 BLK(ctx->cur, l0x + (j & 3), l0y + (j >> 2)) =
                                     BLK(ctx->cur, l0x + (j & 3) - mx, l0y + (j >> 2) - my);
@@ -127,6 +131,10 @@ static int kmvc_decode_intra_8x8(KmvcContext * ctx, int w, int h)
                                     val = bytestream2_get_byte(&ctx->g);
                                     mx = val & 0xF;
                                     my = val >> 4;
+                                    if ((l1x-mx) + 320*(l1y-my) < 0 || (l1x-mx) + 320*(l1y-my) > 318*198) {
+                                        av_log(ctx->avctx, AV_LOG_ERROR, "Invalid MV\n");
+                                        return AVERROR_INVALIDDATA;
+                                    }
                                     BLK(ctx->cur, l1x, l1y) = BLK(ctx->cur, l1x - mx, l1y - my);
                                     BLK(ctx->cur, l1x + 1, l1y) =
                                         BLK(ctx->cur, l1x + 1 - mx, l1y - my);
@@ -198,6 +206,10 @@ static int kmvc_decode_inter_8x8(KmvcContext * ctx, int w, int h)
                             val = bytestream2_get_byte(&ctx->g);
                             mx = (val & 0xF) - 8;
                             my = (val >> 4) - 8;
+                            if ((l0x+mx) + 320*(l0y+my) < 0 || (l0x+mx) + 320*(l0y+my) > 318*198) {
+                                av_log(ctx->avctx, AV_LOG_ERROR, "Invalid MV\n");
+                                return AVERROR_INVALIDDATA;
+                            }
                             for (j = 0; j < 16; j++)
                                 BLK(ctx->cur, l0x + (j & 3), l0y + (j >> 2)) =
                                     BLK(ctx->prev, l0x + (j & 3) + mx, l0y + (j >> 2) + my);
@@ -219,6 +231,10 @@ static int kmvc_decode_inter_8x8(KmvcContext * ctx, int w, int h)
                                     val = bytestream2_get_byte(&ctx->g);
                                     mx = (val & 0xF) - 8;
                                     my = (val >> 4) - 8;
+                                    if ((l1x+mx) + 320*(l1y+my) < 0 || (l1x+mx) + 320*(l1y+my) > 318*198) {
+                                        av_log(ctx->avctx, AV_LOG_ERROR, "Invalid MV\n");
+                                        return AVERROR_INVALIDDATA;
+                                    }
                                     BLK(ctx->cur, l1x, l1y) = BLK(ctx->prev, l1x + mx, l1y + my);
                                     BLK(ctx->cur, l1x + 1, l1y) =
                                         BLK(ctx->prev, l1x + 1 + mx, l1y + my);