dfa: Disallow odd width/height and add proper bounds check for DDS1 chunks

DDS1 chunks are decoded in 2x2 blocks, odd chunk width or height is not
allowed in that case. Also ensure that the decode buffer is big enough
for all blocks being processed.

Bug-Id: CVE-2017-9992
CC: libav-stable@libav.org

libavcodec/dfa.c

@@ -144,6 +144,8 @@ static int decode_dds1(GetByteContext *gb, uint8_t *frame, int width, int height
     int mask = 0x10000, bitbuf = 0;
     int i, v, offset, count, segments;
 
+    if ((width | height) & 1)
+        return AVERROR_INVALIDDATA;
     segments = bytestream2_get_le16(gb);
     while (segments--) {
         if (bytestream2_get_bytes_left(gb) < 2)
@@ -171,7 +173,7 @@ static int decode_dds1(GetByteContext *gb, uint8_t *frame, int width, int height
                 return AVERROR_INVALIDDATA;
             frame += v;
         } else {
-            if (frame_end - frame < width + 3)
+            if (width < 4 || frame_end - frame < width + 4)
                 return AVERROR_INVALIDDATA;
             frame[0] = frame[1] =
             frame[width] = frame[width + 1] =  bytestream2_get_byte(gb);