dfa: add some checks to ensure that decoder won't write past frame end

(cherry picked from commit 8099187e89)

Signed-off-by: Reinhard Tartler <siretart@tauware.de>

libavcodec/dfa.c

@@ -176,6 +176,8 @@ static int decode_dds1(uint8_t *frame, int width, int height,
         } else if (bitbuf & (mask << 1)) {
             frame += bytestream_get_le16(&src) * 2;
         } else {
+            if (frame_end - frame < width + 2)
+                return AVERROR_INVALIDDATA;
             frame[0] = frame[1] =
             frame[width] = frame[width + 1] =  *src++;
             frame += 2;
@@ -237,6 +239,7 @@ static int decode_wdlt(uint8_t *frame, int width, int height,
     const uint8_t *frame_end   = frame + width * height;
     uint8_t *line_ptr;
     int count, i, v, lines, segments;
+    int y = 0;
 
     lines = bytestream_get_le16(&src);
     if (lines > height || src >= src_end)
@@ -245,10 +248,12 @@ static int decode_wdlt(uint8_t *frame, int width, int height,
     while (lines--) {
         segments = bytestream_get_le16(&src);
         while ((segments & 0xC000) == 0xC000) {
+            unsigned skip_lines = -(int16_t)segments;
             unsigned delta = -((int16_t)segments * width);
-            if (frame_end - frame <= delta)
+            if (frame_end - frame <= delta || y + lines + skip_lines > height)
                 return -1;
             frame    += delta;
+            y        += skip_lines;
             segments = bytestream_get_le16(&src);
         }
         if (segments & 0x8000) {
@@ -257,6 +262,7 @@ static int decode_wdlt(uint8_t *frame, int width, int height,
         }
         line_ptr = frame;
         frame += width;
+        y++;
         while (segments--) {
             if (src_end - src < 2)
                 return -1;