dsicinav: Check for overread in RLE decode.

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

libavcodec/dsicinav.c

@@ -179,24 +179,29 @@ static int cin_decode_lzss(const unsigned char *src, int src_size, unsigned char
     return 0;
 }
 
-static void cin_decode_rle(const unsigned char *src, int src_size, unsigned char *dst, int dst_size)
+static int cin_decode_rle(const unsigned char *src, int src_size, unsigned char *dst, int dst_size)
 {
     int len, code;
     unsigned char *dst_end = dst + dst_size;
     const unsigned char *src_end = src + src_size;
 
-    while (src < src_end && dst < dst_end) {
+    while (src + 1 < src_end && dst < dst_end) {
         code = *src++;
         if (code & 0x80) {
             len = code - 0x7F;
             memset(dst, *src++, FFMIN(len, dst_end - dst));
         } else {
             len = code + 1;
+            if (len > src_end-src) {
+                av_log(0, AV_LOG_ERROR, "RLE overread\n");
+                return AVERROR_INVALIDDATA;
+            }
             memcpy(dst, src, FFMIN(len, dst_end - dst));
             src += len;
         }
         dst += len;
     }
+    return 0;
 }
 
 static int cinvideo_decode_frame(AVCodecContext *avctx,