Do not overread input buffer.

Fixes issue 2503.

Patch by Daniel Kang, daniel.d.kang at gmail

Originally committed as revision 26256 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavcodec/dpx.c

@@ -55,6 +55,7 @@ static int decode_frame(AVCodecContext *avctx,
                         AVPacket *avpkt)
 {
     const uint8_t *buf = avpkt->data;
+    const uint8_t *buf_end = avpkt->data + avpkt->size;
     int buf_size       = avpkt->size;
     DPXContext *const s = avctx->priv_data;
     AVFrame *picture  = data;
@@ -172,6 +173,10 @@ static int decode_frame(AVCodecContext *avctx,
         case 8:
         case 12: // Treat 12-bit as 16-bit
         case 16:
+            if (source_packet_size*avctx->width*avctx->height > buf_end - buf) {
+                av_log(avctx, AV_LOG_ERROR, "Overread buffer. Invalid header?\n");
+                return -1;
+            }
             if (source_packet_size == target_packet_size) {
                 for (x = 0; x < avctx->height; x++) {
                     memcpy(ptr, buf, target_packet_size*avctx->width);