adding a few checks to the audio packet descrambling, this should hopefully...

adding a few checks to the audio packet descrambling, this should hopefully catch all related out of array accesses
note, the original code might have been exploitable

Originally committed as revision 7640 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavformat/asf.c

@@ -244,7 +244,8 @@ static int asf_read_header(AVFormatContext *s, AVFormatParameters *ap)
                 //       asf_st->ds_data_size, asf_st->ds_span, asf_st->ds_silence_data);
                 if (asf_st->ds_span > 1) {
                     if (!asf_st->ds_chunk_size
-                        || (asf_st->ds_packet_size/asf_st->ds_chunk_size <= 1))
+                        || (asf_st->ds_packet_size/asf_st->ds_chunk_size <= 1)
+                        || asf_st->ds_packet_size % asf_st->ds_chunk_size)
                         asf_st->ds_span = 0; // disable descrambling
                 }
                 switch (st->codec->codec_id) {
@@ -702,6 +703,9 @@ static int asf_read_packet(AVFormatContext *s, AVPacket *pkt)
         if (asf_st->frag_offset == asf_st->pkt.size) {
             /* return packet */
             if (asf_st->ds_span > 1) {
+              if(asf_st->pkt.size != asf_st->ds_packet_size * asf_st->ds_span){
+                    av_log(s, AV_LOG_ERROR, "pkt.size != ds_packet_size * ds_span\n");
+              }else{
                 /* packet descrambling */
                 uint8_t *newdata = av_malloc(asf_st->pkt.size);
                 if (newdata) {
@@ -712,6 +716,9 @@ static int asf_read_packet(AVFormatContext *s, AVPacket *pkt)
                         int col = off % asf_st->ds_span;
                         int idx = row + col * asf_st->ds_packet_size / asf_st->ds_chunk_size;
                         //printf("off:%d  row:%d  col:%d  idx:%d\n", off, row, col, idx);
+
+                        assert(offset + asf_st->ds_chunk_size <= asf_st->pkt.size);
+                        assert(idx+1 <= asf_st->pkt.size / asf_st->ds_chunk_size);
                         memcpy(newdata + offset,
                                asf_st->pkt.data + idx * asf_st->ds_chunk_size,
                                asf_st->ds_chunk_size);
@@ -720,6 +727,7 @@ static int asf_read_packet(AVFormatContext *s, AVPacket *pkt)
                     av_free(asf_st->pkt.data);
                     asf_st->pkt.data = newdata;
                 }
+              }
             }
             asf_st->frag_offset = 0;
             *pkt= asf_st->pkt;