avcodec/dcadec: Check nchans

Fixes CID1239110
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavcodec/dcadec.c

@@ -229,6 +229,14 @@ static int dca_parse_audio_coding_header(DCAContext *s, int base_channel,
     }
 
     nchans = get_bits(&s->gb, 3) + 1;
+    if (xxch && nchans >= 3) {
+        av_log(s->avctx, AV_LOG_ERROR, "nchans %d is too large\n", nchans);
+        return AVERROR_INVALIDDATA;
+    } else if (nchans + base_channel > DCA_PRIM_CHANNELS_MAX) {
+        av_log(s->avctx, AV_LOG_ERROR, "channel sum %d + %d is too large\n", nchans, base_channel);
+        return AVERROR_INVALIDDATA;
+    }
+
     s->total_channels = nchans + base_channel;
     s->prim_channels  = s->total_channels;