[SQUASH ME] ng_icmpv6: prevent buffer leaking

sys/net/network_layer/ng_icmpv6/ng_icmpv6.c

@@ -69,11 +69,13 @@ void ng_icmpv6_demux(ng_pktsnip_t *pkt)
 {
     ng_pktsnip_t *icmpv6, *ipv6;
     ng_icmpv6_hdr_t *hdr;
+    size_t receiver_num = 0;
 
     LL_SEARCH_SCALAR(pkt, icmpv6, type, NG_NETTYPE_ICMPV6);
 
     if (icmpv6 == NULL) {
         DEBUG("icmpv6: received packet has no payload\n");
+        /* don't release: IPv6 does this */
         return;
     }
 
@@ -83,13 +85,15 @@ void ng_icmpv6_demux(ng_pktsnip_t *pkt)
 
     if (ipv6 == NULL) {
         DEBUG("ipv6: received packet has no IPv6 header\n");
+        /* don't release: IPv6 does this */
         return;
     }
 
     hdr = (ng_icmpv6_hdr_t *)icmpv6->data;
 
     if (_icmpv6_inet_csum((ng_ipv6_hdr_t *)(ipv6->data), hdr, icmpv6->size) != 0xffff) {
         DEBUG("icmpv6: wrong checksum.\n");
+        /* don't release: IPv6 does this */
         return;
     }
 
@@ -127,7 +131,15 @@ void ng_icmpv6_demux(ng_pktsnip_t *pkt)
     /* ICMPv6-all will be send send in ng_ipv6.c so only dispatch of
      * subtypes is needed */
 
-    ng_pktbuf_hold(pkt, ng_netreg_num(NG_NETTYPE_ICMPV6, hdr->type) - 1);
+    receiver_num = ng_netreg_num(NG_NETTYPE_ICMPV6, hdr->type);
+
+    if (receiver_num == 0) {
+        DEBUG("icmpv6: no receivers for ICMPv6 type %" PRIu8 "\n", hdr->type);
+        /* don't release: IPv6 does this */
+        return;
+    }
+
+    ng_pktbuf_hold(pkt, receiver_num - 1);
     /* ICMPv6 is not interested anymore so `- 1` */
     _dispatch_received(NG_NETTYPE_ICMPV6, hdr->type, pkt);
 }