dns: prevent repeatedly overwriting resolved entries

When a packet contains multiple conflicting names for the same address,
it would result in modification of the resolved name every time this DNS
packet is selected. In Qt, this causes a periodic (one second)
redissection of the current (DNS!) packet which interferes with user
interaction. To avoid this, only add the address on the first visit.

Bug: 13533
Change-Id: Ic71515131da4d666bfd589df9ff90a866a30778c
Reviewed-on: https://code.wireshark.org/review/20800
Petri-Dish: Peter Wu <peter@lekensteyn.nl>
Tested-by: Petri Dish Buildbot <buildbot-no-reply@wireshark.org>
Reviewed-by: Anders Broman <a.broman58@gmail.com>

epan/dissectors/packet-dns.c

@@ -1826,7 +1826,8 @@ dissect_dns_answer(tvbuff_t *tvb, int offsetx, int dns_data_offset,
       proto_item_append_text(trr, ", addr %s", addr);
       proto_tree_add_item(rr_tree, hf_dns_a, tvb, cur_offset, 4, ENC_BIG_ENDIAN);
 
-      if (gbl_resolv_flags.dns_pkt_addr_resolution && (dns_class & 0x7f) == C_IN) {
+      if (gbl_resolv_flags.dns_pkt_addr_resolution && (dns_class & 0x7f) == C_IN &&
+          !PINFO_FD_VISITED(pinfo)) {
         guint32 addr_int;
         tvb_memcpy(tvb, &addr_int, cur_offset, sizeof(addr_int));
         add_ipv4_name(addr_int, name);
@@ -2399,7 +2400,8 @@ dissect_dns_answer(tvbuff_t *tvb, int offsetx, int dns_data_offset,
       proto_tree_add_item(rr_tree, hf_dns_aaaa, tvb, cur_offset, 16, ENC_NA);
 
 
-      if (gbl_resolv_flags.dns_pkt_addr_resolution && (dns_class & 0x7f) == C_IN) {
+      if (gbl_resolv_flags.dns_pkt_addr_resolution && (dns_class & 0x7f) == C_IN &&
+          !PINFO_FD_VISITED(pinfo)) {
         struct e_in6_addr  addr_in6;
         tvb_memcpy(tvb, &addr_in6, cur_offset, sizeof(addr_in6));
         add_ipv6_name(&addr_in6, name);