DNS: Implement NAPTR RR support

My phone is sending NAPTR queries and we reported an unknown RR type 35
in weird.log for the response, so figured I'd just add it.

NEWS

@@ -114,6 +114,9 @@ New Functionality
 
 	redef Intel::manage_seen_event_groups = F;
 
+- The DNS analyzer was extended to support NAPTR RRs (RFC 2915, RFC 3403).
+  A corresponding ``dns_NAPTR_reply`` event was added.
+
 Changed Functionality
 ---------------------
 

scripts/base/init-bare.zeek

@@ -3048,6 +3048,20 @@ type dns_svcb_rr: record {
 	target_name: string;	##< Target name, the hostname of the service endpoint.
 };
 
+## A NAPTR record.
+##
+## See also RFC 2915 - The Naming Authority Pointer (NAPTR) DNS Resource Record.
+##
+## .. zeek:see:: dns_NAPTR_reply
+type dns_naptr_rr: record {
+	order: count;        ##< Order in which to process NAPTR records.
+	preference: count;   ##< Preference specifying processing order for *equal* :zeek:field:`dns_naptr_rr$order` fields.
+	flags: string;       ##< Flags to control rewriting. E.g. "u", "a", "s" or "p".
+	service: string;     ##< The services available down this rewrite path.
+	regexp: string;      ##< Substitution expression to be applied to the original query.
+	replacement: string; ##< The next name to query, where the type is depending on the :zeek:field:`dns_naptr_rr$flags` field.
+};
+
 # DNS answer types.
 #
 # .. zeek:see:: dns_answer

scripts/base/protocols/dns/main.zeek

@@ -537,6 +537,27 @@ event dns_SRV_reply(c: connection, msg: dns_msg, ans: dns_answer, target: string
 	hook DNS::do_reply(c, msg, ans, target);
 	}
 
+event dns_NAPTR_reply(c: connection, msg: dns_msg, ans: dns_answer, naptr: dns_naptr_rr) &priority=5
+	{
+	# Just encode all the fields for NAPTR RR in the reply string.
+	local tmp = "";
+
+	if ( |naptr$regexp| > 0 )
+		tmp += naptr$regexp;
+
+	if ( |naptr$replacement| > 0 )
+		{
+		if ( |tmp| > 0 )
+			tmp += " ";
+
+		tmp += naptr$replacement;
+		}
+
+	local r = fmt("NAPTR %s %s %s %s %s", naptr$order, naptr$preference, naptr$flags, naptr$service, tmp);
+
+	hook DNS::do_reply(c, msg, ans, r);
+	}
+
 # TODO: figure out how to handle these
 #event dns_EDNS(c: connection, msg: dns_msg, ans: dns_answer)
 #	{

src/analyzer/protocol/dns/DNS.cc

@@ -11,6 +11,7 @@
 #include "zeek/Event.h"
 #include "zeek/NetVar.h"
 #include "zeek/RunState.h"
+#include "zeek/Val.h"
 #include "zeek/ZeekString.h"
 #include "zeek/analyzer/protocol/dns/events.bif.h"
 #include "zeek/session/Manager.h"
@@ -299,6 +300,8 @@ bool DNS_Interpreter::ParseAnswer(detail::DNS_MsgInfo* msg, const u_char*& data,
 
             break;
 
+        case detail::TYPE_NAPTR: status = ParseRR_NAPTR(msg, data, len, rdlength, msg_start); break;
+
         case detail::TYPE_EDNS: status = ParseRR_EDNS(msg, data, len, rdlength, msg_start); break;
 
         case detail::TYPE_TKEY: status = ParseRR_TKEY(msg, data, len, rdlength, msg_start); break;
@@ -628,6 +631,50 @@ bool DNS_Interpreter::ParseRR_SRV(detail::DNS_MsgInfo* msg, const u_char*& data,
     return true;
 }
 
+bool DNS_Interpreter::ParseRR_NAPTR(detail::DNS_MsgInfo* msg, const u_char*& data, int& len, int rdlength,
+                                    const u_char* msg_start) {
+    zeek_uint_t order = ExtractShort(data, len);
+    zeek_uint_t preference = ExtractShort(data, len);
+    rdlength -= 4;
+
+    if ( len <= 0 || rdlength <= 0 ) {
+        analyzer->AnalyzerViolation("DNS_NAPTR_too_short");
+        return false;
+    }
+
+    // These all check rdlength and return nullptr if there's not enough data available.
+    auto flags = extract_char_string(analyzer, data, len, rdlength);
+    auto service = extract_char_string(analyzer, data, len, rdlength);
+    auto regexp = extract_char_string(analyzer, data, len, rdlength);
+
+    // The replacement string is a name. Compression shouldn't be used, but doesn't seem
+    // we have a helper that would allow to control this.
+    u_char replacement[513];
+    int replacement_len = sizeof(replacement) - 1;
+    u_char* replacement_end = ExtractName(data, len, replacement, replacement_len, msg_start, false);
+
+    if ( ! flags || ! service || ! regexp || ! replacement_end ) {
+        analyzer->AnalyzerViolation("DNS_NAPTR_RR_too_short");
+        return false;
+    }
+
+    if ( dns_NAPTR_reply && ! msg->skip_event ) {
+        static auto dns_naptr_rr = id::find_type<RecordType>("dns_naptr_rr");
+        auto r = make_intrusive<RecordVal>(dns_naptr_rr);
+
+        r->Assign(0, order);
+        r->Assign(1, preference);
+        r->Assign(2, std::move(flags));
+        r->Assign(3, std::move(service));
+        r->Assign(4, std::move(regexp));
+        r->Assign(5, zeek::make_intrusive<StringVal>(new String(replacement, replacement_end - replacement, true)));
+
+        analyzer->EnqueueConnEvent(dns_NAPTR_reply, analyzer->ConnVal(), msg->BuildHdrVal(), msg->BuildAnswerVal(), r);
+    }
+
+    return true;
+}
+
 bool DNS_Interpreter::ParseRR_EDNS(detail::DNS_MsgInfo* msg, const u_char*& data, int& len, int rdlength,
                                    const u_char* msg_start) {
     if ( dns_EDNS_addl && ! msg->skip_event )

src/analyzer/protocol/dns/DNS.h

@@ -360,6 +360,7 @@ protected:
     bool ParseRR_MX(detail::DNS_MsgInfo* msg, const u_char*& data, int& len, int rdlength, const u_char* msg_start);
     bool ParseRR_NBS(detail::DNS_MsgInfo* msg, const u_char*& data, int& len, int rdlength, const u_char* msg_start);
     bool ParseRR_SRV(detail::DNS_MsgInfo* msg, const u_char*& data, int& len, int rdlength, const u_char* msg_start);
+    bool ParseRR_NAPTR(detail::DNS_MsgInfo* msg, const u_char*& data, int& len, int rdlength, const u_char* msg_start);
     bool ParseRR_EDNS(detail::DNS_MsgInfo* msg, const u_char*& data, int& len, int rdlength, const u_char* msg_start);
     bool ParseRR_EDNS_ECS(detail::DNS_MsgInfo* msg, const u_char*& data, int& len, int rdlength,
                           const u_char* msg_start);

src/analyzer/protocol/dns/events.bif

@@ -467,6 +467,23 @@ event dns_CAA_reply%(c: connection, msg: dns_msg, ans: dns_answer, flags: count,
 ##    dns_skip_addl dns_skip_all_addl dns_skip_all_auth dns_skip_auth
 event dns_SRV_reply%(c: connection, msg: dns_msg, ans: dns_answer, target: string, priority: count, weight: count, p: count%);
 
+## Generated for DNS replies of type *NAPTR*. For replies with multiple answers,
+## an individual event of the corresponding type is raised for each.
+##
+## c: The connection, which may be UDP or TCP depending on the type of the
+##    transport-layer session being analyzed.
+##
+## msg: The parsed DNS message header.
+##
+## ans: The type-independent part of the parsed answer record.
+##
+## naptr: The parsed RDATA of NAPTR type record.
+##
+## .. zeek:see:: dns_AAAA_reply dns_A_reply dns_CNAME_reply dns_EDNS_addl
+##    dns_HINFO_reply dns_MX_reply dns_NS_reply dns_PTR_reply dns_SOA_reply
+##    dns_TSIG_addl dns_TXT_reply dns_SPF_reply dns_WKS_reply dns_SRV_reply dns_end
+event dns_NAPTR_reply%(c: connection, msg: dns_msg, ans: dns_answer, naptr: dns_naptr_rr%);
+
 ## Generated on DNS reply resource records when the type of record is not one
 ## that Zeek knows how to parse and generate another more specific event.
 ##

testing/btest/Baseline/scripts.base.protocols.dns.naptr/.stdout

@@ -0,0 +1,2 @@
+### BTest baseline data generated by btest-diff. Do not edit. Use "btest -U/-u" to update. Requires BTest >= 0.63.
+NAPTR, [id=20970, opcode=0, rcode=0, QR=T, AA=F, TC=F, RD=T, RA=T, Z=0, AD=F, CD=F, num_queries=1, num_answers=1, num_auth=0, num_addl=0], [answer_type=1, query=fp-de-carrier-vodafone.rcs.telephony.goog, qtype=35, qclass=1, TTL=2.0 mins 48.0 secs], [order=100, preference=100, flags=s, service=SIPS+D2T, regexp=, replacement=_sips._tcp.fp-de-carrier-vodafone.rcs.telephony.goog]

testing/btest/Baseline/scripts.base.protocols.dns.naptr/dns.log.cut

@@ -0,0 +1,3 @@
+### BTest baseline data generated by btest-diff. Do not edit. Use "btest -U/-u" to update. Requires BTest >= 0.63.
+uid	query	qclass_name	qtype_name	answers
+CHhAvVGS1DHFjwGM9	fp-de-carrier-vodafone.rcs.telephony.goog	C_INTERNET	NAPTR	NAPTR 100 100 s SIPS+D2T _sips._tcp.fp-de-carrier-vodafone.rcs.telephony.goog

testing/btest/Baseline/scripts.base.protocols.dns.naptr/out

@@ -0,0 +1,2 @@
+### BTest baseline data generated by btest-diff. Do not edit. Use "btest -U/-u" to update. Requires BTest >= 0.63.
+NAPTR, [id=20970, opcode=0, rcode=0, QR=T, AA=F, TC=F, RD=T, RA=T, Z=0, AD=F, CD=F, num_queries=1, num_answers=1, num_auth=0, num_addl=0], [answer_type=1, query=fp-de-carrier-vodafone.rcs.telephony.goog, qtype=35, qclass=1, TTL=2.0 mins 48.0 secs], [order=100, preference=100, flags=s, service=SIPS+D2T, regexp=, replacement=_sips._tcp.fp-de-carrier-vodafone.rcs.telephony.goog]

testing/btest/scripts/base/protocols/dns/naptr.zeek

@@ -0,0 +1,11 @@
+# @TEST-EXEC: zeek -b -r $TRACES/dns/naptr.pcap %INPUT >out
+# @TEST-EXEC: btest-diff out
+# @TEST-EXEC: zeek-cut -m uid query qclass_name qtype_name answers < dns.log > dns.log.cut
+# @TEST-EXEC: btest-diff dns.log.cut
+
+@load base/protocols/dns
+
+event dns_NAPTR_reply(c: connection, msg: dns_msg, ans: dns_answer, naptr: dns_naptr_rr)
+	{
+	print "NAPTR", msg, ans, naptr;
+	}