Add dns_resolver option

This allows one to configure the address of the DNS server to use for
lookup operations.

Addresses GH-216

scripts/base/init-bare.bro

@@ -3656,6 +3656,12 @@ global dns_skip_all_addl = T &redef;
 ## traffic and do not process it.  Set to 0 to turn off this functionality.
 global dns_max_queries = 25 &redef;
 
+## The address of the DNS resolver to use.  If not changed from the
+## unspecified address, ``[::]``, the first nameserver from /etc/resolv.conf
+## gets used (IPv6 is currently only supported if set via this option, not
+## when parsed from the file).
+const dns_resolver = [::] &redef;
+
 ## HTTP session statistics.
 ##
 ## .. bro:see:: http_stats

src/DNS_Mgr.cc

@@ -376,12 +376,6 @@ DNS_Mgr::DNS_Mgr(DNS_MgrMode arg_mode)
 
 	mode = arg_mode;
 
-	char err[NB_DNS_ERRSIZE];
-	nb_dns = nb_dns_init(err);
-
-	if ( ! nb_dns )
-		reporter->Warning("problem initializing NB-DNS: %s", err);
-
 	dns_mapping_valid = dns_mapping_unverified = dns_mapping_new_name =
 		dns_mapping_lost_name = dns_mapping_name_changed =
 			dns_mapping_altered =  0;
@@ -410,6 +404,35 @@ void DNS_Mgr::InitPostScript()
 	if ( did_init )
 		return;
 
+	auto dns_resolver_id = global_scope()->Lookup("dns_resolver");
+	auto dns_resolver_addr = dns_resolver_id->ID_Val()->AsAddr();
+	char err[NB_DNS_ERRSIZE];
+
+	if ( dns_resolver_addr == IPAddr("::") )
+		nb_dns = nb_dns_init(err);
+	else
+		{
+		struct sockaddr_storage ss = {0};
+
+		if ( dns_resolver_addr.GetFamily() == IPv4 )
+			{
+			struct sockaddr_in* sa = (struct sockaddr_in*)&ss;
+			sa->sin_family = AF_INET;
+			dns_resolver_addr.CopyIPv4(&sa->sin_addr);
+			}
+		else
+			{
+			struct sockaddr_in6* sa = (struct sockaddr_in6*)&ss;
+			sa->sin6_family = AF_INET6;
+			dns_resolver_addr.CopyIPv6(&sa->sin6_addr);
+			}
+
+		nb_dns = nb_dns_init2(err, (struct sockaddr*)&ss);
+		}
+
+	if ( ! nb_dns )
+		reporter->Warning("problem initializing NB-DNS: %s", err);
+
 	const char* cache_dir = dir ? dir : ".";
 
 	if ( mode == DNS_PRIME && ! ensure_dir(cache_dir) )
@@ -471,15 +494,15 @@ static const char* fake_addr_lookup_result(const IPAddr& addr)
 
 TableVal* DNS_Mgr::LookupHost(const char* name)
 	{
+	if ( mode == DNS_FAKE )
+		return fake_name_lookup_result(name);
+
 	if ( ! nb_dns )
 		return empty_addr_set();
 
 	if ( ! did_init )
 		Init();
 
-	if ( mode == DNS_FAKE )
-		return fake_name_lookup_result(name);
-
 	if ( mode != DNS_PRIME )
 		{
 		HostMap::iterator it = host_mappings.find(name);

src/nb_dns.c

@@ -86,7 +86,7 @@ struct nb_dns_hostent {
 
 struct nb_dns_info {
 	int s;				/* Resolver file descriptor */
-	struct sockaddr_in server;	/* server address to bind to */
+	struct sockaddr_storage server;	/* server address to bind to */
 	struct nb_dns_entry *list;	/* outstanding requests */
 	struct nb_dns_hostent dns_hostent;
 };
@@ -109,6 +109,18 @@ my_strerror(int errnum)
 #endif
 }
 
+static const char* sa_ntop(struct sockaddr* sa, char* buf, int len)
+	{
+	if ( sa->sa_family == AF_INET )
+		return inet_ntop(sa->sa_family,
+		                 &(((struct sockaddr_in*)sa)->sin_addr),
+		                 buf, len);
+	else
+		return inet_ntop(sa->sa_family,
+		                 &(((struct sockaddr_in6*)sa)->sin6_addr),
+		                 buf, len);
+	}
+
 struct nb_dns_info *
 nb_dns_init(char *errstr)
 {
@@ -136,13 +148,12 @@ nb_dns_init(char *errstr)
 
 	for ( i = 0; i < _res.nscount; ++i )
 		{
-		nd->server = _res.nsaddr_list[i];
-
+		memcpy(&nd->server, &_res.nsaddr_list[i], sizeof(struct sockaddr_in));
 		/* XXX support IPv6 */
-		if ( nd->server.sin_family != AF_INET )
+		if ( nd->server.ss_family != AF_INET )
 			continue;
 
-		nd->s = socket(nd->server.sin_family, SOCK_DGRAM, 0);
+		nd->s = socket(nd->server.ss_family, SOCK_DGRAM, 0);
 
 		if ( nd->s < 0 )
 			{
@@ -153,10 +164,14 @@ nb_dns_init(char *errstr)
 			}
 
 		if ( connect(nd->s, (struct sockaddr *)&nd->server,
-		             sizeof(struct sockaddr)) < 0 )
+	                 nd->server.ss_family == AF_INET ?
+	                           sizeof(struct sockaddr_in) :
+	                           sizeof(struct sockaddr_in6)) < 0 )
 			{
-			snprintf(errstr, NB_DNS_ERRSIZE, "connect(%s): %s",
-			         inet_ntoa(nd->server.sin_addr), my_strerror(errno));
+			char s[INET6_ADDRSTRLEN];
+			sa_ntop((struct sockaddr*)&nd->server, s, INET6_ADDRSTRLEN);
+			snprintf(errstr, NB_DNS_ERRSIZE, "connect(%s): %s", s,
+			         my_strerror(errno));
 			close(nd->s);
 			free(nd);
 			return (NULL);
@@ -170,6 +185,58 @@ nb_dns_init(char *errstr)
 	return (NULL);
 }
 
+struct nb_dns_info *
+nb_dns_init2(char *errstr, struct sockaddr* sa)
+{
+	register struct nb_dns_info *nd;
+
+	nd = (struct nb_dns_info *)malloc(sizeof(*nd));
+	if (nd == NULL) {
+		snprintf(errstr, NB_DNS_ERRSIZE, "nb_dns_init: malloc(): %s",
+		    my_strerror(errno));
+		return (NULL);
+	}
+	memset(nd, 0, sizeof(*nd));
+	nd->s = -1;
+
+	if ( sa->sa_family == AF_INET )
+		{
+		memcpy(&nd->server, sa, sizeof(struct sockaddr_in));
+		((struct sockaddr_in*)&nd->server)->sin_port = htons(53);
+		}
+	else
+		{
+		memcpy(&nd->server, sa, sizeof(struct sockaddr_in6));
+		((struct sockaddr_in6*)&nd->server)->sin6_port = htons(53);
+		}
+
+	nd->s = socket(nd->server.ss_family, SOCK_DGRAM, 0);
+
+	if ( nd->s < 0 )
+		{
+		snprintf(errstr, NB_DNS_ERRSIZE, "socket(): %s",
+		         my_strerror(errno));
+		free(nd);
+		return (NULL);
+		}
+
+	if ( connect(nd->s, (struct sockaddr *)&nd->server,
+	             nd->server.ss_family == AF_INET ?
+	                       sizeof(struct sockaddr_in) :
+	                       sizeof(struct sockaddr_in6)) < 0 )
+		{
+		char s[INET6_ADDRSTRLEN];
+		sa_ntop((struct sockaddr*)&nd->server, s, INET6_ADDRSTRLEN);
+		snprintf(errstr, NB_DNS_ERRSIZE, "connect(%s): %s", s,
+		         my_strerror(errno));
+		close(nd->s);
+		free(nd);
+		return (NULL);
+		}
+
+	return (nd);
+}
+
 void
 nb_dns_finish(struct nb_dns_info *nd)
 {
@@ -226,12 +293,12 @@ _nb_dns_cmpsockaddr(register struct sockaddr *sa1,
 		sin6a = (struct sockaddr_in6 *)sa1;
 		sin6b = (struct sockaddr_in6 *)sa2;
 		if (sin6a->sin6_port != sin6b->sin6_port) {
-			snprintf(errstr, NB_DNS_ERRSIZE, serr, 2);
+			snprintf(errstr, NB_DNS_ERRSIZE, serr, 62);
 			return (-1);
 		}
 		if (memcmp(&sin6a->sin6_addr, &sin6b->sin6_addr,
 		    sizeof(sin6a->sin6_addr)) != 0) {
-			snprintf(errstr, NB_DNS_ERRSIZE, serr, 3);
+			snprintf(errstr, NB_DNS_ERRSIZE, serr, 63);
 			return (-1);
 		}
 		break;
@@ -446,7 +513,7 @@ nb_dns_activity(struct nb_dns_info *nd, struct nb_dns_result *nr, char *errstr)
 	register int msglen, qtype, atype, n, i;
 	register struct nb_dns_entry *ne, *lastne;
 	socklen_t fromlen;
-	struct sockaddr from;
+	struct sockaddr_storage from;
 	u_long msg[MAXPACKET / sizeof(u_long)];
 	register char *bp, *ep;
 	register char **ap, **hap;
@@ -460,7 +527,8 @@ nb_dns_activity(struct nb_dns_info *nd, struct nb_dns_result *nr, char *errstr)
 
 	/* This comes from the second half of do_query() */
 	fromlen = sizeof(from);
-	msglen = recvfrom(nd->s, (char *)msg, sizeof(msg), 0, &from, &fromlen);
+	msglen = recvfrom(nd->s, (char *)msg, sizeof(msg), 0,
+	                  (struct sockaddr*)&from, &fromlen);
 	if (msglen <= 0) {
 		snprintf(errstr, NB_DNS_ERRSIZE, "recvfrom(): %s",
 		    my_strerror(errno));
@@ -479,8 +547,8 @@ nb_dns_activity(struct nb_dns_info *nd, struct nb_dns_result *nr, char *errstr)
 	}
 
 	/* RES_INSECURE1 style check */
-	if (_nb_dns_cmpsockaddr((struct sockaddr *)&nd->server, &from,
-	    errstr) < 0) {
+	if (_nb_dns_cmpsockaddr((struct sockaddr*)&nd->server,
+	                        (struct sockaddr*)&from, errstr) < 0) {
 		nr->host_errno = NO_RECOVERY;
 		return (-1);
 	}

src/nb_dns.h

@@ -17,6 +17,7 @@ typedef unsigned int nb_uint32_t;
 
 /* Public routines */
 struct nb_dns_info *nb_dns_init(char *);
+struct nb_dns_info *nb_dns_init2(char *, struct sockaddr*);
 void nb_dns_finish(struct nb_dns_info *);
 
 int nb_dns_fd(struct nb_dns_info *);