Allow to provide multiple host names

Author: David Graeff

README.md

@@ -64,6 +64,13 @@ enable LLMNR name resolution over IPv6 use:
 $ llmnrd -6
 ```
 
+By default, `llmnrd` respond to name requests matching the systems hostname.
+Provide one or more additional names via the `-H` argument:
+
+```
+$ llmnrd -H a_name -H another_name
+```
+
 Use `llmnrd --help` to show additional usage information.
 
 Additionally, the `llmnr-query` utility is shipped together with llmnrd and

llmnr.c

@@ -40,38 +40,73 @@
 
 static bool llmnr_ipv6 = false;
 /* Host name in DNS name format (length octet + name + 0 byte) */
-static char llmnr_hostname[LLMNR_LABEL_MAX_SIZE + 2];
+#define LLMNR_LABEL_LEN (LLMNR_LABEL_MAX_SIZE + 2)
+static char** llmnr_hostnames = NULL;
+int llmnr_hostname_count = 0;
+
+static void set_hostname(int entry_index, const char *hostname)
+{
+	char* entry_llmnr_hostname = NULL;
+
+	llmnr_hostnames[entry_index] = xzalloc(LLMNR_LABEL_LEN);
+	entry_llmnr_hostname = llmnr_hostnames[entry_index];
+
+	entry_llmnr_hostname[0] = strlen(hostname);
+	strncpy(&entry_llmnr_hostname[1], hostname, LLMNR_LABEL_MAX_SIZE);
+	entry_llmnr_hostname[LLMNR_LABEL_MAX_SIZE + 1] = '\0';
+}
 
 void llmnr_set_hostname(const char *hostname)
 {
-	llmnr_hostname[0] = strlen(hostname);
-	strncpy(&llmnr_hostname[1], hostname, LLMNR_LABEL_MAX_SIZE);
-	llmnr_hostname[LLMNR_LABEL_MAX_SIZE + 1] = '\0';
+	set_hostname(0, hostname);
 }
 
-void llmnr_init(const char *hostname, bool ipv6)
+void llmnr_init(const char *hostnames[], int hostname_count, bool ipv6)
 {
-	llmnr_set_hostname(hostname);
+	int name_i = 0;
+	llmnr_hostname_count = hostname_count;
+	llmnr_hostnames = xzalloc(hostname_count);
+	for (;name_i < hostname_count; ++name_i) {
+		set_hostname(name_i, hostnames[name_i]);
+	}
 	llmnr_ipv6 = ipv6;
 }
 
-static bool llmnr_name_matches(const uint8_t *query)
+void llmnr_release() {
+	int name_i = 0;
+	for(; name_i < llmnr_hostname_count; ++name_i) {
+		free(llmnr_hostnames[name_i]);
+	}
+	free(llmnr_hostnames);
+}
+
+/* Return the matched name entry (first byte represents the string length) or NULL */
+static char* llmnr_name_matches(const uint8_t *query)
 {
-	uint8_t n = llmnr_hostname[0];
+    uint8_t n;
+    int name_i = 0;
+
+    for(; name_i < llmnr_hostname_count; ++name_i) {
+        n = llmnr_hostnames[name_i][0];
+
+        /* length */
+        if (query[0] != n)
+            continue;
+        /* NULL byte */
+        if (query[1 + n] != 0)
+            continue;
+
+        if (strncasecmp((const char *)&query[1], &llmnr_hostnames[name_i][1], n) == 0)
+            return llmnr_hostnames[name_i];
+    }
 
-	/* length */
-	if (query[0] != n)
-		return false;
-	/* NULL byte */
-	if (query[1 + n] != 0)
-		return false;
 
-	return strncasecmp((const char *)&query[1], &llmnr_hostname[1], n) == 0;
+	return NULL;
 }
 
 static void llmnr_respond(unsigned int ifindex, const struct llmnr_hdr *hdr,
 			  const uint8_t *query, size_t query_len, int sock,
-			  const struct sockaddr_storage *sst)
+			  const struct sockaddr_storage *sst, char* matched_hostname_entry)
 {
 	uint16_t qtype, qclass;
 	uint8_t name_len = query[0];
@@ -164,7 +199,7 @@ static void llmnr_respond(unsigned int ifindex, const struct llmnr_hdr *hdr,
 
 		/* NAME */
 		if (i == 0)
-			memcpy(pkt_put(p, llmnr_hostname[0] + 2), llmnr_hostname, llmnr_hostname[0] + 2);
+			memcpy(pkt_put(p, matched_hostname_entry[0] + 2), matched_hostname_entry, matched_hostname_entry[0] + 2);
 		else {
 			/* message compression (RFC 1035, section 4.1.3) */
 			uint16_t ptr = 0xC000 | (sizeof(*hdr) + query_len);
@@ -196,6 +231,7 @@ static void llmnr_packet_process(int ifindex, const uint8_t *pktbuf, size_t len,
 	const uint8_t *query;
 	size_t query_len;
 	uint8_t name_len;
+    char* matched_hostname_entry;
 
 	/* Query too short? */
 	if (len < sizeof(struct llmnr_hdr))
@@ -218,8 +254,9 @@ static void llmnr_packet_process(int ifindex, const uint8_t *pktbuf, size_t len,
 		return;
 
 	/* Authoritative? */
-	if (llmnr_name_matches(query))
-		llmnr_respond(ifindex, hdr, query, query_len, sock, sst);
+	matched_hostname_entry = llmnr_name_matches(query);
+	if (matched_hostname_entry)
+		llmnr_respond(ifindex, hdr, query, query_len, sock, sst, matched_hostname_entry);
 }
 
 void llmnr_recv(int sock)

llmnr.h

@@ -22,7 +22,8 @@
 #include <stdbool.h>
 
 void llmnr_set_hostname(const char *hostname);
-void llmnr_init(const char *hostname, bool ipv6);
+void llmnr_init(const char *hostnames[], int hostname_count, bool ipv6);
+void llmnr_release(void);
 void llmnr_recv(int sock);
 
 #endif /* LLMNR_H */

llmnrd.c

@@ -187,7 +187,8 @@ int main(int argc, char **argv)
 	int c, ret = -1;
 	long num_arg;
 	bool daemonize = false, ipv6 = false;
-	char *hostname = NULL;
+	char **hostnames = NULL;
+	int name_count = 0, name_i = 0;
 	char *iface = NULL;
 	uint16_t port = LLMNR_UDP_PORT;
 	int llmnrd_sock_rtnl = -1;
@@ -196,6 +197,17 @@ int main(int argc, char **argv)
 
 	setlinebuf(stdout);
 
+	/* First count given (host)names, if any, to allocate memory */
+	while ((c = getopt_long(argc, argv, short_opts, long_opts, NULL)) != -1) {
+		if (c == 'H')
+			++name_count;
+	}
+
+	if (!name_count)
+		name_count = 1;
+	hostnames = xzalloc(name_count);
+
+	optind = 1;
 	while ((c = getopt_long(argc, argv, short_opts, long_opts, NULL)) != -1) {
 		switch (c) {
 		case 'd':
@@ -206,7 +218,8 @@ int main(int argc, char **argv)
 			log_to_syslog();
 			break;
 		case 'H':
-			hostname = xstrdup(optarg);
+			hostnames[name_i] = xstrdup(optarg);
+			++name_i;
 			break;
 		case 'i':
 			iface = xstrdup(optarg);
@@ -236,13 +249,13 @@ int main(int argc, char **argv)
 	register_signal(SIGTERM, signal_handler);
 	register_signal(SIGHUP, signal_handler);
 
-	if (!hostname) {
-		hostname = xzalloc(MAXHOSTNAMELEN);
-		if (gethostname(hostname, MAXHOSTNAMELEN) != 0) {
+	if (name_i == 0) {
+		hostnames[0] = xzalloc(MAXHOSTNAMELEN);
+		if (gethostname(hostnames[0], MAXHOSTNAMELEN) != 0) {
 			log_err("Failed to get hostname");
 			return EXIT_FAILURE;
 		}
-		hostname[MAXHOSTNAMELEN - 1] = '\0';
+		hostnames[0][MAXHOSTNAMELEN - 1] = '\0';
 
 		llmnrd_fd_hostname = open("/proc/sys/kernel/hostname", O_RDONLY|O_CLOEXEC|O_NDELAY);
 	}
@@ -257,7 +270,11 @@ int main(int argc, char **argv)
 		rm_pid_file = true;
 	}
 
-	log_info("Starting llmnrd on port %u, hostname %s\n", port, hostname);
+	log_info("Starting llmnrd on port %u, hostname(s): ", port);
+    for(name_i = 0; name_i < name_count; ++name_i)
+        log_info("%s ", hostnames[name_i]);
+    log_info("\n");
+
 	if (iface)
 		log_info("Binding to interface %s\n", iface);
 
@@ -275,7 +292,7 @@ int main(int argc, char **argv)
 	if (llmnrd_sock_rtnl < 0)
 		goto out;
 
-	llmnr_init(hostname, ipv6);
+	llmnr_init((const char **) hostnames, name_count, ipv6);
 
 	ret = iface_init(llmnrd_sock_rtnl, iface, ipv6, &iface_event_handle);
 	if (ret < 0)
@@ -318,7 +335,7 @@ int main(int argc, char **argv)
 			if (llmnrd_sock_ipv6 >= 0 && FD_ISSET(llmnrd_sock_ipv6, &rfds))
 				llmnr_recv(llmnrd_sock_ipv6);
 			if (llmnrd_fd_hostname >= 0 && FD_ISSET(llmnrd_fd_hostname, &efds))
-				hostname_change_handle(hostname, MAXHOSTNAMELEN);
+				hostname_change_handle(hostnames[0], MAXHOSTNAMELEN);
 		}
 	}
 
@@ -332,7 +349,11 @@ int main(int argc, char **argv)
 		close(llmnrd_sock_ipv6);
 	if (llmnrd_sock_ipv4 >= 0)
 		close(llmnrd_sock_ipv4);
-	free(hostname);
+	for(name_i = 0; name_i < name_count; ++name_i) {
+		free(hostnames[name_i]);
+	}
+	free(hostnames);
+	llmnr_release();
 	if (rm_pid_file)
 		unlink(PIDFILE);
 	return ret == 0 ? EXIT_SUCCESS : EXIT_FAILURE;