Fix bind_interface option.

Closes #1999. Thanks to Joerg55.

ChangeLog.txt

@@ -8,6 +8,7 @@ Broker:
 - Fix apparmor incorrectly denying access to
  /var/lib/mosquitto/mosquitto.db.new. Closes #1978.
 - Fix potential intermittent initial bridge connections when using poll().
+- Fix `bind_interface` option. Closes #1999.
 
 Apps:
 - Disallow control characters in mosquitto_passwd usernames.

man/mosquitto.conf.5.xml

@@ -1035,21 +1035,13 @@ log_timestamp_format %Y-%m-%dT%H:%M:%S
  <option>bind_address</option> option but is useful
  when an interface has multiple addresses or the
  address may change.</para>
- <para>It is valid to use this option together with
+ <para>If used at the same time as the
  <option>bind_address</option> for the default
  listener, or the <replaceable>bind
- address/host</replaceable> part of the
- <option>listener</option> definition. Care should
- be taken to ensure that the address being bound to
- is on the interface being bound to. If you set the
- <option>bind_interface</option> to be
- <replaceable>eth0</replaceable>, and
- <option>bind_address</option> to
- <replaceable>127.0.0.1</replaceable>, then the
- broker will start correctly but you will be unable
- to connect.</para>
- <para>This option is currently only available on
- Linux, and requires elevated privileges.</para>
+ address/host</replaceable> part of the
+ <option>listener</option>, then <option>bind_interface</option>
+ will take priority.</para>
+ <para>This option is not available on Windows.</para>
  <para>Not reloaded on reload signal.</para>
  </listitem>
  </varlistentry>

mosquitto.conf

@@ -229,11 +229,10 @@
 
 # Bind the listener to a specific interface. This is similar to
 # the [ip address/host name] part of the listener definition, but is useful
-# when an interface has multiple addresses or the address may change. It is
-# valid to use this with the [ip address/host name] part of the listener
-# definition, but take care that the interface you are binding to contains the
-# address you are binding to, otherwise you will not be able to connect.
-# Only available on Linux and requires elevated privileges.
+# when an interface has multiple addresses or the address may change. If used
+# with the [ip address/host name] part of the listener definition, then the
+# bind_interface option will take priority.
+# Not available on Windows.
 #
 # Example: bind_interface eth0
 #bind_interface

src/net.c

@@ -24,7 +24,7 @@ SPDX-License-Identifier: EPL-2.0 OR EDL-1.0
 #include <arpa/inet.h>
 #include <sys/socket.h>
 #include <netinet/tcp.h>
-#include <net/if.h>
+#include <ifaddrs.h>
 #else
 #include <winsock2.h>
 #include <ws2tcpip.h>
@@ -607,6 +607,52 @@ int net__tls_load_verify(struct mosquitto__listener *listener)
 }
 
 
+#ifndef WIN32
+static int net__bind_interface(struct mosquitto__listener *listener, mosq_sock_t sock, struct addrinfo *rp)
+{
+ /*
+ * This binds the listener sock to a network interface.
+ * The use of SO_BINDTODEVICE requires root access, which we don't have, so instead
+ * use getifaddrs to find the interface addresses, and attempt to bind to
+ * the IP of the matching interface.
+ */
+ struct ifaddrs *ifaddr, *ifa;
+ if(getifaddrs(&ifaddr) < 0){
+ net__print_error(MOSQ_LOG_ERR, "Error: %s");
+ return MOSQ_ERR_ERRNO;
+ }
+
+ for(ifa=ifaddr; ifa!=NULL; ifa=ifa->ifa_next){
+ if(ifa->ifa_addr == NULL){
+ continue;
+ }
+
+ if(!strcasecmp(listener->bind_interface, ifa->ifa_name)
+ && ifa->ifa_addr->sa_family == rp->ai_addr->sa_family){
+
+ if(rp->ai_addr->sa_family == AF_INET){
+ memcpy(&((struct sockaddr_in *)rp->ai_addr)->sin_addr,
+ &((struct sockaddr_in *)ifa->ifa_addr)->sin_addr,
+ sizeof(struct in_addr));
+
+ freeifaddrs(ifaddr);
+ return MOSQ_ERR_SUCCESS;
+ }else if(rp->ai_addr->sa_family == AF_INET6){
+ memcpy(&((struct sockaddr_in6 *)rp->ai_addr)->sin6_addr,
+ &((struct sockaddr_in6 *)ifa->ifa_addr)->sin6_addr,
+ sizeof(struct in6_addr));
+ freeifaddrs(ifaddr);
+ return MOSQ_ERR_SUCCESS;
+ }
+ }
+ }
+ freeifaddrs(ifaddr);
+ log__printf(NULL, MOSQ_LOG_ERR, "Error: Interface %s not found.", listener->bind_interface);
+ return MOSQ_ERR_NOT_FOUND;
+}
+#endif
+
+
 static int net__socket_listen_tcp(struct mosquitto__listener *listener)
 {
  mosq_sock_t sock = INVALID_SOCKET;
@@ -615,9 +661,6 @@ static int net__socket_listen_tcp(struct mosquitto__listener *listener)
  char service[10];
  int rc;
  int ss_opt = 1;
-#ifdef SO_BINDTODEVICE
- struct ifreq ifr;
-#endif
 
  if(!listener) return MOSQ_ERR_INVAL;
 
@@ -680,14 +723,9 @@ static int net__socket_listen_tcp(struct mosquitto__listener *listener)
  return 1;
  }
 
-#ifdef SO_BINDTODEVICE
+#ifndef WIN32
  if(listener->bind_interface){
- memset(&ifr, 0, sizeof(ifr));
- strncpy(ifr.ifr_name, listener->bind_interface, sizeof(ifr.ifr_name)-1);
- ifr.ifr_name[sizeof(ifr.ifr_name)-1] = '\0';
- log__printf(NULL, MOSQ_LOG_INFO, "Binding listener to interface \"%s\".", ifr.ifr_name);
- if(setsockopt(sock, SOL_SOCKET, SO_BINDTODEVICE, (void *)&ifr, sizeof(ifr)) < 0) {
- net__print_error(MOSQ_LOG_ERR, "Error: %s");
+ if(net__bind_interface(listener, sock, rp)){
  COMPAT_CLOSE(sock);
  freeaddrinfo(ainfo);
  mosquitto__free(listener->socks);