Log SO_BINDTODEVICE use at startup.

src/dhcp-common.c

@@ -444,7 +444,7 @@ void dhcp_update_configs(struct dhcp_config *configs)
 }
 
 #ifdef HAVE_LINUX_NETWORK 
-void bindtodevice(int fd)
+char *whichdevice(void)
 {
   /* If we are doing DHCP on exactly one interface, and running linux, do SO_BINDTODEVICE
      to that device. This is for the use case of  (eg) OpenStack, which runs a new
@@ -461,11 +461,11 @@ void bindtodevice(int fd)
   struct iname *if_tmp;
   
   if (!daemon->if_names)
-    return;
+    return NULL;
   
   for (if_tmp = daemon->if_names; if_tmp; if_tmp = if_tmp->next)
     if (if_tmp->name && (!if_tmp->used || strchr(if_tmp->name, '*')))
-      return;
+      return NULL;
 
   for (found = NULL, iface = daemon->interfaces; iface; iface = iface->next)
     if (iface->dhcp_ok)
@@ -473,18 +473,24 @@ void bindtodevice(int fd)
 	if (!found)
 	  found = iface;
 	else if (strcmp(found->name, iface->name) != 0) 
-	  return; /* more than one. */
+	  return NULL; /* more than one. */
       }
 
   if (found)
-    {
-      struct ifreq ifr;
-      strcpy(ifr.ifr_name, found->name);
-      /* only allowed by root. */
-      if (setsockopt(fd, SOL_SOCKET, SO_BINDTODEVICE, (void *)&ifr, sizeof(ifr)) == -1 &&
-	  errno != EPERM)
-	die(_("failed to set SO_BINDTODEVICE on DHCP socket: %s"), NULL, EC_BADNET);
-    }
+    return found->name;
+
+  return NULL;
+}
+ 
+void  bindtodevice(char *device, int fd)
+{
+  struct ifreq ifr;
+  
+  strcpy(ifr.ifr_name, device);
+  /* only allowed by root. */
+  if (setsockopt(fd, SOL_SOCKET, SO_BINDTODEVICE, (void *)&ifr, sizeof(ifr)) == -1 &&
+      errno != EPERM)
+    die(_("failed to set SO_BINDTODEVICE on DHCP socket: %s"), NULL, EC_BADNET);
 }
 #endif
 

src/dnsmasq.c

@@ -50,6 +50,8 @@ int main (int argc, char **argv)
 #if defined(HAVE_LINUX_NETWORK)
   cap_user_header_t hdr = NULL;
   cap_user_data_t data = NULL;
+  char *bound_device = NULL;
+  int did_bind = 0;
 #endif 
 #if defined(HAVE_DHCP) || defined(HAVE_DHCP6)
   struct dhcp_context *context;
@@ -239,18 +241,29 @@ int main (int argc, char **argv)
 
 #if defined(HAVE_LINUX_NETWORK) && defined(HAVE_DHCP)
       /* after enumerate_interfaces()  */
+      bound_device = whichdevice();
+      
       if (daemon->dhcp)
 	{
-	  if (!daemon->relay4)
-	    bindtodevice(daemon->dhcpfd);
-	  if (daemon->enable_pxe)
-	    bindtodevice(daemon->pxefd);
+	  if (!daemon->relay4 && bound_device)
+	    {
+	      bindtodevice(bound_device, daemon->dhcpfd);
+	      did_bind = 1;
+	    }
+	  if (daemon->enable_pxe && bound_device)
+	    {
+	      bindtodevice(bound_device, daemon->pxefd);
+	      did_bind = 1;
+	    }
 	}
 #endif
 
 #if defined(HAVE_LINUX_NETWORK) && defined(HAVE_DHCP6)
-      if (daemon->doing_dhcp6 && !daemon->relay6)
-	bindtodevice(daemon->dhcp6fd);
+      if (daemon->doing_dhcp6 && !daemon->relay6 && bound_device)
+	{
+	  bindtodevice(bound_device, daemon->dhcp6fd);
+	  did_bind = 1;
+	}
 #endif
     }
   else 
@@ -659,6 +672,11 @@ int main (int argc, char **argv)
     my_syslog(MS_DHCP | LOG_INFO, _("IPv6 router advertisement enabled"));
 #  endif
 
+#  ifdef HAVE_LINUX_NETWORK
+  if (did_bind)
+    my_syslog(MS_DHCP | LOG_INFO, _("DHCP, sockets bound exclusively to interface %s"), bound_device);
+#  endif
+
   /* after dhcp_contruct_contexts */
   if (daemon->dhcp || daemon->doing_dhcp6)
     lease_find_interfaces(now);

src/dnsmasq.h

@@ -1268,7 +1268,8 @@ struct dhcp_config *find_config(struct dhcp_config *configs,
 				int hw_type, char *hostname);
 int config_has_mac(struct dhcp_config *config, unsigned char *hwaddr, int len, int type);
 #ifdef HAVE_LINUX_NETWORK
-void bindtodevice(int fd);
+char *whichdevice(void);
+void bindtodevice(char *device, int fd);
 #endif
 #  ifdef HAVE_DHCP6
 void display_opts6(void);