From 49bdf1ead9046c5c554c18ff62fe6e6a9e8a880c Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Petr=20Men=C5=A1=C3=ADk?= <pemensik@redhat.com>
Date: Mon, 15 Jul 2019 17:13:12 +0200
Subject: [PATCH] Handle listening on duplicate addresses

Save listening address into listener. Use it to find existing listeners
before creating new one. If it exist, increase just used counter.
Release only listeners not already used.

Duplicates family in listener.
---
 src/dnsmasq.h |   3 +-
 src/network.c | 125 ++++++++++++++++++++++++++++++++++++--------------
 2 files changed, 93 insertions(+), 35 deletions(-)

diff --git a/src/dnsmasq.h b/src/dnsmasq.h
index b877fbb..4f2874f 100644
--- a/src/dnsmasq.h
+++ b/src/dnsmasq.h
@@ -572,7 +572,8 @@ struct irec {
 };
 
 struct listener {
-  int fd, tcpfd, tftpfd, family;
+  int fd, tcpfd, tftpfd, family, used;
+  union mysockaddr addr;
   struct irec *iface; /* only sometimes valid for non-wildcard */
   struct listener *next;
 };
diff --git a/src/network.c b/src/network.c
index 90fb3ae..7fe6e37 100644
--- a/src/network.c
+++ b/src/network.c
@@ -557,6 +557,58 @@ static void clean_interfaces()
   }
 }
 
+/** Release listener if no other interface needs it.
+ *
+ * @return 1 if released, 0 if still required
+ */
+static int release_listener(struct listener *l)
+{
+  if (l->used > 1)
+    {
+      struct irec *iface;
+      for (iface = daemon->interfaces; iface; iface = iface->next)
+	if (iface->done && sockaddr_isequal(&l->addr, &iface->addr))
+	  {
+	    if (iface->found)
+	      {
+		/* update listener to point to active interface instead */
+		if (!l->iface->found)
+		  l->iface = iface;
+	      }
+	    else
+	      {
+		l->used--;
+		iface->done = 0;
+	      }
+	  }
+
+      /* Someone is still using this listener, skip its deletion */
+      if (l->used > 0)
+	return 0;
+    }
+
+  if (l->iface->done)
+    {
+      int port;
+
+      port = prettyprint_addr(&l->iface->addr, daemon->addrbuff);
+      my_syslog(LOG_DEBUG, _("stopped listening on %s(#%d): %s port %d"),
+		l->iface->name, l->iface->index, daemon->addrbuff, port);
+      /* In case it ever returns */
+      l->iface->done = 0;
+    }
+
+  if (l->fd != -1)
+    close(l->fd);
+  if (l->tcpfd != -1)
+    close(l->tcpfd);
+  if (l->tftpfd != -1)
+    close(l->tftpfd);
+
+  free(l);
+  return 1;
+}
+
 int enumerate_interfaces(int reset)
 {
   static struct addrlist *spare = NULL;
@@ -662,29 +714,10 @@ int enumerate_interfaces(int reset)
 	  
 	  if (!l->iface || l->iface->found)
 	    up = &l->next;
-	  else
+	  else if (release_listener(l))
 	    {
-	      *up = l->next;
-	      if (l->iface->done)
-	        {
-	          iface = l->iface;
-	          (void)prettyprint_addr(&iface->addr, daemon->addrbuff);
-	          my_syslog(LOG_DEBUG, _("stopped listening on %s(#%d): %s"),
-	                    iface->name, iface->index, daemon->addrbuff);
-	        }
-	      
-	      /* In case it ever returns */
-	      l->iface->done = 0;
-	      
-	      if (l->fd != -1)
-		close(l->fd);
-	      if (l->tcpfd != -1)
-		close(l->tcpfd);
-	      if (l->tftpfd != -1)
-		close(l->tftpfd);
-	      
-	      free(l);
-	      freed = 1;
+	      *up = tmp;
+		freed = 1;
 	    }
 	}
 
@@ -934,7 +967,9 @@ static struct listener *create_listeners(union mysockaddr *addr, int do_tftp, in
       l->family = addr->sa.sa_family;
       l->fd = fd;
       l->tcpfd = tcpfd;
-      l->tftpfd = tftpfd;	
+      l->tftpfd = tftpfd;
+      l->addr = *addr;
+      l->used = 1;
       l->iface = NULL;
     }
 
@@ -973,23 +1008,43 @@ void create_wildcard_listeners(void)
   daemon->listeners = l;
 }
 
+static struct listener *find_listener(union mysockaddr *addr)
+{
+  struct listener *l;
+  for (l = daemon->listeners; l; l = l->next)
+    if (sockaddr_isequal(&l->addr, addr))
+      return l;
+  return NULL;
+}
+
 void create_bound_listeners(int dienow)
 {
   struct listener *new;
   struct irec *iface;
   struct iname *if_tmp;
+  struct listener *existing;
 
   for (iface = daemon->interfaces; iface; iface = iface->next)
-    if (!iface->done && !iface->dad && iface->found &&
-	(new = create_listeners(&iface->addr, iface->tftp_ok, dienow)))
+    if (!iface->done && !iface->dad && iface->found)
       {
-	new->iface = iface;
-	new->next = daemon->listeners;
-	daemon->listeners = new;
-	iface->done = 1;
-	(void)prettyprint_addr(&iface->addr, daemon->addrbuff);
-	my_syslog(LOG_DEBUG, _("listening on %s(#%d): %s"),
-	          iface->name, iface->index, daemon->addrbuff);
+	existing = find_listener(&iface->addr);
+	if (existing)
+	  {
+	    iface->done = 1;
+	    existing->used++; /* increase usage counter */
+	  }
+	else if ((new = create_listeners(&iface->addr, iface->tftp_ok, dienow)))
+	  {
+	    int port;
+
+	    new->iface = iface;
+	    new->next = daemon->listeners;
+	    daemon->listeners = new;
+	    iface->done = 1;
+	    port = prettyprint_addr(&iface->addr, daemon->addrbuff);
+	    my_syslog(LOG_DEBUG, _("listening on %s(#%d): %s port %d"),
+		      iface->name, iface->index, daemon->addrbuff, port);
+	  }
       }
 
   /* Check for --listen-address options that haven't been used because there's
@@ -1007,10 +1062,12 @@ void create_bound_listeners(int dienow)
     if (!if_tmp->used && 
 	(new = create_listeners(&if_tmp->addr, !!option_bool(OPT_TFTP), dienow)))
       {
+	int port;
+
 	new->next = daemon->listeners;
 	daemon->listeners = new;
-	(void)prettyprint_addr(&if_tmp->addr, daemon->addrbuff);
-	my_syslog(LOG_DEBUG, _("listening on %s"), daemon->addrbuff);
+	port = prettyprint_addr(&if_tmp->addr, daemon->addrbuff);
+	my_syslog(LOG_DEBUG, _("listening on %s port %d"), daemon->addrbuff, port);
       }
 }