From 2675f2061525bc954be14988d64384b74aa7bf8b Mon Sep 17 00:00:00 2001
From: Beniamino Galvani <bgalvani@redhat.com>
Date: Sun, 28 Aug 2016 20:44:05 +0100
Subject: [PATCH] Handle binding upstream servers to an interface
 (--server=1.2.3.4@eth0) when the named interface is destroyed and recreated
 in the kernel.

---
 CHANGELOG     |  5 +++++
 src/dnsmasq.h |  1 +
 src/network.c | 31 +++++++++++++++++++++++++++++--
 3 files changed, 35 insertions(+), 2 deletions(-)

diff --git a/src/dnsmasq.h b/src/dnsmasq.h
index 27385a9..f239ce5 100644
--- a/src/dnsmasq.h
+++ b/src/dnsmasq.h
@@ -488,6 +488,7 @@ struct serverfd {
   int fd;
   union mysockaddr source_addr;
   char interface[IF_NAMESIZE+1];
+  unsigned int ifindex, used;
   struct serverfd *next;
 };
 
diff --git a/src/network.c b/src/network.c
index e7722fd..ddf8d31 100644
--- a/src/network.c
+++ b/src/network.c
@@ -1204,6 +1204,7 @@ int local_bind(int fd, union mysockaddr *addr, char *intname, int is_tcp)
 static struct serverfd *allocate_sfd(union mysockaddr *addr, char *intname)
 {
   struct serverfd *sfd;
+  unsigned int ifindex = 0;
   int errsave;
 
   /* when using random ports, servers which would otherwise use
@@ -1224,11 +1225,15 @@ static struct serverfd *allocate_sfd(union mysockaddr *addr, char *intname)
 	return NULL;
 #endif
     }
+
+  if (intname && strlen(intname) != 0)
+    ifindex = if_nametoindex(intname); /* index == 0 when not binding to an interface */
       
   /* may have a suitable one already */
   for (sfd = daemon->sfds; sfd; sfd = sfd->next )
     if (sockaddr_isequal(&sfd->source_addr, addr) &&
-	strcmp(intname, sfd->interface) == 0)
+	strcmp(intname, sfd->interface) == 0 &&
+	ifindex == sfd->ifindex) 
       return sfd;
   
   /* need to make a new one. */
@@ -1250,11 +1255,13 @@ static struct serverfd *allocate_sfd(union mysockaddr *addr, char *intname)
       errno = errsave;
       return NULL;
     }
-    
+
   strcpy(sfd->interface, intname); 
   sfd->source_addr = *addr;
   sfd->next = daemon->sfds;
+  sfd->ifindex = ifindex;
   daemon->sfds = sfd;
+
   return sfd; 
 }
 
@@ -1429,12 +1436,16 @@ void check_servers(void)
 {
   struct irec *iface;
   struct server *serv;
+  struct serverfd *sfd, *tmp, **up;
   int port = 0, count;
 
   /* interface may be new since startup */
   if (!option_bool(OPT_NOWILD))
     enumerate_interfaces(0);
   
+  for (sfd = daemon->sfds; sfd; sfd = sfd->next)
+    sfd->used = 0;
+
 #ifdef HAVE_DNSSEC
  /* Disable DNSSEC validation when using server=/domain/.... servers
     unless there's a configured trust anchor. */
@@ -1505,6 +1516,8 @@ void check_servers(void)
 	      serv->flags |= SERV_MARK;
 	      continue;
 	    }
+
+	  serv->sfd->used = 1;
 	}
       
       if (!(serv->flags & SERV_NO_REBIND) && !(serv->flags & SERV_LITERAL_ADDRESS))
@@ -1547,6 +1560,20 @@ void check_servers(void)
   if (count - 1 > SERVERS_LOGGED)
     my_syslog(LOG_INFO, _("using %d more nameservers"), count - SERVERS_LOGGED - 1);
 
+  /* Remove unused sfds */
+  for (sfd = daemon->sfds, up = &daemon->sfds; sfd; sfd = tmp)
+    {
+       tmp = sfd->next;
+       if (!sfd->used) 
+	{
+	  *up = sfd->next;
+	  close(sfd->fd);
+	  free(sfd);
+	} 
+      else
+	up = &sfd->next;
+    }
+  
   cleanup_servers();
 }
 
-- 
2.7.4