Hi Vladislav,

I think I found usable solution for duplicate addresses. I think there
is many list of interfaces without clear distinction between them. For
example, daemon->int_names contains all addresses quite similar to
daemon->interfaces. And there is also if_names and if_addrs. I were able
just decipher interfaces is always made from real interface names found
on system. No wildcards are used.

Anyway, made two new patches on top of previous. First includes address
in listener structure and check existing addresses before creating new
address. If there is already such listener, note it is used more times.
If one interface stops listening, do not stop listening yet until all
listeners end.

Because address includes family, patch 5 removes duplicate family. Made
that separate because it kind of cover what is important change.

Cheers,

Petr

On 7/11/19 12:23 PM, Petr Mensik wrote:
> Oh, tested it and confirm it breaks the same IP addreses listeners. If
> the same address is used, second address listener is not created
> successfully. It reports:
> 
> dnsmasq: failed to create listening socket for 10.129.1.1: Address
> already in use
> 
> When the first one is destroyed, second one cannot take over it.
> Unfortunately, it seems interfaces list works as unique addresses at the
> same time.
> 
> One possible solution is socket option SO_REUSEPORT, which would allow
> binding multiple times to the same address. However, it seems its
> support is not very portable, at least on stack overflow article. It
> might create more problem than it solves. I think its usage should be
> configurable. Not a good solution.
> 
> There is also secondary list in daemon->if_addrs, which maybe should be
> used instead to create real listeners. Now it creates listeners for
> explicitly given addresses without interface name.
> 
> Unless TCP queries should stop checking interface indexes, list of
> current indexes is required somewhere. I think daemon->interfaces is the
> best list for it. But when creating listeners, just single should be
> created for a shared address. Current structures do not allow such
> sharing AFAIK. Either irec should be only one for single physical
> interface and should have address records for each address nested.
> 
> I am looking on possible solutions. I do not have any good solution yet.
> I doubt it can be solved with as little changes as I used before.
> 
> 1.
> https://stackoverflow.com/questions/14388706/socket-options-so-reuseaddr-and-so-reuseport-how-do-they-differ-do-they-mean-t
> 
> On 7/10/19 1:34 PM, Vladislav Grishenko wrote:
>> Hi Petr,
>>
>>> Not tested this specific case, but I think it should be handled correctly, 
>>> unlike previous code. Because it now compares also interface index, it will 
>>> mark existing entry as found only if interface index also match. If it does 
>>> not, new entry is created with correct index instead.
>>
>> Checked, unfortunately interface index comparison breaks the things.
>> If there's 2+ interface with same address on startup, no error is happen, 
>> single TCP and multiple UDP (unlike before) sockets are created, on any of 
>> such interface shutdown - thins single TCP socket is closed (unlike before), 
>> so there are noting listens on TCP:53 after that.
>> If there's only one interface on startup - single TCP&UDP sockets are 
>> created, on subsequent interface up with the same address - bind error 
>> raised and only UDP socket is created additionally (unlike before).
>>
>> At the moment, dnsmasq logic expects single TCP/UDP socket per address even 
>> for multiple interfaces.
>> For example, comment in iface_allowed() states that:
>>      /* check whether the interface IP has been added already
>>       * we call this routine multiple times */
>> So, I'm afraid, seems proposed changes does not play well with that.
>> How do you think, can it be solved too?
>> Reproduction this case is quite easy, just need to create dummy interface 
>> with same address (different netmask) and up/down it.
>>
>>> Ok, I forgot to follow style on 3rd patch. Attached fixed formatting and 
>>> removed debug log on interface removal.
>>
>> Thanks,  fyi sed -r 's/[ ]{8}/\t/' is missed too.
>>
>>> I think that is better to state explicitly return value is not used.
>>
>> I think that would be better to rip it off from functional patch, and let it 
>> be as separate full patch for all prettyprint_* instances not just for some 
>> selected.
>> At the other hand, with no __attribute__((warn_unused_result)) it will not 
>> generate warning anyway.
>>
>> Best Regards, Vladislav Grishenko
>>
>> -----Original Message-----
>> From: Petr Mensik <pemen...@redhat.com> 
>> Sent: Wednesday, July 10, 2019 3:01 PM
>> To: Vladislav Grishenko <themiron...@gmail.com>; 
>> dnsmasq-discuss@lists.thekelleys.org.uk
>> Subject: Re: [Dnsmasq-discuss] [PATCH] Issues with TCP queries on recreated 
>> interfaces.
>>
>> Hi Vladislav
>>
>> On 7/9/19 10:00 PM, Vladislav Grishenko wrote:
>>> Hi Petr,
>>>
>>> Regarding 0002-Compare-address-and-interface-index-for-allowed-inte.patch, 
>>> does it support case with different valid interfaces with the same address?
>>> For example:
>>>     eth0 192.168.1.1/24
>>>     tun0 192.168.1.1./16 (created/destroyed dynamically)
>>
>> Not tested this specific case, but I think it should be handled correctly, 
>> unlike previous code. Because it now compares also interface index, it will 
>> mark existing entry as found only if interface index also match. If it does 
>> not, new entry is created with correct index instead.
>> It should work, unlike previous code, it should keep both interface 
>> addresses stored separately.
>>
>> If tun0 is often destroyed and recreated, number of interfaces records might 
>> grow. That is reason for patch #3, which removes dropped interfaces after 
>> creating new ones.
>>>
>>> Regarding appearance, seems newly added code doesn’t fully follow dnsmasq 
>>> code style in several places:
>>> * indentation (should be ident ==2 spaces, 8 spaces == \t)
>>> * brackets on the same code lines
>> Ok, I forgot to follow style on 3rd patch. Attached fixed formatting and 
>> removed debug log on interface removal.
>>> * function args on the next line are not aligned with the first 
>>> argument
>>> * prettyprint_addr() result is forcibly ignored with (void) unlike 
>>> other places
>> I think that is better to state explicitly return value is not used.
>>>
>>> Best Regards, Vladislav Grishenko
>>>
>>> -----Original Message-----
>>> From: Dnsmasq-discuss 
>>> <dnsmasq-discuss-boun...@lists.thekelleys.org.uk> On Behalf Of Petr 
>>> Mensik
>>> Sent: Tuesday, July 9, 2019 5:31 PM
>>> To: dnsmasq-discuss@lists.thekelleys.org.uk
>>> Subject: [Dnsmasq-discuss] [PATCH] Issues with TCP queries on recreated 
>>> interfaces.
>>>
>>> Hello Simon and others,
>>>
>>> we have discovered issues with TCP DNS query on dnsmasq, when running in 
>>> bind-dynamic or bind-interfaces mode. dnsmasq scans automatically new 
>>> interfaces or do that on new query in second case. However, because used 
>>> speedup comparing only IP adresses in iface_allowed function, it never gets 
>>> updated index of an interface.
>>>
>>> In case where named interface is destroyed and created again, that drops 
>>> TCP queries on that interface. They are checked for incoming interface 
>>> number. If such number is not found in interfaces list, query is denied.
>>>
>>> Luckily, there was a bug in checking, hiding this problem from usual 
>>> configuration. If IPv6 address is enabled on the new device, new iface 
>>> entry would be created, because scope_id of sockaddr_in6 does not match 
>>> previous. That makes even IPv4 queries succeed.
>>>
>>> Bug on bugzilla [1] is partly private.
>>>
>>> I propose three changes. First is just helper to log what happens with 
>>> listeners on bind-dynamic configuration.
>>>
>>> Second is the most important. Create new interface every time index 
>>> changes. Also test address family of incoming TCP query when checking 
>>> allowed clients.
>>>
>>> Third is cleanup of unused interfaces. On some virtual machines hosts, 
>>> interfaces may often be created and destroyed. It might have negative 
>>> effect on walking trough interfaces list. I think listeners should be 
>>> garbage collected also on bind-interfaces configuration. But for now, 
>>> release memory for unused interfaces at least for bind-dynamic.
>>>
>>> 1. https://bugzilla.redhat.com/show_bug.cgi?id=1721668
>>> --
>>> Petr Menšík
>>> Software Engineer
>>> Red Hat, http://www.redhat.com/
>>> email: pemen...@redhat.com  PGP: 65C6C973
>>>
>>
>> --
>> Petr Menšík
>> Software Engineer
>> Red Hat, http://www.redhat.com/
>> email: pemen...@redhat.com  PGP: 65C6C973
>>
> 

-- 
Petr Menšík
Software Engineer
Red Hat, http://www.redhat.com/
email: pemen...@redhat.com  PGP: 65C6C973
From 3bb9e937c811e4aca26d5efaa1cb8cf50cfdda43 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Petr=20Men=C5=A1=C3=ADk?= <pemen...@redhat.com>
Date: Mon, 15 Jul 2019 17:16:44 +0200
Subject: [PATCH 5/5] Remove duplicate address family from listener

Since address already contain family, remove separate family from
listener. Use now family from address itself.
---
 src/dnsmasq.h |  2 +-
 src/forward.c | 27 ++++++++++++++-------------
 src/network.c |  1 -
 src/tftp.c    | 29 +++++++++++++++--------------
 4 files changed, 30 insertions(+), 29 deletions(-)

diff --git a/src/dnsmasq.h b/src/dnsmasq.h
index f31ec6a..978d02f 100644
--- a/src/dnsmasq.h
+++ b/src/dnsmasq.h
@@ -563,7 +563,7 @@ struct irec {
 };
 
 struct listener {
-  int fd, tcpfd, tftpfd, family, used;
+  int fd, tcpfd, tftpfd, used;
   union mysockaddr addr;
   struct irec *iface; /* only sometimes valid for non-wildcard */
   struct listener *next;
diff --git a/src/forward.c b/src/forward.c
index dd22a45..d8bbe04 100644
--- a/src/forward.c
+++ b/src/forward.c
@@ -1271,8 +1271,9 @@ void receive_query(struct listener *listen, time_t now)
 		 CMSG_SPACE(sizeof(struct sockaddr_dl))];
 #endif
   } control_u;
+  int family = listen->addr.sa.sa_family;
    /* Can always get recvd interface for IPv6 */
-  int check_dst = !option_bool(OPT_NOWILD) || listen->family == AF_INET6;
+  int check_dst = !option_bool(OPT_NOWILD) || family == AF_INET6;
 
   /* packet buffer overwritten */
   daemon->srv_save = NULL;
@@ -1284,7 +1285,7 @@ void receive_query(struct listener *listen, time_t now)
     {
       auth_dns = listen->iface->dns_auth;
      
-      if (listen->family == AF_INET)
+      if (family == AF_INET)
 	{
 	  dst_addr_4 = dst_addr.addr4 = listen->iface->addr.in.sin_addr;
 	  netmask = listen->iface->netmask;
@@ -1314,9 +1315,9 @@ void receive_query(struct listener *listen, time_t now)
      information disclosure. */
   memset(daemon->packet + n, 0, daemon->edns_pktsz - n);
   
-  source_addr.sa.sa_family = listen->family;
+  source_addr.sa.sa_family = family;
   
-  if (listen->family == AF_INET)
+  if (family == AF_INET)
     {
        /* Source-port == 0 is an error, we can't send back to that. 
 	  http://www.ietf.org/mail-archive/web/dnsop/current/msg11441.html */
@@ -1336,7 +1337,7 @@ void receive_query(struct listener *listen, time_t now)
     {
       struct addrlist *addr;
 
-      if (listen->family == AF_INET6) 
+      if (family == AF_INET6) 
 	{
 	  for (addr = daemon->interface_addrs; addr; addr = addr->next)
 	    if ((addr->flags & ADDRLIST_IPV6) &&
@@ -1374,7 +1375,7 @@ void receive_query(struct listener *listen, time_t now)
 	return;
 
 #if defined(HAVE_LINUX_NETWORK)
-      if (listen->family == AF_INET)
+      if (family == AF_INET)
 	for (cmptr = CMSG_FIRSTHDR(&msg); cmptr; cmptr = CMSG_NXTHDR(&msg, cmptr))
 	  if (cmptr->cmsg_level == IPPROTO_IP && cmptr->cmsg_type == IP_PKTINFO)
 	    {
@@ -1387,7 +1388,7 @@ void receive_query(struct listener *listen, time_t now)
 	      if_index = p.p->ipi_ifindex;
 	    }
 #elif defined(IP_RECVDSTADDR) && defined(IP_RECVIF)
-      if (listen->family == AF_INET)
+      if (family == AF_INET)
 	{
 	  for (cmptr = CMSG_FIRSTHDR(&msg); cmptr; cmptr = CMSG_NXTHDR(&msg, cmptr))
 	    {
@@ -1412,7 +1413,7 @@ void receive_query(struct listener *listen, time_t now)
 	}
 #endif
       
-      if (listen->family == AF_INET6)
+      if (family == AF_INET6)
 	{
 	  for (cmptr = CMSG_FIRSTHDR(&msg); cmptr; cmptr = CMSG_NXTHDR(&msg, cmptr))
 	    if (cmptr->cmsg_level == IPPROTO_IPV6 && cmptr->cmsg_type == daemon->v6pktinfo)
@@ -1433,16 +1434,16 @@ void receive_query(struct listener *listen, time_t now)
       if (!indextoname(listen->fd, if_index, ifr.ifr_name))
 	return;
       
-      if (!iface_check(listen->family, &dst_addr, ifr.ifr_name, &auth_dns))
+      if (!iface_check(family, &dst_addr, ifr.ifr_name, &auth_dns))
 	{
 	   if (!option_bool(OPT_CLEVERBIND))
 	     enumerate_interfaces(0); 
-	   if (!loopback_exception(listen->fd, listen->family, &dst_addr, ifr.ifr_name) &&
-	       !label_exception(if_index, listen->family, &dst_addr))
+	   if (!loopback_exception(listen->fd, family, &dst_addr, ifr.ifr_name) &&
+	       !label_exception(if_index, family, &dst_addr))
 	     return;
 	}
 
-      if (listen->family == AF_INET && option_bool(OPT_LOCALISE))
+      if (family == AF_INET && option_bool(OPT_LOCALISE))
 	{
 	  struct irec *iface;
 	  
@@ -1487,7 +1488,7 @@ void receive_query(struct listener *listen, time_t now)
 #endif
       char *types = querystr(auth_dns ? "auth" : "query", type);
       
-      if (listen->family == AF_INET) 
+      if (family == AF_INET) 
 	log_query(F_QUERY | F_IPV4 | F_FORWARD, daemon->namebuff, 
 		  (union all_addr *)&source_addr.in.sin_addr, types);
       else
diff --git a/src/network.c b/src/network.c
index fc2af05..c57d06c 100644
--- a/src/network.c
+++ b/src/network.c
@@ -960,7 +960,6 @@ static struct listener *create_listeners(union mysockaddr *addr, int do_tftp, in
     {
       l = safe_malloc(sizeof(struct listener));
       l->next = NULL;
-      l->family = addr->sa.sa_family;
       l->fd = fd;
       l->tcpfd = tcpfd;
       l->tftpfd = tftpfd;
diff --git a/src/tftp.c b/src/tftp.c
index 435b216..13b2bc0 100644
--- a/src/tftp.c
+++ b/src/tftp.c
@@ -60,8 +60,9 @@ void tftp_request(struct listener *listen, time_t now)
   char *prefix = daemon->tftp_prefix;
   struct tftp_prefix *pref;
   union all_addr addra;
+  int family = listen->addr.sa.sa_family;
   /* Can always get recvd interface for IPv6 */
-  int check_dest = !option_bool(OPT_NOWILD) || listen->family == AF_INET6;
+  int check_dest = !option_bool(OPT_NOWILD) || family == AF_INET6;
   union {
     struct cmsghdr align; /* this ensures alignment */
     char control6[CMSG_SPACE(sizeof(struct in6_pktinfo))];
@@ -118,10 +119,10 @@ void tftp_request(struct listener *listen, time_t now)
       if (msg.msg_controllen < sizeof(struct cmsghdr))
         return;
       
-      addr.sa.sa_family = listen->family;
+      addr.sa.sa_family = family;
       
 #if defined(HAVE_LINUX_NETWORK)
-      if (listen->family == AF_INET)
+      if (family == AF_INET)
 	for (cmptr = CMSG_FIRSTHDR(&msg); cmptr; cmptr = CMSG_NXTHDR(&msg, cmptr))
 	  if (cmptr->cmsg_level == IPPROTO_IP && cmptr->cmsg_type == IP_PKTINFO)
 	    {
@@ -135,7 +136,7 @@ void tftp_request(struct listener *listen, time_t now)
 	    }
       
 #elif defined(HAVE_SOLARIS_NETWORK)
-      if (listen->family == AF_INET)
+      if (family == AF_INET)
 	for (cmptr = CMSG_FIRSTHDR(&msg); cmptr; cmptr = CMSG_NXTHDR(&msg, cmptr))
 	  {
 	    union {
@@ -151,7 +152,7 @@ void tftp_request(struct listener *listen, time_t now)
 	  }
       
 #elif defined(IP_RECVDSTADDR) && defined(IP_RECVIF)
-      if (listen->family == AF_INET)
+      if (family == AF_INET)
 	for (cmptr = CMSG_FIRSTHDR(&msg); cmptr; cmptr = CMSG_NXTHDR(&msg, cmptr))
 	  {
 	    union {
@@ -168,7 +169,7 @@ void tftp_request(struct listener *listen, time_t now)
 	  
 #endif
 
-      if (listen->family == AF_INET6)
+      if (family == AF_INET6)
         {
           for (cmptr = CMSG_FIRSTHDR(&msg); cmptr; cmptr = CMSG_NXTHDR(&msg, cmptr))
             if (cmptr->cmsg_level == IPPROTO_IPV6 && cmptr->cmsg_type == daemon->v6pktinfo)
@@ -191,7 +192,7 @@ void tftp_request(struct listener *listen, time_t now)
       
       addra.addr4 = addr.in.sin_addr;
 
-      if (listen->family == AF_INET6)
+      if (family == AF_INET6)
 	addra.addr6 = addr.in6.sin6_addr;
 
       if (daemon->tftp_interfaces)
@@ -207,12 +208,12 @@ void tftp_request(struct listener *listen, time_t now)
       else
 	{
 	  /* Do the same as DHCP */
-	  if (!iface_check(listen->family, &addra, name, NULL))
+	  if (!iface_check(family, &addra, name, NULL))
 	    {
 	      if (!option_bool(OPT_CLEVERBIND))
 		enumerate_interfaces(0); 
-	      if (!loopback_exception(listen->tftpfd, listen->family, &addra, name) &&
-		  !label_exception(if_index, listen->family, &addra))
+	      if (!loopback_exception(listen->tftpfd, family, &addra, name) &&
+		  !label_exception(if_index, family, &addra))
 		return;
 	    }
 	  
@@ -245,7 +246,7 @@ void tftp_request(struct listener *listen, time_t now)
 	  prefix = pref->prefix;  
     }
 
-  if (listen->family == AF_INET)
+  if (family == AF_INET)
     {
       addr.in.sin_port = htons(port);
 #ifdef HAVE_SOCKADDR_SA_LEN
@@ -265,7 +266,7 @@ void tftp_request(struct listener *listen, time_t now)
   if (!(transfer = whine_malloc(sizeof(struct tftp_transfer))))
     return;
   
-  if ((transfer->sockfd = socket(listen->family, SOCK_DGRAM, 0)) == -1)
+  if ((transfer->sockfd = socket(family, SOCK_DGRAM, 0)) == -1)
     {
       free(transfer);
       return;
@@ -296,7 +297,7 @@ void tftp_request(struct listener *listen, time_t now)
 	    {
 	      if (++port <= daemon->end_tftp_port)
 		{ 
-		  if (listen->family == AF_INET)
+		  if (family == AF_INET)
 		    addr.in.sin_port = htons(port);
 		  else
 		    addr.in6.sin6_port = htons(port);
@@ -334,7 +335,7 @@ void tftp_request(struct listener *listen, time_t now)
 	      if ((opt = next(&p, end)) && !option_bool(OPT_TFTP_NOBLOCK))
 		{
 		  /* 32 bytes for IP, UDP and TFTP headers, 52 bytes for IPv6 */
-		  int overhead = (listen->family == AF_INET) ? 32 : 52;
+		  int overhead = (family == AF_INET) ? 32 : 52;
 		  transfer->blocksize = atoi(opt);
 		  if (transfer->blocksize < 1)
 		    transfer->blocksize = 1;
-- 
2.20.1

From 9b20139cf802464bafad7123970e5e31f653388d Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Petr=20Men=C5=A1=C3=ADk?= <pemen...@redhat.com>
Date: Mon, 15 Jul 2019 17:13:12 +0200
Subject: [PATCH 4/5] 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 | 115 ++++++++++++++++++++++++++++++++++++--------------
 2 files changed, 85 insertions(+), 33 deletions(-)

diff --git a/src/dnsmasq.h b/src/dnsmasq.h
index ff3204a..f31ec6a 100644
--- a/src/dnsmasq.h
+++ b/src/dnsmasq.h
@@ -563,7 +563,8 @@ 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 44bb757..fc2af05 100644
--- a/src/network.c
+++ b/src/network.c
@@ -557,6 +557,56 @@ 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)
+    {
+      (void)prettyprint_addr(&l->iface->addr, daemon->addrbuff);
+      my_syslog(LOG_DEBUG, _("stopped listening on %s(#%d): %s"),
+		l->iface->name, l->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);
+  return 1;
+}
+
 int enumerate_interfaces(int reset)
 {
   static struct addrlist *spare = NULL;
@@ -662,29 +712,10 @@ 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;
 	    }
 	}
 
@@ -932,7 +963,9 @@ 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;
     }
 
@@ -971,23 +1004,41 @@ 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)))
+	  {
+	    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);
+	  }
       }
 
   /* Check for --listen-address options that haven't been used because there's
-- 
2.20.1

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