Allow wildcard aliases in --bridge-interface option

This is useful when using dnsmasq as DHCP server for a set of VMs
whose data is routed by the host instead of being bridged.  In this
scenario:

- There is an unbounded set of TAP interfaces that have no IP address
  at the host end.

- DHCP allocation is done from an IPv4 address range associated with a
  dummy interface.

- We run dnsmasq with --interface dummy --interface tap*
  --bind-dynamic, so that it listens on all the TAP interfaces, and
  --bridge-interface=dummy,tap*, so that it will allocate IP addresses
  via the TAP interfaces from the range associated with the dummy
  interface.

5 files changed, 23 insertions, 2 deletions

diff --git a/man/dnsmasq.8 b/man/dnsmasq.8
index f25119d..0530a19 100644
--- a/man/dnsmasq.8
+++ b/man/dnsmasq.8
@@ -1550,6 +1550,7 @@ Treat DHCP request packets arriving at any of the <alias> interfaces
 as if they had arrived at <interface>. This option is necessary when
 using "old style" bridging on BSD platforms, since
 packets arrive at tap interfaces which don't have an IP address.
+A trailing '*' wildcard can be used in each <alias>.
 .TP
 .B \-s, --domain=<domain>[,<address range>[,local]]
 Specifies DNS domains for the DHCP server. Domains may be be given 
diff --git a/man/fr/dnsmasq.8 b/man/fr/dnsmasq.8
index 2f329ee..e0d1e9a 100644
--- a/man/fr/dnsmasq.8
+++ b/man/fr/dnsmasq.8
@@ -1659,7 +1659,7 @@ Traiter les requêtes DHCP arrivant sur n'importe laquelle des interfaces <alias
 comme si elles arrivaient de l'interface <interface>. Cette option est
 nécessaire lors de l'utilisation de pont ethernet "ancien mode" sur plate-forme
 BSD, puisque dans ce cas les paquets arrivent sur des interfaces "tap" n'ont
-pas d'adresse IP.
+pas d'adresse IP.  Chaque <alias> peut finir avec un simple '*' joker.
 .TP
 .B \-s, --domain=<domaine>[,<gamme d'adresses>[,local]]
 Spécifie le domaine du serveur DHCP. Le domaine peut être donné de manière
diff --git a/src/dhcp.c b/src/dhcp.c
index 9463e23..7acf2c4 100644
--- a/src/dhcp.c
+++ b/src/dhcp.c
@@ -232,7 +232,7 @@ void dhcp_packet(time_t now, int pxe_fd)
   for (bridge = daemon->bridges; bridge; bridge = bridge->next)
     {
       for (alias = bridge->alias; alias; alias = alias->next)
-	if (strncmp(ifr.ifr_name, alias->iface, IF_NAMESIZE) == 0)
+	if (wildcard_matchn(alias->iface, ifr.ifr_name, IF_NAMESIZE))
 	  {
 	    if (!(iface_index = if_nametoindex(bridge->iface)))
 	      {
diff --git a/src/dnsmasq.h b/src/dnsmasq.h
index de98956..dfa9773 100644
--- a/src/dnsmasq.h
+++ b/src/dnsmasq.h
@@ -1150,6 +1150,7 @@ void bump_maxfd(int fd, int *max);
 int read_write(int fd, unsigned char *packet, int size, int rw);
 
 int wildcard_match(const char* wildcard, const char* match);
+int wildcard_matchn(const char* wildcard, const char* match, int num);
 
 /* log.c */
 void die(char *message, char *arg1, int exit_code);
diff --git a/src/util.c b/src/util.c
index 7c46d40..a503082 100644
--- a/src/util.c
+++ b/src/util.c
@@ -602,3 +602,22 @@ int wildcard_match(const char* wildcard, const char* match)
 
   return *wildcard == *match;
 }
+
+/* The same but comparing a maximum of NUM characters, like strncmp.  */
+int wildcard_matchn(const char* wildcard, const char* match, int num)
+{
+  while (*wildcard && *match && num)
+    {
+      if (*wildcard == '*')
+        return 1;
+
+      if (*wildcard != *match)
+        return 0; 
+
+      ++wildcard;
+      ++match;
+      --num;
+    }
+
+  return (!num) || (*wildcard == *match);
+}