From dbb6ea3a52664be89b2cd745eaba32519b8c273e Mon Sep 17 00:00:00 2001
From: Gerhard Rieger <gerhard@dest-unreach.org>
Date: Fri, 16 Nov 2012 21:08:46 +0100
Subject: [PATCH] allow tun/tap specification without IP address

---
 CHANGES      |  2 ++
 doc/socat.yo | 13 +++++++------
 xio-tun.c    | 51 ++++++++++++++++++++++++++-------------------------
 3 files changed, 35 insertions(+), 31 deletions(-)

diff --git a/CHANGES b/CHANGES
index aecf384..6029f00 100644
--- a/CHANGES
+++ b/CHANGES
@@ -133,6 +133,8 @@ new features:
 	added option max-children that limits the number of concurrent child
 	processes. Thanks to Sam Liddicott for providing the patch.
 
+	Till Maas added support for tun/tap addresses without IP address
+
 ####################### V 2.0.0-b7:
 
 security:
diff --git a/doc/socat.yo b/doc/socat.yo
index 531a5e1..2c8b295 100644
--- a/doc/socat.yo
+++ b/doc/socat.yo
@@ -1021,12 +1021,13 @@ label(ADDRESS_TCP6_LISTEN)dit(bf(tt(TCP6-LISTEN:<port>)))
    Additional useful option:
    link(ipv6only)(OPTION_IPV6_V6ONLY)nl()
    Option groups: link(FD)(GROUP_FD),link(SOCKET)(GROUP_SOCKET),link(LISTEN)(GROUP_LISTEN),link(CHILD)(GROUP_CHILD),link(RANGE)(GROUP_RANGE),link(IP6)(GROUP_IP6),link(TCP)(GROUP_TCP),link(RETRY)(GROUP_RETRY) nl()
-label(ADDRESS_TUN)dit(bf(tt(TUN:<if-addr>/<bits>)))
-   Creates a Linux TUN/TAP device and assignes to it the address and netmask
-   defined by the parameters. The resulting network interface is ready for use
-   by other processes; socat() serves its "wire side". This address requires read
-   and write access to the tunnel cloning device, usually code(/dev/net/tun).
-   nl() 
+label(ADDRESS_TUN)dit(bf(tt(TUN[:<if-addr>/<bits>])))
+   Creates a Linux TUN/TAP device and optionally assignes it the address and
+   netmask given by the parameters. The resulting network interface is almost
+   ready for use by other processes; socat serves its "wire side". This address
+   requires read and write access to the tunnel cloning device, usually
+   code(/dev/net/tun), as well as permission to set some tt(ioctl()s).
+   bf(Option iff-up is required to immediately activate the interface!)nl() 
    Option groups: link(FD)(GROUP_FD),link(NAMED)(GROUP_NAMED),link(OPEN)(GROUP_OPEN),link(TUN)(GROUP_TUN) nl()
    Useful options:
    link(iff-up)(OPTION_IFF_UP),
diff --git a/xio-tun.c b/xio-tun.c
index c98da81..0fd92ac 100644
--- a/xio-tun.c
+++ b/xio-tun.c
@@ -83,8 +83,8 @@ static int xioopen_tun(int argc, const char *argv[], struct opt *opts, int xiofl
    char *ifaddr;
    int result;
 
-   if (argc != 2) {
-      Error2("%s: wrong number of parameters (%d instead of 1)",
+   if (argc > 2 || argc < 0) {
+      Error2("%s: wrong number of parameters (%d instead of 0 or 1)",
 	     argv[0], argc-1);
    }
 
@@ -152,30 +152,31 @@ static int xioopen_tun(int argc, const char *argv[], struct opt *opts, int xiofl
    }
 
    /*--------------------- setting interface address and netmask ------------*/
-   if ((ifaddr = strdup(argv[1])) == NULL) {
-      Error1("strdup(\"%s\"): out of memory", argv[1]);
-      return STAT_RETRYLATER;
+   if (argc == 2) {
+      if ((ifaddr = strdup(argv[1])) == NULL) {
+	 Error1("strdup(\"%s\"): out of memory", argv[1]);
+	 return STAT_RETRYLATER;
+      }
+      if ((result = xioparsenetwork(ifaddr, pf, &network)) != STAT_OK) {
+	 /*! recover */
+	 return result;
+      }
+      socket_init(pf, (union sockaddr_union *)&ifr.ifr_addr);
+      ((struct sockaddr_in *)&ifr.ifr_addr)->sin_addr =
+	 network.netaddr.ip4.sin_addr;
+      if (Ioctl(sockfd, SIOCSIFADDR, &ifr) < 0) {
+	 Error4("ioctl(%d, SIOCSIFADDR, {\"%s\", \"%s\"}: %s",
+		sockfd, ifr.ifr_name, ifaddr, strerror(errno));
+      }
+      ((struct sockaddr_in *)&ifr.ifr_netmask)->sin_addr =
+	 network.netmask.ip4.sin_addr;
+      if (Ioctl(sockfd, SIOCSIFNETMASK, &ifr) < 0) {
+	 Error4("ioctl(%d, SIOCSIFNETMASK, {\"0x%08u\", \"%s\"}, %s",
+		sockfd, ((struct sockaddr_in *)&ifr.ifr_netmask)->sin_addr.s_addr,
+		ifaddr, strerror(errno));
+      }
+      free(ifaddr);
    }
-   if ((result = xioparsenetwork(ifaddr, pf, &network)) != STAT_OK) {
-      /*! recover */
-      return result;
-   }
-   socket_init(pf, (union sockaddr_union *)&ifr.ifr_addr);
-   ((struct sockaddr_in *)&ifr.ifr_addr)->sin_addr =
-      network.netaddr.ip4.sin_addr;
-   if (Ioctl(sockfd, SIOCSIFADDR, &ifr) < 0) {
-      Error4("ioctl(%d, SIOCSIFADDR, {\"%s\", \"%s\"}: %s",
-	     sockfd, ifr.ifr_name, ifaddr, strerror(errno));
-   }
-   ((struct sockaddr_in *)&ifr.ifr_netmask)->sin_addr =
-      network.netmask.ip4.sin_addr;
-   if (Ioctl(sockfd, SIOCSIFNETMASK, &ifr) < 0) {
-      Error4("ioctl(%d, SIOCSIFNETMASK, {\"0x%08u\", \"%s\"}, %s",
-	     sockfd, ((struct sockaddr_in *)&ifr.ifr_netmask)->sin_addr.s_addr,
-	     ifaddr, strerror(errno));
-   }
-   free(ifaddr);
-
    /*--------------------- setting interface flags --------------------------*/
    applyopts_single(&xfd->stream, opts, PH_FD);