diff -up socat-1.7.1.3/xio-tun.c.orig socat-1.7.1.3/xio-tun.c

--- socat-1.7.1.3/xio-tun.c.orig	2011-05-19 20:25:38.654799000 +0200

+++ socat-1.7.1.3/xio-tun.c	2011-05-19 20:37:48.675627004 +0200

@@ -78,8 +78,8 @@ static int xioopen_tun(int argc, const c

    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);

    }

@@ -146,30 +146,31 @@ static int xioopen_tun(int argc, const c

    }

    /*--------------------- 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);