/*      $NetBSD: fix_options.c,v 1.11 2012/03/21 10:10:37 matt Exp $    */

/*
 * Routine to disable IP-level socket options. This code was taken from 4.4BSD
 * rlogind and kernel source, but all mistakes in it are my fault.
 *
 * Author: Wietse Venema, Eindhoven University of Technology, The Netherlands.
 */

#include <sys/cdefs.h>
#ifndef lint
#if 0
static char sccsid[] = "@(#) fix_options.c 1.6 97/04/08 02:29:19";
#else
__RCSID("$NetBSD: fix_options.c,v 1.11 2012/03/21 10:10:37 matt Exp $");
#endif
#endif

#include <sys/types.h>
#include <sys/param.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <netinet/in_systm.h>
#include <netinet/ip.h>
#include <netdb.h>
#include <stdio.h>
#include <syslog.h>
#include <stdlib.h>
#include <unistd.h>

#ifndef IPOPT_OPTVAL
#define IPOPT_OPTVAL    0
#define IPOPT_OLEN      1
#endif

#include "tcpd.h"

#define BUFFER_SIZE     512             /* Was: BUFSIZ */

/* fix_options - get rid of IP-level socket options */

void
fix_options(struct request_info *request)
{
#ifdef IP_OPTIONS
   unsigned char optbuf[BUFFER_SIZE / 3], *cp;
   char    lbuf[BUFFER_SIZE], *lp;
   int     ipproto;
   socklen_t optsize = sizeof(optbuf);
   struct protoent *ip;
   int     fd = request->fd;
   int     len = sizeof lbuf;
   unsigned int opt;
   int     optlen;
   struct in_addr dummy;
   struct sockaddr_storage ss;
   socklen_t sslen;

   /*
    * check if this is AF_INET socket
    * XXX IPv6 support?
    */
   sslen = sizeof(ss);
   if (getsockname(fd, (struct sockaddr *)(void *)&ss, &sslen) < 0) {
       syslog(LOG_ERR, "getsockname: %m");
       clean_exit(request);
   }
   if (ss.ss_family != AF_INET)
       return;

   if ((ip = getprotobyname("ip")) != 0)
       ipproto = ip->p_proto;
   else
       ipproto = IPPROTO_IP;

   if (getsockopt(fd, ipproto, IP_OPTIONS, optbuf, &optsize) == 0
       && optsize != 0) {

       /*
        * Horror! 4.[34] BSD getsockopt() prepends the first-hop destination
        * address to the result IP options list when source routing options
        * are present (see <netinet/ip_var.h>), but produces no output for
        * other IP options. Solaris 2.x getsockopt() does produce output for
        * non-routing IP options, and uses the same format as BSD even when
        * the space for the destination address is unused. The code below
        * does the right thing with 4.[34]BSD derivatives and Solaris 2, but
        * may occasionally miss source routing options on incompatible
        * systems such as Linux. Their choice.
        *
        * Look for source routing options. Drop the connection when one is
        * found. Just wiping the IP options is insufficient: we would still
        * help the attacker by providing a real TCP sequence number, and the
        * attacker would still be able to send packets (blind spoofing). I
        * discussed this attack with Niels Provos, half a year before the
        * attack was described in open mailing lists.
        *
        * It would be cleaner to just return a yes/no reply and let the caller
        * decide how to deal with it. Resident servers should not terminate.
        * However I am not prepared to make changes to internal interfaces
        * on short notice.
        */
#define ADDR_LEN sizeof(dummy.s_addr)

       for (cp = optbuf + ADDR_LEN; cp < optbuf + optsize; cp += optlen) {
           opt = cp[IPOPT_OPTVAL];
           if (opt == IPOPT_LSRR || opt == IPOPT_SSRR) {
               syslog(LOG_WARNING,
                  "refused connect from %s with IP source routing options",
                      eval_client(request));
               shutdown(fd, 2);
               return;
           }
           if (opt == IPOPT_EOL)
               break;
           if (opt == IPOPT_NOP) {
               optlen = 1;
           } else if (&cp[IPOPT_OLEN] < optbuf + optsize) {
               optlen = cp[IPOPT_OLEN];
               if (optlen < 2 || cp + optlen >= optbuf + optsize) {
                   syslog(LOG_WARNING,
                      "refused connect from %s with malformed IP options",
                          eval_client(request));
                   shutdown(fd, 2);
                   return;
               }
           } else {
               syslog(LOG_WARNING,
                  "refused connect from %s with malformed IP options",
                      eval_client(request));
               shutdown(fd, 2);
               return;
           }
       }
       lp = lbuf;
       for (cp = optbuf; optsize > 0; cp++, optsize--, lp += 3)
           len -= snprintf(lp, len, " %2.2x", *cp);
       syslog(LOG_NOTICE,
              "connect from %s with IP options (ignored):%s",
              eval_client(request), lbuf);
       if (setsockopt(fd, ipproto, IP_OPTIONS, (char *) 0, optsize) != 0) {
           syslog(LOG_ERR, "setsockopt IP_OPTIONS NULL: %m");
           shutdown(fd, 2);
       }
   }
#endif
}