contrib/tcp_wrappers/fix_options.c

   1  /*
   2   * Routine to disable IP-level socket options. This code was taken from 4.4BSD
   3   * rlogind and kernel source, but all mistakes in it are my fault.
   4   *
   5   * Author: Wietse Venema, Eindhoven University of Technology, The Netherlands.
   6   *
   7   * $FreeBSD: src/contrib/tcp_wrappers/fix_options.c,v 1.2 2000/02/03 10:26:57 shin Exp $
   8   */
   9
  10 #include <sys/types.h>
  11 #include <sys/param.h>
  12 #ifdef INET6
  13 #include <sys/socket.h>
  14 #endif
  15 #include <netinet/in.h>
  16 #include <netinet/in_systm.h>
  17 #include <netinet/ip.h>
  18 #include <netdb.h>
  19 #include <stdio.h>
  20 #include <syslog.h>
  21
  22 #ifndef IPOPT_OPTVAL
  23 #define IPOPT_OPTVAL    0
  24 #define IPOPT_OLEN      1
  25 #endif
  26
  27 #include "tcpd.h"
  28
  29 #define BUFFER_SIZE     512             /* Was: BUFSIZ */
  30
  31 /* fix_options - get rid of IP-level socket options */
  32
  33 void
  34 fix_options(request)
  35 struct request_info *request;
  36 {
  37 #ifdef IP_OPTIONS
  38     unsigned char optbuf[BUFFER_SIZE / 3], *cp;
  39     char    lbuf[BUFFER_SIZE], *lp;
  40     int     optsize = sizeof(optbuf), ipproto;
  41     struct protoent *ip;
  42     int     fd = request->fd;
  43     unsigned int opt;
  44     int     optlen;
  45     struct in_addr dummy;
  46 #ifdef INET6
  47     struct sockaddr_storage ss;
  48     int sslen;
  49
  50     /*
  51      * check if this is AF_INET socket
  52      * XXX IPv6 support?
  53      */
  54     sslen = sizeof(ss);
  55     if (getsockname(fd, (struct sockaddr *)&ss, &sslen) < 0) {
  56         syslog(LOG_ERR, "getpeername: %m");
  57         clean_exit(request);
  58     }
  59     if (ss.ss_family != AF_INET)
  60         return;
  61 #endif
  62
  63     if ((ip = getprotobyname("ip")) != 0)
  64         ipproto = ip->p_proto;
  65     else
  66         ipproto = IPPROTO_IP;
  67
  68     if (getsockopt(fd, ipproto, IP_OPTIONS, (char *) optbuf, &optsize) == 0
  69         && optsize != 0) {
  70
  71         /*
  72          * Horror! 4.[34] BSD getsockopt() prepends the first-hop destination
  73          * address to the result IP options list when source routing options
  74          * are present (see <netinet/ip_var.h>), but produces no output for
  75          * other IP options. Solaris 2.x getsockopt() does produce output for
  76          * non-routing IP options, and uses the same format as BSD even when
  77          * the space for the destination address is unused. The code below
  78          * does the right thing with 4.[34]BSD derivatives and Solaris 2, but
  79          * may occasionally miss source routing options on incompatible
  80          * systems such as Linux. Their choice.
  81          *
  82          * Look for source routing options. Drop the connection when one is
  83          * found. Just wiping the IP options is insufficient: we would still
  84          * help the attacker by providing a real TCP sequence number, and the
  85          * attacker would still be able to send packets (blind spoofing). I
  86          * discussed this attack with Niels Provos, half a year before the
  87          * attack was described in open mailing lists.
  88          *
  89          * It would be cleaner to just return a yes/no reply and let the caller
  90          * decide how to deal with it. Resident servers should not terminate.
  91          * However I am not prepared to make changes to internal interfaces
  92          * on short notice.
  93          */
  94 #define ADDR_LEN sizeof(dummy.s_addr)
  95
  96         for (cp = optbuf + ADDR_LEN; cp < optbuf + optsize; cp += optlen) {
  97             opt = cp[IPOPT_OPTVAL];
  98             if (opt == IPOPT_LSRR || opt == IPOPT_SSRR) {
  99                 syslog(LOG_WARNING,
 100                    "refused connect from %s with IP source routing options",
 101                        eval_client(request));
 102                 shutdown(fd, 2);
 103                 return;
 104             }
 105             if (opt == IPOPT_EOL)
 106                 break;
 107             if (opt == IPOPT_NOP) {
 108                 optlen = 1;
 109             } else {
 110                 optlen = cp[IPOPT_OLEN];
 111                 if (optlen <= 0)                /* Do not loop! */
 112                     break;
 113             }
 114         }
 115         lp = lbuf;
 116         for (cp = optbuf; optsize > 0; cp++, optsize--, lp += 3)
 117             sprintf(lp, " %2.2x", *cp);
 118         syslog(LOG_NOTICE,
 119                "connect from %s with IP options (ignored):%s",
 120                eval_client(request), lbuf);
 121         if (setsockopt(fd, ipproto, IP_OPTIONS, (char *) 0, optsize) != 0) {
 122             syslog(LOG_ERR, "setsockopt IP_OPTIONS NULL: %m");
 123             shutdown(fd, 2);
 124         }
 125     }
 126 #endif
 127 }