usr/src/lib/libwrap/fix_options.c

   1 /*
   2  * Copyright 2004 Sun Microsystems, Inc.  All rights reserved.
   3  * Use is subject to license terms.
   4  */
   5
   6  /*
   7   * Routine to disable IP-level socket options. This code was taken from 4.4BSD
   8   * rlogind and kernel source, but all mistakes in it are my fault.
   9   *
  10   * Author: Wietse Venema, Eindhoven University of Technology, The Netherlands.
  11   */
  12
  13 #ifndef lint
  14 static char sccsid[] = "@(#) fix_options.c 1.6 97/04/08 02:29:19";
  15 #endif
  16
  17 #include <sys/types.h>
  18 #include <sys/param.h>
  19 #include <netinet/in.h>
  20 #include <netinet/in_systm.h>
  21 #include <netinet/ip.h>
  22 #include <netdb.h>
  23 #include <stdio.h>
  24 #include <stdlib.h>
  25 #include <unistd.h>
  26 #include <syslog.h>
  27
  28 #ifndef IPOPT_OPTVAL
  29 #define IPOPT_OPTVAL    0
  30 #define IPOPT_OLEN      1
  31 #endif
  32
  33 #include "tcpd.h"
  34
  35 #define BUFFER_SIZE     512             /* Was: BUFSIZ */
  36
  37 /* fix_options - get rid of IP-level socket options */
  38
  39 void
  40 fix_options(request)
  41 struct request_info *request;
  42 {
  43 #ifdef IP_OPTIONS
  44     unsigned char optbuf[BUFFER_SIZE / 3], *cp;
  45     char    lbuf[BUFFER_SIZE], *lp;
  46     int     optsize = sizeof(optbuf), ipproto;
  47     struct protoent *ip;
  48     int     fd = request->fd;
  49     unsigned int opt;
  50     int     optlen;
  51     struct in_addr dummy;
  52
  53     if ((ip = getprotobyname("ip")) != 0)
  54         ipproto = ip->p_proto;
  55     else
  56         ipproto = IPPROTO_IP;
  57
  58     if (getsockopt(fd, ipproto, IP_OPTIONS, (char *) optbuf, &optsize) == 0
  59         && optsize != 0) {
  60
  61         /*
  62          * Horror! 4.[34] BSD getsockopt() prepends the first-hop destination
  63          * address to the result IP options list when source routing options
  64          * are present (see <netinet/ip_var.h>), but produces no output for
  65          * other IP options. Solaris 2.x getsockopt() does produce output for
  66          * non-routing IP options, and uses the same format as BSD even when
  67          * the space for the destination address is unused. The code below
  68          * does the right thing with 4.[34]BSD derivatives and Solaris 2, but
  69          * may occasionally miss source routing options on incompatible
  70          * systems such as Linux. Their choice.
  71          *
  72          * Look for source routing options. Drop the connection when one is
  73          * found. Just wiping the IP options is insufficient: we would still
  74          * help the attacker by providing a real TCP sequence number, and the
  75          * attacker would still be able to send packets (blind spoofing). I
  76          * discussed this attack with Niels Provos, half a year before the
  77          * attack was described in open mailing lists.
  78          *
  79          * It would be cleaner to just return a yes/no reply and let the caller
  80          * decide how to deal with it. Resident servers should not terminate.
  81          * However I am not prepared to make changes to internal interfaces
  82          * on short notice.
  83          */
  84 #define ADDR_LEN sizeof(dummy.s_addr)
  85
  86         for (cp = optbuf + ADDR_LEN; cp < optbuf + optsize; cp += optlen) {
  87             opt = cp[IPOPT_OPTVAL];
  88             if (opt == IPOPT_LSRR || opt == IPOPT_SSRR) {
  89                 syslog(LOG_WARNING,
  90                    "refused connect from %s with IP source routing options",
  91                        eval_client(request));
  92                 shutdown(fd, 2);
  93                 return;
  94             }
  95             if (opt == IPOPT_EOL)
  96                 break;
  97             if (opt == IPOPT_NOP) {
  98                 optlen = 1;
  99             } else {
 100                 optlen = cp[IPOPT_OLEN];
 101                 if (optlen <= 0)                /* Do not loop! */
 102                     break;
 103             }
 104         }
 105         lp = lbuf;
 106         for (cp = optbuf; optsize > 0; cp++, optsize--, lp += 3)
 107             sprintf(lp, " %2.2x", *cp);
 108         syslog(LOG_NOTICE,
 109                "connect from %s with IP options (ignored):%s",
 110                eval_client(request), lbuf);
 111         if (setsockopt(fd, ipproto, IP_OPTIONS, (char *) 0, optsize) != 0) {
 112             syslog(LOG_ERR, "setsockopt IP_OPTIONS NULL: %m");
 113             shutdown(fd, 2);
 114         }
 115     }
 116 #endif
 117 }