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 #pragma ident   "%Z%%M% %I%     %E% SMI"
   7
   8  /*
   9   * Routine to disable IP-level socket options. This code was taken from 4.4BSD
  10   * rlogind and kernel source, but all mistakes in it are my fault.
  11   *
  12   * Author: Wietse Venema, Eindhoven University of Technology, The Netherlands.
  13   */
  14
  15 #ifndef lint
  16 static char sccsid[] = "@(#) fix_options.c 1.6 97/04/08 02:29:19";
  17 #endif
  18
  19 #include <sys/types.h>
  20 #include <sys/param.h>
  21 #include <netinet/in.h>
  22 #include <netinet/in_systm.h>
  23 #include <netinet/ip.h>
  24 #include <netdb.h>
  25 #include <stdio.h>
  26 #include <stdlib.h>
  27 #include <unistd.h>
  28 #include <syslog.h>
  29
  30 #ifndef IPOPT_OPTVAL
  31 #define IPOPT_OPTVAL    0
  32 #define IPOPT_OLEN      1
  33 #endif
  34
  35 #include "tcpd.h"
  36
  37 #define BUFFER_SIZE     512             /* Was: BUFSIZ */
  38
  39 /* fix_options - get rid of IP-level socket options */
  40
  41 void
  42 fix_options(request)
  43 struct request_info *request;
  44 {
  45 #ifdef IP_OPTIONS
  46     unsigned char optbuf[BUFFER_SIZE / 3], *cp;
  47     char    lbuf[BUFFER_SIZE], *lp;
  48     int     optsize = sizeof(optbuf), ipproto;
  49     struct protoent *ip;
  50     int     fd = request->fd;
  51     unsigned int opt;
  52     int     optlen;
  53     struct in_addr dummy;
  54
  55     if ((ip = getprotobyname("ip")) != 0)
  56         ipproto = ip->p_proto;
  57     else
  58         ipproto = IPPROTO_IP;
  59
  60     if (getsockopt(fd, ipproto, IP_OPTIONS, (char *) optbuf, &optsize) == 0
  61         && optsize != 0) {
  62
  63         /*
  64          * Horror! 4.[34] BSD getsockopt() prepends the first-hop destination
  65          * address to the result IP options list when source routing options
  66          * are present (see <netinet/ip_var.h>), but produces no output for
  67          * other IP options. Solaris 2.x getsockopt() does produce output for
  68          * non-routing IP options, and uses the same format as BSD even when
  69          * the space for the destination address is unused. The code below
  70          * does the right thing with 4.[34]BSD derivatives and Solaris 2, but
  71          * may occasionally miss source routing options on incompatible
  72          * systems such as Linux. Their choice.
  73          *
  74          * Look for source routing options. Drop the connection when one is
  75          * found. Just wiping the IP options is insufficient: we would still
  76          * help the attacker by providing a real TCP sequence number, and the
  77          * attacker would still be able to send packets (blind spoofing). I
  78          * discussed this attack with Niels Provos, half a year before the
  79          * attack was described in open mailing lists.
  80          *
  81          * It would be cleaner to just return a yes/no reply and let the caller
  82          * decide how to deal with it. Resident servers should not terminate.
  83          * However I am not prepared to make changes to internal interfaces
  84          * on short notice.
  85          */
  86 #define ADDR_LEN sizeof(dummy.s_addr)
  87
  88         for (cp = optbuf + ADDR_LEN; cp < optbuf + optsize; cp += optlen) {
  89             opt = cp[IPOPT_OPTVAL];
  90             if (opt == IPOPT_LSRR || opt == IPOPT_SSRR) {
  91                 syslog(LOG_WARNING,
  92                    "refused connect from %s with IP source routing options",
  93                        eval_client(request));
  94                 shutdown(fd, 2);
  95                 return;
  96             }
  97             if (opt == IPOPT_EOL)
  98                 break;
  99             if (opt == IPOPT_NOP) {
 100                 optlen = 1;
 101             } else {
 102                 optlen = cp[IPOPT_OLEN];
 103                 if (optlen <= 0)                /* Do not loop! */
 104                     break;
 105             }
 106         }
 107         lp = lbuf;
 108         for (cp = optbuf; optsize > 0; cp++, optsize--, lp += 3)
 109             sprintf(lp, " %2.2x", *cp);
 110         syslog(LOG_NOTICE,
 111                "connect from %s with IP options (ignored):%s",
 112                eval_client(request), lbuf);
 113         if (setsockopt(fd, ipproto, IP_OPTIONS, (char *) 0, optsize) != 0) {
 114             syslog(LOG_ERR, "setsockopt IP_OPTIONS NULL: %m");
 115             shutdown(fd, 2);
 116         }
 117     }
 118 #endif
 119 }