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fix_options.c revision 1.1.1.2 
      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 
      8 #ifndef lint
      9 static char sccsid[] = "@(#) fix_options.c 1.6 97/04/08 02:29:19";
     10 #endif
     11 
     12 #include <sys/types.h>
     13 #include <sys/param.h>
     14 #include <netinet/in.h>
     15 #include <netinet/in_systm.h>
     16 #include <netinet/ip.h>
     17 #include <netdb.h>
     18 #include <stdio.h>
     19 #include <syslog.h>
     20 
     21 #ifndef IPOPT_OPTVAL
     22 #define IPOPT_OPTVAL	0
     23 #define IPOPT_OLEN	1
     24 #endif
     25 
     26 #include "tcpd.h"
     27 
     28 #define BUFFER_SIZE	512		/* Was: BUFSIZ */
     29 
     30 /* fix_options - get rid of IP-level socket options */
     31 
     32 fix_options(request)
     33 struct request_info *request;
     34 {
     35 #ifdef IP_OPTIONS
     36     unsigned char optbuf[BUFFER_SIZE / 3], *cp;
     37     char    lbuf[BUFFER_SIZE], *lp;
     38     int     optsize = sizeof(optbuf), ipproto;
     39     struct protoent *ip;
     40     int     fd = request->fd;
     41     unsigned int opt;
     42     int     optlen;
     43     struct in_addr dummy;
     44 
     45     if ((ip = getprotobyname("ip")) != 0)
     46 	ipproto = ip->p_proto;
     47     else
     48 	ipproto = IPPROTO_IP;
     49 
     50     if (getsockopt(fd, ipproto, IP_OPTIONS, (char *) optbuf, &optsize) == 0
     51 	&& optsize != 0) {
     52 
     53 	/*
     54 	 * Horror! 4.[34] BSD getsockopt() prepends the first-hop destination
     55 	 * address to the result IP options list when source routing options
     56 	 * are present (see <netinet/ip_var.h>), but produces no output for
     57 	 * other IP options. Solaris 2.x getsockopt() does produce output for
     58 	 * non-routing IP options, and uses the same format as BSD even when
     59 	 * the space for the destination address is unused. The code below
     60 	 * does the right thing with 4.[34]BSD derivatives and Solaris 2, but
     61 	 * may occasionally miss source routing options on incompatible
     62 	 * systems such as Linux. Their choice.
     63 	 *
     64 	 * Look for source routing options. Drop the connection when one is
     65 	 * found. Just wiping the IP options is insufficient: we would still
     66 	 * help the attacker by providing a real TCP sequence number, and the
     67 	 * attacker would still be able to send packets (blind spoofing). I
     68 	 * discussed this attack with Niels Provos, half a year before the
     69 	 * attack was described in open mailing lists.
     70 	 *
     71 	 * It would be cleaner to just return a yes/no reply and let the caller
     72 	 * decide how to deal with it. Resident servers should not terminate.
     73 	 * However I am not prepared to make changes to internal interfaces
     74 	 * on short notice.
     75 	 */
     76 #define ADDR_LEN sizeof(dummy.s_addr)
     77 
     78 	for (cp = optbuf + ADDR_LEN; cp < optbuf + optsize; cp += optlen) {
     79 	    opt = cp[IPOPT_OPTVAL];
     80 	    if (opt == IPOPT_LSRR || opt == IPOPT_SSRR) {
     81 		syslog(LOG_WARNING,
     82 		   "refused connect from %s with IP source routing options",
     83 		       eval_client(request));
     84 		shutdown(fd, 2);
     85 		return;
     86 	    }
     87 	    if (opt == IPOPT_EOL)
     88 		break;
     89 	    if (opt == IPOPT_NOP) {
     90 		optlen = 1;
     91 	    } else {
     92 		optlen = cp[IPOPT_OLEN];
     93 		if (optlen <= 0)		/* Do not loop! */
     94 		    break;
     95 	    }
     96 	}
     97 	lp = lbuf;
     98 	for (cp = optbuf; optsize > 0; cp++, optsize--, lp += 3)
     99 	    sprintf(lp, " %2.2x", *cp);
    100 	syslog(LOG_NOTICE,
    101 	       "connect from %s with IP options (ignored):%s",
    102 	       eval_client(request), lbuf);
    103 	if (setsockopt(fd, ipproto, IP_OPTIONS, (char *) 0, optsize) != 0) {
    104 	    syslog(LOG_ERR, "setsockopt IP_OPTIONS NULL: %m");
    105 	    shutdown(fd, 2);
    106 	}
    107     }
    108 #endif
    109 }
    110