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 } 118