1 /* $NetBSD: fix_options.c,v 1.10 2006/05/09 20:18:06 mrg Exp $ */ 2 3 /* 4 * Routine to disable IP-level socket options. This code was taken from 4.4BSD 5 * rlogind and kernel source, but all mistakes in it are my fault. 6 * 7 * Author: Wietse Venema, Eindhoven University of Technology, The Netherlands. 8 */ 9 10 #include <sys/cdefs.h> 11 #ifndef lint 12 #if 0 13 static char sccsid[] = "@(#) fix_options.c 1.6 97/04/08 02:29:19"; 14 #else 15 __RCSID("$NetBSD: fix_options.c,v 1.10 2006/05/09 20:18:06 mrg Exp $"); 16 #endif 17 #endif 18 19 #include <sys/types.h> 20 #include <sys/param.h> 21 #include <sys/socket.h> 22 #include <netinet/in.h> 23 #include <netinet/in_systm.h> 24 #include <netinet/ip.h> 25 #include <netdb.h> 26 #include <stdio.h> 27 #include <syslog.h> 28 #include <stdlib.h> 29 #include <unistd.h> 30 31 #ifndef IPOPT_OPTVAL 32 #define IPOPT_OPTVAL 0 33 #define IPOPT_OLEN 1 34 #endif 35 36 #include "tcpd.h" 37 38 #define BUFFER_SIZE 512 /* Was: BUFSIZ */ 39 40 /* fix_options - get rid of IP-level socket options */ 41 42 void 43 fix_options(request) 44 struct request_info *request; 45 { 46 #ifdef IP_OPTIONS 47 unsigned char optbuf[BUFFER_SIZE / 3], *cp; 48 char lbuf[BUFFER_SIZE], *lp; 49 int ipproto; 50 socklen_t optsize = sizeof(optbuf); 51 struct protoent *ip; 52 int fd = request->fd; 53 int len = sizeof lbuf; 54 unsigned int opt; 55 int optlen; 56 struct in_addr dummy; 57 struct sockaddr_storage ss; 58 socklen_t sslen; 59 60 /* 61 * check if this is AF_INET socket 62 * XXX IPv6 support? 63 */ 64 sslen = sizeof(ss); 65 if (getsockname(fd, (struct sockaddr *)(void *)&ss, &sslen) < 0) { 66 syslog(LOG_ERR, "getsockname: %m"); 67 clean_exit(request); 68 } 69 if (ss.ss_family != AF_INET) 70 return; 71 72 if ((ip = getprotobyname("ip")) != 0) 73 ipproto = ip->p_proto; 74 else 75 ipproto = IPPROTO_IP; 76 77 if (getsockopt(fd, ipproto, IP_OPTIONS, optbuf, &optsize) == 0 78 && optsize != 0) { 79 80 /* 81 * Horror! 4.[34] BSD getsockopt() prepends the first-hop destination 82 * address to the result IP options list when source routing options 83 * are present (see <netinet/ip_var.h>), but produces no output for 84 * other IP options. Solaris 2.x getsockopt() does produce output for 85 * non-routing IP options, and uses the same format as BSD even when 86 * the space for the destination address is unused. The code below 87 * does the right thing with 4.[34]BSD derivatives and Solaris 2, but 88 * may occasionally miss source routing options on incompatible 89 * systems such as Linux. Their choice. 90 * 91 * Look for source routing options. Drop the connection when one is 92 * found. Just wiping the IP options is insufficient: we would still 93 * help the attacker by providing a real TCP sequence number, and the 94 * attacker would still be able to send packets (blind spoofing). I 95 * discussed this attack with Niels Provos, half a year before the 96 * attack was described in open mailing lists. 97 * 98 * It would be cleaner to just return a yes/no reply and let the caller 99 * decide how to deal with it. Resident servers should not terminate. 100 * However I am not prepared to make changes to internal interfaces 101 * on short notice. 102 */ 103 #define ADDR_LEN sizeof(dummy.s_addr) 104 105 for (cp = optbuf + ADDR_LEN; cp < optbuf + optsize; cp += optlen) { 106 opt = cp[IPOPT_OPTVAL]; 107 if (opt == IPOPT_LSRR || opt == IPOPT_SSRR) { 108 syslog(LOG_WARNING, 109 "refused connect from %s with IP source routing options", 110 eval_client(request)); 111 shutdown(fd, 2); 112 return; 113 } 114 if (opt == IPOPT_EOL) 115 break; 116 if (opt == IPOPT_NOP) { 117 optlen = 1; 118 } else if (&cp[IPOPT_OLEN] < optbuf + optsize) { 119 optlen = cp[IPOPT_OLEN]; 120 if (optlen < 2 || cp + optlen >= optbuf + optsize) { 121 syslog(LOG_WARNING, 122 "refused connect from %s with malformed IP options", 123 eval_client(request)); 124 shutdown(fd, 2); 125 return; 126 } 127 } else { 128 syslog(LOG_WARNING, 129 "refused connect from %s with malformed IP options", 130 eval_client(request)); 131 shutdown(fd, 2); 132 return; 133 } 134 } 135 lp = lbuf; 136 for (cp = optbuf; optsize > 0; cp++, optsize--, lp += 3) 137 len -= snprintf(lp, len, " %2.2x", *cp); 138 syslog(LOG_NOTICE, 139 "connect from %s with IP options (ignored):%s", 140 eval_client(request), lbuf); 141 if (setsockopt(fd, ipproto, IP_OPTIONS, (char *) 0, optsize) != 0) { 142 syslog(LOG_ERR, "setsockopt IP_OPTIONS NULL: %m"); 143 shutdown(fd, 2); 144 } 145 } 146 #endif 147 } 148