1 /* $NetBSD: fix_options.c,v 1.11 2012/03/21 10:10:37 matt 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 1.11 2012/03/21 10:10:37 matt 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(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 ipproto; 49 socklen_t optsize = sizeof(optbuf); 50 struct protoent *ip; 51 int fd = request->fd; 52 int len = sizeof lbuf; 53 unsigned int opt; 54 int optlen; 55 struct in_addr dummy; 56 struct sockaddr_storage ss; 57 socklen_t sslen; 58 59 /* 60 * check if this is AF_INET socket 61 * XXX IPv6 support? 62 */ 63 sslen = sizeof(ss); 64 if (getsockname(fd, (struct sockaddr *)(void *)&ss, &sslen) < 0) { 65 syslog(LOG_ERR, "getsockname: %m"); 66 clean_exit(request); 67 } 68 if (ss.ss_family != AF_INET) 69 return; 70 71 if ((ip = getprotobyname("ip")) != 0) 72 ipproto = ip->p_proto; 73 else 74 ipproto = IPPROTO_IP; 75 76 if (getsockopt(fd, ipproto, IP_OPTIONS, optbuf, &optsize) == 0 77 && optsize != 0) { 78 79 /* 80 * Horror! 4.[34] BSD getsockopt() prepends the first-hop destination 81 * address to the result IP options list when source routing options 82 * are present (see <netinet/ip_var.h>), but produces no output for 83 * other IP options. Solaris 2.x getsockopt() does produce output for 84 * non-routing IP options, and uses the same format as BSD even when 85 * the space for the destination address is unused. The code below 86 * does the right thing with 4.[34]BSD derivatives and Solaris 2, but 87 * may occasionally miss source routing options on incompatible 88 * systems such as Linux. Their choice. 89 * 90 * Look for source routing options. Drop the connection when one is 91 * found. Just wiping the IP options is insufficient: we would still 92 * help the attacker by providing a real TCP sequence number, and the 93 * attacker would still be able to send packets (blind spoofing). I 94 * discussed this attack with Niels Provos, half a year before the 95 * attack was described in open mailing lists. 96 * 97 * It would be cleaner to just return a yes/no reply and let the caller 98 * decide how to deal with it. Resident servers should not terminate. 99 * However I am not prepared to make changes to internal interfaces 100 * on short notice. 101 */ 102 #define ADDR_LEN sizeof(dummy.s_addr) 103 104 for (cp = optbuf + ADDR_LEN; cp < optbuf + optsize; cp += optlen) { 105 opt = cp[IPOPT_OPTVAL]; 106 if (opt == IPOPT_LSRR || opt == IPOPT_SSRR) { 107 syslog(LOG_WARNING, 108 "refused connect from %s with IP source routing options", 109 eval_client(request)); 110 shutdown(fd, 2); 111 return; 112 } 113 if (opt == IPOPT_EOL) 114 break; 115 if (opt == IPOPT_NOP) { 116 optlen = 1; 117 } else if (&cp[IPOPT_OLEN] < optbuf + optsize) { 118 optlen = cp[IPOPT_OLEN]; 119 if (optlen < 2 || cp + optlen >= optbuf + optsize) { 120 syslog(LOG_WARNING, 121 "refused connect from %s with malformed IP options", 122 eval_client(request)); 123 shutdown(fd, 2); 124 return; 125 } 126 } else { 127 syslog(LOG_WARNING, 128 "refused connect from %s with malformed IP options", 129 eval_client(request)); 130 shutdown(fd, 2); 131 return; 132 } 133 } 134 lp = lbuf; 135 for (cp = optbuf; optsize > 0; cp++, optsize--, lp += 3) 136 len -= snprintf(lp, len, " %2.2x", *cp); 137 syslog(LOG_NOTICE, 138 "connect from %s with IP options (ignored):%s", 139 eval_client(request), lbuf); 140 if (setsockopt(fd, ipproto, IP_OPTIONS, (char *) 0, optsize) != 0) { 141 syslog(LOG_ERR, "setsockopt IP_OPTIONS NULL: %m"); 142 shutdown(fd, 2); 143 } 144 } 145 #endif 146 } 147