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 * $FreeBSD: src/contrib/tcp_wrappers/fix_options.c,v 1.2 2000/02/03 10:26:57 shin Exp $ 8 * $DragonFly: src/contrib/tcp_wrappers/fix_options.c,v 1.2 2003/06/17 04:24:06 dillon Exp $ 9 */ 10 11 #ifndef lint 12 static char sccsid[] = "@(#) fix_options.c 1.6 97/04/08 02:29:19"; 13 #endif 14 15 #include <sys/types.h> 16 #include <sys/param.h> 17 #ifdef INET6 18 #include <sys/socket.h> 19 #endif 20 #include <netinet/in.h> 21 #include <netinet/in_systm.h> 22 #include <netinet/ip.h> 23 #include <netdb.h> 24 #include <stdio.h> 25 #include <syslog.h> 26 27 #ifndef IPOPT_OPTVAL 28 #define IPOPT_OPTVAL 0 29 #define IPOPT_OLEN 1 30 #endif 31 32 #include "tcpd.h" 33 34 #define BUFFER_SIZE 512 /* Was: BUFSIZ */ 35 36 /* fix_options - get rid of IP-level socket options */ 37 38 void 39 fix_options(request) 40 struct request_info *request; 41 { 42 #ifdef IP_OPTIONS 43 unsigned char optbuf[BUFFER_SIZE / 3], *cp; 44 char lbuf[BUFFER_SIZE], *lp; 45 int optsize = sizeof(optbuf), ipproto; 46 struct protoent *ip; 47 int fd = request->fd; 48 unsigned int opt; 49 int optlen; 50 struct in_addr dummy; 51 #ifdef INET6 52 struct sockaddr_storage ss; 53 int sslen; 54 55 /* 56 * check if this is AF_INET socket 57 * XXX IPv6 support? 58 */ 59 sslen = sizeof(ss); 60 if (getsockname(fd, (struct sockaddr *)&ss, &sslen) < 0) { 61 syslog(LOG_ERR, "getpeername: %m"); 62 clean_exit(request); 63 } 64 if (ss.ss_family != AF_INET) 65 return; 66 #endif 67 68 if ((ip = getprotobyname("ip")) != 0) 69 ipproto = ip->p_proto; 70 else 71 ipproto = IPPROTO_IP; 72 73 if (getsockopt(fd, ipproto, IP_OPTIONS, (char *) optbuf, &optsize) == 0 74 && optsize != 0) { 75 76 /* 77 * Horror! 4.[34] BSD getsockopt() prepends the first-hop destination 78 * address to the result IP options list when source routing options 79 * are present (see <netinet/ip_var.h>), but produces no output for 80 * other IP options. Solaris 2.x getsockopt() does produce output for 81 * non-routing IP options, and uses the same format as BSD even when 82 * the space for the destination address is unused. The code below 83 * does the right thing with 4.[34]BSD derivatives and Solaris 2, but 84 * may occasionally miss source routing options on incompatible 85 * systems such as Linux. Their choice. 86 * 87 * Look for source routing options. Drop the connection when one is 88 * found. Just wiping the IP options is insufficient: we would still 89 * help the attacker by providing a real TCP sequence number, and the 90 * attacker would still be able to send packets (blind spoofing). I 91 * discussed this attack with Niels Provos, half a year before the 92 * attack was described in open mailing lists. 93 * 94 * It would be cleaner to just return a yes/no reply and let the caller 95 * decide how to deal with it. Resident servers should not terminate. 96 * However I am not prepared to make changes to internal interfaces 97 * on short notice. 98 */ 99 #define ADDR_LEN sizeof(dummy.s_addr) 100 101 for (cp = optbuf + ADDR_LEN; cp < optbuf + optsize; cp += optlen) { 102 opt = cp[IPOPT_OPTVAL]; 103 if (opt == IPOPT_LSRR || opt == IPOPT_SSRR) { 104 syslog(LOG_WARNING, 105 "refused connect from %s with IP source routing options", 106 eval_client(request)); 107 shutdown(fd, 2); 108 return; 109 } 110 if (opt == IPOPT_EOL) 111 break; 112 if (opt == IPOPT_NOP) { 113 optlen = 1; 114 } else { 115 optlen = cp[IPOPT_OLEN]; 116 if (optlen <= 0) /* Do not loop! */ 117 break; 118 } 119 } 120 lp = lbuf; 121 for (cp = optbuf; optsize > 0; cp++, optsize--, lp += 3) 122 sprintf(lp, " %2.2x", *cp); 123 syslog(LOG_NOTICE, 124 "connect from %s with IP options (ignored):%s", 125 eval_client(request), lbuf); 126 if (setsockopt(fd, ipproto, IP_OPTIONS, (char *) 0, optsize) != 0) { 127 syslog(LOG_ERR, "setsockopt IP_OPTIONS NULL: %m"); 128 shutdown(fd, 2); 129 } 130 } 131 #endif 132 } 133