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