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
fix_options(request)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