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
9static 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
32fix_options(request)
33struct 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}