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.
5 * Author: Wietse Venema, Eindhoven University of Technology, The Netherlands.
7 * $FreeBSD: src/contrib/tcp_wrappers/fix_options.c,v 1.2 2000/02/03 10:26:57 shin Exp $
10 #include <sys/types.h>
11 #include <sys/param.h>
13 #include <sys/socket.h>
15 #include <netinet/in.h>
16 #include <netinet/in_systm.h>
17 #include <netinet/ip.h>
23 #define IPOPT_OPTVAL 0
29 #define BUFFER_SIZE 512 /* Was: BUFSIZ */
31 /* fix_options - get rid of IP-level socket options */
35 struct request_info *request;
38 unsigned char optbuf[BUFFER_SIZE / 3], *cp;
39 char lbuf[BUFFER_SIZE], *lp;
40 int optsize = sizeof(optbuf), ipproto;
47 struct sockaddr_storage ss;
51 * check if this is AF_INET socket
55 if (getsockname(fd, (struct sockaddr *)&ss, &sslen) < 0) {
56 syslog(LOG_ERR, "getpeername: %m");
59 if (ss.ss_family != AF_INET)
63 if ((ip = getprotobyname("ip")) != 0)
64 ipproto = ip->p_proto;
68 if (getsockopt(fd, ipproto, IP_OPTIONS, (char *) optbuf, &optsize) == 0
72 * Horror! 4.[34] BSD getsockopt() prepends the first-hop destination
73 * address to the result IP options list when source routing options
74 * are present (see <netinet/ip_var.h>), but produces no output for
75 * other IP options. Solaris 2.x getsockopt() does produce output for
76 * non-routing IP options, and uses the same format as BSD even when
77 * the space for the destination address is unused. The code below
78 * does the right thing with 4.[34]BSD derivatives and Solaris 2, but
79 * may occasionally miss source routing options on incompatible
80 * systems such as Linux. Their choice.
82 * Look for source routing options. Drop the connection when one is
83 * found. Just wiping the IP options is insufficient: we would still
84 * help the attacker by providing a real TCP sequence number, and the
85 * attacker would still be able to send packets (blind spoofing). I
86 * discussed this attack with Niels Provos, half a year before the
87 * attack was described in open mailing lists.
89 * It would be cleaner to just return a yes/no reply and let the caller
90 * decide how to deal with it. Resident servers should not terminate.
91 * However I am not prepared to make changes to internal interfaces
94 #define ADDR_LEN sizeof(dummy.s_addr)
96 for (cp = optbuf + ADDR_LEN; cp < optbuf + optsize; cp += optlen) {
97 opt = cp[IPOPT_OPTVAL];
98 if (opt == IPOPT_LSRR || opt == IPOPT_SSRR) {
100 "refused connect from %s with IP source routing options",
101 eval_client(request));
105 if (opt == IPOPT_EOL)
107 if (opt == IPOPT_NOP) {
110 optlen = cp[IPOPT_OLEN];
111 if (optlen <= 0) /* Do not loop! */
116 for (cp = optbuf; optsize > 0; cp++, optsize--, lp += 3)
117 sprintf(lp, " %2.2x", *cp);
119 "connect from %s with IP options (ignored):%s",
120 eval_client(request), lbuf);
121 if (setsockopt(fd, ipproto, IP_OPTIONS, (char *) 0, optsize) != 0) {
122 syslog(LOG_ERR, "setsockopt IP_OPTIONS NULL: %m");