xref: /freebsd/crypto/openssh/canohost.c (revision 6472ac3d8a86336899b6cfb789a4cd9897e3fab5)
1 /* $OpenBSD: canohost.c,v 1.66 2010/01/13 01:20:20 dtucker Exp $ */
2 /*
3  * Author: Tatu Ylonen <ylo@cs.hut.fi>
4  * Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
5  *                    All rights reserved
6  * Functions for returning the canonical host name of the remote site.
7  *
8  * As far as I am concerned, the code I have written for this software
9  * can be used freely for any purpose.  Any derived versions of this
10  * software must be clearly marked as such, and if the derived work is
11  * incompatible with the protocol description in the RFC file, it must be
12  * called by a name other than "ssh" or "Secure Shell".
13  */
14 
15 #include "includes.h"
16 
17 #include <sys/types.h>
18 #include <sys/socket.h>
19 
20 #include <netinet/in.h>
21 #include <arpa/inet.h>
22 
23 #include <ctype.h>
24 #include <errno.h>
25 #include <netdb.h>
26 #include <stdio.h>
27 #include <stdlib.h>
28 #include <string.h>
29 #include <stdarg.h>
30 #include <unistd.h>
31 
32 #include "xmalloc.h"
33 #include "packet.h"
34 #include "log.h"
35 #include "canohost.h"
36 #include "misc.h"
37 
38 static void check_ip_options(int, char *);
39 static char *canonical_host_ip = NULL;
40 static int cached_port = -1;
41 
42 /*
43  * Return the canonical name of the host at the other end of the socket. The
44  * caller should free the returned string with xfree.
45  */
46 
47 static char *
48 get_remote_hostname(int sock, int use_dns)
49 {
50 	struct sockaddr_storage from;
51 	int i;
52 	socklen_t fromlen;
53 	struct addrinfo hints, *ai, *aitop;
54 	char name[NI_MAXHOST], ntop[NI_MAXHOST], ntop2[NI_MAXHOST];
55 
56 	/* Get IP address of client. */
57 	fromlen = sizeof(from);
58 	memset(&from, 0, sizeof(from));
59 	if (getpeername(sock, (struct sockaddr *)&from, &fromlen) < 0) {
60 		debug("getpeername failed: %.100s", strerror(errno));
61 		cleanup_exit(255);
62 	}
63 
64 	if (from.ss_family == AF_INET)
65 		check_ip_options(sock, ntop);
66 
67 	ipv64_normalise_mapped(&from, &fromlen);
68 
69 	if (from.ss_family == AF_INET6)
70 		fromlen = sizeof(struct sockaddr_in6);
71 
72 	if (getnameinfo((struct sockaddr *)&from, fromlen, ntop, sizeof(ntop),
73 	    NULL, 0, NI_NUMERICHOST) != 0)
74 		fatal("get_remote_hostname: getnameinfo NI_NUMERICHOST failed");
75 
76 	if (!use_dns)
77 		return xstrdup(ntop);
78 
79 	debug3("Trying to reverse map address %.100s.", ntop);
80 	/* Map the IP address to a host name. */
81 	if (getnameinfo((struct sockaddr *)&from, fromlen, name, sizeof(name),
82 	    NULL, 0, NI_NAMEREQD) != 0) {
83 		/* Host name not found.  Use ip address. */
84 		return xstrdup(ntop);
85 	}
86 
87 	/*
88 	 * if reverse lookup result looks like a numeric hostname,
89 	 * someone is trying to trick us by PTR record like following:
90 	 *	1.1.1.10.in-addr.arpa.	IN PTR	2.3.4.5
91 	 */
92 	memset(&hints, 0, sizeof(hints));
93 	hints.ai_socktype = SOCK_DGRAM;	/*dummy*/
94 	hints.ai_flags = AI_NUMERICHOST;
95 	if (getaddrinfo(name, NULL, &hints, &ai) == 0) {
96 		logit("Nasty PTR record \"%s\" is set up for %s, ignoring",
97 		    name, ntop);
98 		freeaddrinfo(ai);
99 		return xstrdup(ntop);
100 	}
101 
102 	/*
103 	 * Convert it to all lowercase (which is expected by the rest
104 	 * of this software).
105 	 */
106 	for (i = 0; name[i]; i++)
107 		if (isupper(name[i]))
108 			name[i] = (char)tolower(name[i]);
109 	/*
110 	 * Map it back to an IP address and check that the given
111 	 * address actually is an address of this host.  This is
112 	 * necessary because anyone with access to a name server can
113 	 * define arbitrary names for an IP address. Mapping from
114 	 * name to IP address can be trusted better (but can still be
115 	 * fooled if the intruder has access to the name server of
116 	 * the domain).
117 	 */
118 	memset(&hints, 0, sizeof(hints));
119 	hints.ai_family = from.ss_family;
120 	hints.ai_socktype = SOCK_STREAM;
121 	if (getaddrinfo(name, NULL, &hints, &aitop) != 0) {
122 		logit("reverse mapping checking getaddrinfo for %.700s "
123 		    "[%s] failed - POSSIBLE BREAK-IN ATTEMPT!", name, ntop);
124 		return xstrdup(ntop);
125 	}
126 	/* Look for the address from the list of addresses. */
127 	for (ai = aitop; ai; ai = ai->ai_next) {
128 		if (getnameinfo(ai->ai_addr, ai->ai_addrlen, ntop2,
129 		    sizeof(ntop2), NULL, 0, NI_NUMERICHOST) == 0 &&
130 		    (strcmp(ntop, ntop2) == 0))
131 				break;
132 	}
133 	freeaddrinfo(aitop);
134 	/* If we reached the end of the list, the address was not there. */
135 	if (!ai) {
136 		/* Address not found for the host name. */
137 		logit("Address %.100s maps to %.600s, but this does not "
138 		    "map back to the address - POSSIBLE BREAK-IN ATTEMPT!",
139 		    ntop, name);
140 		return xstrdup(ntop);
141 	}
142 	return xstrdup(name);
143 }
144 
145 /*
146  * If IP options are supported, make sure there are none (log and
147  * disconnect them if any are found).  Basically we are worried about
148  * source routing; it can be used to pretend you are somebody
149  * (ip-address) you are not. That itself may be "almost acceptable"
150  * under certain circumstances, but rhosts autentication is useless
151  * if source routing is accepted. Notice also that if we just dropped
152  * source routing here, the other side could use IP spoofing to do
153  * rest of the interaction and could still bypass security.  So we
154  * exit here if we detect any IP options.
155  */
156 /* IPv4 only */
157 static void
158 check_ip_options(int sock, char *ipaddr)
159 {
160 #ifdef IP_OPTIONS
161 	u_char options[200];
162 	char text[sizeof(options) * 3 + 1];
163 	socklen_t option_size;
164 	u_int i;
165 	int ipproto;
166 	struct protoent *ip;
167 
168 	if ((ip = getprotobyname("ip")) != NULL)
169 		ipproto = ip->p_proto;
170 	else
171 		ipproto = IPPROTO_IP;
172 	option_size = sizeof(options);
173 	if (getsockopt(sock, ipproto, IP_OPTIONS, options,
174 	    &option_size) >= 0 && option_size != 0) {
175 		text[0] = '\0';
176 		for (i = 0; i < option_size; i++)
177 			snprintf(text + i*3, sizeof(text) - i*3,
178 			    " %2.2x", options[i]);
179 		fatal("Connection from %.100s with IP options:%.800s",
180 		    ipaddr, text);
181 	}
182 #endif /* IP_OPTIONS */
183 }
184 
185 void
186 ipv64_normalise_mapped(struct sockaddr_storage *addr, socklen_t *len)
187 {
188 	struct sockaddr_in6 *a6 = (struct sockaddr_in6 *)addr;
189 	struct sockaddr_in *a4 = (struct sockaddr_in *)addr;
190 	struct in_addr inaddr;
191 	u_int16_t port;
192 
193 	if (addr->ss_family != AF_INET6 ||
194 	    !IN6_IS_ADDR_V4MAPPED(&a6->sin6_addr))
195 		return;
196 
197 	debug3("Normalising mapped IPv4 in IPv6 address");
198 
199 	memcpy(&inaddr, ((char *)&a6->sin6_addr) + 12, sizeof(inaddr));
200 	port = a6->sin6_port;
201 
202 	bzero(a4, sizeof(*a4));
203 
204 	a4->sin_family = AF_INET;
205 	*len = sizeof(*a4);
206 	memcpy(&a4->sin_addr, &inaddr, sizeof(inaddr));
207 	a4->sin_port = port;
208 }
209 
210 /*
211  * Return the canonical name of the host in the other side of the current
212  * connection.  The host name is cached, so it is efficient to call this
213  * several times.
214  */
215 
216 const char *
217 get_canonical_hostname(int use_dns)
218 {
219 	char *host;
220 	static char *canonical_host_name = NULL;
221 	static char *remote_ip = NULL;
222 
223 	/* Check if we have previously retrieved name with same option. */
224 	if (use_dns && canonical_host_name != NULL)
225 		return canonical_host_name;
226 	if (!use_dns && remote_ip != NULL)
227 		return remote_ip;
228 
229 	/* Get the real hostname if socket; otherwise return UNKNOWN. */
230 	if (packet_connection_is_on_socket())
231 		host = get_remote_hostname(packet_get_connection_in(), use_dns);
232 	else
233 		host = "UNKNOWN";
234 
235 	if (use_dns)
236 		canonical_host_name = host;
237 	else
238 		remote_ip = host;
239 	return host;
240 }
241 
242 /*
243  * Returns the local/remote IP-address/hostname of socket as a string.
244  * The returned string must be freed.
245  */
246 static char *
247 get_socket_address(int sock, int remote, int flags)
248 {
249 	struct sockaddr_storage addr;
250 	socklen_t addrlen;
251 	char ntop[NI_MAXHOST];
252 	int r;
253 
254 	/* Get IP address of client. */
255 	addrlen = sizeof(addr);
256 	memset(&addr, 0, sizeof(addr));
257 
258 	if (remote) {
259 		if (getpeername(sock, (struct sockaddr *)&addr, &addrlen)
260 		    < 0)
261 			return NULL;
262 	} else {
263 		if (getsockname(sock, (struct sockaddr *)&addr, &addrlen)
264 		    < 0)
265 			return NULL;
266 	}
267 
268 	/* Work around Linux IPv6 weirdness */
269 	if (addr.ss_family == AF_INET6)
270 		addrlen = sizeof(struct sockaddr_in6);
271 
272 	ipv64_normalise_mapped(&addr, &addrlen);
273 
274 	/* Get the address in ascii. */
275 	if ((r = getnameinfo((struct sockaddr *)&addr, addrlen, ntop,
276 	    sizeof(ntop), NULL, 0, flags)) != 0) {
277 		error("get_socket_address: getnameinfo %d failed: %s", flags,
278 		    ssh_gai_strerror(r));
279 		return NULL;
280 	}
281 	return xstrdup(ntop);
282 }
283 
284 char *
285 get_peer_ipaddr(int sock)
286 {
287 	char *p;
288 
289 	if ((p = get_socket_address(sock, 1, NI_NUMERICHOST)) != NULL)
290 		return p;
291 	return xstrdup("UNKNOWN");
292 }
293 
294 char *
295 get_local_ipaddr(int sock)
296 {
297 	char *p;
298 
299 	if ((p = get_socket_address(sock, 0, NI_NUMERICHOST)) != NULL)
300 		return p;
301 	return xstrdup("UNKNOWN");
302 }
303 
304 char *
305 get_local_name(int fd)
306 {
307 	char *host, myname[NI_MAXHOST];
308 
309 	/* Assume we were passed a socket */
310 	if ((host = get_socket_address(fd, 0, NI_NAMEREQD)) != NULL)
311 		return host;
312 
313 	/* Handle the case where we were passed a pipe */
314 	if (gethostname(myname, sizeof(myname)) == -1) {
315 		verbose("get_local_name: gethostname: %s", strerror(errno));
316 	} else {
317 		host = xstrdup(myname);
318 	}
319 
320 	return host;
321 }
322 
323 void
324 clear_cached_addr(void)
325 {
326 	if (canonical_host_ip != NULL) {
327 		xfree(canonical_host_ip);
328 		canonical_host_ip = NULL;
329 	}
330 	cached_port = -1;
331 }
332 
333 /*
334  * Returns the IP-address of the remote host as a string.  The returned
335  * string must not be freed.
336  */
337 
338 const char *
339 get_remote_ipaddr(void)
340 {
341 	/* Check whether we have cached the ipaddr. */
342 	if (canonical_host_ip == NULL) {
343 		if (packet_connection_is_on_socket()) {
344 			canonical_host_ip =
345 			    get_peer_ipaddr(packet_get_connection_in());
346 			if (canonical_host_ip == NULL)
347 				cleanup_exit(255);
348 		} else {
349 			/* If not on socket, return UNKNOWN. */
350 			canonical_host_ip = xstrdup("UNKNOWN");
351 		}
352 	}
353 	return canonical_host_ip;
354 }
355 
356 const char *
357 get_remote_name_or_ip(u_int utmp_len, int use_dns)
358 {
359 	static const char *remote = "";
360 	if (utmp_len > 0)
361 		remote = get_canonical_hostname(use_dns);
362 	if (utmp_len == 0 || strlen(remote) > utmp_len)
363 		remote = get_remote_ipaddr();
364 	return remote;
365 }
366 
367 /* Returns the local/remote port for the socket. */
368 
369 int
370 get_sock_port(int sock, int local)
371 {
372 	struct sockaddr_storage from;
373 	socklen_t fromlen;
374 	char strport[NI_MAXSERV];
375 	int r;
376 
377 	/* Get IP address of client. */
378 	fromlen = sizeof(from);
379 	memset(&from, 0, sizeof(from));
380 	if (local) {
381 		if (getsockname(sock, (struct sockaddr *)&from, &fromlen) < 0) {
382 			error("getsockname failed: %.100s", strerror(errno));
383 			return 0;
384 		}
385 	} else {
386 		if (getpeername(sock, (struct sockaddr *)&from, &fromlen) < 0) {
387 			debug("getpeername failed: %.100s", strerror(errno));
388 			return -1;
389 		}
390 	}
391 
392 	/* Work around Linux IPv6 weirdness */
393 	if (from.ss_family == AF_INET6)
394 		fromlen = sizeof(struct sockaddr_in6);
395 
396 	/* Return port number. */
397 	if ((r = getnameinfo((struct sockaddr *)&from, fromlen, NULL, 0,
398 	    strport, sizeof(strport), NI_NUMERICSERV)) != 0)
399 		fatal("get_sock_port: getnameinfo NI_NUMERICSERV failed: %s",
400 		    ssh_gai_strerror(r));
401 	return atoi(strport);
402 }
403 
404 /* Returns remote/local port number for the current connection. */
405 
406 static int
407 get_port(int local)
408 {
409 	/*
410 	 * If the connection is not a socket, return 65535.  This is
411 	 * intentionally chosen to be an unprivileged port number.
412 	 */
413 	if (!packet_connection_is_on_socket())
414 		return 65535;
415 
416 	/* Get socket and return the port number. */
417 	return get_sock_port(packet_get_connection_in(), local);
418 }
419 
420 int
421 get_peer_port(int sock)
422 {
423 	return get_sock_port(sock, 0);
424 }
425 
426 int
427 get_remote_port(void)
428 {
429 	/* Cache to avoid getpeername() on a dead connection */
430 	if (cached_port == -1)
431 		cached_port = get_port(0);
432 
433 	return cached_port;
434 }
435 
436 int
437 get_local_port(void)
438 {
439 	return get_port(1);
440 }
441