canohost.c

   1 /* $OpenBSD: canohost.c,v 1.65 2009/05/27 06:31:25 andreas 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
  31 #include "xmalloc.h"
  32 #include "packet.h"
  33 #include "log.h"
  34 #include "canohost.h"
  35 #include "misc.h"
  36
  37 static void check_ip_options(int, char *);
  38 static char *canonical_host_ip = NULL;
  39 static int cached_port = -1;
  40
  41 /*
  42  * Return the canonical name of the host at the other end of the socket. The
  43  * caller should free the returned string with xfree.
  44  */
  45
  46 static char *
  47 get_remote_hostname(int sock, int use_dns)
  48 {
  49         struct sockaddr_storage from;
  50         int i;
  51         socklen_t fromlen;
  52         struct addrinfo hints, *ai, *aitop;
  53         char name[NI_MAXHOST], ntop[NI_MAXHOST], ntop2[NI_MAXHOST];
  54
  55         /* Get IP address of client. */
  56         fromlen = sizeof(from);
  57         memset(&from, 0, sizeof(from));
  58         if (getpeername(sock, (struct sockaddr *)&from, &fromlen) < 0) {
  59                 debug("getpeername failed: %.100s", strerror(errno));
  60                 cleanup_exit(255);
  61         }
  62
  63         if (from.ss_family == AF_INET)
  64                 check_ip_options(sock, ntop);
  65
  66         ipv64_normalise_mapped(&from, &fromlen);
  67
  68         if (from.ss_family == AF_INET6)
  69                 fromlen = sizeof(struct sockaddr_in6);
  70
  71         if (getnameinfo((struct sockaddr *)&from, fromlen, ntop, sizeof(ntop),
  72             NULL, 0, NI_NUMERICHOST) != 0)
  73                 fatal("get_remote_hostname: getnameinfo NI_NUMERICHOST failed");
  74
  75         if (!use_dns)
  76                 return xstrdup(ntop);
  77
  78         debug3("Trying to reverse map address %.100s.", ntop);
  79         /* Map the IP address to a host name. */
  80         if (getnameinfo((struct sockaddr *)&from, fromlen, name, sizeof(name),
  81             NULL, 0, NI_NAMEREQD) != 0) {
  82                 /* Host name not found.  Use ip address. */
  83                 return xstrdup(ntop);
  84         }
  85
  86         /*
  87          * if reverse lookup result looks like a numeric hostname,
  88          * someone is trying to trick us by PTR record like following:
  89          *      1.1.1.10.in-addr.arpa.  IN PTR  2.3.4.5
  90          */
  91         memset(&hints, 0, sizeof(hints));
  92         hints.ai_socktype = SOCK_DGRAM; /*dummy*/
  93         hints.ai_flags = AI_NUMERICHOST;
  94         if (getaddrinfo(name, NULL, &hints, &ai) == 0) {
  95                 logit("Nasty PTR record \"%s\" is set up for %s, ignoring",
  96                     name, ntop);
  97                 freeaddrinfo(ai);
  98                 return xstrdup(ntop);
  99         }
 100
 101         /*
 102          * Convert it to all lowercase (which is expected by the rest
 103          * of this software).
 104          */
 105         for (i = 0; name[i]; i++)
 106                 if (isupper(name[i]))
 107                         name[i] = (char)tolower(name[i]);
 108         /*
 109          * Map it back to an IP address and check that the given
 110          * address actually is an address of this host.  This is
 111          * necessary because anyone with access to a name server can
 112          * define arbitrary names for an IP address. Mapping from
 113          * name to IP address can be trusted better (but can still be
 114          * fooled if the intruder has access to the name server of
 115          * the domain).
 116          */
 117         memset(&hints, 0, sizeof(hints));
 118         hints.ai_family = from.ss_family;
 119         hints.ai_socktype = SOCK_STREAM;
 120         if (getaddrinfo(name, NULL, &hints, &aitop) != 0) {
 121                 logit("reverse mapping checking getaddrinfo for %.700s "
 122                     "[%s] failed - POSSIBLE BREAK-IN ATTEMPT!", name, ntop);
 123                 return xstrdup(ntop);
 124         }
 125         /* Look for the address from the list of addresses. */
 126         for (ai = aitop; ai; ai = ai->ai_next) {
 127                 if (getnameinfo(ai->ai_addr, ai->ai_addrlen, ntop2,
 128                     sizeof(ntop2), NULL, 0, NI_NUMERICHOST) == 0 &&
 129                     (strcmp(ntop, ntop2) == 0))
 130                                 break;
 131         }
 132         freeaddrinfo(aitop);
 133         /* If we reached the end of the list, the address was not there. */
 134         if (!ai) {
 135                 /* Address not found for the host name. */
 136                 logit("Address %.100s maps to %.600s, but this does not "
 137                     "map back to the address - POSSIBLE BREAK-IN ATTEMPT!",
 138                     ntop, name);
 139                 return xstrdup(ntop);
 140         }
 141         return xstrdup(name);
 142 }
 143
 144 /*
 145  * If IP options are supported, make sure there are none (log and
 146  * disconnect them if any are found).  Basically we are worried about
 147  * source routing; it can be used to pretend you are somebody
 148  * (ip-address) you are not. That itself may be "almost acceptable"
 149  * under certain circumstances, but rhosts autentication is useless
 150  * if source routing is accepted. Notice also that if we just dropped
 151  * source routing here, the other side could use IP spoofing to do
 152  * rest of the interaction and could still bypass security.  So we
 153  * exit here if we detect any IP options.
 154  */
 155 /* IPv4 only */
 156 static void
 157 check_ip_options(int sock, char *ipaddr)
 158 {
 159 #ifdef IP_OPTIONS
 160         u_char options[200];
 161         char text[sizeof(options) * 3 + 1];
 162         socklen_t option_size;
 163         u_int i;
 164         int ipproto;
 165         struct protoent *ip;
 166
 167         if ((ip = getprotobyname("ip")) != NULL)
 168                 ipproto = ip->p_proto;
 169         else
 170                 ipproto = IPPROTO_IP;
 171         option_size = sizeof(options);
 172         if (getsockopt(sock, ipproto, IP_OPTIONS, options,
 173             &option_size) >= 0 && option_size != 0) {
 174                 text[0] = '\0';
 175                 for (i = 0; i < option_size; i++)
 176                         snprintf(text + i*3, sizeof(text) - i*3,
 177                             " %2.2x", options[i]);
 178                 fatal("Connection from %.100s with IP options:%.800s",
 179                     ipaddr, text);
 180         }
 181 #endif /* IP_OPTIONS */
 182 }
 183
 184 void
 185 ipv64_normalise_mapped(struct sockaddr_storage *addr, socklen_t *len)
 186 {
 187         struct sockaddr_in6 *a6 = (struct sockaddr_in6 *)addr;
 188         struct sockaddr_in *a4 = (struct sockaddr_in *)addr;
 189         struct in_addr inaddr;
 190         u_int16_t port;
 191
 192         if (addr->ss_family != AF_INET6 ||
 193             !IN6_IS_ADDR_V4MAPPED(&a6->sin6_addr))
 194                 return;
 195
 196         debug3("Normalising mapped IPv4 in IPv6 address");
 197
 198         memcpy(&inaddr, ((char *)&a6->sin6_addr) + 12, sizeof(inaddr));
 199         port = a6->sin6_port;
 200
 201         memset(addr, 0, sizeof(*a4));
 202
 203         a4->sin_family = AF_INET;
 204         *len = sizeof(*a4);
 205         memcpy(&a4->sin_addr, &inaddr, sizeof(inaddr));
 206         a4->sin_port = port;
 207 }
 208
 209 /*
 210  * Return the canonical name of the host in the other side of the current
 211  * connection.  The host name is cached, so it is efficient to call this
 212  * several times.
 213  */
 214
 215 const char *
 216 get_canonical_hostname(int use_dns)
 217 {
 218         char *host;
 219         static char *canonical_host_name = NULL;
 220         static char *remote_ip = NULL;
 221
 222         /* Check if we have previously retrieved name with same option. */
 223         if (use_dns && canonical_host_name != NULL)
 224                 return canonical_host_name;
 225         if (!use_dns && remote_ip != NULL)
 226                 return remote_ip;
 227
 228         /* Get the real hostname if socket; otherwise return UNKNOWN. */
 229         if (packet_connection_is_on_socket())
 230                 host = get_remote_hostname(packet_get_connection_in(), use_dns);
 231         else
 232                 host = "UNKNOWN";
 233
 234         if (use_dns)
 235                 canonical_host_name = host;
 236         else
 237                 remote_ip = host;
 238         return host;
 239 }
 240
 241 /*
 242  * Returns the local/remote IP-address/hostname of socket as a string.
 243  * The returned string must be freed.
 244  */
 245 static char *
 246 get_socket_address(int sock, int remote, int flags)
 247 {
 248         struct sockaddr_storage addr;
 249         socklen_t addrlen;
 250         char ntop[NI_MAXHOST];
 251         int r;
 252
 253         /* Get IP address of client. */
 254         addrlen = sizeof(addr);
 255         memset(&addr, 0, sizeof(addr));
 256
 257         if (remote) {
 258                 if (getpeername(sock, (struct sockaddr *)&addr, &addrlen)
 259                     < 0)
 260                         return NULL;
 261         } else {
 262                 if (getsockname(sock, (struct sockaddr *)&addr, &addrlen)
 263                     < 0)
 264                         return NULL;
 265         }
 266
 267         /* Work around Linux IPv6 weirdness */
 268         if (addr.ss_family == AF_INET6)
 269                 addrlen = sizeof(struct sockaddr_in6);
 270
 271         ipv64_normalise_mapped(&addr, &addrlen);
 272
 273         /* Get the address in ascii. */
 274         if ((r = getnameinfo((struct sockaddr *)&addr, addrlen, ntop,
 275             sizeof(ntop), NULL, 0, flags)) != 0) {
 276                 error("get_socket_address: getnameinfo %d failed: %s", flags,
 277                     ssh_gai_strerror(r));
 278                 return NULL;
 279         }
 280         return xstrdup(ntop);
 281 }
 282
 283 char *
 284 get_peer_ipaddr(int sock)
 285 {
 286         char *p;
 287
 288         if ((p = get_socket_address(sock, 1, NI_NUMERICHOST)) != NULL)
 289                 return p;
 290         return xstrdup("UNKNOWN");
 291 }
 292
 293 char *
 294 get_local_ipaddr(int sock)
 295 {
 296         char *p;
 297
 298         if ((p = get_socket_address(sock, 0, NI_NUMERICHOST)) != NULL)
 299                 return p;
 300         return xstrdup("UNKNOWN");
 301 }
 302
 303 char *
 304 get_local_name(int sock)
 305 {
 306         return get_socket_address(sock, 0, NI_NAMEREQD);
 307 }
 308
 309 void
 310 clear_cached_addr(void)
 311 {
 312         if (canonical_host_ip != NULL) {
 313                 xfree(canonical_host_ip);
 314                 canonical_host_ip = NULL;
 315         }
 316         cached_port = -1;
 317 }
 318
 319 /*
 320  * Returns the IP-address of the remote host as a string.  The returned
 321  * string must not be freed.
 322  */
 323
 324 const char *
 325 get_remote_ipaddr(void)
 326 {
 327         /* Check whether we have cached the ipaddr. */
 328         if (canonical_host_ip == NULL) {
 329                 if (packet_connection_is_on_socket()) {
 330                         canonical_host_ip =
 331                             get_peer_ipaddr(packet_get_connection_in());
 332                         if (canonical_host_ip == NULL)
 333                                 cleanup_exit(255);
 334                 } else {
 335                         /* If not on socket, return UNKNOWN. */
 336                         canonical_host_ip = xstrdup("UNKNOWN");
 337                 }
 338         }
 339         return canonical_host_ip;
 340 }
 341
 342 const char *
 343 get_remote_name_or_ip(u_int utmp_len, int use_dns)
 344 {
 345         static const char *remote = "";
 346         if (utmp_len > 0)
 347                 remote = get_canonical_hostname(use_dns);
 348         if (utmp_len == 0 || strlen(remote) > utmp_len)
 349                 remote = get_remote_ipaddr();
 350         return remote;
 351 }
 352
 353 /* Returns the local/remote port for the socket. */
 354
 355 int
 356 get_sock_port(int sock, int local)
 357 {
 358         struct sockaddr_storage from;
 359         socklen_t fromlen;
 360         char strport[NI_MAXSERV];
 361         int r;
 362
 363         /* Get IP address of client. */
 364         fromlen = sizeof(from);
 365         memset(&from, 0, sizeof(from));
 366         if (local) {
 367                 if (getsockname(sock, (struct sockaddr *)&from, &fromlen) < 0) {
 368                         error("getsockname failed: %.100s", strerror(errno));
 369                         return 0;
 370                 }
 371         } else {
 372                 if (getpeername(sock, (struct sockaddr *)&from, &fromlen) < 0) {
 373                         debug("getpeername failed: %.100s", strerror(errno));
 374                         return -1;
 375                 }
 376         }
 377
 378         /* Work around Linux IPv6 weirdness */
 379         if (from.ss_family == AF_INET6)
 380                 fromlen = sizeof(struct sockaddr_in6);
 381
 382         /* Return port number. */
 383         if ((r = getnameinfo((struct sockaddr *)&from, fromlen, NULL, 0,
 384             strport, sizeof(strport), NI_NUMERICSERV)) != 0)
 385                 fatal("get_sock_port: getnameinfo NI_NUMERICSERV failed: %s",
 386                     ssh_gai_strerror(r));
 387         return atoi(strport);
 388 }
 389
 390 /* Returns remote/local port number for the current connection. */
 391
 392 static int
 393 get_port(int local)
 394 {
 395         /*
 396          * If the connection is not a socket, return 65535.  This is
 397          * intentionally chosen to be an unprivileged port number.
 398          */
 399         if (!packet_connection_is_on_socket())
 400                 return 65535;
 401
 402         /* Get socket and return the port number. */
 403         return get_sock_port(packet_get_connection_in(), local);
 404 }
 405
 406 int
 407 get_peer_port(int sock)
 408 {
 409         return get_sock_port(sock, 0);
 410 }
 411
 412 int
 413 get_remote_port(void)
 414 {
 415         /* Cache to avoid getpeername() on a dead connection */
 416         if (cached_port == -1)
 417                 cached_port = get_port(0);
 418
 419         return cached_port;
 420 }
 421
 422 int
 423 get_local_port(void)
 424 {
 425         return get_port(1);
 426 }