canohost.c

   1 /* $OpenBSD: canohost.c,v 1.58 2006/07/22 20:48:22 stevesk 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
  22 #include <ctype.h>
  23 #include <errno.h>
  24 #include <netdb.h>
  25 #include <string.h>
  26
  27 #include "packet.h"
  28 #include "xmalloc.h"
  29 #include "log.h"
  30 #include "canohost.h"
  31
  32 static void check_ip_options(int, char *);
  33
  34 /*
  35  * Return the canonical name of the host at the other end of the socket. The
  36  * caller should free the returned string with xfree.
  37  */
  38
  39 static char *
  40 get_remote_hostname(int sock, int use_dns)
  41 {
  42         struct sockaddr_storage from;
  43         int i;
  44         socklen_t fromlen;
  45         struct addrinfo hints, *ai, *aitop;
  46         char name[NI_MAXHOST], ntop[NI_MAXHOST], ntop2[NI_MAXHOST];
  47
  48         /* Get IP address of client. */
  49         fromlen = sizeof(from);
  50         memset(&from, 0, sizeof(from));
  51         if (getpeername(sock, (struct sockaddr *)&from, &fromlen) < 0) {
  52                 debug("getpeername failed: %.100s", strerror(errno));
  53                 cleanup_exit(255);
  54         }
  55
  56         if (from.ss_family == AF_INET)
  57                 check_ip_options(sock, ntop);
  58
  59         ipv64_normalise_mapped(&from, &fromlen);
  60
  61         if (from.ss_family == AF_INET6)
  62                 fromlen = sizeof(struct sockaddr_in6);
  63
  64         if (getnameinfo((struct sockaddr *)&from, fromlen, ntop, sizeof(ntop),
  65             NULL, 0, NI_NUMERICHOST) != 0)
  66                 fatal("get_remote_hostname: getnameinfo NI_NUMERICHOST failed");
  67
  68         if (!use_dns)
  69                 return xstrdup(ntop);
  70
  71         debug3("Trying to reverse map address %.100s.", ntop);
  72         /* Map the IP address to a host name. */
  73         if (getnameinfo((struct sockaddr *)&from, fromlen, name, sizeof(name),
  74             NULL, 0, NI_NAMEREQD) != 0) {
  75                 /* Host name not found.  Use ip address. */
  76                 return xstrdup(ntop);
  77         }
  78
  79         /*
  80          * if reverse lookup result looks like a numeric hostname,
  81          * someone is trying to trick us by PTR record like following:
  82          *      1.1.1.10.in-addr.arpa.  IN PTR  2.3.4.5
  83          */
  84         memset(&hints, 0, sizeof(hints));
  85         hints.ai_socktype = SOCK_DGRAM; /*dummy*/
  86         hints.ai_flags = AI_NUMERICHOST;
  87         if (getaddrinfo(name, "0", &hints, &ai) == 0) {
  88                 logit("Nasty PTR record \"%s\" is set up for %s, ignoring",
  89                     name, ntop);
  90                 freeaddrinfo(ai);
  91                 return xstrdup(ntop);
  92         }
  93
  94         /*
  95          * Convert it to all lowercase (which is expected by the rest
  96          * of this software).
  97          */
  98         for (i = 0; name[i]; i++)
  99                 if (isupper(name[i]))
 100                         name[i] = (char)tolower(name[i]);
 101         /*
 102          * Map it back to an IP address and check that the given
 103          * address actually is an address of this host.  This is
 104          * necessary because anyone with access to a name server can
 105          * define arbitrary names for an IP address. Mapping from
 106          * name to IP address can be trusted better (but can still be
 107          * fooled if the intruder has access to the name server of
 108          * the domain).
 109          */
 110         memset(&hints, 0, sizeof(hints));
 111         hints.ai_family = from.ss_family;
 112         hints.ai_socktype = SOCK_STREAM;
 113         if (getaddrinfo(name, NULL, &hints, &aitop) != 0) {
 114                 logit("reverse mapping checking getaddrinfo for %.700s "
 115                     "[%s] failed - POSSIBLE BREAK-IN ATTEMPT!", name, ntop);
 116                 return xstrdup(ntop);
 117         }
 118         /* Look for the address from the list of addresses. */
 119         for (ai = aitop; ai; ai = ai->ai_next) {
 120                 if (getnameinfo(ai->ai_addr, ai->ai_addrlen, ntop2,
 121                     sizeof(ntop2), NULL, 0, NI_NUMERICHOST) == 0 &&
 122                     (strcmp(ntop, ntop2) == 0))
 123                                 break;
 124         }
 125         freeaddrinfo(aitop);
 126         /* If we reached the end of the list, the address was not there. */
 127         if (!ai) {
 128                 /* Address not found for the host name. */
 129                 logit("Address %.100s maps to %.600s, but this does not "
 130                     "map back to the address - POSSIBLE BREAK-IN ATTEMPT!",
 131                     ntop, name);
 132                 return xstrdup(ntop);
 133         }
 134         return xstrdup(name);
 135 }
 136
 137 /*
 138  * If IP options are supported, make sure there are none (log and
 139  * disconnect them if any are found).  Basically we are worried about
 140  * source routing; it can be used to pretend you are somebody
 141  * (ip-address) you are not. That itself may be "almost acceptable"
 142  * under certain circumstances, but rhosts autentication is useless
 143  * if source routing is accepted. Notice also that if we just dropped
 144  * source routing here, the other side could use IP spoofing to do
 145  * rest of the interaction and could still bypass security.  So we
 146  * exit here if we detect any IP options.
 147  */
 148 /* IPv4 only */
 149 static void
 150 check_ip_options(int sock, char *ipaddr)
 151 {
 152 #ifdef IP_OPTIONS
 153         u_char options[200];
 154         char text[sizeof(options) * 3 + 1];
 155         socklen_t option_size;
 156         u_int i;
 157         int ipproto;
 158         struct protoent *ip;
 159
 160         if ((ip = getprotobyname("ip")) != NULL)
 161                 ipproto = ip->p_proto;
 162         else
 163                 ipproto = IPPROTO_IP;
 164         option_size = sizeof(options);
 165         if (getsockopt(sock, ipproto, IP_OPTIONS, options,
 166             &option_size) >= 0 && option_size != 0) {
 167                 text[0] = '\0';
 168                 for (i = 0; i < option_size; i++)
 169                         snprintf(text + i*3, sizeof(text) - i*3,
 170                             " %2.2x", options[i]);
 171                 fatal("Connection from %.100s with IP options:%.800s",
 172                     ipaddr, text);
 173         }
 174 #endif /* IP_OPTIONS */
 175 }
 176
 177 void
 178 ipv64_normalise_mapped(struct sockaddr_storage *addr, socklen_t *len)
 179 {
 180         struct sockaddr_in6 *a6 = (struct sockaddr_in6 *)addr;
 181         struct sockaddr_in *a4 = (struct sockaddr_in *)addr;
 182         struct in_addr inaddr;
 183         u_int16_t port;
 184
 185         if (addr->ss_family != AF_INET6 ||
 186             !IN6_IS_ADDR_V4MAPPED(&a6->sin6_addr))
 187                 return;
 188
 189         debug3("Normalising mapped IPv4 in IPv6 address");
 190
 191         memcpy(&inaddr, ((char *)&a6->sin6_addr) + 12, sizeof(inaddr));
 192         port = a6->sin6_port;
 193
 194         memset(addr, 0, sizeof(*a4));
 195
 196         a4->sin_family = AF_INET;
 197         *len = sizeof(*a4);
 198         memcpy(&a4->sin_addr, &inaddr, sizeof(inaddr));
 199         a4->sin_port = port;
 200 }
 201
 202 /*
 203  * Return the canonical name of the host in the other side of the current
 204  * connection.  The host name is cached, so it is efficient to call this
 205  * several times.
 206  */
 207
 208 const char *
 209 get_canonical_hostname(int use_dns)
 210 {
 211         char *host;
 212         static char *canonical_host_name = NULL;
 213         static char *remote_ip = NULL;
 214
 215         /* Check if we have previously retrieved name with same option. */
 216         if (use_dns && canonical_host_name != NULL)
 217                 return canonical_host_name;
 218         if (!use_dns && remote_ip != NULL)
 219                 return remote_ip;
 220
 221         /* Get the real hostname if socket; otherwise return UNKNOWN. */
 222         if (packet_connection_is_on_socket())
 223                 host = get_remote_hostname(packet_get_connection_in(), use_dns);
 224         else
 225                 host = "UNKNOWN";
 226
 227         if (use_dns)
 228                 canonical_host_name = host;
 229         else
 230                 remote_ip = host;
 231         return host;
 232 }
 233
 234 /*
 235  * Returns the local/remote IP-address/hostname of socket as a string.
 236  * The returned string must be freed.
 237  */
 238 static char *
 239 get_socket_address(int sock, int remote, int flags)
 240 {
 241         struct sockaddr_storage addr;
 242         socklen_t addrlen;
 243         char ntop[NI_MAXHOST];
 244         int r;
 245
 246         /* Get IP address of client. */
 247         addrlen = sizeof(addr);
 248         memset(&addr, 0, sizeof(addr));
 249
 250         if (remote) {
 251                 if (getpeername(sock, (struct sockaddr *)&addr, &addrlen)
 252                     < 0)
 253                         return NULL;
 254         } else {
 255                 if (getsockname(sock, (struct sockaddr *)&addr, &addrlen)
 256                     < 0)
 257                         return NULL;
 258         }
 259
 260         /* Work around Linux IPv6 weirdness */
 261         if (addr.ss_family == AF_INET6)
 262                 addrlen = sizeof(struct sockaddr_in6);
 263
 264         ipv64_normalise_mapped(&addr, &addrlen);
 265
 266         /* Get the address in ascii. */
 267         if ((r = getnameinfo((struct sockaddr *)&addr, addrlen, ntop,
 268             sizeof(ntop), NULL, 0, flags)) != 0) {
 269                 error("get_socket_address: getnameinfo %d failed: %s", flags,
 270                     r == EAI_SYSTEM ? strerror(errno) : gai_strerror(r));
 271                 return NULL;
 272         }
 273         return xstrdup(ntop);
 274 }
 275
 276 char *
 277 get_peer_ipaddr(int sock)
 278 {
 279         char *p;
 280
 281         if ((p = get_socket_address(sock, 1, NI_NUMERICHOST)) != NULL)
 282                 return p;
 283         return xstrdup("UNKNOWN");
 284 }
 285
 286 char *
 287 get_local_ipaddr(int sock)
 288 {
 289         char *p;
 290
 291         if ((p = get_socket_address(sock, 0, NI_NUMERICHOST)) != NULL)
 292                 return p;
 293         return xstrdup("UNKNOWN");
 294 }
 295
 296 char *
 297 get_local_name(int sock)
 298 {
 299         return get_socket_address(sock, 0, NI_NAMEREQD);
 300 }
 301
 302 /*
 303  * Returns the IP-address of the remote host as a string.  The returned
 304  * string must not be freed.
 305  */
 306
 307 const char *
 308 get_remote_ipaddr(void)
 309 {
 310         static char *canonical_host_ip = NULL;
 311
 312         /* Check whether we have cached the ipaddr. */
 313         if (canonical_host_ip == NULL) {
 314                 if (packet_connection_is_on_socket()) {
 315                         canonical_host_ip =
 316                             get_peer_ipaddr(packet_get_connection_in());
 317                         if (canonical_host_ip == NULL)
 318                                 cleanup_exit(255);
 319                 } else {
 320                         /* If not on socket, return UNKNOWN. */
 321                         canonical_host_ip = xstrdup("UNKNOWN");
 322                 }
 323         }
 324         return canonical_host_ip;
 325 }
 326
 327 const char *
 328 get_remote_name_or_ip(u_int utmp_len, int use_dns)
 329 {
 330         static const char *remote = "";
 331         if (utmp_len > 0)
 332                 remote = get_canonical_hostname(use_dns);
 333         if (utmp_len == 0 || strlen(remote) > utmp_len)
 334                 remote = get_remote_ipaddr();
 335         return remote;
 336 }
 337
 338 /* Returns the local/remote port for the socket. */
 339
 340 static int
 341 get_sock_port(int sock, int local)
 342 {
 343         struct sockaddr_storage from;
 344         socklen_t fromlen;
 345         char strport[NI_MAXSERV];
 346         int r;
 347
 348         /* Get IP address of client. */
 349         fromlen = sizeof(from);
 350         memset(&from, 0, sizeof(from));
 351         if (local) {
 352                 if (getsockname(sock, (struct sockaddr *)&from, &fromlen) < 0) {
 353                         error("getsockname failed: %.100s", strerror(errno));
 354                         return 0;
 355                 }
 356         } else {
 357                 if (getpeername(sock, (struct sockaddr *)&from, &fromlen) < 0) {
 358                         debug("getpeername failed: %.100s", strerror(errno));
 359                         return -1;
 360                 }
 361         }
 362
 363         /* Work around Linux IPv6 weirdness */
 364         if (from.ss_family == AF_INET6)
 365                 fromlen = sizeof(struct sockaddr_in6);
 366
 367         /* Return port number. */
 368         if ((r = getnameinfo((struct sockaddr *)&from, fromlen, NULL, 0,
 369             strport, sizeof(strport), NI_NUMERICSERV)) != 0)
 370                 fatal("get_sock_port: getnameinfo NI_NUMERICSERV failed: %s",
 371                     r == EAI_SYSTEM ? strerror(errno) : gai_strerror(r));
 372         return atoi(strport);
 373 }
 374
 375 /* Returns remote/local port number for the current connection. */
 376
 377 static int
 378 get_port(int local)
 379 {
 380         /*
 381          * If the connection is not a socket, return 65535.  This is
 382          * intentionally chosen to be an unprivileged port number.
 383          */
 384         if (!packet_connection_is_on_socket())
 385                 return 65535;
 386
 387         /* Get socket and return the port number. */
 388         return get_sock_port(packet_get_connection_in(), local);
 389 }
 390
 391 int
 392 get_peer_port(int sock)
 393 {
 394         return get_sock_port(sock, 0);
 395 }
 396
 397 int
 398 get_remote_port(void)
 399 {
 400         static int port = -1;
 401
 402         /* Cache to avoid getpeername() on a dead connection */
 403         if (port == -1)
 404                 port = get_port(0);
 405
 406         return port;
 407 }
 408
 409 int
 410 get_local_port(void)
 411 {
 412         return get_port(1);
 413 }