crypto/openssh/auth1.c

   1 /*
   2  * Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
   3  *                    All rights reserved
   4  *
   5  * As far as I am concerned, the code I have written for this software
   6  * can be used freely for any purpose.  Any derived versions of this
   7  * software must be clearly marked as such, and if the derived work is
   8  * incompatible with the protocol description in the RFC file, it must be
   9  * called by a name other than "ssh" or "Secure Shell".
  10  */
  11
  12 #include "includes.h"
  13 RCSID("$OpenBSD: auth1.c,v 1.44 2002/09/26 11:38:43 markus Exp $");
  14 RCSID("$FreeBSD: src/crypto/openssh/auth1.c,v 1.3.2.10 2003/04/07 09:56:46 des Exp $");
  15 RCSID("$DragonFly: src/crypto/openssh/Attic/auth1.c,v 1.2 2003/06/17 04:24:36 dillon Exp $");
  16
  17 #include "xmalloc.h"
  18 #include "rsa.h"
  19 #include "ssh1.h"
  20 #include "packet.h"
  21 #include "buffer.h"
  22 #include "mpaux.h"
  23 #include "log.h"
  24 #include "servconf.h"
  25 #include "compat.h"
  26 #include "auth.h"
  27 #include "channels.h"
  28 #include "session.h"
  29 #include "uidswap.h"
  30 #include "monitor_wrap.h"
  31
  32 /* import */
  33 extern ServerOptions options;
  34
  35 /*
  36  * convert ssh auth msg type into description
  37  */
  38 static char *
  39 get_authname(int type)
  40 {
  41         static char buf[1024];
  42         switch (type) {
  43         case SSH_CMSG_AUTH_PASSWORD:
  44                 return "password";
  45         case SSH_CMSG_AUTH_RSA:
  46                 return "rsa";
  47         case SSH_CMSG_AUTH_RHOSTS_RSA:
  48                 return "rhosts-rsa";
  49         case SSH_CMSG_AUTH_RHOSTS:
  50                 return "rhosts";
  51         case SSH_CMSG_AUTH_TIS:
  52         case SSH_CMSG_AUTH_TIS_RESPONSE:
  53                 return "challenge-response";
  54 #if defined(KRB4) || defined(KRB5)
  55         case SSH_CMSG_AUTH_KERBEROS:
  56                 return "kerberos";
  57 #endif
  58         }
  59         snprintf(buf, sizeof buf, "bad-auth-msg-%d", type);
  60         return buf;
  61 }
  62
  63 /*
  64  * read packets, try to authenticate the user and
  65  * return only if authentication is successful
  66  */
  67 static void
  68 do_authloop(Authctxt *authctxt)
  69 {
  70         int authenticated = 0;
  71         u_int bits;
  72         Key *client_host_key;
  73         BIGNUM *n;
  74         char *client_user, *password;
  75         char info[1024];
  76         u_int dlen;
  77         u_int ulen;
  78         int prev, type = 0;
  79         struct passwd *pw = authctxt->pw;
  80
  81         debug("Attempting authentication for %s%.100s.",
  82             authctxt->valid ? "" : "illegal user ", authctxt->user);
  83
  84         /* If the user has no password, accept authentication immediately. */
  85         if (options.password_authentication &&
  86 #if defined(KRB4) || defined(KRB5)
  87             (!options.kerberos_authentication || options.kerberos_or_local_passwd) &&
  88 #endif
  89             PRIVSEP(auth_password(authctxt, ""))) {
  90                 auth_log(authctxt, 1, "without authentication", "");
  91                 return;
  92         }
  93
  94         /* Indicate that authentication is needed. */
  95         packet_start(SSH_SMSG_FAILURE);
  96         packet_send();
  97         packet_write_wait();
  98
  99         client_user = NULL;
 100
 101         for (;;) {
 102                 /* default to fail */
 103                 authenticated = 0;
 104
 105                 info[0] = '\0';
 106
 107                 /* Get a packet from the client. */
 108                 prev = type;
 109                 type = packet_read();
 110
 111                 /*
 112                  * If we started challenge-response authentication but the
 113                  * next packet is not a response to our challenge, release
 114                  * the resources allocated by get_challenge() (which would
 115                  * normally have been released by verify_response() had we
 116                  * received such a response)
 117                  */
 118                 if (prev == SSH_CMSG_AUTH_TIS &&
 119                     type != SSH_CMSG_AUTH_TIS_RESPONSE)
 120                         abandon_challenge_response(authctxt);
 121
 122                 /* Process the packet. */
 123                 switch (type) {
 124
 125 #if defined(KRB4) || defined(KRB5)
 126                 case SSH_CMSG_AUTH_KERBEROS:
 127                         if (!options.kerberos_authentication) {
 128                                 verbose("Kerberos authentication disabled.");
 129                         } else {
 130                                 char *kdata = packet_get_string(&dlen);
 131                                 packet_check_eom();
 132
 133                                 if (kdata[0] == 4) { /* KRB_PROT_VERSION */
 134 #ifdef KRB4
 135                                         KTEXT_ST tkt, reply;
 136                                         tkt.length = dlen;
 137                                         if (tkt.length < MAX_KTXT_LEN)
 138                                                 memcpy(tkt.dat, kdata, tkt.length);
 139
 140                                         if (PRIVSEP(auth_krb4(authctxt, &tkt,
 141                                             &client_user, &reply))) {
 142                                                 authenticated = 1;
 143                                                 snprintf(info, sizeof(info),
 144                                                     " tktuser %.100s",
 145                                                     client_user);
 146
 147                                                 packet_start(
 148                                                     SSH_SMSG_AUTH_KERBEROS_RESPONSE);
 149                                                 packet_put_string((char *)
 150                                                     reply.dat, reply.length);
 151                                                 packet_send();
 152                                                 packet_write_wait();
 153                                         }
 154 #endif /* KRB4 */
 155                                 } else {
 156 #ifdef KRB5
 157                                         krb5_data tkt, reply;
 158                                         tkt.length = dlen;
 159                                         tkt.data = kdata;
 160
 161                                         if (PRIVSEP(auth_krb5(authctxt, &tkt,
 162                                             &client_user, &reply))) {
 163                                                 authenticated = 1;
 164                                                 snprintf(info, sizeof(info),
 165                                                     " tktuser %.100s",
 166                                                     client_user);
 167
 168                                                 /* Send response to client */
 169                                                 packet_start(
 170                                                     SSH_SMSG_AUTH_KERBEROS_RESPONSE);
 171                                                 packet_put_string((char *)
 172                                                     reply.data, reply.length);
 173                                                 packet_send();
 174                                                 packet_write_wait();
 175
 176                                                 if (reply.length)
 177                                                         xfree(reply.data);
 178                                         }
 179 #endif /* KRB5 */
 180                                 }
 181                                 xfree(kdata);
 182                         }
 183                         break;
 184 #endif /* KRB4 || KRB5 */
 185
 186 #if defined(AFS) || defined(KRB5)
 187                         /* XXX - punt on backward compatibility here. */
 188                 case SSH_CMSG_HAVE_KERBEROS_TGT:
 189                         packet_send_debug("Kerberos TGT passing disabled before authentication.");
 190                         break;
 191 #ifdef AFS
 192                 case SSH_CMSG_HAVE_AFS_TOKEN:
 193                         packet_send_debug("AFS token passing disabled before authentication.");
 194                         break;
 195 #endif /* AFS */
 196 #endif /* AFS || KRB5 */
 197
 198                 case SSH_CMSG_AUTH_RHOSTS:
 199                         if (!options.rhosts_authentication) {
 200                                 verbose("Rhosts authentication disabled.");
 201                                 break;
 202                         }
 203                         /*
 204                          * Get client user name.  Note that we just have to
 205                          * trust the client; this is one reason why rhosts
 206                          * authentication is insecure. (Another is
 207                          * IP-spoofing on a local network.)
 208                          */
 209                         client_user = packet_get_string(&ulen);
 210                         packet_check_eom();
 211
 212                         /* Try to authenticate using /etc/hosts.equiv and .rhosts. */
 213                         authenticated = auth_rhosts(pw, client_user);
 214
 215                         snprintf(info, sizeof info, " ruser %.100s", client_user);
 216                         break;
 217
 218                 case SSH_CMSG_AUTH_RHOSTS_RSA:
 219                         if (!options.rhosts_rsa_authentication) {
 220                                 verbose("Rhosts with RSA authentication disabled.");
 221                                 break;
 222                         }
 223                         /*
 224                          * Get client user name.  Note that we just have to
 225                          * trust the client; root on the client machine can
 226                          * claim to be any user.
 227                          */
 228                         client_user = packet_get_string(&ulen);
 229
 230                         /* Get the client host key. */
 231                         client_host_key = key_new(KEY_RSA1);
 232                         bits = packet_get_int();
 233                         packet_get_bignum(client_host_key->rsa->e);
 234                         packet_get_bignum(client_host_key->rsa->n);
 235
 236                         if (bits != BN_num_bits(client_host_key->rsa->n))
 237                                 verbose("Warning: keysize mismatch for client_host_key: "
 238                                     "actual %d, announced %d",
 239                                     BN_num_bits(client_host_key->rsa->n), bits);
 240                         packet_check_eom();
 241
 242                         authenticated = auth_rhosts_rsa(pw, client_user,
 243                             client_host_key);
 244                         key_free(client_host_key);
 245
 246                         snprintf(info, sizeof info, " ruser %.100s", client_user);
 247                         break;
 248
 249                 case SSH_CMSG_AUTH_RSA:
 250                         if (!options.rsa_authentication) {
 251                                 verbose("RSA authentication disabled.");
 252                                 break;
 253                         }
 254                         /* RSA authentication requested. */
 255                         if ((n = BN_new()) == NULL)
 256                                 fatal("do_authloop: BN_new failed");
 257                         packet_get_bignum(n);
 258                         packet_check_eom();
 259                         authenticated = auth_rsa(pw, n);
 260                         BN_clear_free(n);
 261                         break;
 262
 263                 case SSH_CMSG_AUTH_PASSWORD:
 264                         if (!options.password_authentication) {
 265                                 verbose("Password authentication disabled.");
 266                                 break;
 267                         }
 268                         /*
 269                          * Read user password.  It is in plain text, but was
 270                          * transmitted over the encrypted channel so it is
 271                          * not visible to an outside observer.
 272                          */
 273                         password = packet_get_string(&dlen);
 274                         packet_check_eom();
 275
 276                         /* Try authentication with the password. */
 277                         authenticated = PRIVSEP(auth_password(authctxt, password));
 278
 279                         memset(password, 0, strlen(password));
 280                         xfree(password);
 281                         break;
 282
 283                 case SSH_CMSG_AUTH_TIS:
 284                         debug("rcvd SSH_CMSG_AUTH_TIS");
 285                         if (options.challenge_response_authentication == 1) {
 286                                 char *challenge = get_challenge(authctxt);
 287                                 if (challenge != NULL) {
 288                                         debug("sending challenge '%s'", challenge);
 289                                         packet_start(SSH_SMSG_AUTH_TIS_CHALLENGE);
 290                                         packet_put_cstring(challenge);
 291                                         xfree(challenge);
 292                                         packet_send();
 293                                         packet_write_wait();
 294                                         continue;
 295                                 }
 296                         }
 297                         break;
 298                 case SSH_CMSG_AUTH_TIS_RESPONSE:
 299                         debug("rcvd SSH_CMSG_AUTH_TIS_RESPONSE");
 300                         if (options.challenge_response_authentication == 1) {
 301                                 char *response = packet_get_string(&dlen);
 302                                 debug("got response '%s'", response);
 303                                 packet_check_eom();
 304                                 authenticated = verify_response(authctxt, response);
 305                                 memset(response, 'r', dlen);
 306                                 xfree(response);
 307                         }
 308                         break;
 309
 310                 default:
 311                         /*
 312                          * Any unknown messages will be ignored (and failure
 313                          * returned) during authentication.
 314                          */
 315                         log("Unknown message during authentication: type %d", type);
 316                         break;
 317                 }
 318 #ifdef BSD_AUTH
 319                 if (authctxt->as) {
 320                         auth_close(authctxt->as);
 321                         authctxt->as = NULL;
 322                 }
 323 #endif
 324                 if (!authctxt->valid && authenticated)
 325                         fatal("INTERNAL ERROR: authenticated invalid user %s",
 326                             authctxt->user);
 327
 328 #ifdef _UNICOS
 329                 if (type == SSH_CMSG_AUTH_PASSWORD && !authenticated)
 330                         cray_login_failure(authctxt->user, IA_UDBERR);
 331                 if (authenticated && cray_access_denied(authctxt->user)) {
 332                         authenticated = 0;
 333                         fatal("Access denied for user %s.",authctxt->user);
 334                 }
 335 #endif /* _UNICOS */
 336
 337 #ifdef HAVE_CYGWIN
 338                 if (authenticated &&
 339                     !check_nt_auth(type == SSH_CMSG_AUTH_PASSWORD, pw)) {
 340                         packet_disconnect("Authentication rejected for uid %d.",
 341                         pw == NULL ? -1 : pw->pw_uid);
 342                         authenticated = 0;
 343                 }
 344 #else
 345                 /* Special handling for root */
 346                 if (!use_privsep &&
 347                     authenticated && authctxt->pw->pw_uid == 0 &&
 348                     !auth_root_allowed(get_authname(type)))
 349                         authenticated = 0;
 350 #endif
 351 #ifdef USE_PAM
 352                 if (!use_privsep && authenticated &&
 353                     !do_pam_account(pw->pw_name, client_user))
 354                         authenticated = 0;
 355 #endif
 356
 357                 /* Log before sending the reply */
 358                 auth_log(authctxt, authenticated, get_authname(type), info);
 359
 360                 if (client_user != NULL) {
 361                         xfree(client_user);
 362                         client_user = NULL;
 363                 }
 364
 365                 if (authenticated)
 366                         return;
 367
 368                 if (authctxt->failures++ > AUTH_FAIL_MAX) {
 369                         packet_disconnect(AUTH_FAIL_MSG, authctxt->user);
 370                 }
 371
 372                 packet_start(SSH_SMSG_FAILURE);
 373                 packet_send();
 374                 packet_write_wait();
 375         }
 376 }
 377
 378 /*
 379  * Performs authentication of an incoming connection.  Session key has already
 380  * been exchanged and encryption is enabled.
 381  */
 382 Authctxt *
 383 do_authentication(void)
 384 {
 385         Authctxt *authctxt;
 386         u_int ulen;
 387         char *user, *style = NULL;
 388
 389         /* Get the name of the user that we wish to log in as. */
 390         packet_read_expect(SSH_CMSG_USER);
 391
 392         /* Get the user name. */
 393         user = packet_get_string(&ulen);
 394         packet_check_eom();
 395
 396         if ((style = strchr(user, ':')) != NULL)
 397                 *style++ = '\0';
 398
 399 #ifdef KRB5
 400         /* XXX - SSH.com Kerberos v5 braindeath. */
 401         if ((datafellows & SSH_BUG_K5USER) &&
 402             options.kerberos_authentication) {
 403                 char *p;
 404                 if ((p = strchr(user, '@')) != NULL)
 405                         *p = '\0';
 406         }
 407 #endif
 408
 409         authctxt = authctxt_new();
 410         authctxt->user = user;
 411         authctxt->style = style;
 412
 413         /* Verify that the user is a valid user. */
 414         if ((authctxt->pw = PRIVSEP(getpwnamallow(user))) != NULL)
 415                 authctxt->valid = 1;
 416         else
 417                 debug("do_authentication: illegal user %s", user);
 418
 419         setproctitle("%s%s", authctxt->pw ? user : "unknown",
 420             use_privsep ? " [net]" : "");
 421
 422 #ifdef USE_PAM
 423         PRIVSEP(start_pam(authctxt->pw == NULL ? "NOUSER" : user));
 424 #endif
 425
 426         /*
 427          * If we are not running as root, the user must have the same uid as
 428          * the server. (Unless you are running Windows)
 429          */
 430 #ifndef HAVE_CYGWIN
 431         if (!use_privsep && getuid() != 0 && authctxt->pw &&
 432             authctxt->pw->pw_uid != getuid())
 433                 packet_disconnect("Cannot change user when server not running as root.");
 434 #endif
 435
 436         /*
 437          * Loop until the user has been authenticated or the connection is
 438          * closed, do_authloop() returns only if authentication is successful
 439          */
 440         do_authloop(authctxt);
 441
 442         /* The user has been authenticated and accepted. */
 443         packet_start(SSH_SMSG_SUCCESS);
 444         packet_send();
 445         packet_write_wait();
 446
 447         return (authctxt);
 448 }