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 1.18 2001/02/22 21:59:43 markus Exp $");
  14
  15 #include "xmalloc.h"
  16 #include "rsa.h"
  17 #include "ssh1.h"
  18 #include "packet.h"
  19 #include "buffer.h"
  20 #include "mpaux.h"
  21 #include "log.h"
  22 #include "servconf.h"
  23 #include "compat.h"
  24 #include "auth.h"
  25 #include "session.h"
  26 #include "misc.h"
  27
  28 /* import */
  29 extern ServerOptions options;
  30 extern char *forced_command;
  31
  32 #ifdef WITH_AIXAUTHENTICATE
  33 extern char *aixloginmsg;
  34 #endif /* WITH_AIXAUTHENTICATE */
  35
  36 /*
  37  * convert ssh auth msg type into description
  38  */
  39 char *
  40 get_authname(int type)
  41 {
  42         static char buf[1024];
  43         switch (type) {
  44         case SSH_CMSG_AUTH_PASSWORD:
  45                 return "password";
  46         case SSH_CMSG_AUTH_RSA:
  47                 return "rsa";
  48         case SSH_CMSG_AUTH_RHOSTS_RSA:
  49                 return "rhosts-rsa";
  50         case SSH_CMSG_AUTH_RHOSTS:
  51                 return "rhosts";
  52         case SSH_CMSG_AUTH_TIS:
  53         case SSH_CMSG_AUTH_TIS_RESPONSE:
  54                 return "challenge-response";
  55 #ifdef KRB4
  56         case SSH_CMSG_AUTH_KERBEROS:
  57                 return "kerberos";
  58 #endif
  59         }
  60         snprintf(buf, sizeof buf, "bad-auth-msg-%d", type);
  61         return buf;
  62 }
  63
  64 /*
  65  * read packets, try to authenticate the user and
  66  * return only if authentication is successful
  67  */
  68 void
  69 do_authloop(Authctxt *authctxt)
  70 {
  71         int authenticated = 0;
  72         u_int bits;
  73         RSA *client_host_key;
  74         BIGNUM *n;
  75         char *client_user, *password;
  76         char info[1024];
  77         u_int dlen;
  78         int plen, nlen, elen;
  79         u_int ulen;
  80         int type = 0;
  81         struct passwd *pw = authctxt->pw;
  82
  83         debug("Attempting authentication for %s%.100s.",
  84              authctxt->valid ? "" : "illegal user ", authctxt->user);
  85
  86         /* If the user has no password, accept authentication immediately. */
  87         if (options.password_authentication &&
  88 #ifdef KRB4
  89             (!options.kerberos_authentication || options.kerberos_or_local_passwd) &&
  90 #endif
  91 #ifdef USE_PAM
  92             auth_pam_password(pw, "")) {
  93 #elif defined(HAVE_OSF_SIA)
  94             0) {
  95 #else
  96             auth_password(authctxt, "")) {
  97 #endif
  98                 auth_log(authctxt, 1, "without authentication", "");
  99                 return;
 100         }
 101
 102         /* Indicate that authentication is needed. */
 103         packet_start(SSH_SMSG_FAILURE);
 104         packet_send();
 105         packet_write_wait();
 106
 107         client_user = NULL;
 108
 109         for (;;) {
 110                 /* default to fail */
 111                 authenticated = 0;
 112
 113                 info[0] = '\0';
 114
 115                 /* Get a packet from the client. */
 116                 type = packet_read(&plen);
 117
 118                 /* Process the packet. */
 119                 switch (type) {
 120 #ifdef AFS
 121                 case SSH_CMSG_HAVE_KERBEROS_TGT:
 122                         if (!options.kerberos_tgt_passing) {
 123                                 verbose("Kerberos tgt passing disabled.");
 124                                 break;
 125                         } else {
 126                                 /* Accept Kerberos tgt. */
 127                                 char *tgt = packet_get_string(&dlen);
 128                                 packet_integrity_check(plen, 4 + dlen, type);
 129                                 if (!auth_kerberos_tgt(pw, tgt))
 130                                         verbose("Kerberos tgt REFUSED for %.100s", authctxt->user);
 131                                 xfree(tgt);
 132                         }
 133                         continue;
 134
 135                 case SSH_CMSG_HAVE_AFS_TOKEN:
 136                         if (!options.afs_token_passing || !k_hasafs()) {
 137                                 verbose("AFS token passing disabled.");
 138                                 break;
 139                         } else {
 140                                 /* Accept AFS token. */
 141                                 char *token_string = packet_get_string(&dlen);
 142                                 packet_integrity_check(plen, 4 + dlen, type);
 143                                 if (!auth_afs_token(pw, token_string))
 144                                         verbose("AFS token REFUSED for %.100s", authctxt->user);
 145                                 xfree(token_string);
 146                         }
 147                         continue;
 148 #endif /* AFS */
 149 #ifdef KRB4
 150                 case SSH_CMSG_AUTH_KERBEROS:
 151                         if (!options.kerberos_authentication) {
 152                                 verbose("Kerberos authentication disabled.");
 153                                 break;
 154                         } else {
 155                                 /* Try Kerberos v4 authentication. */
 156                                 KTEXT_ST auth;
 157                                 char *tkt_user = NULL;
 158                                 char *kdata = packet_get_string((u_int *) &auth.length);
 159                                 packet_integrity_check(plen, 4 + auth.length, type);
 160
 161                                 if (authctxt->valid) {
 162                                         if (auth.length < MAX_KTXT_LEN)
 163                                                 memcpy(auth.dat, kdata, auth.length);
 164                                         authenticated = auth_krb4(pw->pw_name, &auth, &tkt_user);
 165                                         if (authenticated) {
 166                                                 snprintf(info, sizeof info,
 167                                                     " tktuser %.100s", tkt_user);
 168                                                 xfree(tkt_user);
 169                                         }
 170                                 }
 171                                 xfree(kdata);
 172                         }
 173                         break;
 174 #endif /* KRB4 */
 175
 176                 case SSH_CMSG_AUTH_RHOSTS:
 177                         if (!options.rhosts_authentication) {
 178                                 verbose("Rhosts authentication disabled.");
 179                                 break;
 180                         }
 181                         /*
 182                          * Get client user name.  Note that we just have to
 183                          * trust the client; this is one reason why rhosts
 184                          * authentication is insecure. (Another is
 185                          * IP-spoofing on a local network.)
 186                          */
 187                         client_user = packet_get_string(&ulen);
 188                         packet_integrity_check(plen, 4 + ulen, type);
 189
 190                         /* Try to authenticate using /etc/hosts.equiv and .rhosts. */
 191                         authenticated = auth_rhosts(pw, client_user);
 192
 193                         snprintf(info, sizeof info, " ruser %.100s", client_user);
 194                         break;
 195
 196                 case SSH_CMSG_AUTH_RHOSTS_RSA:
 197                         if (!options.rhosts_rsa_authentication) {
 198                                 verbose("Rhosts with RSA authentication disabled.");
 199                                 break;
 200                         }
 201                         /*
 202                          * Get client user name.  Note that we just have to
 203                          * trust the client; root on the client machine can
 204                          * claim to be any user.
 205                          */
 206                         client_user = packet_get_string(&ulen);
 207
 208                         /* Get the client host key. */
 209                         client_host_key = RSA_new();
 210                         if (client_host_key == NULL)
 211                                 fatal("RSA_new failed");
 212                         client_host_key->e = BN_new();
 213                         client_host_key->n = BN_new();
 214                         if (client_host_key->e == NULL || client_host_key->n == NULL)
 215                                 fatal("BN_new failed");
 216                         bits = packet_get_int();
 217                         packet_get_bignum(client_host_key->e, &elen);
 218                         packet_get_bignum(client_host_key->n, &nlen);
 219
 220                         if (bits != BN_num_bits(client_host_key->n))
 221                                 verbose("Warning: keysize mismatch for client_host_key: "
 222                                     "actual %d, announced %d", BN_num_bits(client_host_key->n), bits);
 223                         packet_integrity_check(plen, (4 + ulen) + 4 + elen + nlen, type);
 224
 225                         authenticated = auth_rhosts_rsa(pw, client_user, client_host_key);
 226                         RSA_free(client_host_key);
 227
 228                         snprintf(info, sizeof info, " ruser %.100s", client_user);
 229                         break;
 230
 231                 case SSH_CMSG_AUTH_RSA:
 232                         if (!options.rsa_authentication) {
 233                                 verbose("RSA authentication disabled.");
 234                                 break;
 235                         }
 236                         /* RSA authentication requested. */
 237                         n = BN_new();
 238                         packet_get_bignum(n, &nlen);
 239                         packet_integrity_check(plen, nlen, type);
 240                         authenticated = auth_rsa(pw, n);
 241                         BN_clear_free(n);
 242                         break;
 243
 244                 case SSH_CMSG_AUTH_PASSWORD:
 245                         if (!options.password_authentication) {
 246                                 verbose("Password authentication disabled.");
 247                                 break;
 248                         }
 249                         /*
 250                          * Read user password.  It is in plain text, but was
 251                          * transmitted over the encrypted channel so it is
 252                          * not visible to an outside observer.
 253                          */
 254                         password = packet_get_string(&dlen);
 255                         packet_integrity_check(plen, 4 + dlen, type);
 256
 257 #ifdef USE_PAM
 258                         /* Do PAM auth with password */
 259                         authenticated = auth_pam_password(pw, password);
 260 #elif defined(HAVE_OSF_SIA)
 261                         /* Do SIA auth with password */
 262                         authenticated = auth_sia_password(authctxt->user,
 263                             password);
 264 #else /* !USE_PAM && !HAVE_OSF_SIA */
 265                         /* Try authentication with the password. */
 266                         authenticated = auth_password(authctxt, password);
 267 #endif /* USE_PAM */
 268
 269                         memset(password, 0, strlen(password));
 270                         xfree(password);
 271                         break;
 272
 273                 case SSH_CMSG_AUTH_TIS:
 274                         debug("rcvd SSH_CMSG_AUTH_TIS");
 275                         if (options.challenge_reponse_authentication == 1) {
 276                                 char *challenge = get_challenge(authctxt, authctxt->style);
 277                                 if (challenge != NULL) {
 278                                         debug("sending challenge '%s'", challenge);
 279                                         packet_start(SSH_SMSG_AUTH_TIS_CHALLENGE);
 280                                         packet_put_cstring(challenge);
 281                                         packet_send();
 282                                         packet_write_wait();
 283                                         continue;
 284                                 }
 285                         }
 286                         break;
 287                 case SSH_CMSG_AUTH_TIS_RESPONSE:
 288                         debug("rcvd SSH_CMSG_AUTH_TIS_RESPONSE");
 289                         if (options.challenge_reponse_authentication == 1) {
 290                                 char *response = packet_get_string(&dlen);
 291                                 debug("got response '%s'", response);
 292                                 packet_integrity_check(plen, 4 + dlen, type);
 293                                 authenticated = verify_response(authctxt, response);
 294                                 memset(response, 'r', dlen);
 295                                 xfree(response);
 296                         }
 297                         break;
 298
 299                 default:
 300                         /*
 301                          * Any unknown messages will be ignored (and failure
 302                          * returned) during authentication.
 303                          */
 304                         log("Unknown message during authentication: type %d", type);
 305                         break;
 306                 }
 307 #ifdef BSD_AUTH
 308                 if (authctxt->as) {
 309                         auth_close(authctxt->as);
 310                         authctxt->as = NULL;
 311                 }
 312 #endif
 313                 if (!authctxt->valid && authenticated)
 314                         fatal("INTERNAL ERROR: authenticated invalid user %s",
 315                             authctxt->user);
 316
 317 #ifdef HAVE_CYGWIN
 318                 if (authenticated &&
 319                     !check_nt_auth(type == SSH_CMSG_AUTH_PASSWORD,pw->pw_uid)) {
 320                         packet_disconnect("Authentication rejected for uid %d.",
 321                         (int)pw->pw_uid);
 322                         authenticated = 0;
 323                 }
 324 #else
 325                 /* Special handling for root */
 326                 if (authenticated && authctxt->pw->pw_uid == 0 &&
 327                     !auth_root_allowed(get_authname(type)))
 328                         authenticated = 0;
 329 #endif
 330 #ifdef USE_PAM
 331                 if (authenticated && !do_pam_account(pw->pw_name, client_user))
 332                         authenticated = 0;
 333 #endif
 334
 335                 /* Log before sending the reply */
 336                 auth_log(authctxt, authenticated, get_authname(type), info);
 337
 338                 if (client_user != NULL) {
 339                         xfree(client_user);
 340                         client_user = NULL;
 341                 }
 342
 343                 if (authenticated)
 344                         return;
 345
 346                 if (authctxt->failures++ > AUTH_FAIL_MAX) {
 347 #ifdef WITH_AIXAUTHENTICATE
 348                         loginfailed(authctxt->user,
 349                             get_canonical_hostname(options.reverse_mapping_check),
 350                             "ssh");
 351 #endif /* WITH_AIXAUTHENTICATE */
 352                         packet_disconnect(AUTH_FAIL_MSG, authctxt->user);
 353                 }
 354
 355                 packet_start(SSH_SMSG_FAILURE);
 356                 packet_send();
 357                 packet_write_wait();
 358         }
 359 }
 360
 361 /*
 362  * Performs authentication of an incoming connection.  Session key has already
 363  * been exchanged and encryption is enabled.
 364  */
 365 void
 366 do_authentication()
 367 {
 368         Authctxt *authctxt;
 369         struct passwd *pw;
 370         int plen;
 371         u_int ulen;
 372         char *user, *style = NULL;
 373
 374         /* Get the name of the user that we wish to log in as. */
 375         packet_read_expect(&plen, SSH_CMSG_USER);
 376
 377         /* Get the user name. */
 378         user = packet_get_string(&ulen);
 379         packet_integrity_check(plen, (4 + ulen), SSH_CMSG_USER);
 380
 381         if ((style = strchr(user, ':')) != NULL)
 382                 *style++ = 0;
 383
 384         authctxt = authctxt_new();
 385         authctxt->user = user;
 386         authctxt->style = style;
 387
 388         /* Verify that the user is a valid user. */
 389         pw = getpwnam(user);
 390         if (pw && allowed_user(pw)) {
 391                 authctxt->valid = 1;
 392                 pw = pwcopy(pw);
 393         } else {
 394                 debug("do_authentication: illegal user %s", user);
 395                 pw = NULL;
 396         }
 397         authctxt->pw = pw;
 398
 399         setproctitle("%s", pw ? user : "unknown");
 400
 401 #ifdef USE_PAM
 402         if (pw)
 403                 start_pam(user);
 404 #endif
 405
 406         /*
 407          * If we are not running as root, the user must have the same uid as
 408          * the server. (Unless you are running Windows)
 409          */
 410 #ifndef HAVE_CYGWIN
 411         if (getuid() != 0 && pw && pw->pw_uid != getuid())
 412                 packet_disconnect("Cannot change user when server not running as root.");
 413 #endif
 414
 415         /*
 416          * Loop until the user has been authenticated or the connection is
 417          * closed, do_authloop() returns only if authentication is successful
 418          */
 419         do_authloop(authctxt);
 420
 421         /* The user has been authenticated and accepted. */
 422         packet_start(SSH_SMSG_SUCCESS);
 423         packet_send();
 424         packet_write_wait();
 425
 426 #ifdef WITH_AIXAUTHENTICATE
 427         /* We don't have a pty yet, so just label the line as "ssh" */
 428         if (loginsuccess(authctxt->user,
 429             get_canonical_hostname(options.reverse_mapping_check),
 430             "ssh", &aixloginmsg) < 0)
 431                 aixloginmsg = NULL;
 432 #endif /* WITH_AIXAUTHENTICATE */
 433
 434         xfree(authctxt->user);
 435         xfree(authctxt);
 436
 437         /* Perform session preparation. */
 438         do_authenticated(pw);
 439 }