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