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 1.47 2003/02/06 21:22:42 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 "channels.h"
  26 #include "session.h"
  27 #include "uidswap.h"
  28 #include "monitor_wrap.h"
  29
  30 /* import */
  31 extern ServerOptions options;
  32
  33 /*
  34  * convert ssh auth msg type into description
  35  */
  36 static char *
  37 get_authname(int type)
  38 {
  39         static char buf[1024];
  40         switch (type) {
  41         case SSH_CMSG_AUTH_PASSWORD:
  42                 return "password";
  43         case SSH_CMSG_AUTH_RSA:
  44                 return "rsa";
  45         case SSH_CMSG_AUTH_RHOSTS_RSA:
  46                 return "rhosts-rsa";
  47         case SSH_CMSG_AUTH_RHOSTS:
  48                 return "rhosts";
  49         case SSH_CMSG_AUTH_TIS:
  50         case SSH_CMSG_AUTH_TIS_RESPONSE:
  51                 return "challenge-response";
  52 #if defined(KRB4) || defined(KRB5)
  53         case SSH_CMSG_AUTH_KERBEROS:
  54                 return "kerberos";
  55 #endif
  56         }
  57         snprintf(buf, sizeof buf, "bad-auth-msg-%d", type);
  58         return buf;
  59 }
  60
  61 /*
  62  * read packets, try to authenticate the user and
  63  * return only if authentication is successful
  64  */
  65 static void
  66 do_authloop(Authctxt *authctxt)
  67 {
  68         int authenticated = 0;
  69         u_int bits;
  70         Key *client_host_key;
  71         BIGNUM *n;
  72         char *client_user, *password;
  73         char info[1024];
  74         u_int dlen;
  75         u_int ulen;
  76         int type = 0;
  77         struct passwd *pw = authctxt->pw;
  78
  79         debug("Attempting authentication for %s%.100s.",
  80             authctxt->valid ? "" : "illegal user ", authctxt->user);
  81
  82         /* If the user has no password, accept authentication immediately. */
  83         if (options.password_authentication &&
  84 #if defined(KRB4) || defined(KRB5)
  85             (!options.kerberos_authentication || options.kerberos_or_local_passwd) &&
  86 #endif
  87             PRIVSEP(auth_password(authctxt, ""))) {
  88                 auth_log(authctxt, 1, "without authentication", "");
  89                 return;
  90         }
  91
  92         /* Indicate that authentication is needed. */
  93         packet_start(SSH_SMSG_FAILURE);
  94         packet_send();
  95         packet_write_wait();
  96
  97         client_user = NULL;
  98
  99         for (;;) {
 100                 /* default to fail */
 101                 authenticated = 0;
 102
 103                 info[0] = '\0';
 104
 105                 /* Get a packet from the client. */
 106                 type = packet_read();
 107
 108                 /* Process the packet. */
 109                 switch (type) {
 110
 111 #if defined(KRB4) || defined(KRB5)
 112                 case SSH_CMSG_AUTH_KERBEROS:
 113                         if (!options.kerberos_authentication) {
 114                                 verbose("Kerberos authentication disabled.");
 115                         } else {
 116                                 char *kdata = packet_get_string(&dlen);
 117                                 packet_check_eom();
 118
 119                                 if (kdata[0] == 4) { /* KRB_PROT_VERSION */
 120 #ifdef KRB4
 121                                         KTEXT_ST tkt, reply;
 122                                         tkt.length = dlen;
 123                                         if (tkt.length < MAX_KTXT_LEN)
 124                                                 memcpy(tkt.dat, kdata, tkt.length);
 125
 126                                         if (PRIVSEP(auth_krb4(authctxt, &tkt,
 127                                             &client_user, &reply))) {
 128                                                 authenticated = 1;
 129                                                 snprintf(info, sizeof(info),
 130                                                     " tktuser %.100s",
 131                                                     client_user);
 132
 133                                                 packet_start(
 134                                                     SSH_SMSG_AUTH_KERBEROS_RESPONSE);
 135                                                 packet_put_string((char *)
 136                                                     reply.dat, reply.length);
 137                                                 packet_send();
 138                                                 packet_write_wait();
 139                                         }
 140 #endif /* KRB4 */
 141                                 } else {
 142 #ifdef KRB5
 143                                         krb5_data tkt, reply;
 144                                         tkt.length = dlen;
 145                                         tkt.data = kdata;
 146
 147                                         if (PRIVSEP(auth_krb5(authctxt, &tkt,
 148                                             &client_user, &reply))) {
 149                                                 authenticated = 1;
 150                                                 snprintf(info, sizeof(info),
 151                                                     " tktuser %.100s",
 152                                                     client_user);
 153
 154                                                 /* Send response to client */
 155                                                 packet_start(
 156                                                     SSH_SMSG_AUTH_KERBEROS_RESPONSE);
 157                                                 packet_put_string((char *)
 158                                                     reply.data, reply.length);
 159                                                 packet_send();
 160                                                 packet_write_wait();
 161
 162                                                 if (reply.length)
 163                                                         xfree(reply.data);
 164                                         }
 165 #endif /* KRB5 */
 166                                 }
 167                                 xfree(kdata);
 168                         }
 169                         break;
 170 #endif /* KRB4 || KRB5 */
 171
 172 #if defined(AFS) || defined(KRB5)
 173                         /* XXX - punt on backward compatibility here. */
 174                 case SSH_CMSG_HAVE_KERBEROS_TGT:
 175                         packet_send_debug("Kerberos TGT passing disabled before authentication.");
 176                         break;
 177 #ifdef AFS
 178                 case SSH_CMSG_HAVE_AFS_TOKEN:
 179                         packet_send_debug("AFS token passing disabled before authentication.");
 180                         break;
 181 #endif /* AFS */
 182 #endif /* AFS || KRB5 */
 183
 184                 case SSH_CMSG_AUTH_RHOSTS:
 185                         if (!options.rhosts_authentication) {
 186                                 verbose("Rhosts authentication disabled.");
 187                                 break;
 188                         }
 189                         /*
 190                          * Get client user name.  Note that we just have to
 191                          * trust the client; this is one reason why rhosts
 192                          * authentication is insecure. (Another is
 193                          * IP-spoofing on a local network.)
 194                          */
 195                         client_user = packet_get_string(&ulen);
 196                         packet_check_eom();
 197
 198                         /* Try to authenticate using /etc/hosts.equiv and .rhosts. */
 199                         authenticated = auth_rhosts(pw, client_user);
 200
 201                         snprintf(info, sizeof info, " ruser %.100s", client_user);
 202                         break;
 203
 204                 case SSH_CMSG_AUTH_RHOSTS_RSA:
 205                         if (!options.rhosts_rsa_authentication) {
 206                                 verbose("Rhosts with RSA authentication disabled.");
 207                                 break;
 208                         }
 209                         /*
 210                          * Get client user name.  Note that we just have to
 211                          * trust the client; root on the client machine can
 212                          * claim to be any user.
 213                          */
 214                         client_user = packet_get_string(&ulen);
 215
 216                         /* Get the client host key. */
 217                         client_host_key = key_new(KEY_RSA1);
 218                         bits = packet_get_int();
 219                         packet_get_bignum(client_host_key->rsa->e);
 220                         packet_get_bignum(client_host_key->rsa->n);
 221
 222                         if (bits != BN_num_bits(client_host_key->rsa->n))
 223                                 verbose("Warning: keysize mismatch for client_host_key: "
 224                                     "actual %d, announced %d",
 225                                     BN_num_bits(client_host_key->rsa->n), bits);
 226                         packet_check_eom();
 227
 228                         authenticated = auth_rhosts_rsa(pw, client_user,
 229                             client_host_key);
 230                         key_free(client_host_key);
 231
 232                         snprintf(info, sizeof info, " ruser %.100s", client_user);
 233                         break;
 234
 235                 case SSH_CMSG_AUTH_RSA:
 236                         if (!options.rsa_authentication) {
 237                                 verbose("RSA authentication disabled.");
 238                                 break;
 239                         }
 240                         /* RSA authentication requested. */
 241                         if ((n = BN_new()) == NULL)
 242                                 fatal("do_authloop: BN_new failed");
 243                         packet_get_bignum(n);
 244                         packet_check_eom();
 245                         authenticated = auth_rsa(pw, n);
 246                         BN_clear_free(n);
 247                         break;
 248
 249                 case SSH_CMSG_AUTH_PASSWORD:
 250                         if (!options.password_authentication) {
 251                                 verbose("Password authentication disabled.");
 252                                 break;
 253                         }
 254                         /*
 255                          * Read user password.  It is in plain text, but was
 256                          * transmitted over the encrypted channel so it is
 257                          * not visible to an outside observer.
 258                          */
 259                         password = packet_get_string(&dlen);
 260                         packet_check_eom();
 261
 262                         /* Try authentication with the password. */
 263                         authenticated = PRIVSEP(auth_password(authctxt, password));
 264
 265                         memset(password, 0, strlen(password));
 266                         xfree(password);
 267                         break;
 268
 269                 case SSH_CMSG_AUTH_TIS:
 270                         debug("rcvd SSH_CMSG_AUTH_TIS");
 271                         if (options.challenge_response_authentication == 1) {
 272                                 char *challenge = get_challenge(authctxt);
 273                                 if (challenge != NULL) {
 274                                         debug("sending challenge '%s'", challenge);
 275                                         packet_start(SSH_SMSG_AUTH_TIS_CHALLENGE);
 276                                         packet_put_cstring(challenge);
 277                                         xfree(challenge);
 278                                         packet_send();
 279                                         packet_write_wait();
 280                                         continue;
 281                                 }
 282                         }
 283                         break;
 284                 case SSH_CMSG_AUTH_TIS_RESPONSE:
 285                         debug("rcvd SSH_CMSG_AUTH_TIS_RESPONSE");
 286                         if (options.challenge_response_authentication == 1) {
 287                                 char *response = packet_get_string(&dlen);
 288                                 packet_check_eom();
 289                                 authenticated = verify_response(authctxt, response);
 290                                 memset(response, 'r', dlen);
 291                                 xfree(response);
 292                         }
 293                         break;
 294
 295                 default:
 296                         /*
 297                          * Any unknown messages will be ignored (and failure
 298                          * returned) during authentication.
 299                          */
 300                         log("Unknown message during authentication: type %d", type);
 301                         break;
 302                 }
 303 #ifdef BSD_AUTH
 304                 if (authctxt->as) {
 305                         auth_close(authctxt->as);
 306                         authctxt->as = NULL;
 307                 }
 308 #endif
 309                 if (!authctxt->valid && authenticated)
 310                         fatal("INTERNAL ERROR: authenticated invalid user %s",
 311                             authctxt->user);
 312
 313 #ifdef _UNICOS
 314                 if (type == SSH_CMSG_AUTH_PASSWORD && !authenticated)
 315                         cray_login_failure(authctxt->user, IA_UDBERR);
 316                 if (authenticated && cray_access_denied(authctxt->user)) {
 317                         authenticated = 0;
 318                         fatal("Access denied for user %s.",authctxt->user);
 319                 }
 320 #endif /* _UNICOS */
 321
 322 #ifdef HAVE_CYGWIN
 323                 if (authenticated &&
 324                     !check_nt_auth(type == SSH_CMSG_AUTH_PASSWORD, pw)) {
 325                         packet_disconnect("Authentication rejected for uid %d.",
 326                         pw == NULL ? -1 : pw->pw_uid);
 327                         authenticated = 0;
 328                 }
 329 #else
 330                 /* Special handling for root */
 331                 if (authenticated && authctxt->pw->pw_uid == 0 &&
 332                     !auth_root_allowed(get_authname(type)))
 333                         authenticated = 0;
 334 #endif
 335 #ifdef USE_PAM
 336                 if (!use_privsep && authenticated &&
 337                     !do_pam_account(pw->pw_name, client_user))
 338                         authenticated = 0;
 339 #endif
 340
 341                 /* Log before sending the reply */
 342                 auth_log(authctxt, authenticated, get_authname(type), info);
 343
 344                 if (client_user != NULL) {
 345                         xfree(client_user);
 346                         client_user = NULL;
 347                 }
 348
 349                 if (authenticated)
 350                         return;
 351
 352                 if (authctxt->failures++ > AUTH_FAIL_MAX) {
 353                         packet_disconnect(AUTH_FAIL_MSG, authctxt->user);
 354                 }
 355
 356                 packet_start(SSH_SMSG_FAILURE);
 357                 packet_send();
 358                 packet_write_wait();
 359         }
 360 }
 361
 362 /*
 363  * Performs authentication of an incoming connection.  Session key has already
 364  * been exchanged and encryption is enabled.
 365  */
 366 Authctxt *
 367 do_authentication(void)
 368 {
 369         Authctxt *authctxt;
 370         u_int ulen;
 371         char *user, *style = NULL;
 372
 373         /* Get the name of the user that we wish to log in as. */
 374         packet_read_expect(SSH_CMSG_USER);
 375
 376         /* Get the user name. */
 377         user = packet_get_string(&ulen);
 378         packet_check_eom();
 379
 380         if ((style = strchr(user, ':')) != NULL)
 381                 *style++ = '\0';
 382
 383 #ifdef KRB5
 384         /* XXX - SSH.com Kerberos v5 braindeath. */
 385         if ((datafellows & SSH_BUG_K5USER) &&
 386             options.kerberos_authentication) {
 387                 char *p;
 388                 if ((p = strchr(user, '@')) != NULL)
 389                         *p = '\0';
 390         }
 391 #endif
 392
 393         authctxt = authctxt_new();
 394         authctxt->user = user;
 395         authctxt->style = style;
 396
 397         /* Verify that the user is a valid user. */
 398         if ((authctxt->pw = PRIVSEP(getpwnamallow(user))) != NULL)
 399                 authctxt->valid = 1;
 400         else
 401                 debug("do_authentication: illegal user %s", user);
 402
 403         setproctitle("%s%s", authctxt->pw ? user : "unknown",
 404             use_privsep ? " [net]" : "");
 405
 406 #ifdef USE_PAM
 407         PRIVSEP(start_pam(authctxt->pw == NULL ? "NOUSER" : user));
 408 #endif
 409
 410         /*
 411          * If we are not running as root, the user must have the same uid as
 412          * the server. (Unless you are running Windows)
 413          */
 414 #ifndef HAVE_CYGWIN
 415         if (!use_privsep && getuid() != 0 && authctxt->pw &&
 416             authctxt->pw->pw_uid != getuid())
 417                 packet_disconnect("Cannot change user when server not running as root.");
 418 #endif
 419
 420         /*
 421          * Loop until the user has been authenticated or the connection is
 422          * closed, do_authloop() returns only if authentication is successful
 423          */
 424         do_authloop(authctxt);
 425
 426         /* The user has been authenticated and accepted. */
 427         packet_start(SSH_SMSG_SUCCESS);
 428         packet_send();
 429         packet_write_wait();
 430
 431         return (authctxt);
 432 }