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 1.27 2001/12/19 07:18:56 deraadt 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 #include "uidswap.h"
  28
  29 /* import */
  30 extern ServerOptions options;
  31
  32 /*
  33  * convert ssh auth msg type into description
  34  */
  35 static char *
  36 get_authname(int type)
  37 {
  38         static char buf[1024];
  39         switch (type) {
  40         case SSH_CMSG_AUTH_PASSWORD:
  41                 return "password";
  42         case SSH_CMSG_AUTH_RSA:
  43                 return "rsa";
  44         case SSH_CMSG_AUTH_RHOSTS_RSA:
  45                 return "rhosts-rsa";
  46         case SSH_CMSG_AUTH_RHOSTS:
  47                 return "rhosts";
  48         case SSH_CMSG_AUTH_TIS:
  49         case SSH_CMSG_AUTH_TIS_RESPONSE:
  50                 return "challenge-response";
  51 #if defined(KRB4) || defined(KRB5)
  52         case SSH_CMSG_AUTH_KERBEROS:
  53                 return "kerberos";
  54 #endif
  55         }
  56         snprintf(buf, sizeof buf, "bad-auth-msg-%d", type);
  57         return buf;
  58 }
  59
  60 /*
  61  * read packets, try to authenticate the user and
  62  * return only if authentication is successful
  63  */
  64 static void
  65 do_authloop(Authctxt *authctxt)
  66 {
  67         int authenticated = 0;
  68         u_int bits;
  69         RSA *client_host_key;
  70         BIGNUM *n;
  71         char *client_user, *password;
  72         char info[1024];
  73         u_int dlen;
  74         int plen, nlen, elen;
  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 #ifdef USE_PAM
  88             auth_pam_password(pw, "")) {
  89 #elif defined(HAVE_OSF_SIA)
  90             0) {
  91 #else
  92             auth_password(authctxt, "")) {
  93 #endif
  94                 auth_log(authctxt, 1, "without authentication", "");
  95                 return;
  96         }
  97
  98         /* Indicate that authentication is needed. */
  99         packet_start(SSH_SMSG_FAILURE);
 100         packet_send();
 101         packet_write_wait();
 102
 103         client_user = NULL;
 104
 105         for (;;) {
 106                 /* default to fail */
 107                 authenticated = 0;
 108
 109                 info[0] = '\0';
 110
 111                 /* Get a packet from the client. */
 112                 type = packet_read(&plen);
 113
 114                 /* Process the packet. */
 115                 switch (type) {
 116
 117 #if defined(KRB4) || defined(KRB5)
 118                 case SSH_CMSG_AUTH_KERBEROS:
 119                         if (!options.kerberos_authentication) {
 120                                 verbose("Kerberos authentication disabled.");
 121                         } else {
 122                                 char *kdata = packet_get_string(&dlen);
 123
 124                                 packet_integrity_check(plen, 4 + dlen, type);
 125
 126                                 if (kdata[0] == 4) { /* KRB_PROT_VERSION */
 127 #ifdef KRB4
 128                                         KTEXT_ST tkt;
 129
 130                                         tkt.length = dlen;
 131                                         if (tkt.length < MAX_KTXT_LEN)
 132                                                 memcpy(tkt.dat, kdata, tkt.length);
 133
 134                                         if (auth_krb4(authctxt, &tkt, &client_user)) {
 135                                                 authenticated = 1;
 136                                                 snprintf(info, sizeof(info),
 137                                                     " tktuser %.100s",
 138                                                     client_user);
 139                                         }
 140 #endif /* KRB4 */
 141                                 } else {
 142 #ifdef KRB5
 143                                         krb5_data tkt;
 144                                         tkt.length = dlen;
 145                                         tkt.data = kdata;
 146
 147                                         if (auth_krb5(authctxt, &tkt, &client_user)) {
 148                                                 authenticated = 1;
 149                                                 snprintf(info, sizeof(info),
 150                                                     " tktuser %.100s",
 151                                                     client_user);
 152                                         }
 153 #endif /* KRB5 */
 154                                 }
 155                                 xfree(kdata);
 156                         }
 157                         break;
 158 #endif /* KRB4 || KRB5 */
 159
 160 #if defined(AFS) || defined(KRB5)
 161                         /* XXX - punt on backward compatibility here. */
 162                 case SSH_CMSG_HAVE_KERBEROS_TGT:
 163                         packet_send_debug("Kerberos TGT passing disabled before authentication.");
 164                         break;
 165 #ifdef AFS
 166                 case SSH_CMSG_HAVE_AFS_TOKEN:
 167                         packet_send_debug("AFS token passing disabled before authentication.");
 168                         break;
 169 #endif /* AFS */
 170 #endif /* AFS || KRB5 */
 171
 172                 case SSH_CMSG_AUTH_RHOSTS:
 173                         if (!options.rhosts_authentication) {
 174                                 verbose("Rhosts authentication disabled.");
 175                                 break;
 176                         }
 177                         /*
 178                          * Get client user name.  Note that we just have to
 179                          * trust the client; this is one reason why rhosts
 180                          * authentication is insecure. (Another is
 181                          * IP-spoofing on a local network.)
 182                          */
 183                         client_user = packet_get_string(&ulen);
 184                         packet_integrity_check(plen, 4 + ulen, type);
 185
 186                         /* Try to authenticate using /etc/hosts.equiv and .rhosts. */
 187                         authenticated = auth_rhosts(pw, client_user);
 188
 189                         snprintf(info, sizeof info, " ruser %.100s", client_user);
 190                         break;
 191
 192                 case SSH_CMSG_AUTH_RHOSTS_RSA:
 193                         if (!options.rhosts_rsa_authentication) {
 194                                 verbose("Rhosts with RSA authentication disabled.");
 195                                 break;
 196                         }
 197                         /*
 198                          * Get client user name.  Note that we just have to
 199                          * trust the client; root on the client machine can
 200                          * claim to be any user.
 201                          */
 202                         client_user = packet_get_string(&ulen);
 203
 204                         /* Get the client host key. */
 205                         client_host_key = RSA_new();
 206                         if (client_host_key == NULL)
 207                                 fatal("RSA_new failed");
 208                         client_host_key->e = BN_new();
 209                         client_host_key->n = BN_new();
 210                         if (client_host_key->e == NULL || client_host_key->n == NULL)
 211                                 fatal("BN_new failed");
 212                         bits = packet_get_int();
 213                         packet_get_bignum(client_host_key->e, &elen);
 214                         packet_get_bignum(client_host_key->n, &nlen);
 215
 216                         if (bits != BN_num_bits(client_host_key->n))
 217                                 verbose("Warning: keysize mismatch for client_host_key: "
 218                                     "actual %d, announced %d", BN_num_bits(client_host_key->n), bits);
 219                         packet_integrity_check(plen, (4 + ulen) + 4 + elen + nlen, type);
 220
 221                         authenticated = auth_rhosts_rsa(pw, client_user, client_host_key);
 222                         RSA_free(client_host_key);
 223
 224                         snprintf(info, sizeof info, " ruser %.100s", client_user);
 225                         break;
 226
 227                 case SSH_CMSG_AUTH_RSA:
 228                         if (!options.rsa_authentication) {
 229                                 verbose("RSA authentication disabled.");
 230                                 break;
 231                         }
 232                         /* RSA authentication requested. */
 233                         n = BN_new();
 234                         packet_get_bignum(n, &nlen);
 235                         packet_integrity_check(plen, nlen, type);
 236                         authenticated = auth_rsa(pw, n);
 237                         BN_clear_free(n);
 238                         break;
 239
 240                 case SSH_CMSG_AUTH_PASSWORD:
 241                         if (!options.password_authentication) {
 242                                 verbose("Password authentication disabled.");
 243                                 break;
 244                         }
 245                         /*
 246                          * Read user password.  It is in plain text, but was
 247                          * transmitted over the encrypted channel so it is
 248                          * not visible to an outside observer.
 249                          */
 250                         password = packet_get_string(&dlen);
 251                         packet_integrity_check(plen, 4 + dlen, type);
 252
 253 #ifdef USE_PAM
 254                         /* Do PAM auth with password */
 255                         authenticated = auth_pam_password(pw, password);
 256 #elif defined(HAVE_OSF_SIA)
 257                         /* Do SIA auth with password */
 258                         authenticated = auth_sia_password(authctxt->user,
 259                             password);
 260 #else /* !USE_PAM && !HAVE_OSF_SIA */
 261                         /* Try authentication with the password. */
 262                         authenticated = auth_password(authctxt, password);
 263 #endif /* USE_PAM */
 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                                 debug("got response '%s'", response);
 289                                 packet_integrity_check(plen, 4 + dlen, type);
 290                                 authenticated = verify_response(authctxt, response);
 291                                 memset(response, 'r', dlen);
 292                                 xfree(response);
 293                         }
 294                         break;
 295
 296                 default:
 297                         /*
 298                          * Any unknown messages will be ignored (and failure
 299                          * returned) during authentication.
 300                          */
 301                         log("Unknown message during authentication: type %d", type);
 302                         break;
 303                 }
 304 #ifdef BSD_AUTH
 305                 if (authctxt->as) {
 306                         auth_close(authctxt->as);
 307                         authctxt->as = NULL;
 308                 }
 309 #endif
 310                 if (!authctxt->valid && authenticated)
 311                         fatal("INTERNAL ERROR: authenticated invalid user %s",
 312                             authctxt->user);
 313
 314 #ifdef HAVE_CYGWIN
 315                 if (authenticated &&
 316                     !check_nt_auth(type == SSH_CMSG_AUTH_PASSWORD, pw)) {
 317                         packet_disconnect("Authentication rejected for uid %d.",
 318                         pw == NULL ? -1 : pw->pw_uid);
 319                         authenticated = 0;
 320                 }
 321 #else
 322                 /* Special handling for root */
 323                 if (authenticated && authctxt->pw->pw_uid == 0 &&
 324                     !auth_root_allowed(get_authname(type)))
 325                         authenticated = 0;
 326 #endif
 327 #ifdef USE_PAM
 328                 if (authenticated && !do_pam_account(pw->pw_name, client_user))
 329                         authenticated = 0;
 330 #endif
 331
 332                 /* Log before sending the reply */
 333                 auth_log(authctxt, authenticated, get_authname(type), info);
 334
 335                 if (client_user != NULL) {
 336                         xfree(client_user);
 337                         client_user = NULL;
 338                 }
 339
 340                 if (authenticated)
 341                         return;
 342
 343                 if (authctxt->failures++ > AUTH_FAIL_MAX) {
 344 #ifdef WITH_AIXAUTHENTICATE
 345                         loginfailed(authctxt->user,
 346                             get_canonical_hostname(options.reverse_mapping_check),
 347                             "ssh");
 348 #endif /* WITH_AIXAUTHENTICATE */
 349                         packet_disconnect(AUTH_FAIL_MSG, authctxt->user);
 350                 }
 351
 352                 packet_start(SSH_SMSG_FAILURE);
 353                 packet_send();
 354                 packet_write_wait();
 355         }
 356 }
 357
 358 /*
 359  * Performs authentication of an incoming connection.  Session key has already
 360  * been exchanged and encryption is enabled.
 361  */
 362 void
 363 do_authentication(void)
 364 {
 365         Authctxt *authctxt;
 366         struct passwd *pw;
 367         int plen;
 368         u_int ulen;
 369         char *p, *user, *style = NULL;
 370
 371         /* Get the name of the user that we wish to log in as. */
 372         packet_read_expect(&plen, SSH_CMSG_USER);
 373
 374         /* Get the user name. */
 375         user = packet_get_string(&ulen);
 376         packet_integrity_check(plen, (4 + ulen), SSH_CMSG_USER);
 377
 378         if ((style = strchr(user, ':')) != NULL)
 379                 *style++ = '\0';
 380
 381         /* XXX - SSH.com Kerberos v5 braindeath. */
 382         if ((p = strchr(user, '@')) != NULL)
 383                 *p = '\0';
 384
 385         authctxt = authctxt_new();
 386         authctxt->user = user;
 387         authctxt->style = style;
 388
 389         /* Verify that the user is a valid user. */
 390         pw = getpwnam(user);
 391         if (pw && allowed_user(pw)) {
 392                 authctxt->valid = 1;
 393                 pw = pwcopy(pw);
 394         } else {
 395                 debug("do_authentication: illegal user %s", user);
 396                 pw = NULL;
 397         }
 398         authctxt->pw = pw;
 399
 400         setproctitle("%s", pw ? user : "unknown");
 401
 402 #ifdef USE_PAM
 403         if (pw)
 404                 start_pam(user);
 405 #endif
 406
 407         /*
 408          * If we are not running as root, the user must have the same uid as
 409          * the server. (Unless you are running Windows)
 410          */
 411 #ifndef HAVE_CYGWIN
 412         if (getuid() != 0 && pw && pw->pw_uid != getuid())
 413                 packet_disconnect("Cannot change user when server not running as root.");
 414 #endif
 415
 416         /*
 417          * Loop until the user has been authenticated or the connection is
 418          * closed, do_authloop() returns only if authentication is successful
 419          */
 420         do_authloop(authctxt);
 421
 422         /* The user has been authenticated and accepted. */
 423         packet_start(SSH_SMSG_SUCCESS);
 424         packet_send();
 425         packet_write_wait();
 426
 427         /* Perform session preparation. */
 428         do_authenticated(authctxt);
 429 }