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 1.20 2001/03/20 18:57:04 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
  31 #ifdef WITH_AIXAUTHENTICATE
  32 extern char *aixloginmsg;
  33 #endif /* WITH_AIXAUTHENTICATE */
  34
  35 /*
  36  * convert ssh auth msg type into description
  37  */
  38 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 #ifdef KRB4
  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 void
  68 do_authloop(Authctxt *authctxt)
  69 {
  70         int authenticated = 0;
  71         u_int bits;
  72         RSA *client_host_key;
  73         BIGNUM *n;
  74         char *client_user, *password;
  75         char info[1024];
  76         u_int dlen;
  77         int plen, nlen, elen;
  78         u_int ulen;
  79         int type = 0;
  80         struct passwd *pw = authctxt->pw;
  81
  82         debug("Attempting authentication for %s%.100s.",
  83              authctxt->valid ? "" : "illegal user ", authctxt->user);
  84
  85         /* If the user has no password, accept authentication immediately. */
  86         if (options.password_authentication &&
  87 #ifdef KRB4
  88             (!options.kerberos_authentication || options.kerberos_or_local_passwd) &&
  89 #endif
  90 #ifdef USE_PAM
  91             auth_pam_password(pw, "")) {
  92 #elif defined(HAVE_OSF_SIA)
  93             0) {
  94 #else
  95             auth_password(authctxt, "")) {
  96 #endif
  97                 auth_log(authctxt, 1, "without authentication", "");
  98                 return;
  99         }
 100
 101         /* Indicate that authentication is needed. */
 102         packet_start(SSH_SMSG_FAILURE);
 103         packet_send();
 104         packet_write_wait();
 105
 106         client_user = NULL;
 107
 108         for (;;) {
 109                 /* default to fail */
 110                 authenticated = 0;
 111
 112                 info[0] = '\0';
 113
 114                 /* Get a packet from the client. */
 115                 type = packet_read(&plen);
 116
 117                 /* Process the packet. */
 118                 switch (type) {
 119 #ifdef AFS
 120                 case SSH_CMSG_HAVE_KERBEROS_TGT:
 121                         if (!options.kerberos_tgt_passing) {
 122                                 verbose("Kerberos tgt passing disabled.");
 123                                 break;
 124                         } else {
 125                                 /* Accept Kerberos tgt. */
 126                                 char *tgt = packet_get_string(&dlen);
 127                                 packet_integrity_check(plen, 4 + dlen, type);
 128                                 if (!auth_kerberos_tgt(pw, tgt))
 129                                         verbose("Kerberos tgt REFUSED for %.100s", authctxt->user);
 130                                 xfree(tgt);
 131                         }
 132                         continue;
 133
 134                 case SSH_CMSG_HAVE_AFS_TOKEN:
 135                         if (!options.afs_token_passing || !k_hasafs()) {
 136                                 verbose("AFS token passing disabled.");
 137                                 break;
 138                         } else {
 139                                 /* Accept AFS token. */
 140                                 char *token_string = packet_get_string(&dlen);
 141                                 packet_integrity_check(plen, 4 + dlen, type);
 142                                 if (!auth_afs_token(pw, token_string))
 143                                         verbose("AFS token REFUSED for %.100s", authctxt->user);
 144                                 xfree(token_string);
 145                         }
 146                         continue;
 147 #endif /* AFS */
 148 #ifdef KRB4
 149                 case SSH_CMSG_AUTH_KERBEROS:
 150                         if (!options.kerberos_authentication) {
 151                                 verbose("Kerberos authentication disabled.");
 152                                 break;
 153                         } else {
 154                                 /* Try Kerberos v4 authentication. */
 155                                 KTEXT_ST auth;
 156                                 char *tkt_user = NULL;
 157                                 char *kdata = packet_get_string((u_int *) &auth.length);
 158                                 packet_integrity_check(plen, 4 + auth.length, type);
 159
 160                                 if (authctxt->valid) {
 161                                         if (auth.length < MAX_KTXT_LEN)
 162                                                 memcpy(auth.dat, kdata, auth.length);
 163                                         authenticated = auth_krb4(pw->pw_name, &auth, &tkt_user);
 164                                         if (authenticated) {
 165                                                 snprintf(info, sizeof info,
 166                                                     " tktuser %.100s", tkt_user);
 167                                                 xfree(tkt_user);
 168                                         }
 169                                 }
 170                                 xfree(kdata);
 171                         }
 172                         break;
 173 #endif /* KRB4 */
 174
 175                 case SSH_CMSG_AUTH_RHOSTS:
 176                         if (!options.rhosts_authentication) {
 177                                 verbose("Rhosts authentication disabled.");
 178                                 break;
 179                         }
 180                         /*
 181                          * Get client user name.  Note that we just have to
 182                          * trust the client; this is one reason why rhosts
 183                          * authentication is insecure. (Another is
 184                          * IP-spoofing on a local network.)
 185                          */
 186                         client_user = packet_get_string(&ulen);
 187                         packet_integrity_check(plen, 4 + ulen, type);
 188
 189                         /* Try to authenticate using /etc/hosts.equiv and .rhosts. */
 190                         authenticated = auth_rhosts(pw, client_user);
 191
 192                         snprintf(info, sizeof info, " ruser %.100s", client_user);
 193                         break;
 194
 195                 case SSH_CMSG_AUTH_RHOSTS_RSA:
 196                         if (!options.rhosts_rsa_authentication) {
 197                                 verbose("Rhosts with RSA authentication disabled.");
 198                                 break;
 199                         }
 200                         /*
 201                          * Get client user name.  Note that we just have to
 202                          * trust the client; root on the client machine can
 203                          * claim to be any user.
 204                          */
 205                         client_user = packet_get_string(&ulen);
 206
 207                         /* Get the client host key. */
 208                         client_host_key = RSA_new();
 209                         if (client_host_key == NULL)
 210                                 fatal("RSA_new failed");
 211                         client_host_key->e = BN_new();
 212                         client_host_key->n = BN_new();
 213                         if (client_host_key->e == NULL || client_host_key->n == NULL)
 214                                 fatal("BN_new failed");
 215                         bits = packet_get_int();
 216                         packet_get_bignum(client_host_key->e, &elen);
 217                         packet_get_bignum(client_host_key->n, &nlen);
 218
 219                         if (bits != BN_num_bits(client_host_key->n))
 220                                 verbose("Warning: keysize mismatch for client_host_key: "
 221                                     "actual %d, announced %d", BN_num_bits(client_host_key->n), bits);
 222                         packet_integrity_check(plen, (4 + ulen) + 4 + elen + nlen, type);
 223
 224                         authenticated = auth_rhosts_rsa(pw, client_user, client_host_key);
 225                         RSA_free(client_host_key);
 226
 227                         snprintf(info, sizeof info, " ruser %.100s", client_user);
 228                         break;
 229
 230                 case SSH_CMSG_AUTH_RSA:
 231                         if (!options.rsa_authentication) {
 232                                 verbose("RSA authentication disabled.");
 233                                 break;
 234                         }
 235                         /* RSA authentication requested. */
 236                         n = BN_new();
 237                         packet_get_bignum(n, &nlen);
 238                         packet_integrity_check(plen, nlen, type);
 239                         authenticated = auth_rsa(pw, n);
 240                         BN_clear_free(n);
 241                         break;
 242
 243                 case SSH_CMSG_AUTH_PASSWORD:
 244                         if (!options.password_authentication) {
 245                                 verbose("Password authentication disabled.");
 246                                 break;
 247                         }
 248                         /*
 249                          * Read user password.  It is in plain text, but was
 250                          * transmitted over the encrypted channel so it is
 251                          * not visible to an outside observer.
 252                          */
 253                         password = packet_get_string(&dlen);
 254                         packet_integrity_check(plen, 4 + dlen, type);
 255
 256 #ifdef USE_PAM
 257                         /* Do PAM auth with password */
 258                         authenticated = auth_pam_password(pw, password);
 259 #elif defined(HAVE_OSF_SIA)
 260                         /* Do SIA auth with password */
 261                         authenticated = auth_sia_password(authctxt->user,
 262                             password);
 263 #else /* !USE_PAM && !HAVE_OSF_SIA */
 264                         /* Try authentication with the password. */
 265                         authenticated = auth_password(authctxt, password);
 266 #endif /* USE_PAM */
 267
 268                         memset(password, 0, strlen(password));
 269                         xfree(password);
 270                         break;
 271
 272                 case SSH_CMSG_AUTH_TIS:
 273                         debug("rcvd SSH_CMSG_AUTH_TIS");
 274                         if (options.challenge_reponse_authentication == 1) {
 275                                 char *challenge = get_challenge(authctxt, authctxt->style);
 276                                 if (challenge != NULL) {
 277                                         debug("sending challenge '%s'", challenge);
 278                                         packet_start(SSH_SMSG_AUTH_TIS_CHALLENGE);
 279                                         packet_put_cstring(challenge);
 280                                         packet_send();
 281                                         packet_write_wait();
 282                                         continue;
 283                                 }
 284                         }
 285                         break;
 286                 case SSH_CMSG_AUTH_TIS_RESPONSE:
 287                         debug("rcvd SSH_CMSG_AUTH_TIS_RESPONSE");
 288                         if (options.challenge_reponse_authentication == 1) {
 289                                 char *response = packet_get_string(&dlen);
 290                                 debug("got response '%s'", response);
 291                                 packet_integrity_check(plen, 4 + dlen, type);
 292                                 authenticated = verify_response(authctxt, response);
 293                                 memset(response, 'r', dlen);
 294                                 xfree(response);
 295                         }
 296                         break;
 297
 298                 default:
 299                         /*
 300                          * Any unknown messages will be ignored (and failure
 301                          * returned) during authentication.
 302                          */
 303                         log("Unknown message during authentication: type %d", type);
 304                         break;
 305                 }
 306 #ifdef BSD_AUTH
 307                 if (authctxt->as) {
 308                         auth_close(authctxt->as);
 309                         authctxt->as = NULL;
 310                 }
 311 #endif
 312                 if (!authctxt->valid && authenticated)
 313                         fatal("INTERNAL ERROR: authenticated invalid user %s",
 314                             authctxt->user);
 315
 316 #ifdef HAVE_CYGWIN
 317                 if (authenticated &&
 318                     !check_nt_auth(type == SSH_CMSG_AUTH_PASSWORD,pw->pw_uid)) {
 319                         packet_disconnect("Authentication rejected for uid %d.",
 320                         (int)pw->pw_uid);
 321                         authenticated = 0;
 322                 }
 323 #else
 324                 /* Special handling for root */
 325                 if (authenticated && authctxt->pw->pw_uid == 0 &&
 326                     !auth_root_allowed(get_authname(type)))
 327                         authenticated = 0;
 328 #endif
 329 #ifdef USE_PAM
 330                 if (authenticated && !do_pam_account(pw->pw_name, client_user))
 331                         authenticated = 0;
 332 #endif
 333
 334                 /* Log before sending the reply */
 335                 auth_log(authctxt, authenticated, get_authname(type), info);
 336
 337                 if (client_user != NULL) {
 338                         xfree(client_user);
 339                         client_user = NULL;
 340                 }
 341
 342                 if (authenticated)
 343                         return;
 344
 345                 if (authctxt->failures++ > AUTH_FAIL_MAX) {
 346 #ifdef WITH_AIXAUTHENTICATE
 347                         loginfailed(authctxt->user,
 348                             get_canonical_hostname(options.reverse_mapping_check),
 349                             "ssh");
 350 #endif /* WITH_AIXAUTHENTICATE */
 351                         packet_disconnect(AUTH_FAIL_MSG, authctxt->user);
 352                 }
 353
 354                 packet_start(SSH_SMSG_FAILURE);
 355                 packet_send();
 356                 packet_write_wait();
 357         }
 358 }
 359
 360 /*
 361  * Performs authentication of an incoming connection.  Session key has already
 362  * been exchanged and encryption is enabled.
 363  */
 364 void
 365 do_authentication()
 366 {
 367         Authctxt *authctxt;
 368         struct passwd *pw;
 369         int plen;
 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(&plen, SSH_CMSG_USER);
 375
 376         /* Get the user name. */
 377         user = packet_get_string(&ulen);
 378         packet_integrity_check(plen, (4 + ulen), SSH_CMSG_USER);
 379
 380         if ((style = strchr(user, ':')) != NULL)
 381                 *style++ = 0;
 382
 383         authctxt = authctxt_new();
 384         authctxt->user = user;
 385         authctxt->style = style;
 386
 387         /* Verify that the user is a valid user. */
 388         pw = getpwnam(user);
 389         if (pw && allowed_user(pw)) {
 390                 authctxt->valid = 1;
 391                 pw = pwcopy(pw);
 392         } else {
 393                 debug("do_authentication: illegal user %s", user);
 394                 pw = NULL;
 395         }
 396         authctxt->pw = pw;
 397
 398         setproctitle("%s", pw ? user : "unknown");
 399
 400 #ifdef USE_PAM
 401         if (pw)
 402                 start_pam(user);
 403 #endif
 404
 405         /*
 406          * If we are not running as root, the user must have the same uid as
 407          * the server. (Unless you are running Windows)
 408          */
 409 #ifndef HAVE_CYGWIN
 410         if (getuid() != 0 && pw && pw->pw_uid != getuid())
 411                 packet_disconnect("Cannot change user when server not running as root.");
 412 #endif
 413
 414         /*
 415          * Loop until the user has been authenticated or the connection is
 416          * closed, do_authloop() returns only if authentication is successful
 417          */
 418         do_authloop(authctxt);
 419
 420         /* The user has been authenticated and accepted. */
 421         packet_start(SSH_SMSG_SUCCESS);
 422         packet_send();
 423         packet_write_wait();
 424
 425 #ifdef WITH_AIXAUTHENTICATE
 426         /* We don't have a pty yet, so just label the line as "ssh" */
 427         if (loginsuccess(authctxt->user,
 428             get_canonical_hostname(options.reverse_mapping_check),
 429             "ssh", &aixloginmsg) < 0)
 430                 aixloginmsg = NULL;
 431 #endif /* WITH_AIXAUTHENTICATE */
 432
 433         xfree(authctxt->user);
 434         xfree(authctxt);
 435
 436         /* Perform session preparation. */
 437         do_authenticated(pw);
 438 }