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 1.34 2001/12/28 14:50:54 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 #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         Key *client_host_key;
  70         BIGNUM *n;
  71         char *client_user, *password;
  72         char info[1024];
  73         u_int dlen;
  74         u_int ulen;
  75         int type = 0;
  76         struct passwd *pw = authctxt->pw;
  77
  78         debug("Attempting authentication for %s%.100s.",
  79             authctxt->valid ? "" : "illegal user ", authctxt->user);
  80
  81         /* If the user has no password, accept authentication immediately. */
  82         if (options.password_authentication &&
  83 #if defined(KRB4) || defined(KRB5)
  84             (!options.kerberos_authentication || options.kerberos_or_local_passwd) &&
  85 #endif
  86 #ifdef USE_PAM
  87             auth_pam_password(pw, "")) {
  88 #elif defined(HAVE_OSF_SIA)
  89             0) {
  90 #else
  91             auth_password(authctxt, "")) {
  92 #endif
  93                 auth_log(authctxt, 1, "without authentication", "");
  94                 return;
  95         }
  96
  97         /* Indicate that authentication is needed. */
  98         packet_start(SSH_SMSG_FAILURE);
  99         packet_send();
 100         packet_write_wait();
 101
 102         client_user = NULL;
 103
 104         for (;;) {
 105                 /* default to fail */
 106                 authenticated = 0;
 107
 108                 info[0] = '\0';
 109
 110                 /* Get a packet from the client. */
 111                 type = packet_read();
 112
 113                 /* Process the packet. */
 114                 switch (type) {
 115
 116 #if defined(KRB4) || defined(KRB5)
 117                 case SSH_CMSG_AUTH_KERBEROS:
 118                         if (!options.kerberos_authentication) {
 119                                 verbose("Kerberos authentication disabled.");
 120                         } else {
 121                                 char *kdata = packet_get_string(&dlen);
 122                                 packet_check_eom();
 123
 124                                 if (kdata[0] == 4) { /* KRB_PROT_VERSION */
 125 #ifdef KRB4
 126                                         KTEXT_ST tkt;
 127
 128                                         tkt.length = dlen;
 129                                         if (tkt.length < MAX_KTXT_LEN)
 130                                                 memcpy(tkt.dat, kdata, tkt.length);
 131
 132                                         if (auth_krb4(authctxt, &tkt, &client_user)) {
 133                                                 authenticated = 1;
 134                                                 snprintf(info, sizeof(info),
 135                                                     " tktuser %.100s",
 136                                                     client_user);
 137                                         }
 138 #endif /* KRB4 */
 139                                 } else {
 140 #ifdef KRB5
 141                                         krb5_data tkt;
 142                                         tkt.length = dlen;
 143                                         tkt.data = kdata;
 144
 145                                         if (auth_krb5(authctxt, &tkt, &client_user)) {
 146                                                 authenticated = 1;
 147                                                 snprintf(info, sizeof(info),
 148                                                     " tktuser %.100s",
 149                                                     client_user);
 150                                         }
 151 #endif /* KRB5 */
 152                                 }
 153                                 xfree(kdata);
 154                         }
 155                         break;
 156 #endif /* KRB4 || KRB5 */
 157
 158 #if defined(AFS) || defined(KRB5)
 159                         /* XXX - punt on backward compatibility here. */
 160                 case SSH_CMSG_HAVE_KERBEROS_TGT:
 161                         packet_send_debug("Kerberos TGT passing disabled before authentication.");
 162                         break;
 163 #ifdef AFS
 164                 case SSH_CMSG_HAVE_AFS_TOKEN:
 165                         packet_send_debug("AFS token passing disabled before authentication.");
 166                         break;
 167 #endif /* AFS */
 168 #endif /* AFS || KRB5 */
 169
 170                 case SSH_CMSG_AUTH_RHOSTS:
 171                         if (!options.rhosts_authentication) {
 172                                 verbose("Rhosts authentication disabled.");
 173                                 break;
 174                         }
 175                         /*
 176                          * Get client user name.  Note that we just have to
 177                          * trust the client; this is one reason why rhosts
 178                          * authentication is insecure. (Another is
 179                          * IP-spoofing on a local network.)
 180                          */
 181                         client_user = packet_get_string(&ulen);
 182                         packet_check_eom();
 183
 184                         /* Try to authenticate using /etc/hosts.equiv and .rhosts. */
 185                         authenticated = auth_rhosts(pw, client_user);
 186
 187                         snprintf(info, sizeof info, " ruser %.100s", client_user);
 188                         break;
 189
 190                 case SSH_CMSG_AUTH_RHOSTS_RSA:
 191                         if (!options.rhosts_rsa_authentication) {
 192                                 verbose("Rhosts with RSA authentication disabled.");
 193                                 break;
 194                         }
 195                         /*
 196                          * Get client user name.  Note that we just have to
 197                          * trust the client; root on the client machine can
 198                          * claim to be any user.
 199                          */
 200                         client_user = packet_get_string(&ulen);
 201
 202                         /* Get the client host key. */
 203                         client_host_key = key_new(KEY_RSA1);
 204                         bits = packet_get_int();
 205                         packet_get_bignum(client_host_key->rsa->e);
 206                         packet_get_bignum(client_host_key->rsa->n);
 207
 208                         if (bits != BN_num_bits(client_host_key->rsa->n))
 209                                 verbose("Warning: keysize mismatch for client_host_key: "
 210                                     "actual %d, announced %d",
 211                                      BN_num_bits(client_host_key->rsa->n), bits);
 212                         packet_check_eom();
 213
 214                         authenticated = auth_rhosts_rsa(pw, client_user,
 215                             client_host_key);
 216                         key_free(client_host_key);
 217
 218                         snprintf(info, sizeof info, " ruser %.100s", client_user);
 219                         break;
 220
 221                 case SSH_CMSG_AUTH_RSA:
 222                         if (!options.rsa_authentication) {
 223                                 verbose("RSA authentication disabled.");
 224                                 break;
 225                         }
 226                         /* RSA authentication requested. */
 227                         if ((n = BN_new()) == NULL)
 228                                 fatal("do_authloop: BN_new failed");
 229                         packet_get_bignum(n);
 230                         packet_check_eom();
 231                         authenticated = auth_rsa(pw, n);
 232                         BN_clear_free(n);
 233                         break;
 234
 235                 case SSH_CMSG_AUTH_PASSWORD:
 236                         if (!options.password_authentication) {
 237                                 verbose("Password authentication disabled.");
 238                                 break;
 239                         }
 240                         /*
 241                          * Read user password.  It is in plain text, but was
 242                          * transmitted over the encrypted channel so it is
 243                          * not visible to an outside observer.
 244                          */
 245                         password = packet_get_string(&dlen);
 246                         packet_check_eom();
 247
 248 #ifdef USE_PAM
 249                         /* Do PAM auth with password */
 250                         authenticated = auth_pam_password(pw, password);
 251 #elif defined(HAVE_OSF_SIA)
 252                         /* Do SIA auth with password */
 253                         authenticated = auth_sia_password(authctxt->user,
 254                             password);
 255 #else /* !USE_PAM && !HAVE_OSF_SIA */
 256                         /* Try authentication with the password. */
 257                         authenticated = auth_password(authctxt, password);
 258 #endif /* USE_PAM */
 259
 260                         memset(password, 0, strlen(password));
 261                         xfree(password);
 262                         break;
 263
 264                 case SSH_CMSG_AUTH_TIS:
 265                         debug("rcvd SSH_CMSG_AUTH_TIS");
 266                         if (options.challenge_response_authentication == 1) {
 267                                 char *challenge = get_challenge(authctxt);
 268                                 if (challenge != NULL) {
 269                                         debug("sending challenge '%s'", challenge);
 270                                         packet_start(SSH_SMSG_AUTH_TIS_CHALLENGE);
 271                                         packet_put_cstring(challenge);
 272                                         xfree(challenge);
 273                                         packet_send();
 274                                         packet_write_wait();
 275                                         continue;
 276                                 }
 277                         }
 278                         break;
 279                 case SSH_CMSG_AUTH_TIS_RESPONSE:
 280                         debug("rcvd SSH_CMSG_AUTH_TIS_RESPONSE");
 281                         if (options.challenge_response_authentication == 1) {
 282                                 char *response = packet_get_string(&dlen);
 283                                 debug("got response '%s'", response);
 284                                 packet_check_eom();
 285                                 authenticated = verify_response(authctxt, response);
 286                                 memset(response, 'r', dlen);
 287                                 xfree(response);
 288                         }
 289                         break;
 290
 291                 default:
 292                         /*
 293                          * Any unknown messages will be ignored (and failure
 294                          * returned) during authentication.
 295                          */
 296                         log("Unknown message during authentication: type %d", type);
 297                         break;
 298                 }
 299 #ifdef BSD_AUTH
 300                 if (authctxt->as) {
 301                         auth_close(authctxt->as);
 302                         authctxt->as = NULL;
 303                 }
 304 #endif
 305                 if (!authctxt->valid && authenticated)
 306                         fatal("INTERNAL ERROR: authenticated invalid user %s",
 307                             authctxt->user);
 308
 309 #ifdef HAVE_CYGWIN
 310                 if (authenticated &&
 311                     !check_nt_auth(type == SSH_CMSG_AUTH_PASSWORD, pw)) {
 312                         packet_disconnect("Authentication rejected for uid %d.",
 313                         pw == NULL ? -1 : pw->pw_uid);
 314                         authenticated = 0;
 315                 }
 316 #else
 317                 /* Special handling for root */
 318                 if (authenticated && authctxt->pw->pw_uid == 0 &&
 319                     !auth_root_allowed(get_authname(type)))
 320                         authenticated = 0;
 321 #endif
 322 #ifdef USE_PAM
 323                 if (authenticated && !do_pam_account(pw->pw_name, client_user))
 324                         authenticated = 0;
 325 #endif
 326
 327                 /* Log before sending the reply */
 328                 auth_log(authctxt, authenticated, get_authname(type), info);
 329
 330                 if (client_user != NULL) {
 331                         xfree(client_user);
 332                         client_user = NULL;
 333                 }
 334
 335                 if (authenticated)
 336                         return;
 337
 338                 if (authctxt->failures++ > AUTH_FAIL_MAX) {
 339 #ifdef WITH_AIXAUTHENTICATE
 340                         loginfailed(authctxt->user,
 341                             get_canonical_hostname(options.reverse_mapping_check),
 342                             "ssh");
 343 #endif /* WITH_AIXAUTHENTICATE */
 344                         packet_disconnect(AUTH_FAIL_MSG, authctxt->user);
 345                 }
 346
 347                 packet_start(SSH_SMSG_FAILURE);
 348                 packet_send();
 349                 packet_write_wait();
 350         }
 351 }
 352
 353 /*
 354  * Performs authentication of an incoming connection.  Session key has already
 355  * been exchanged and encryption is enabled.
 356  */
 357 void
 358 do_authentication(void)
 359 {
 360         Authctxt *authctxt;
 361         struct passwd *pw;
 362         u_int ulen;
 363         char *p, *user, *style = NULL;
 364
 365         /* Get the name of the user that we wish to log in as. */
 366         packet_read_expect(SSH_CMSG_USER);
 367
 368         /* Get the user name. */
 369         user = packet_get_string(&ulen);
 370         packet_check_eom();
 371
 372         if ((style = strchr(user, ':')) != NULL)
 373                 *style++ = '\0';
 374
 375         /* XXX - SSH.com Kerberos v5 braindeath. */
 376         if ((p = strchr(user, '@')) != NULL)
 377                 *p = '\0';
 378
 379         authctxt = authctxt_new();
 380         authctxt->user = user;
 381         authctxt->style = style;
 382
 383         /* Verify that the user is a valid user. */
 384         pw = getpwnam(user);
 385         if (pw && allowed_user(pw)) {
 386                 authctxt->valid = 1;
 387                 pw = pwcopy(pw);
 388         } else {
 389                 debug("do_authentication: illegal user %s", user);
 390                 pw = NULL;
 391         }
 392         authctxt->pw = pw;
 393
 394         setproctitle("%s", pw ? user : "unknown");
 395
 396 #ifdef USE_PAM
 397         if (pw)
 398                 start_pam(user);
 399 #endif
 400
 401         /*
 402          * If we are not running as root, the user must have the same uid as
 403          * the server. (Unless you are running Windows)
 404          */
 405 #ifndef HAVE_CYGWIN
 406         if (getuid() != 0 && pw && pw->pw_uid != getuid())
 407                 packet_disconnect("Cannot change user when server not running as root.");
 408 #endif
 409
 410         /*
 411          * Loop until the user has been authenticated or the connection is
 412          * closed, do_authloop() returns only if authentication is successful
 413          */
 414         do_authloop(authctxt);
 415
 416         /* The user has been authenticated and accepted. */
 417         packet_start(SSH_SMSG_SUCCESS);
 418         packet_send();
 419         packet_write_wait();
 420
 421         /* Perform session preparation. */
 422         do_authenticated(authctxt);
 423 }