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 1.31 2001/12/27 20:39:58 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         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                                 packet_done();
 124
 125                                 if (kdata[0] == 4) { /* KRB_PROT_VERSION */
 126 #ifdef KRB4
 127                                         KTEXT_ST tkt;
 128
 129                                         tkt.length = dlen;
 130                                         if (tkt.length < MAX_KTXT_LEN)
 131                                                 memcpy(tkt.dat, kdata, tkt.length);
 132
 133                                         if (auth_krb4(authctxt, &tkt, &client_user)) {
 134                                                 authenticated = 1;
 135                                                 snprintf(info, sizeof(info),
 136                                                     " tktuser %.100s",
 137                                                     client_user);
 138                                         }
 139 #endif /* KRB4 */
 140                                 } else {
 141 #ifdef KRB5
 142                                         krb5_data tkt;
 143                                         tkt.length = dlen;
 144                                         tkt.data = kdata;
 145
 146                                         if (auth_krb5(authctxt, &tkt, &client_user)) {
 147                                                 authenticated = 1;
 148                                                 snprintf(info, sizeof(info),
 149                                                     " tktuser %.100s",
 150                                                     client_user);
 151                                         }
 152 #endif /* KRB5 */
 153                                 }
 154                                 xfree(kdata);
 155                         }
 156                         break;
 157 #endif /* KRB4 || KRB5 */
 158
 159 #if defined(AFS) || defined(KRB5)
 160                         /* XXX - punt on backward compatibility here. */
 161                 case SSH_CMSG_HAVE_KERBEROS_TGT:
 162                         packet_send_debug("Kerberos TGT passing disabled before authentication.");
 163                         break;
 164 #ifdef AFS
 165                 case SSH_CMSG_HAVE_AFS_TOKEN:
 166                         packet_send_debug("AFS token passing disabled before authentication.");
 167                         break;
 168 #endif /* AFS */
 169 #endif /* AFS || KRB5 */
 170
 171                 case SSH_CMSG_AUTH_RHOSTS:
 172                         if (!options.rhosts_authentication) {
 173                                 verbose("Rhosts authentication disabled.");
 174                                 break;
 175                         }
 176                         /*
 177                          * Get client user name.  Note that we just have to
 178                          * trust the client; this is one reason why rhosts
 179                          * authentication is insecure. (Another is
 180                          * IP-spoofing on a local network.)
 181                          */
 182                         client_user = packet_get_string(&ulen);
 183                         packet_done();
 184
 185                         /* Try to authenticate using /etc/hosts.equiv and .rhosts. */
 186                         authenticated = auth_rhosts(pw, client_user);
 187
 188                         snprintf(info, sizeof info, " ruser %.100s", client_user);
 189                         break;
 190
 191                 case SSH_CMSG_AUTH_RHOSTS_RSA:
 192                         if (!options.rhosts_rsa_authentication) {
 193                                 verbose("Rhosts with RSA authentication disabled.");
 194                                 break;
 195                         }
 196                         /*
 197                          * Get client user name.  Note that we just have to
 198                          * trust the client; root on the client machine can
 199                          * claim to be any user.
 200                          */
 201                         client_user = packet_get_string(&ulen);
 202
 203                         /* Get the client host key. */
 204                         client_host_key = key_new(KEY_RSA1);
 205                         bits = packet_get_int();
 206                         packet_get_bignum(client_host_key->rsa->e, &elen);
 207                         packet_get_bignum(client_host_key->rsa->n, &nlen);
 208
 209                         if (bits != BN_num_bits(client_host_key->rsa->n))
 210                                 verbose("Warning: keysize mismatch for client_host_key: "
 211                                     "actual %d, announced %d",
 212                                      BN_num_bits(client_host_key->rsa->n), bits);
 213                         packet_done();
 214
 215                         authenticated = auth_rhosts_rsa(pw, client_user,
 216                             client_host_key);
 217                         key_free(client_host_key);
 218
 219                         snprintf(info, sizeof info, " ruser %.100s", client_user);
 220                         break;
 221
 222                 case SSH_CMSG_AUTH_RSA:
 223                         if (!options.rsa_authentication) {
 224                                 verbose("RSA authentication disabled.");
 225                                 break;
 226                         }
 227                         /* RSA authentication requested. */
 228                         if ((n = BN_new()) == NULL)
 229                                 fatal("do_authloop: BN_new failed");
 230                         packet_get_bignum(n, &nlen);
 231                         packet_done();
 232                         authenticated = auth_rsa(pw, n);
 233                         BN_clear_free(n);
 234                         break;
 235
 236                 case SSH_CMSG_AUTH_PASSWORD:
 237                         if (!options.password_authentication) {
 238                                 verbose("Password authentication disabled.");
 239                                 break;
 240                         }
 241                         /*
 242                          * Read user password.  It is in plain text, but was
 243                          * transmitted over the encrypted channel so it is
 244                          * not visible to an outside observer.
 245                          */
 246                         password = packet_get_string(&dlen);
 247                         packet_done();
 248
 249 #ifdef USE_PAM
 250                         /* Do PAM auth with password */
 251                         authenticated = auth_pam_password(pw, password);
 252 #elif defined(HAVE_OSF_SIA)
 253                         /* Do SIA auth with password */
 254                         authenticated = auth_sia_password(authctxt->user,
 255                             password);
 256 #else /* !USE_PAM && !HAVE_OSF_SIA */
 257                         /* Try authentication with the password. */
 258                         authenticated = auth_password(authctxt, password);
 259 #endif /* USE_PAM */
 260
 261                         memset(password, 0, strlen(password));
 262                         xfree(password);
 263                         break;
 264
 265                 case SSH_CMSG_AUTH_TIS:
 266                         debug("rcvd SSH_CMSG_AUTH_TIS");
 267                         if (options.challenge_response_authentication == 1) {
 268                                 char *challenge = get_challenge(authctxt);
 269                                 if (challenge != NULL) {
 270                                         debug("sending challenge '%s'", challenge);
 271                                         packet_start(SSH_SMSG_AUTH_TIS_CHALLENGE);
 272                                         packet_put_cstring(challenge);
 273                                         xfree(challenge);
 274                                         packet_send();
 275                                         packet_write_wait();
 276                                         continue;
 277                                 }
 278                         }
 279                         break;
 280                 case SSH_CMSG_AUTH_TIS_RESPONSE:
 281                         debug("rcvd SSH_CMSG_AUTH_TIS_RESPONSE");
 282                         if (options.challenge_response_authentication == 1) {
 283                                 char *response = packet_get_string(&dlen);
 284                                 debug("got response '%s'", response);
 285                                 packet_done();
 286                                 authenticated = verify_response(authctxt, response);
 287                                 memset(response, 'r', dlen);
 288                                 xfree(response);
 289                         }
 290                         break;
 291
 292                 default:
 293                         /*
 294                          * Any unknown messages will be ignored (and failure
 295                          * returned) during authentication.
 296                          */
 297                         log("Unknown message during authentication: type %d", type);
 298                         break;
 299                 }
 300 #ifdef BSD_AUTH
 301                 if (authctxt->as) {
 302                         auth_close(authctxt->as);
 303                         authctxt->as = NULL;
 304                 }
 305 #endif
 306                 if (!authctxt->valid && authenticated)
 307                         fatal("INTERNAL ERROR: authenticated invalid user %s",
 308                             authctxt->user);
 309
 310 #ifdef HAVE_CYGWIN
 311                 if (authenticated &&
 312                     !check_nt_auth(type == SSH_CMSG_AUTH_PASSWORD, pw)) {
 313                         packet_disconnect("Authentication rejected for uid %d.",
 314                         pw == NULL ? -1 : pw->pw_uid);
 315                         authenticated = 0;
 316                 }
 317 #else
 318                 /* Special handling for root */
 319                 if (authenticated && authctxt->pw->pw_uid == 0 &&
 320                     !auth_root_allowed(get_authname(type)))
 321                         authenticated = 0;
 322 #endif
 323 #ifdef USE_PAM
 324                 if (authenticated && !do_pam_account(pw->pw_name, client_user))
 325                         authenticated = 0;
 326 #endif
 327
 328                 /* Log before sending the reply */
 329                 auth_log(authctxt, authenticated, get_authname(type), info);
 330
 331                 if (client_user != NULL) {
 332                         xfree(client_user);
 333                         client_user = NULL;
 334                 }
 335
 336                 if (authenticated)
 337                         return;
 338
 339                 if (authctxt->failures++ > AUTH_FAIL_MAX) {
 340 #ifdef WITH_AIXAUTHENTICATE
 341                         loginfailed(authctxt->user,
 342                             get_canonical_hostname(options.reverse_mapping_check),
 343                             "ssh");
 344 #endif /* WITH_AIXAUTHENTICATE */
 345                         packet_disconnect(AUTH_FAIL_MSG, authctxt->user);
 346                 }
 347
 348                 packet_start(SSH_SMSG_FAILURE);
 349                 packet_send();
 350                 packet_write_wait();
 351         }
 352 }
 353
 354 /*
 355  * Performs authentication of an incoming connection.  Session key has already
 356  * been exchanged and encryption is enabled.
 357  */
 358 void
 359 do_authentication(void)
 360 {
 361         Authctxt *authctxt;
 362         struct passwd *pw;
 363         int plen;
 364         u_int ulen;
 365         char *p, *user, *style = NULL;
 366
 367         /* Get the name of the user that we wish to log in as. */
 368         packet_read_expect(&plen, SSH_CMSG_USER);
 369
 370         /* Get the user name. */
 371         user = packet_get_string(&ulen);
 372         packet_done();
 373
 374         if ((style = strchr(user, ':')) != NULL)
 375                 *style++ = '\0';
 376
 377         /* XXX - SSH.com Kerberos v5 braindeath. */
 378         if ((p = strchr(user, '@')) != NULL)
 379                 *p = '\0';
 380
 381         authctxt = authctxt_new();
 382         authctxt->user = user;
 383         authctxt->style = style;
 384
 385         /* Verify that the user is a valid user. */
 386         pw = getpwnam(user);
 387         if (pw && allowed_user(pw)) {
 388                 authctxt->valid = 1;
 389                 pw = pwcopy(pw);
 390         } else {
 391                 debug("do_authentication: illegal user %s", user);
 392                 pw = NULL;
 393         }
 394         authctxt->pw = pw;
 395
 396         setproctitle("%s", pw ? user : "unknown");
 397
 398 #ifdef USE_PAM
 399         if (pw)
 400                 start_pam(user);
 401 #endif
 402
 403         /*
 404          * If we are not running as root, the user must have the same uid as
 405          * the server. (Unless you are running Windows)
 406          */
 407 #ifndef HAVE_CYGWIN
 408         if (getuid() != 0 && pw && pw->pw_uid != getuid())
 409                 packet_disconnect("Cannot change user when server not running as root.");
 410 #endif
 411
 412         /*
 413          * Loop until the user has been authenticated or the connection is
 414          * closed, do_authloop() returns only if authentication is successful
 415          */
 416         do_authloop(authctxt);
 417
 418         /* The user has been authenticated and accepted. */
 419         packet_start(SSH_SMSG_SUCCESS);
 420         packet_send();
 421         packet_write_wait();
 422
 423         /* Perform session preparation. */
 424         do_authenticated(authctxt);
 425 }