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 1.29 2001/12/27 18:22:16 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
 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 = key_new(KEY_RSA1);
 206                         bits = packet_get_int();
 207                         packet_get_bignum(client_host_key->rsa->e, &elen);
 208                         packet_get_bignum(client_host_key->rsa->n, &nlen);
 209
 210                         if (bits != BN_num_bits(client_host_key->rsa->n))
 211                                 verbose("Warning: keysize mismatch for client_host_key: "
 212                                     "actual %d, announced %d",
 213                                      BN_num_bits(client_host_key->rsa->n), bits);
 214                         packet_integrity_check(plen, (4 + ulen) + 4 + elen + nlen, type);
 215
 216                         authenticated = auth_rhosts_rsa(pw, client_user,
 217                             client_host_key->rsa);
 218                         key_free(client_host_key);
 219
 220                         snprintf(info, sizeof info, " ruser %.100s", client_user);
 221                         break;
 222
 223                 case SSH_CMSG_AUTH_RSA:
 224                         if (!options.rsa_authentication) {
 225                                 verbose("RSA authentication disabled.");
 226                                 break;
 227                         }
 228                         /* RSA authentication requested. */
 229                         if ((n = BN_new()) == NULL)
 230                                 fatal("do_authloop: BN_new failed");
 231                         packet_get_bignum(n, &nlen);
 232                         packet_integrity_check(plen, nlen, type);
 233                         authenticated = auth_rsa(pw, n);
 234                         BN_clear_free(n);
 235                         break;
 236
 237                 case SSH_CMSG_AUTH_PASSWORD:
 238                         if (!options.password_authentication) {
 239                                 verbose("Password authentication disabled.");
 240                                 break;
 241                         }
 242                         /*
 243                          * Read user password.  It is in plain text, but was
 244                          * transmitted over the encrypted channel so it is
 245                          * not visible to an outside observer.
 246                          */
 247                         password = packet_get_string(&dlen);
 248                         packet_integrity_check(plen, 4 + dlen, type);
 249
 250 #ifdef USE_PAM
 251                         /* Do PAM auth with password */
 252                         authenticated = auth_pam_password(pw, password);
 253 #elif defined(HAVE_OSF_SIA)
 254                         /* Do SIA auth with password */
 255                         authenticated = auth_sia_password(authctxt->user,
 256                             password);
 257 #else /* !USE_PAM && !HAVE_OSF_SIA */
 258                         /* Try authentication with the password. */
 259                         authenticated = auth_password(authctxt, password);
 260 #endif /* USE_PAM */
 261
 262                         memset(password, 0, strlen(password));
 263                         xfree(password);
 264                         break;
 265
 266                 case SSH_CMSG_AUTH_TIS:
 267                         debug("rcvd SSH_CMSG_AUTH_TIS");
 268                         if (options.challenge_response_authentication == 1) {
 269                                 char *challenge = get_challenge(authctxt);
 270                                 if (challenge != NULL) {
 271                                         debug("sending challenge '%s'", challenge);
 272                                         packet_start(SSH_SMSG_AUTH_TIS_CHALLENGE);
 273                                         packet_put_cstring(challenge);
 274                                         xfree(challenge);
 275                                         packet_send();
 276                                         packet_write_wait();
 277                                         continue;
 278                                 }
 279                         }
 280                         break;
 281                 case SSH_CMSG_AUTH_TIS_RESPONSE:
 282                         debug("rcvd SSH_CMSG_AUTH_TIS_RESPONSE");
 283                         if (options.challenge_response_authentication == 1) {
 284                                 char *response = packet_get_string(&dlen);
 285                                 debug("got response '%s'", response);
 286                                 packet_integrity_check(plen, 4 + dlen, type);
 287                                 authenticated = verify_response(authctxt, response);
 288                                 memset(response, 'r', dlen);
 289                                 xfree(response);
 290                         }
 291                         break;
 292
 293                 default:
 294                         /*
 295                          * Any unknown messages will be ignored (and failure
 296                          * returned) during authentication.
 297                          */
 298                         log("Unknown message during authentication: type %d", type);
 299                         break;
 300                 }
 301 #ifdef BSD_AUTH
 302                 if (authctxt->as) {
 303                         auth_close(authctxt->as);
 304                         authctxt->as = NULL;
 305                 }
 306 #endif
 307                 if (!authctxt->valid && authenticated)
 308                         fatal("INTERNAL ERROR: authenticated invalid user %s",
 309                             authctxt->user);
 310
 311 #ifdef HAVE_CYGWIN
 312                 if (authenticated &&
 313                     !check_nt_auth(type == SSH_CMSG_AUTH_PASSWORD, pw)) {
 314                         packet_disconnect("Authentication rejected for uid %d.",
 315                         pw == NULL ? -1 : pw->pw_uid);
 316                         authenticated = 0;
 317                 }
 318 #else
 319                 /* Special handling for root */
 320                 if (authenticated && authctxt->pw->pw_uid == 0 &&
 321                     !auth_root_allowed(get_authname(type)))
 322                         authenticated = 0;
 323 #endif
 324 #ifdef USE_PAM
 325                 if (authenticated && !do_pam_account(pw->pw_name, client_user))
 326                         authenticated = 0;
 327 #endif
 328
 329                 /* Log before sending the reply */
 330                 auth_log(authctxt, authenticated, get_authname(type), info);
 331
 332                 if (client_user != NULL) {
 333                         xfree(client_user);
 334                         client_user = NULL;
 335                 }
 336
 337                 if (authenticated)
 338                         return;
 339
 340                 if (authctxt->failures++ > AUTH_FAIL_MAX) {
 341 #ifdef WITH_AIXAUTHENTICATE
 342                         loginfailed(authctxt->user,
 343                             get_canonical_hostname(options.reverse_mapping_check),
 344                             "ssh");
 345 #endif /* WITH_AIXAUTHENTICATE */
 346                         packet_disconnect(AUTH_FAIL_MSG, authctxt->user);
 347                 }
 348
 349                 packet_start(SSH_SMSG_FAILURE);
 350                 packet_send();
 351                 packet_write_wait();
 352         }
 353 }
 354
 355 /*
 356  * Performs authentication of an incoming connection.  Session key has already
 357  * been exchanged and encryption is enabled.
 358  */
 359 void
 360 do_authentication(void)
 361 {
 362         Authctxt *authctxt;
 363         struct passwd *pw;
 364         int plen;
 365         u_int ulen;
 366         char *p, *user, *style = NULL;
 367
 368         /* Get the name of the user that we wish to log in as. */
 369         packet_read_expect(&plen, SSH_CMSG_USER);
 370
 371         /* Get the user name. */
 372         user = packet_get_string(&ulen);
 373         packet_integrity_check(plen, (4 + ulen), SSH_CMSG_USER);
 374
 375         if ((style = strchr(user, ':')) != NULL)
 376                 *style++ = '\0';
 377
 378         /* XXX - SSH.com Kerberos v5 braindeath. */
 379         if ((p = strchr(user, '@')) != NULL)
 380                 *p = '\0';
 381
 382         authctxt = authctxt_new();
 383         authctxt->user = user;
 384         authctxt->style = style;
 385
 386         /* Verify that the user is a valid user. */
 387         pw = getpwnam(user);
 388         if (pw && allowed_user(pw)) {
 389                 authctxt->valid = 1;
 390                 pw = pwcopy(pw);
 391         } else {
 392                 debug("do_authentication: illegal user %s", user);
 393                 pw = NULL;
 394         }
 395         authctxt->pw = pw;
 396
 397         setproctitle("%s", pw ? user : "unknown");
 398
 399 #ifdef USE_PAM
 400         if (pw)
 401                 start_pam(user);
 402 #endif
 403
 404         /*
 405          * If we are not running as root, the user must have the same uid as
 406          * the server. (Unless you are running Windows)
 407          */
 408 #ifndef HAVE_CYGWIN
 409         if (getuid() != 0 && pw && pw->pw_uid != getuid())
 410                 packet_disconnect("Cannot change user when server not running as root.");
 411 #endif
 412
 413         /*
 414          * Loop until the user has been authenticated or the connection is
 415          * closed, do_authloop() returns only if authentication is successful
 416          */
 417         do_authloop(authctxt);
 418
 419         /* The user has been authenticated and accepted. */
 420         packet_start(SSH_SMSG_SUCCESS);
 421         packet_send();
 422         packet_write_wait();
 423
 424         /* Perform session preparation. */
 425         do_authenticated(authctxt);
 426 }