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 1.40 2002/04/10 08:21:47 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 "channels.h"
  26 #include "session.h"
  27 #include "uidswap.h"
  28 #include "monitor_wrap.h"
  29
  30 /* import */
  31 extern ServerOptions options;
  32
  33 /*
  34  * convert ssh auth msg type into description
  35  */
  36 static char *
  37 get_authname(int type)
  38 {
  39         static char buf[1024];
  40         switch (type) {
  41         case SSH_CMSG_AUTH_PASSWORD:
  42                 return "password";
  43         case SSH_CMSG_AUTH_RSA:
  44                 return "rsa";
  45         case SSH_CMSG_AUTH_RHOSTS_RSA:
  46                 return "rhosts-rsa";
  47         case SSH_CMSG_AUTH_RHOSTS:
  48                 return "rhosts";
  49         case SSH_CMSG_AUTH_TIS:
  50         case SSH_CMSG_AUTH_TIS_RESPONSE:
  51                 return "challenge-response";
  52 #if defined(KRB4) || defined(KRB5)
  53         case SSH_CMSG_AUTH_KERBEROS:
  54                 return "kerberos";
  55 #endif
  56         }
  57         snprintf(buf, sizeof buf, "bad-auth-msg-%d", type);
  58         return buf;
  59 }
  60
  61 /*
  62  * read packets, try to authenticate the user and
  63  * return only if authentication is successful
  64  */
  65 static void
  66 do_authloop(Authctxt *authctxt)
  67 {
  68         int authenticated = 0;
  69         u_int bits;
  70         Key *client_host_key;
  71         BIGNUM *n;
  72         char *client_user, *password;
  73         char info[1024];
  74         u_int dlen;
  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             PRIVSEP(auth_password(authctxt, ""))) {
  88                 auth_log(authctxt, 1, "without authentication", "");
  89                 return;
  90         }
  91
  92         /* Indicate that authentication is needed. */
  93         packet_start(SSH_SMSG_FAILURE);
  94         packet_send();
  95         packet_write_wait();
  96
  97         client_user = NULL;
  98
  99         for (;;) {
 100                 /* default to fail */
 101                 authenticated = 0;
 102
 103                 info[0] = '\0';
 104
 105                 /* Get a packet from the client. */
 106                 type = packet_read();
 107
 108                 /* Process the packet. */
 109                 switch (type) {
 110
 111 #if defined(KRB4) || defined(KRB5)
 112                 case SSH_CMSG_AUTH_KERBEROS:
 113                         if (!options.kerberos_authentication) {
 114                                 verbose("Kerberos authentication disabled.");
 115                         } else {
 116                                 char *kdata = packet_get_string(&dlen);
 117                                 packet_check_eom();
 118
 119                                 if (kdata[0] == 4) { /* KRB_PROT_VERSION */
 120 #ifdef KRB4
 121                                         KTEXT_ST tkt;
 122
 123                                         tkt.length = dlen;
 124                                         if (tkt.length < MAX_KTXT_LEN)
 125                                                 memcpy(tkt.dat, kdata, tkt.length);
 126
 127                                         if (auth_krb4(authctxt, &tkt, &client_user)) {
 128                                                 authenticated = 1;
 129                                                 snprintf(info, sizeof(info),
 130                                                     " tktuser %.100s",
 131                                                     client_user);
 132                                         }
 133 #endif /* KRB4 */
 134                                 } else {
 135 #ifdef KRB5
 136                                         krb5_data tkt;
 137                                         tkt.length = dlen;
 138                                         tkt.data = kdata;
 139
 140                                         if (auth_krb5(authctxt, &tkt, &client_user)) {
 141                                                 authenticated = 1;
 142                                                 snprintf(info, sizeof(info),
 143                                                     " tktuser %.100s",
 144                                                     client_user);
 145                                         }
 146 #endif /* KRB5 */
 147                                 }
 148                                 xfree(kdata);
 149                         }
 150                         break;
 151 #endif /* KRB4 || KRB5 */
 152
 153 #if defined(AFS) || defined(KRB5)
 154                         /* XXX - punt on backward compatibility here. */
 155                 case SSH_CMSG_HAVE_KERBEROS_TGT:
 156                         packet_send_debug("Kerberos TGT passing disabled before authentication.");
 157                         break;
 158 #ifdef AFS
 159                 case SSH_CMSG_HAVE_AFS_TOKEN:
 160                         packet_send_debug("AFS token passing disabled before authentication.");
 161                         break;
 162 #endif /* AFS */
 163 #endif /* AFS || KRB5 */
 164
 165                 case SSH_CMSG_AUTH_RHOSTS:
 166                         if (!options.rhosts_authentication) {
 167                                 verbose("Rhosts authentication disabled.");
 168                                 break;
 169                         }
 170                         /*
 171                          * Get client user name.  Note that we just have to
 172                          * trust the client; this is one reason why rhosts
 173                          * authentication is insecure. (Another is
 174                          * IP-spoofing on a local network.)
 175                          */
 176                         client_user = packet_get_string(&ulen);
 177                         packet_check_eom();
 178
 179                         /* Try to authenticate using /etc/hosts.equiv and .rhosts. */
 180                         authenticated = auth_rhosts(pw, client_user);
 181
 182                         snprintf(info, sizeof info, " ruser %.100s", client_user);
 183                         break;
 184
 185                 case SSH_CMSG_AUTH_RHOSTS_RSA:
 186                         if (!options.rhosts_rsa_authentication) {
 187                                 verbose("Rhosts with RSA authentication disabled.");
 188                                 break;
 189                         }
 190                         /*
 191                          * Get client user name.  Note that we just have to
 192                          * trust the client; root on the client machine can
 193                          * claim to be any user.
 194                          */
 195                         client_user = packet_get_string(&ulen);
 196
 197                         /* Get the client host key. */
 198                         client_host_key = key_new(KEY_RSA1);
 199                         bits = packet_get_int();
 200                         packet_get_bignum(client_host_key->rsa->e);
 201                         packet_get_bignum(client_host_key->rsa->n);
 202
 203                         if (bits != BN_num_bits(client_host_key->rsa->n))
 204                                 verbose("Warning: keysize mismatch for client_host_key: "
 205                                     "actual %d, announced %d",
 206                                      BN_num_bits(client_host_key->rsa->n), bits);
 207                         packet_check_eom();
 208
 209                         authenticated = auth_rhosts_rsa(pw, client_user,
 210                             client_host_key);
 211                         key_free(client_host_key);
 212
 213                         snprintf(info, sizeof info, " ruser %.100s", client_user);
 214                         break;
 215
 216                 case SSH_CMSG_AUTH_RSA:
 217                         if (!options.rsa_authentication) {
 218                                 verbose("RSA authentication disabled.");
 219                                 break;
 220                         }
 221                         /* RSA authentication requested. */
 222                         if ((n = BN_new()) == NULL)
 223                                 fatal("do_authloop: BN_new failed");
 224                         packet_get_bignum(n);
 225                         packet_check_eom();
 226                         authenticated = auth_rsa(pw, n);
 227                         BN_clear_free(n);
 228                         break;
 229
 230                 case SSH_CMSG_AUTH_PASSWORD:
 231                         if (!options.password_authentication) {
 232                                 verbose("Password authentication disabled.");
 233                                 break;
 234                         }
 235                         /*
 236                          * Read user password.  It is in plain text, but was
 237                          * transmitted over the encrypted channel so it is
 238                          * not visible to an outside observer.
 239                          */
 240                         password = packet_get_string(&dlen);
 241                         packet_check_eom();
 242
 243                         /* Try authentication with the password. */
 244                         authenticated = PRIVSEP(auth_password(authctxt, password));
 245
 246                         memset(password, 0, strlen(password));
 247                         xfree(password);
 248                         break;
 249
 250                 case SSH_CMSG_AUTH_TIS:
 251                         debug("rcvd SSH_CMSG_AUTH_TIS");
 252                         if (options.challenge_response_authentication == 1) {
 253                                 char *challenge = get_challenge(authctxt);
 254                                 if (challenge != NULL) {
 255                                         debug("sending challenge '%s'", challenge);
 256                                         packet_start(SSH_SMSG_AUTH_TIS_CHALLENGE);
 257                                         packet_put_cstring(challenge);
 258                                         xfree(challenge);
 259                                         packet_send();
 260                                         packet_write_wait();
 261                                         continue;
 262                                 }
 263                         }
 264                         break;
 265                 case SSH_CMSG_AUTH_TIS_RESPONSE:
 266                         debug("rcvd SSH_CMSG_AUTH_TIS_RESPONSE");
 267                         if (options.challenge_response_authentication == 1) {
 268                                 char *response = packet_get_string(&dlen);
 269                                 debug("got response '%s'", response);
 270                                 packet_check_eom();
 271                                 authenticated = verify_response(authctxt, response);
 272                                 memset(response, 'r', dlen);
 273                                 xfree(response);
 274                         }
 275                         break;
 276
 277                 default:
 278                         /*
 279                          * Any unknown messages will be ignored (and failure
 280                          * returned) during authentication.
 281                          */
 282                         log("Unknown message during authentication: type %d", type);
 283                         break;
 284                 }
 285 #ifdef BSD_AUTH
 286                 if (authctxt->as) {
 287                         auth_close(authctxt->as);
 288                         authctxt->as = NULL;
 289                 }
 290 #endif
 291                 if (!authctxt->valid && authenticated)
 292                         fatal("INTERNAL ERROR: authenticated invalid user %s",
 293                             authctxt->user);
 294
 295 #ifdef HAVE_CYGWIN
 296                 if (authenticated &&
 297                     !check_nt_auth(type == SSH_CMSG_AUTH_PASSWORD, pw)) {
 298                         packet_disconnect("Authentication rejected for uid %d.",
 299                         pw == NULL ? -1 : pw->pw_uid);
 300                         authenticated = 0;
 301                 }
 302 #else
 303                 /* Special handling for root */
 304                 if (authenticated && authctxt->pw->pw_uid == 0 &&
 305                     !auth_root_allowed(get_authname(type)))
 306                         authenticated = 0;
 307 #endif
 308 #ifdef USE_PAM
 309                 if (!use_privsep && authenticated &&
 310                     !do_pam_account(pw->pw_name, client_user))
 311                         authenticated = 0;
 312 #endif
 313
 314                 /* Log before sending the reply */
 315                 auth_log(authctxt, authenticated, get_authname(type), info);
 316
 317                 if (client_user != NULL) {
 318                         xfree(client_user);
 319                         client_user = NULL;
 320                 }
 321
 322                 if (authenticated)
 323                         return;
 324
 325                 if (authctxt->failures++ > AUTH_FAIL_MAX) {
 326 #ifdef WITH_AIXAUTHENTICATE
 327                         loginfailed(authctxt->user,
 328                             get_canonical_hostname(options.verify_reverse_mapping),
 329                             "ssh");
 330 #endif /* WITH_AIXAUTHENTICATE */
 331                         packet_disconnect(AUTH_FAIL_MSG, authctxt->user);
 332                 }
 333
 334                 packet_start(SSH_SMSG_FAILURE);
 335                 packet_send();
 336                 packet_write_wait();
 337         }
 338 }
 339
 340 /*
 341  * Performs authentication of an incoming connection.  Session key has already
 342  * been exchanged and encryption is enabled.
 343  */
 344 Authctxt *
 345 do_authentication(void)
 346 {
 347         Authctxt *authctxt;
 348         u_int ulen;
 349         char *user, *style = NULL;
 350
 351         /* Get the name of the user that we wish to log in as. */
 352         packet_read_expect(SSH_CMSG_USER);
 353
 354         /* Get the user name. */
 355         user = packet_get_string(&ulen);
 356         packet_check_eom();
 357
 358         if ((style = strchr(user, ':')) != NULL)
 359                 *style++ = '\0';
 360
 361 #ifdef KRB5
 362         /* XXX - SSH.com Kerberos v5 braindeath. */
 363         if ((datafellows & SSH_BUG_K5USER) &&
 364             options.kerberos_authentication) {
 365                 char *p;
 366                 if ((p = strchr(user, '@')) != NULL)
 367                         *p = '\0';
 368         }
 369 #endif
 370
 371         authctxt = authctxt_new();
 372         authctxt->user = user;
 373         authctxt->style = style;
 374
 375         /* Verify that the user is a valid user. */
 376         if ((authctxt->pw = PRIVSEP(getpwnamallow(user))) != NULL)
 377                 authctxt->valid = 1;
 378         else
 379                 debug("do_authentication: illegal user %s", user);
 380
 381         setproctitle("%s%s", authctxt->pw ? user : "unknown",
 382             use_privsep ? " [net]" : "");
 383
 384 #ifdef USE_PAM
 385         PRIVSEP(start_pam(authctxt->pw == NULL ? "NOUSER" : user));
 386 #endif
 387
 388         /*
 389          * If we are not running as root, the user must have the same uid as
 390          * the server. (Unless you are running Windows)
 391          */
 392 #ifndef HAVE_CYGWIN
 393         if (!use_privsep && getuid() != 0 && authctxt->pw &&
 394             authctxt->pw->pw_uid != getuid())
 395                 packet_disconnect("Cannot change user when server not running as root.");
 396 #endif
 397
 398         /*
 399          * Loop until the user has been authenticated or the connection is
 400          * closed, do_authloop() returns only if authentication is successful
 401          */
 402         do_authloop(authctxt);
 403
 404         /* The user has been authenticated and accepted. */
 405         packet_start(SSH_SMSG_SUCCESS);
 406         packet_send();
 407         packet_write_wait();
 408
 409         return (authctxt);
 410 }