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 1.43 2002/09/09 06:48:06 itojun 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, reply;
 137                                         tkt.length = dlen;
 138                                         tkt.data = kdata;
 139
 140                                         if (PRIVSEP(auth_krb5(authctxt, &tkt,
 141                                             &client_user, &reply))) {
 142                                                 authenticated = 1;
 143                                                 snprintf(info, sizeof(info),
 144                                                     " tktuser %.100s",
 145                                                     client_user);
 146
 147                                                 /* Send response to client */
 148                                                 packet_start(
 149                                                     SSH_SMSG_AUTH_KERBEROS_RESPONSE);
 150                                                 packet_put_string((char *)
 151                                                     reply.data, reply.length);
 152                                                 packet_send();
 153                                                 packet_write_wait();
 154
 155                                                 if (reply.length)
 156                                                         xfree(reply.data);
 157                                         }
 158 #endif /* KRB5 */
 159                                 }
 160                                 xfree(kdata);
 161                         }
 162                         break;
 163 #endif /* KRB4 || KRB5 */
 164
 165 #if defined(AFS) || defined(KRB5)
 166                         /* XXX - punt on backward compatibility here. */
 167                 case SSH_CMSG_HAVE_KERBEROS_TGT:
 168                         packet_send_debug("Kerberos TGT passing disabled before authentication.");
 169                         break;
 170 #ifdef AFS
 171                 case SSH_CMSG_HAVE_AFS_TOKEN:
 172                         packet_send_debug("AFS token passing disabled before authentication.");
 173                         break;
 174 #endif /* AFS */
 175 #endif /* AFS || KRB5 */
 176
 177                 case SSH_CMSG_AUTH_RHOSTS:
 178                         if (!options.rhosts_authentication) {
 179                                 verbose("Rhosts authentication disabled.");
 180                                 break;
 181                         }
 182                         /*
 183                          * Get client user name.  Note that we just have to
 184                          * trust the client; this is one reason why rhosts
 185                          * authentication is insecure. (Another is
 186                          * IP-spoofing on a local network.)
 187                          */
 188                         client_user = packet_get_string(&ulen);
 189                         packet_check_eom();
 190
 191                         /* Try to authenticate using /etc/hosts.equiv and .rhosts. */
 192                         authenticated = auth_rhosts(pw, client_user);
 193
 194                         snprintf(info, sizeof info, " ruser %.100s", client_user);
 195                         break;
 196
 197                 case SSH_CMSG_AUTH_RHOSTS_RSA:
 198                         if (!options.rhosts_rsa_authentication) {
 199                                 verbose("Rhosts with RSA authentication disabled.");
 200                                 break;
 201                         }
 202                         /*
 203                          * Get client user name.  Note that we just have to
 204                          * trust the client; root on the client machine can
 205                          * claim to be any user.
 206                          */
 207                         client_user = packet_get_string(&ulen);
 208
 209                         /* Get the client host key. */
 210                         client_host_key = key_new(KEY_RSA1);
 211                         bits = packet_get_int();
 212                         packet_get_bignum(client_host_key->rsa->e);
 213                         packet_get_bignum(client_host_key->rsa->n);
 214
 215                         if (bits != BN_num_bits(client_host_key->rsa->n))
 216                                 verbose("Warning: keysize mismatch for client_host_key: "
 217                                     "actual %d, announced %d",
 218                                     BN_num_bits(client_host_key->rsa->n), bits);
 219                         packet_check_eom();
 220
 221                         authenticated = auth_rhosts_rsa(pw, client_user,
 222                             client_host_key);
 223                         key_free(client_host_key);
 224
 225                         snprintf(info, sizeof info, " ruser %.100s", client_user);
 226                         break;
 227
 228                 case SSH_CMSG_AUTH_RSA:
 229                         if (!options.rsa_authentication) {
 230                                 verbose("RSA authentication disabled.");
 231                                 break;
 232                         }
 233                         /* RSA authentication requested. */
 234                         if ((n = BN_new()) == NULL)
 235                                 fatal("do_authloop: BN_new failed");
 236                         packet_get_bignum(n);
 237                         packet_check_eom();
 238                         authenticated = auth_rsa(pw, n);
 239                         BN_clear_free(n);
 240                         break;
 241
 242                 case SSH_CMSG_AUTH_PASSWORD:
 243                         if (!options.password_authentication) {
 244                                 verbose("Password authentication disabled.");
 245                                 break;
 246                         }
 247                         /*
 248                          * Read user password.  It is in plain text, but was
 249                          * transmitted over the encrypted channel so it is
 250                          * not visible to an outside observer.
 251                          */
 252                         password = packet_get_string(&dlen);
 253                         packet_check_eom();
 254
 255                         /* Try authentication with the password. */
 256                         authenticated = PRIVSEP(auth_password(authctxt, password));
 257
 258                         memset(password, 0, strlen(password));
 259                         xfree(password);
 260                         break;
 261
 262                 case SSH_CMSG_AUTH_TIS:
 263                         debug("rcvd SSH_CMSG_AUTH_TIS");
 264                         if (options.challenge_response_authentication == 1) {
 265                                 char *challenge = get_challenge(authctxt);
 266                                 if (challenge != NULL) {
 267                                         debug("sending challenge '%s'", challenge);
 268                                         packet_start(SSH_SMSG_AUTH_TIS_CHALLENGE);
 269                                         packet_put_cstring(challenge);
 270                                         xfree(challenge);
 271                                         packet_send();
 272                                         packet_write_wait();
 273                                         continue;
 274                                 }
 275                         }
 276                         break;
 277                 case SSH_CMSG_AUTH_TIS_RESPONSE:
 278                         debug("rcvd SSH_CMSG_AUTH_TIS_RESPONSE");
 279                         if (options.challenge_response_authentication == 1) {
 280                                 char *response = packet_get_string(&dlen);
 281                                 debug("got response '%s'", response);
 282                                 packet_check_eom();
 283                                 authenticated = verify_response(authctxt, response);
 284                                 memset(response, 'r', dlen);
 285                                 xfree(response);
 286                         }
 287                         break;
 288
 289                 default:
 290                         /*
 291                          * Any unknown messages will be ignored (and failure
 292                          * returned) during authentication.
 293                          */
 294                         log("Unknown message during authentication: type %d", type);
 295                         break;
 296                 }
 297 #ifdef BSD_AUTH
 298                 if (authctxt->as) {
 299                         auth_close(authctxt->as);
 300                         authctxt->as = NULL;
 301                 }
 302 #endif
 303                 if (!authctxt->valid && authenticated)
 304                         fatal("INTERNAL ERROR: authenticated invalid user %s",
 305                             authctxt->user);
 306
 307 #ifdef HAVE_CYGWIN
 308                 if (authenticated &&
 309                     !check_nt_auth(type == SSH_CMSG_AUTH_PASSWORD, pw)) {
 310                         packet_disconnect("Authentication rejected for uid %d.",
 311                         pw == NULL ? -1 : pw->pw_uid);
 312                         authenticated = 0;
 313                 }
 314 #else
 315                 /* Special handling for root */
 316                 if (!use_privsep &&
 317                     authenticated && authctxt->pw->pw_uid == 0 &&
 318                     !auth_root_allowed(get_authname(type)))
 319                         authenticated = 0;
 320 #endif
 321 #ifdef USE_PAM
 322                 if (!use_privsep && authenticated &&
 323                     !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                         packet_disconnect(AUTH_FAIL_MSG, authctxt->user);
 340                 }
 341
 342                 packet_start(SSH_SMSG_FAILURE);
 343                 packet_send();
 344                 packet_write_wait();
 345         }
 346 }
 347
 348 /*
 349  * Performs authentication of an incoming connection.  Session key has already
 350  * been exchanged and encryption is enabled.
 351  */
 352 Authctxt *
 353 do_authentication(void)
 354 {
 355         Authctxt *authctxt;
 356         u_int ulen;
 357         char *user, *style = NULL;
 358
 359         /* Get the name of the user that we wish to log in as. */
 360         packet_read_expect(SSH_CMSG_USER);
 361
 362         /* Get the user name. */
 363         user = packet_get_string(&ulen);
 364         packet_check_eom();
 365
 366         if ((style = strchr(user, ':')) != NULL)
 367                 *style++ = '\0';
 368
 369 #ifdef KRB5
 370         /* XXX - SSH.com Kerberos v5 braindeath. */
 371         if ((datafellows & SSH_BUG_K5USER) &&
 372             options.kerberos_authentication) {
 373                 char *p;
 374                 if ((p = strchr(user, '@')) != NULL)
 375                         *p = '\0';
 376         }
 377 #endif
 378
 379         authctxt = authctxt_new();
 380         authctxt->user = user;
 381         authctxt->style = style;
 382
 383         /* Verify that the user is a valid user. */
 384         if ((authctxt->pw = PRIVSEP(getpwnamallow(user))) != NULL)
 385                 authctxt->valid = 1;
 386         else
 387                 debug("do_authentication: illegal user %s", user);
 388
 389         setproctitle("%s%s", authctxt->pw ? user : "unknown",
 390             use_privsep ? " [net]" : "");
 391
 392 #ifdef USE_PAM
 393         PRIVSEP(start_pam(authctxt->pw == NULL ? "NOUSER" : user));
 394 #endif
 395
 396         /*
 397          * If we are not running as root, the user must have the same uid as
 398          * the server. (Unless you are running Windows)
 399          */
 400 #ifndef HAVE_CYGWIN
 401         if (!use_privsep && getuid() != 0 && authctxt->pw &&
 402             authctxt->pw->pw_uid != getuid())
 403                 packet_disconnect("Cannot change user when server not running as root.");
 404 #endif
 405
 406         /*
 407          * Loop until the user has been authenticated or the connection is
 408          * closed, do_authloop() returns only if authentication is successful
 409          */
 410         do_authloop(authctxt);
 411
 412         /* The user has been authenticated and accepted. */
 413         packet_start(SSH_SMSG_SUCCESS);
 414         packet_send();
 415         packet_write_wait();
 416
 417         return (authctxt);
 418 }