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 1.49 2003/07/22 13:35:22 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 #ifdef 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 prev, 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 #ifdef 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                 prev = type;
 107                 type = packet_read();
 108
 109                 /*
 110                  * If we started challenge-response authentication but the
 111                  * next packet is not a response to our challenge, release
 112                  * the resources allocated by get_challenge() (which would
 113                  * normally have been released by verify_response() had we
 114                  * received such a response)
 115                  */
 116                 if (prev == SSH_CMSG_AUTH_TIS &&
 117                     type != SSH_CMSG_AUTH_TIS_RESPONSE)
 118                         abandon_challenge_response(authctxt);
 119
 120                 /* Process the packet. */
 121                 switch (type) {
 122
 123 #ifdef KRB5
 124                 case SSH_CMSG_AUTH_KERBEROS:
 125                         if (!options.kerberos_authentication) {
 126                                 verbose("Kerberos authentication disabled.");
 127                         } else {
 128                                 char *kdata = packet_get_string(&dlen);
 129                                 packet_check_eom();
 130
 131                                 if (kdata[0] != 4) { /* KRB_PROT_VERSION */
 132                                         krb5_data tkt, reply;
 133                                         tkt.length = dlen;
 134                                         tkt.data = kdata;
 135
 136                                         if (PRIVSEP(auth_krb5(authctxt, &tkt,
 137                                             &client_user, &reply))) {
 138                                                 authenticated = 1;
 139                                                 snprintf(info, sizeof(info),
 140                                                     " tktuser %.100s",
 141                                                     client_user);
 142
 143                                                 /* Send response to client */
 144                                                 packet_start(
 145                                                     SSH_SMSG_AUTH_KERBEROS_RESPONSE);
 146                                                 packet_put_string((char *)
 147                                                     reply.data, reply.length);
 148                                                 packet_send();
 149                                                 packet_write_wait();
 150
 151                                                 if (reply.length)
 152                                                         xfree(reply.data);
 153                                         }
 154                                 }
 155                                 xfree(kdata);
 156                         }
 157                         break;
 158                 case SSH_CMSG_HAVE_KERBEROS_TGT:
 159                         packet_send_debug("Kerberos TGT passing disabled before authentication.");
 160                         break;
 161 #endif
 162
 163                 case SSH_CMSG_AUTH_RHOSTS:
 164                         if (!options.rhosts_authentication) {
 165                                 verbose("Rhosts authentication disabled.");
 166                                 break;
 167                         }
 168                         /*
 169                          * Get client user name.  Note that we just have to
 170                          * trust the client; this is one reason why rhosts
 171                          * authentication is insecure. (Another is
 172                          * IP-spoofing on a local network.)
 173                          */
 174                         client_user = packet_get_string(&ulen);
 175                         packet_check_eom();
 176
 177                         /* Try to authenticate using /etc/hosts.equiv and .rhosts. */
 178                         authenticated = auth_rhosts(pw, client_user);
 179
 180                         snprintf(info, sizeof info, " ruser %.100s", client_user);
 181                         break;
 182
 183                 case SSH_CMSG_AUTH_RHOSTS_RSA:
 184                         if (!options.rhosts_rsa_authentication) {
 185                                 verbose("Rhosts with RSA authentication disabled.");
 186                                 break;
 187                         }
 188                         /*
 189                          * Get client user name.  Note that we just have to
 190                          * trust the client; root on the client machine can
 191                          * claim to be any user.
 192                          */
 193                         client_user = packet_get_string(&ulen);
 194
 195                         /* Get the client host key. */
 196                         client_host_key = key_new(KEY_RSA1);
 197                         bits = packet_get_int();
 198                         packet_get_bignum(client_host_key->rsa->e);
 199                         packet_get_bignum(client_host_key->rsa->n);
 200
 201                         if (bits != BN_num_bits(client_host_key->rsa->n))
 202                                 verbose("Warning: keysize mismatch for client_host_key: "
 203                                     "actual %d, announced %d",
 204                                     BN_num_bits(client_host_key->rsa->n), bits);
 205                         packet_check_eom();
 206
 207                         authenticated = auth_rhosts_rsa(pw, client_user,
 208                             client_host_key);
 209                         key_free(client_host_key);
 210
 211                         snprintf(info, sizeof info, " ruser %.100s", client_user);
 212                         break;
 213
 214                 case SSH_CMSG_AUTH_RSA:
 215                         if (!options.rsa_authentication) {
 216                                 verbose("RSA authentication disabled.");
 217                                 break;
 218                         }
 219                         /* RSA authentication requested. */
 220                         if ((n = BN_new()) == NULL)
 221                                 fatal("do_authloop: BN_new failed");
 222                         packet_get_bignum(n);
 223                         packet_check_eom();
 224                         authenticated = auth_rsa(pw, n);
 225                         BN_clear_free(n);
 226                         break;
 227
 228                 case SSH_CMSG_AUTH_PASSWORD:
 229                         if (!options.password_authentication) {
 230                                 verbose("Password authentication disabled.");
 231                                 break;
 232                         }
 233                         /*
 234                          * Read user password.  It is in plain text, but was
 235                          * transmitted over the encrypted channel so it is
 236                          * not visible to an outside observer.
 237                          */
 238                         password = packet_get_string(&dlen);
 239                         packet_check_eom();
 240
 241                         /* Try authentication with the password. */
 242                         authenticated = PRIVSEP(auth_password(authctxt, password));
 243
 244                         memset(password, 0, strlen(password));
 245                         xfree(password);
 246                         break;
 247
 248                 case SSH_CMSG_AUTH_TIS:
 249                         debug("rcvd SSH_CMSG_AUTH_TIS");
 250                         if (options.challenge_response_authentication == 1) {
 251                                 char *challenge = get_challenge(authctxt);
 252                                 if (challenge != NULL) {
 253                                         debug("sending challenge '%s'", challenge);
 254                                         packet_start(SSH_SMSG_AUTH_TIS_CHALLENGE);
 255                                         packet_put_cstring(challenge);
 256                                         xfree(challenge);
 257                                         packet_send();
 258                                         packet_write_wait();
 259                                         continue;
 260                                 }
 261                         }
 262                         break;
 263                 case SSH_CMSG_AUTH_TIS_RESPONSE:
 264                         debug("rcvd SSH_CMSG_AUTH_TIS_RESPONSE");
 265                         if (options.challenge_response_authentication == 1) {
 266                                 char *response = packet_get_string(&dlen);
 267                                 packet_check_eom();
 268                                 authenticated = verify_response(authctxt, response);
 269                                 memset(response, 'r', dlen);
 270                                 xfree(response);
 271                         }
 272                         break;
 273
 274                 default:
 275                         /*
 276                          * Any unknown messages will be ignored (and failure
 277                          * returned) during authentication.
 278                          */
 279                         logit("Unknown message during authentication: type %d", type);
 280                         break;
 281                 }
 282 #ifdef BSD_AUTH
 283                 if (authctxt->as) {
 284                         auth_close(authctxt->as);
 285                         authctxt->as = NULL;
 286                 }
 287 #endif
 288                 if (!authctxt->valid && authenticated)
 289                         fatal("INTERNAL ERROR: authenticated invalid user %s",
 290                             authctxt->user);
 291
 292 #ifdef _UNICOS
 293                 if (authenticated && cray_access_denied(authctxt->user)) {
 294                         authenticated = 0;
 295                         fatal("Access denied for user %s.",authctxt->user);
 296                 }
 297 #endif /* _UNICOS */
 298
 299 #ifdef HAVE_CYGWIN
 300                 if (authenticated &&
 301                     !check_nt_auth(type == SSH_CMSG_AUTH_PASSWORD, pw)) {
 302                         packet_disconnect("Authentication rejected for uid %d.",
 303                         pw == NULL ? -1 : pw->pw_uid);
 304                         authenticated = 0;
 305                 }
 306 #else
 307                 /* Special handling for root */
 308                 if (authenticated && authctxt->pw->pw_uid == 0 &&
 309                     !auth_root_allowed(get_authname(type)))
 310                         authenticated = 0;
 311 #endif
 312
 313                 /* Log before sending the reply */
 314                 auth_log(authctxt, authenticated, get_authname(type), info);
 315
 316                 if (client_user != NULL) {
 317                         xfree(client_user);
 318                         client_user = NULL;
 319                 }
 320
 321                 if (authenticated)
 322                         return;
 323
 324                 if (authctxt->failures++ > AUTH_FAIL_MAX)
 325                         packet_disconnect(AUTH_FAIL_MSG, authctxt->user);
 326
 327                 packet_start(SSH_SMSG_FAILURE);
 328                 packet_send();
 329                 packet_write_wait();
 330         }
 331 }
 332
 333 /*
 334  * Performs authentication of an incoming connection.  Session key has already
 335  * been exchanged and encryption is enabled.
 336  */
 337 Authctxt *
 338 do_authentication(void)
 339 {
 340         Authctxt *authctxt;
 341         u_int ulen;
 342         char *user, *style = NULL;
 343
 344         /* Get the name of the user that we wish to log in as. */
 345         packet_read_expect(SSH_CMSG_USER);
 346
 347         /* Get the user name. */
 348         user = packet_get_string(&ulen);
 349         packet_check_eom();
 350
 351         if ((style = strchr(user, ':')) != NULL)
 352                 *style++ = '\0';
 353
 354 #ifdef KRB5
 355         /* XXX - SSH.com Kerberos v5 braindeath. */
 356         if ((datafellows & SSH_BUG_K5USER) &&
 357             options.kerberos_authentication) {
 358                 char *p;
 359                 if ((p = strchr(user, '@')) != NULL)
 360                         *p = '\0';
 361         }
 362 #endif
 363
 364         authctxt = authctxt_new();
 365         authctxt->user = user;
 366         authctxt->style = style;
 367
 368         /* Verify that the user is a valid user. */
 369         if ((authctxt->pw = PRIVSEP(getpwnamallow(user))) != NULL)
 370                 authctxt->valid = 1;
 371         else
 372                 debug("do_authentication: illegal user %s", user);
 373
 374         setproctitle("%s%s", authctxt->pw ? user : "unknown",
 375             use_privsep ? " [net]" : "");
 376
 377 #ifdef USE_PAM
 378         if (options.use_pam)
 379                 PRIVSEP(start_pam(user));
 380 #endif
 381
 382         /*
 383          * If we are not running as root, the user must have the same uid as
 384          * the server. (Unless you are running Windows)
 385          */
 386 #ifndef HAVE_CYGWIN
 387         if (!use_privsep && getuid() != 0 && authctxt->pw &&
 388             authctxt->pw->pw_uid != getuid())
 389                 packet_disconnect("Cannot change user when server not running as root.");
 390 #endif
 391
 392         /*
 393          * Loop until the user has been authenticated or the connection is
 394          * closed, do_authloop() returns only if authentication is successful
 395          */
 396         do_authloop(authctxt);
 397
 398         /* The user has been authenticated and accepted. */
 399         packet_start(SSH_SMSG_SUCCESS);
 400         packet_send();
 401         packet_write_wait();
 402
 403         return (authctxt);
 404 }