auth1.c

   1 /* $OpenBSD: auth1.c,v 1.75 2010/08/31 09:58:37 djm Exp $ */
   2 /*
   3  * Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
   4  *                    All rights reserved
   5  *
   6  * As far as I am concerned, the code I have written for this software
   7  * can be used freely for any purpose.  Any derived versions of this
   8  * software must be clearly marked as such, and if the derived work is
   9  * incompatible with the protocol description in the RFC file, it must be
  10  * called by a name other than "ssh" or "Secure Shell".
  11  */
  12
  13 #include "includes.h"
  14
  15 #include <sys/types.h>
  16
  17 #include <stdarg.h>
  18 #include <stdio.h>
  19 #include <string.h>
  20 #include <unistd.h>
  21 #include <pwd.h>
  22
  23 #include "openbsd-compat/sys-queue.h"
  24 #include "xmalloc.h"
  25 #include "rsa.h"
  26 #include "ssh1.h"
  27 #include "packet.h"
  28 #include "buffer.h"
  29 #include "log.h"
  30 #include "servconf.h"
  31 #include "compat.h"
  32 #include "key.h"
  33 #include "hostfile.h"
  34 #include "auth.h"
  35 #include "channels.h"
  36 #include "session.h"
  37 #include "uidswap.h"
  38 #ifdef GSSAPI
  39 #include "ssh-gss.h"
  40 #endif
  41 #include "monitor_wrap.h"
  42 #include "buffer.h"
  43
  44 /* import */
  45 extern ServerOptions options;
  46 extern Buffer loginmsg;
  47
  48 static int auth1_process_password(Authctxt *, char *, size_t);
  49 static int auth1_process_rsa(Authctxt *, char *, size_t);
  50 static int auth1_process_rhosts_rsa(Authctxt *, char *, size_t);
  51 static int auth1_process_tis_challenge(Authctxt *, char *, size_t);
  52 static int auth1_process_tis_response(Authctxt *, char *, size_t);
  53
  54 static char *client_user = NULL;    /* Used to fill in remote user for PAM */
  55
  56 struct AuthMethod1 {
  57         int type;
  58         char *name;
  59         int *enabled;
  60         int (*method)(Authctxt *, char *, size_t);
  61 };
  62
  63 const struct AuthMethod1 auth1_methods[] = {
  64         {
  65                 SSH_CMSG_AUTH_PASSWORD, "password",
  66                 &options.password_authentication, auth1_process_password
  67         },
  68         {
  69                 SSH_CMSG_AUTH_RSA, "rsa",
  70                 &options.rsa_authentication, auth1_process_rsa
  71         },
  72         {
  73                 SSH_CMSG_AUTH_RHOSTS_RSA, "rhosts-rsa",
  74                 &options.rhosts_rsa_authentication, auth1_process_rhosts_rsa
  75         },
  76         {
  77                 SSH_CMSG_AUTH_TIS, "challenge-response",
  78                 &options.challenge_response_authentication,
  79                 auth1_process_tis_challenge
  80         },
  81         {
  82                 SSH_CMSG_AUTH_TIS_RESPONSE, "challenge-response",
  83                 &options.challenge_response_authentication,
  84                 auth1_process_tis_response
  85         },
  86         { -1, NULL, NULL, NULL}
  87 };
  88
  89 static const struct AuthMethod1
  90 *lookup_authmethod1(int type)
  91 {
  92         int i;
  93
  94         for (i = 0; auth1_methods[i].name != NULL; i++)
  95                 if (auth1_methods[i].type == type)
  96                         return (&(auth1_methods[i]));
  97
  98         return (NULL);
  99 }
 100
 101 static char *
 102 get_authname(int type)
 103 {
 104         const struct AuthMethod1 *a;
 105         static char buf[64];
 106
 107         if ((a = lookup_authmethod1(type)) != NULL)
 108                 return (a->name);
 109         snprintf(buf, sizeof(buf), "bad-auth-msg-%d", type);
 110         return (buf);
 111 }
 112
 113 /*ARGSUSED*/
 114 static int
 115 auth1_process_password(Authctxt *authctxt, char *info, size_t infolen)
 116 {
 117         int authenticated = 0;
 118         char *password;
 119         u_int dlen;
 120
 121         /*
 122          * Read user password.  It is in plain text, but was
 123          * transmitted over the encrypted channel so it is
 124          * not visible to an outside observer.
 125          */
 126         password = packet_get_string(&dlen);
 127         packet_check_eom();
 128
 129         /* Try authentication with the password. */
 130         authenticated = PRIVSEP(auth_password(authctxt, password));
 131
 132         memset(password, 0, dlen);
 133         xfree(password);
 134
 135         return (authenticated);
 136 }
 137
 138 /*ARGSUSED*/
 139 static int
 140 auth1_process_rsa(Authctxt *authctxt, char *info, size_t infolen)
 141 {
 142         int authenticated = 0;
 143         BIGNUM *n;
 144
 145         /* RSA authentication requested. */
 146         if ((n = BN_new()) == NULL)
 147                 fatal("do_authloop: BN_new failed");
 148         packet_get_bignum(n);
 149         packet_check_eom();
 150         authenticated = auth_rsa(authctxt, n);
 151         BN_clear_free(n);
 152
 153         return (authenticated);
 154 }
 155
 156 /*ARGSUSED*/
 157 static int
 158 auth1_process_rhosts_rsa(Authctxt *authctxt, char *info, size_t infolen)
 159 {
 160         int keybits, authenticated = 0;
 161         u_int bits;
 162         Key *client_host_key;
 163         u_int ulen;
 164
 165         /*
 166          * Get client user name.  Note that we just have to
 167          * trust the client; root on the client machine can
 168          * claim to be any user.
 169          */
 170         client_user = packet_get_cstring(&ulen);
 171
 172         /* Get the client host key. */
 173         client_host_key = key_new(KEY_RSA1);
 174         bits = packet_get_int();
 175         packet_get_bignum(client_host_key->rsa->e);
 176         packet_get_bignum(client_host_key->rsa->n);
 177
 178         keybits = BN_num_bits(client_host_key->rsa->n);
 179         if (keybits < 0 || bits != (u_int)keybits) {
 180                 verbose("Warning: keysize mismatch for client_host_key: "
 181                     "actual %d, announced %d",
 182                     BN_num_bits(client_host_key->rsa->n), bits);
 183         }
 184         packet_check_eom();
 185
 186         authenticated = auth_rhosts_rsa(authctxt, client_user,
 187             client_host_key);
 188         key_free(client_host_key);
 189
 190         snprintf(info, infolen, " ruser %.100s", client_user);
 191
 192         return (authenticated);
 193 }
 194
 195 /*ARGSUSED*/
 196 static int
 197 auth1_process_tis_challenge(Authctxt *authctxt, char *info, size_t infolen)
 198 {
 199         char *challenge;
 200
 201         if ((challenge = get_challenge(authctxt)) == NULL)
 202                 return (0);
 203
 204         debug("sending challenge '%s'", challenge);
 205         packet_start(SSH_SMSG_AUTH_TIS_CHALLENGE);
 206         packet_put_cstring(challenge);
 207         xfree(challenge);
 208         packet_send();
 209         packet_write_wait();
 210
 211         return (-1);
 212 }
 213
 214 /*ARGSUSED*/
 215 static int
 216 auth1_process_tis_response(Authctxt *authctxt, char *info, size_t infolen)
 217 {
 218         int authenticated = 0;
 219         char *response;
 220         u_int dlen;
 221
 222         response = packet_get_string(&dlen);
 223         packet_check_eom();
 224         authenticated = verify_response(authctxt, response);
 225         memset(response, 'r', dlen);
 226         xfree(response);
 227
 228         return (authenticated);
 229 }
 230
 231 /*
 232  * read packets, try to authenticate the user and
 233  * return only if authentication is successful
 234  */
 235 static void
 236 do_authloop(Authctxt *authctxt)
 237 {
 238         int authenticated = 0;
 239         char info[1024];
 240         int prev = 0, type = 0;
 241         const struct AuthMethod1 *meth;
 242
 243         debug("Attempting authentication for %s%.100s.",
 244             authctxt->valid ? "" : "invalid user ", authctxt->user);
 245
 246         /* If the user has no password, accept authentication immediately. */
 247         if (options.permit_empty_passwd && options.password_authentication &&
 248 #ifdef KRB5
 249             (!options.kerberos_authentication || options.kerberos_or_local_passwd) &&
 250 #endif
 251             PRIVSEP(auth_password(authctxt, ""))) {
 252 #ifdef USE_PAM
 253                 if (options.use_pam && (PRIVSEP(do_pam_account())))
 254 #endif
 255                 {
 256                         auth_log(authctxt, 1, "without authentication", "");
 257                         return;
 258                 }
 259         }
 260
 261         /* Indicate that authentication is needed. */
 262         packet_start(SSH_SMSG_FAILURE);
 263         packet_send();
 264         packet_write_wait();
 265
 266         for (;;) {
 267                 /* default to fail */
 268                 authenticated = 0;
 269
 270                 info[0] = '\0';
 271
 272                 /* Get a packet from the client. */
 273                 prev = type;
 274                 type = packet_read();
 275
 276                 /*
 277                  * If we started challenge-response authentication but the
 278                  * next packet is not a response to our challenge, release
 279                  * the resources allocated by get_challenge() (which would
 280                  * normally have been released by verify_response() had we
 281                  * received such a response)
 282                  */
 283                 if (prev == SSH_CMSG_AUTH_TIS &&
 284                     type != SSH_CMSG_AUTH_TIS_RESPONSE)
 285                         abandon_challenge_response(authctxt);
 286
 287                 if (authctxt->failures >= options.max_authtries)
 288                         goto skip;
 289                 if ((meth = lookup_authmethod1(type)) == NULL) {
 290                         logit("Unknown message during authentication: "
 291                             "type %d", type);
 292                         goto skip;
 293                 }
 294
 295                 if (!*(meth->enabled)) {
 296                         verbose("%s authentication disabled.", meth->name);
 297                         goto skip;
 298                 }
 299
 300                 authenticated = meth->method(authctxt, info, sizeof(info));
 301                 if (authenticated == -1)
 302                         continue; /* "postponed" */
 303
 304 #ifdef BSD_AUTH
 305                 if (authctxt->as) {
 306                         auth_close(authctxt->as);
 307                         authctxt->as = NULL;
 308                 }
 309 #endif
 310                 if (!authctxt->valid && authenticated)
 311                         fatal("INTERNAL ERROR: authenticated invalid user %s",
 312                             authctxt->user);
 313
 314 #ifdef _UNICOS
 315                 if (authenticated && cray_access_denied(authctxt->user)) {
 316                         authenticated = 0;
 317                         fatal("Access denied for user %s.",authctxt->user);
 318                 }
 319 #endif /* _UNICOS */
 320
 321 #ifndef HAVE_CYGWIN
 322                 /* Special handling for root */
 323                 if (authenticated && authctxt->pw->pw_uid == 0 &&
 324                     !auth_root_allowed(meth->name)) {
 325                         authenticated = 0;
 326 # ifdef SSH_AUDIT_EVENTS
 327                         PRIVSEP(audit_event(SSH_LOGIN_ROOT_DENIED));
 328 # endif
 329                 }
 330 #endif
 331
 332 #ifdef USE_PAM
 333                 if (options.use_pam && authenticated &&
 334                     !PRIVSEP(do_pam_account())) {
 335                         char *msg;
 336                         size_t len;
 337
 338                         error("Access denied for user %s by PAM account "
 339                             "configuration", authctxt->user);
 340                         len = buffer_len(&loginmsg);
 341                         buffer_append(&loginmsg, "\0", 1);
 342                         msg = buffer_ptr(&loginmsg);
 343                         /* strip trailing newlines */
 344                         if (len > 0)
 345                                 while (len > 0 && msg[--len] == '\n')
 346                                         msg[len] = '\0';
 347                         else
 348                                 msg = "Access denied.";
 349                         packet_disconnect("%s", msg);
 350                 }
 351 #endif
 352
 353  skip:
 354                 /* Log before sending the reply */
 355                 auth_log(authctxt, authenticated, get_authname(type), info);
 356
 357                 if (client_user != NULL) {
 358                         xfree(client_user);
 359                         client_user = NULL;
 360                 }
 361
 362                 if (authenticated)
 363                         return;
 364
 365                 if (++authctxt->failures >= options.max_authtries) {
 366 #ifdef SSH_AUDIT_EVENTS
 367                         PRIVSEP(audit_event(SSH_LOGIN_EXCEED_MAXTRIES));
 368 #endif
 369                         packet_disconnect(AUTH_FAIL_MSG, authctxt->user);
 370                 }
 371
 372                 packet_start(SSH_SMSG_FAILURE);
 373                 packet_send();
 374                 packet_write_wait();
 375         }
 376 }
 377
 378 /*
 379  * Performs authentication of an incoming connection.  Session key has already
 380  * been exchanged and encryption is enabled.
 381  */
 382 void
 383 do_authentication(Authctxt *authctxt)
 384 {
 385         u_int ulen;
 386         char *user, *style = NULL;
 387
 388         /* Get the name of the user that we wish to log in as. */
 389         packet_read_expect(SSH_CMSG_USER);
 390
 391         /* Get the user name. */
 392         user = packet_get_cstring(&ulen);
 393         packet_check_eom();
 394
 395         if ((style = strchr(user, ':')) != NULL)
 396                 *style++ = '\0';
 397
 398         authctxt->user = user;
 399         authctxt->style = style;
 400
 401         /* Verify that the user is a valid user. */
 402         if ((authctxt->pw = PRIVSEP(getpwnamallow(user))) != NULL)
 403                 authctxt->valid = 1;
 404         else {
 405                 debug("do_authentication: invalid user %s", user);
 406                 authctxt->pw = fakepw();
 407         }
 408
 409         setproctitle("%s%s", authctxt->valid ? user : "unknown",
 410             use_privsep ? " [net]" : "");
 411
 412 #ifdef USE_PAM
 413         if (options.use_pam)
 414                 PRIVSEP(start_pam(authctxt));
 415 #endif
 416
 417         /*
 418          * If we are not running as root, the user must have the same uid as
 419          * the server.
 420          */
 421 #ifndef HAVE_CYGWIN
 422         if (!use_privsep && getuid() != 0 && authctxt->pw &&
 423             authctxt->pw->pw_uid != getuid())
 424                 packet_disconnect("Cannot change user when server not running as root.");
 425 #endif
 426
 427         /*
 428          * Loop until the user has been authenticated or the connection is
 429          * closed, do_authloop() returns only if authentication is successful
 430          */
 431         do_authloop(authctxt);
 432
 433         /* The user has been authenticated and accepted. */
 434         packet_start(SSH_SMSG_SUCCESS);
 435         packet_send();
 436         packet_write_wait();
 437 }