crypto/openssh/auth1.c

   1 /* $OpenBSD: auth1.c,v 1.82 2014/07/15 15:54:14 millert 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 #ifdef WITH_SSH1
  16
  17 #include <sys/types.h>
  18
  19 #include <stdarg.h>
  20 #include <stdio.h>
  21 #include <string.h>
  22 #include <unistd.h>
  23 #include <pwd.h>
  24
  25 #include "openbsd-compat/sys-queue.h"
  26 #include "xmalloc.h"
  27 #include "rsa.h"
  28 #include "ssh1.h"
  29 #include "packet.h"
  30 #include "buffer.h"
  31 #include "log.h"
  32 #include "misc.h"
  33 #include "servconf.h"
  34 #include "compat.h"
  35 #include "key.h"
  36 #include "hostfile.h"
  37 #include "auth.h"
  38 #include "channels.h"
  39 #include "session.h"
  40 #include "uidswap.h"
  41 #ifdef GSSAPI
  42 #include "ssh-gss.h"
  43 #endif
  44 #include "monitor_wrap.h"
  45 #include "buffer.h"
  46
  47 /* import */
  48 extern ServerOptions options;
  49 extern Buffer loginmsg;
  50
  51 static int auth1_process_password(Authctxt *);
  52 static int auth1_process_rsa(Authctxt *);
  53 static int auth1_process_rhosts_rsa(Authctxt *);
  54 static int auth1_process_tis_challenge(Authctxt *);
  55 static int auth1_process_tis_response(Authctxt *);
  56
  57 static char *client_user = NULL;    /* Used to fill in remote user for PAM */
  58
  59 struct AuthMethod1 {
  60         int type;
  61         char *name;
  62         int *enabled;
  63         int (*method)(Authctxt *);
  64 };
  65
  66 const struct AuthMethod1 auth1_methods[] = {
  67         {
  68                 SSH_CMSG_AUTH_PASSWORD, "password",
  69                 &options.password_authentication, auth1_process_password
  70         },
  71         {
  72                 SSH_CMSG_AUTH_RSA, "rsa",
  73                 &options.rsa_authentication, auth1_process_rsa
  74         },
  75         {
  76                 SSH_CMSG_AUTH_RHOSTS_RSA, "rhosts-rsa",
  77                 &options.rhosts_rsa_authentication, auth1_process_rhosts_rsa
  78         },
  79         {
  80                 SSH_CMSG_AUTH_TIS, "challenge-response",
  81                 &options.challenge_response_authentication,
  82                 auth1_process_tis_challenge
  83         },
  84         {
  85                 SSH_CMSG_AUTH_TIS_RESPONSE, "challenge-response",
  86                 &options.challenge_response_authentication,
  87                 auth1_process_tis_response
  88         },
  89         { -1, NULL, NULL, NULL}
  90 };
  91
  92 static const struct AuthMethod1
  93 *lookup_authmethod1(int type)
  94 {
  95         int i;
  96
  97         for (i = 0; auth1_methods[i].name != NULL; i++)
  98                 if (auth1_methods[i].type == type)
  99                         return (&(auth1_methods[i]));
 100
 101         return (NULL);
 102 }
 103
 104 static char *
 105 get_authname(int type)
 106 {
 107         const struct AuthMethod1 *a;
 108         static char buf[64];
 109
 110         if ((a = lookup_authmethod1(type)) != NULL)
 111                 return (a->name);
 112         snprintf(buf, sizeof(buf), "bad-auth-msg-%d", type);
 113         return (buf);
 114 }
 115
 116 /*ARGSUSED*/
 117 static int
 118 auth1_process_password(Authctxt *authctxt)
 119 {
 120         int authenticated = 0;
 121         char *password;
 122         u_int dlen;
 123
 124         /*
 125          * Read user password.  It is in plain text, but was
 126          * transmitted over the encrypted channel so it is
 127          * not visible to an outside observer.
 128          */
 129         password = packet_get_string(&dlen);
 130         packet_check_eom();
 131
 132         /* Try authentication with the password. */
 133         authenticated = PRIVSEP(auth_password(authctxt, password));
 134
 135         explicit_bzero(password, dlen);
 136         free(password);
 137
 138         return (authenticated);
 139 }
 140
 141 /*ARGSUSED*/
 142 static int
 143 auth1_process_rsa(Authctxt *authctxt)
 144 {
 145         int authenticated = 0;
 146         BIGNUM *n;
 147
 148         /* RSA authentication requested. */
 149         if ((n = BN_new()) == NULL)
 150                 fatal("do_authloop: BN_new failed");
 151         packet_get_bignum(n);
 152         packet_check_eom();
 153         authenticated = auth_rsa(authctxt, n);
 154         BN_clear_free(n);
 155
 156         return (authenticated);
 157 }
 158
 159 /*ARGSUSED*/
 160 static int
 161 auth1_process_rhosts_rsa(Authctxt *authctxt)
 162 {
 163         int keybits, authenticated = 0;
 164         u_int bits;
 165         Key *client_host_key;
 166         u_int ulen;
 167
 168         /*
 169          * Get client user name.  Note that we just have to
 170          * trust the client; root on the client machine can
 171          * claim to be any user.
 172          */
 173         client_user = packet_get_cstring(&ulen);
 174
 175         /* Get the client host key. */
 176         client_host_key = key_new(KEY_RSA1);
 177         bits = packet_get_int();
 178         packet_get_bignum(client_host_key->rsa->e);
 179         packet_get_bignum(client_host_key->rsa->n);
 180
 181         keybits = BN_num_bits(client_host_key->rsa->n);
 182         if (keybits < 0 || bits != (u_int)keybits) {
 183                 verbose("Warning: keysize mismatch for client_host_key: "
 184                     "actual %d, announced %d",
 185                     BN_num_bits(client_host_key->rsa->n), bits);
 186         }
 187         packet_check_eom();
 188
 189         authenticated = auth_rhosts_rsa(authctxt, client_user,
 190             client_host_key);
 191         key_free(client_host_key);
 192
 193         auth_info(authctxt, "ruser %.100s", client_user);
 194
 195         return (authenticated);
 196 }
 197
 198 /*ARGSUSED*/
 199 static int
 200 auth1_process_tis_challenge(Authctxt *authctxt)
 201 {
 202         char *challenge;
 203
 204         if ((challenge = get_challenge(authctxt)) == NULL)
 205                 return (0);
 206
 207         debug("sending challenge '%s'", challenge);
 208         packet_start(SSH_SMSG_AUTH_TIS_CHALLENGE);
 209         packet_put_cstring(challenge);
 210         free(challenge);
 211         packet_send();
 212         packet_write_wait();
 213
 214         return (-1);
 215 }
 216
 217 /*ARGSUSED*/
 218 static int
 219 auth1_process_tis_response(Authctxt *authctxt)
 220 {
 221         int authenticated = 0;
 222         char *response;
 223         u_int dlen;
 224
 225         response = packet_get_string(&dlen);
 226         packet_check_eom();
 227         authenticated = verify_response(authctxt, response);
 228         explicit_bzero(response, dlen);
 229         free(response);
 230
 231         return (authenticated);
 232 }
 233
 234 /*
 235  * read packets, try to authenticate the user and
 236  * return only if authentication is successful
 237  */
 238 static void
 239 do_authloop(Authctxt *authctxt)
 240 {
 241         int authenticated = 0;
 242         int prev = 0, type = 0;
 243         const struct AuthMethod1 *meth;
 244
 245         debug("Attempting authentication for %s%.100s.",
 246             authctxt->valid ? "" : "invalid user ", authctxt->user);
 247
 248         /* If the user has no password, accept authentication immediately. */
 249         if (options.permit_empty_passwd && options.password_authentication &&
 250 #ifdef KRB5
 251             (!options.kerberos_authentication || options.kerberos_or_local_passwd) &&
 252 #endif
 253             PRIVSEP(auth_password(authctxt, ""))) {
 254 #ifdef USE_PAM
 255                 if (options.use_pam && (PRIVSEP(do_pam_account())))
 256 #endif
 257                 {
 258                         auth_log(authctxt, 1, 0, "without authentication",
 259                             NULL);
 260                         return;
 261                 }
 262         }
 263
 264         /* Indicate that authentication is needed. */
 265         packet_start(SSH_SMSG_FAILURE);
 266         packet_send();
 267         packet_write_wait();
 268
 269         for (;;) {
 270                 /* default to fail */
 271                 authenticated = 0;
 272
 273
 274                 /* Get a packet from the client. */
 275                 prev = type;
 276                 type = packet_read();
 277
 278                 /*
 279                  * If we started challenge-response authentication but the
 280                  * next packet is not a response to our challenge, release
 281                  * the resources allocated by get_challenge() (which would
 282                  * normally have been released by verify_response() had we
 283                  * received such a response)
 284                  */
 285                 if (prev == SSH_CMSG_AUTH_TIS &&
 286                     type != SSH_CMSG_AUTH_TIS_RESPONSE)
 287                         abandon_challenge_response(authctxt);
 288
 289                 if (authctxt->failures >= options.max_authtries)
 290                         goto skip;
 291                 if ((meth = lookup_authmethod1(type)) == NULL) {
 292                         logit("Unknown message during authentication: "
 293                             "type %d", type);
 294                         goto skip;
 295                 }
 296
 297                 if (!*(meth->enabled)) {
 298                         verbose("%s authentication disabled.", meth->name);
 299                         goto skip;
 300                 }
 301
 302                 authenticated = meth->method(authctxt);
 303                 if (authenticated == -1)
 304                         continue; /* "postponed" */
 305
 306 #ifdef BSD_AUTH
 307                 if (authctxt->as) {
 308                         auth_close(authctxt->as);
 309                         authctxt->as = NULL;
 310                 }
 311 #endif
 312                 if (!authctxt->valid && authenticated)
 313                         fatal("INTERNAL ERROR: authenticated invalid user %s",
 314                             authctxt->user);
 315
 316 #ifdef _UNICOS
 317                 if (authenticated && cray_access_denied(authctxt->user)) {
 318                         authenticated = 0;
 319                         fatal("Access denied for user %s.",authctxt->user);
 320                 }
 321 #endif /* _UNICOS */
 322
 323 #ifndef HAVE_CYGWIN
 324                 /* Special handling for root */
 325                 if (authenticated && authctxt->pw->pw_uid == 0 &&
 326                     !auth_root_allowed(meth->name)) {
 327                         authenticated = 0;
 328 # ifdef SSH_AUDIT_EVENTS
 329                         PRIVSEP(audit_event(SSH_LOGIN_ROOT_DENIED));
 330 # endif
 331                 }
 332 #endif
 333
 334 #ifdef USE_PAM
 335                 if (options.use_pam && authenticated &&
 336                     !PRIVSEP(do_pam_account())) {
 337                         char *msg;
 338                         size_t len;
 339
 340                         error("Access denied for user %s by PAM account "
 341                             "configuration", authctxt->user);
 342                         len = buffer_len(&loginmsg);
 343                         buffer_append(&loginmsg, "\0", 1);
 344                         msg = buffer_ptr(&loginmsg);
 345                         /* strip trailing newlines */
 346                         if (len > 0)
 347                                 while (len > 0 && msg[--len] == '\n')
 348                                         msg[len] = '\0';
 349                         else
 350                                 msg = "Access denied.";
 351                         packet_disconnect("%s", msg);
 352                 }
 353 #endif
 354
 355  skip:
 356                 /* Log before sending the reply */
 357                 auth_log(authctxt, authenticated, 0, get_authname(type), NULL);
 358
 359                 free(client_user);
 360                 client_user = NULL;
 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                         auth_maxtries_exceeded(authctxt);
 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         /* Configuration may have changed as a result of Match */
 410         if (options.num_auth_methods != 0)
 411                 fatal("AuthenticationMethods is not supported with SSH "
 412                     "protocol 1");
 413
 414         setproctitle("%s%s", authctxt->valid ? user : "unknown",
 415             use_privsep ? " [net]" : "");
 416
 417 #ifdef USE_PAM
 418         if (options.use_pam)
 419                 PRIVSEP(start_pam(authctxt));
 420 #endif
 421
 422         /*
 423          * If we are not running as root, the user must have the same uid as
 424          * the server.
 425          */
 426 #ifndef HAVE_CYGWIN
 427         if (!use_privsep && getuid() != 0 && authctxt->pw &&
 428             authctxt->pw->pw_uid != getuid())
 429                 packet_disconnect("Cannot change user when server not running as root.");
 430 #endif
 431
 432         /*
 433          * Loop until the user has been authenticated or the connection is
 434          * closed, do_authloop() returns only if authentication is successful
 435          */
 436         do_authloop(authctxt);
 437
 438         /* The user has been authenticated and accepted. */
 439         packet_start(SSH_SMSG_SUCCESS);
 440         packet_send();
 441         packet_write_wait();
 442 }
 443
 444 #endif /* WITH_SSH1 */