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 #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 "misc.h"
  31 #include "servconf.h"
  32 #include "compat.h"
  33 #include "key.h"
  34 #include "hostfile.h"
  35 #include "auth.h"
  36 #include "channels.h"
  37 #include "session.h"
  38 #include "uidswap.h"
  39 #ifdef GSSAPI
  40 #include "ssh-gss.h"
  41 #endif
  42 #include "monitor_wrap.h"
  43 #include "buffer.h"
  44
  45 /* import */
  46 extern ServerOptions options;
  47 extern Buffer loginmsg;
  48
  49 static int auth1_process_password(Authctxt *);
  50 static int auth1_process_rsa(Authctxt *);
  51 static int auth1_process_rhosts_rsa(Authctxt *);
  52 static int auth1_process_tis_challenge(Authctxt *);
  53 static int auth1_process_tis_response(Authctxt *);
  54
  55 static char *client_user = NULL;    /* Used to fill in remote user for PAM */
  56
  57 struct AuthMethod1 {
  58         int type;
  59         char *name;
  60         int *enabled;
  61         int (*method)(Authctxt *);
  62 };
  63
  64 const struct AuthMethod1 auth1_methods[] = {
  65         {
  66                 SSH_CMSG_AUTH_PASSWORD, "password",
  67                 &options.password_authentication, auth1_process_password
  68         },
  69         {
  70                 SSH_CMSG_AUTH_RSA, "rsa",
  71                 &options.rsa_authentication, auth1_process_rsa
  72         },
  73         {
  74                 SSH_CMSG_AUTH_RHOSTS_RSA, "rhosts-rsa",
  75                 &options.rhosts_rsa_authentication, auth1_process_rhosts_rsa
  76         },
  77         {
  78                 SSH_CMSG_AUTH_TIS, "challenge-response",
  79                 &options.challenge_response_authentication,
  80                 auth1_process_tis_challenge
  81         },
  82         {
  83                 SSH_CMSG_AUTH_TIS_RESPONSE, "challenge-response",
  84                 &options.challenge_response_authentication,
  85                 auth1_process_tis_response
  86         },
  87         { -1, NULL, NULL, NULL}
  88 };
  89
  90 static const struct AuthMethod1
  91 *lookup_authmethod1(int type)
  92 {
  93         int i;
  94
  95         for (i = 0; auth1_methods[i].name != NULL; i++)
  96                 if (auth1_methods[i].type == type)
  97                         return (&(auth1_methods[i]));
  98
  99         return (NULL);
 100 }
 101
 102 static char *
 103 get_authname(int type)
 104 {
 105         const struct AuthMethod1 *a;
 106         static char buf[64];
 107
 108         if ((a = lookup_authmethod1(type)) != NULL)
 109                 return (a->name);
 110         snprintf(buf, sizeof(buf), "bad-auth-msg-%d", type);
 111         return (buf);
 112 }
 113
 114 /*ARGSUSED*/
 115 static int
 116 auth1_process_password(Authctxt *authctxt)
 117 {
 118         int authenticated = 0;
 119         char *password;
 120         u_int dlen;
 121
 122         /*
 123          * Read user password.  It is in plain text, but was
 124          * transmitted over the encrypted channel so it is
 125          * not visible to an outside observer.
 126          */
 127         password = packet_get_string(&dlen);
 128         packet_check_eom();
 129
 130         /* Try authentication with the password. */
 131         authenticated = PRIVSEP(auth_password(authctxt, password));
 132
 133         explicit_bzero(password, dlen);
 134         free(password);
 135
 136         return (authenticated);
 137 }
 138
 139 /*ARGSUSED*/
 140 static int
 141 auth1_process_rsa(Authctxt *authctxt)
 142 {
 143         int authenticated = 0;
 144         BIGNUM *n;
 145
 146         /* RSA authentication requested. */
 147         if ((n = BN_new()) == NULL)
 148                 fatal("do_authloop: BN_new failed");
 149         packet_get_bignum(n);
 150         packet_check_eom();
 151         authenticated = auth_rsa(authctxt, n);
 152         BN_clear_free(n);
 153
 154         return (authenticated);
 155 }
 156
 157 /*ARGSUSED*/
 158 static int
 159 auth1_process_rhosts_rsa(Authctxt *authctxt)
 160 {
 161         int keybits, authenticated = 0;
 162         u_int bits;
 163         Key *client_host_key;
 164         u_int ulen;
 165
 166         /*
 167          * Get client user name.  Note that we just have to
 168          * trust the client; root on the client machine can
 169          * claim to be any user.
 170          */
 171         client_user = packet_get_cstring(&ulen);
 172
 173         /* Get the client host key. */
 174         client_host_key = key_new(KEY_RSA1);
 175         bits = packet_get_int();
 176         packet_get_bignum(client_host_key->rsa->e);
 177         packet_get_bignum(client_host_key->rsa->n);
 178
 179         keybits = BN_num_bits(client_host_key->rsa->n);
 180         if (keybits < 0 || bits != (u_int)keybits) {
 181                 verbose("Warning: keysize mismatch for client_host_key: "
 182                     "actual %d, announced %d",
 183                     BN_num_bits(client_host_key->rsa->n), bits);
 184         }
 185         packet_check_eom();
 186
 187         authenticated = auth_rhosts_rsa(authctxt, client_user,
 188             client_host_key);
 189         key_free(client_host_key);
 190
 191         auth_info(authctxt, "ruser %.100s", client_user);
 192
 193         return (authenticated);
 194 }
 195
 196 /*ARGSUSED*/
 197 static int
 198 auth1_process_tis_challenge(Authctxt *authctxt)
 199 {
 200         char *challenge;
 201
 202         if ((challenge = get_challenge(authctxt)) == NULL)
 203                 return (0);
 204
 205         debug("sending challenge '%s'", challenge);
 206         packet_start(SSH_SMSG_AUTH_TIS_CHALLENGE);
 207         packet_put_cstring(challenge);
 208         free(challenge);
 209         packet_send();
 210         packet_write_wait();
 211
 212         return (-1);
 213 }
 214
 215 /*ARGSUSED*/
 216 static int
 217 auth1_process_tis_response(Authctxt *authctxt)
 218 {
 219         int authenticated = 0;
 220         char *response;
 221         u_int dlen;
 222
 223         response = packet_get_string(&dlen);
 224         packet_check_eom();
 225         authenticated = verify_response(authctxt, response);
 226         explicit_bzero(response, dlen);
 227         free(response);
 228
 229         return (authenticated);
 230 }
 231
 232 /*
 233  * read packets, try to authenticate the user and
 234  * return only if authentication is successful
 235  */
 236 static void
 237 do_authloop(Authctxt *authctxt)
 238 {
 239         int authenticated = 0;
 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, 0, "without authentication",
 257                             NULL);
 258                         return;
 259                 }
 260         }
 261
 262         /* Indicate that authentication is needed. */
 263         packet_start(SSH_SMSG_FAILURE);
 264         packet_send();
 265         packet_write_wait();
 266
 267         for (;;) {
 268                 /* default to fail */
 269                 authenticated = 0;
 270
 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);
 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, 0, get_authname(type), NULL);
 356
 357                 free(client_user);
 358                 client_user = NULL;
 359
 360                 if (authenticated)
 361                         return;
 362
 363                 if (++authctxt->failures >= options.max_authtries) {
 364 #ifdef SSH_AUDIT_EVENTS
 365                         PRIVSEP(audit_event(SSH_LOGIN_EXCEED_MAXTRIES));
 366 #endif
 367                         auth_maxtries_exceeded(authctxt);
 368                 }
 369
 370                 packet_start(SSH_SMSG_FAILURE);
 371                 packet_send();
 372                 packet_write_wait();
 373         }
 374 }
 375
 376 /*
 377  * Performs authentication of an incoming connection.  Session key has already
 378  * been exchanged and encryption is enabled.
 379  */
 380 void
 381 do_authentication(Authctxt *authctxt)
 382 {
 383         u_int ulen;
 384         char *user, *style = NULL;
 385
 386         /* Get the name of the user that we wish to log in as. */
 387         packet_read_expect(SSH_CMSG_USER);
 388
 389         /* Get the user name. */
 390         user = packet_get_cstring(&ulen);
 391         packet_check_eom();
 392
 393         if ((style = strchr(user, ':')) != NULL)
 394                 *style++ = '\0';
 395
 396         authctxt->user = user;
 397         authctxt->style = style;
 398
 399         /* Verify that the user is a valid user. */
 400         if ((authctxt->pw = PRIVSEP(getpwnamallow(user))) != NULL)
 401                 authctxt->valid = 1;
 402         else {
 403                 debug("do_authentication: invalid user %s", user);
 404                 authctxt->pw = fakepw();
 405         }
 406
 407         /* Configuration may have changed as a result of Match */
 408         if (options.num_auth_methods != 0)
 409                 fatal("AuthenticationMethods is not supported with SSH "
 410                     "protocol 1");
 411
 412         setproctitle("%s%s", authctxt->valid ? user : "unknown",
 413             use_privsep ? " [net]" : "");
 414
 415 #ifdef USE_PAM
 416         if (options.use_pam)
 417                 PRIVSEP(start_pam(authctxt));
 418 #endif
 419
 420         /*
 421          * If we are not running as root, the user must have the same uid as
 422          * the server.
 423          */
 424 #ifndef HAVE_CYGWIN
 425         if (!use_privsep && getuid() != 0 && authctxt->pw &&
 426             authctxt->pw->pw_uid != getuid())
 427                 packet_disconnect("Cannot change user when server not running as root.");
 428 #endif
 429
 430         /*
 431          * Loop until the user has been authenticated or the connection is
 432          * closed, do_authloop() returns only if authentication is successful
 433          */
 434         do_authloop(authctxt);
 435
 436         /* The user has been authenticated and accepted. */
 437         packet_start(SSH_SMSG_SUCCESS);
 438         packet_send();
 439         packet_write_wait();
 440 }