auth1.c

   1 /* $OpenBSD: auth1.c,v 1.68 2006/07/22 20:48:22 stevesk 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 <string.h>
  18 #include <unistd.h>
  19
  20 #include "xmalloc.h"
  21 #include "rsa.h"
  22 #include "ssh1.h"
  23 #include "packet.h"
  24 #include "buffer.h"
  25 #include "log.h"
  26 #include "servconf.h"
  27 #include "compat.h"
  28 #include "auth.h"
  29 #include "channels.h"
  30 #include "session.h"
  31 #include "uidswap.h"
  32 #include "monitor_wrap.h"
  33 #include "buffer.h"
  34
  35 /* import */
  36 extern ServerOptions options;
  37 extern Buffer loginmsg;
  38
  39 static int auth1_process_password(Authctxt *, char *, size_t);
  40 static int auth1_process_rsa(Authctxt *, char *, size_t);
  41 static int auth1_process_rhosts_rsa(Authctxt *, char *, size_t);
  42 static int auth1_process_tis_challenge(Authctxt *, char *, size_t);
  43 static int auth1_process_tis_response(Authctxt *, char *, size_t);
  44
  45 static char *client_user = NULL;    /* Used to fill in remote user for PAM */
  46
  47 struct AuthMethod1 {
  48         int type;
  49         char *name;
  50         int *enabled;
  51         int (*method)(Authctxt *, char *, size_t);
  52 };
  53
  54 const struct AuthMethod1 auth1_methods[] = {
  55         {
  56                 SSH_CMSG_AUTH_PASSWORD, "password",
  57                 &options.password_authentication, auth1_process_password
  58         },
  59         {
  60                 SSH_CMSG_AUTH_RSA, "rsa",
  61                 &options.rsa_authentication, auth1_process_rsa
  62         },
  63         {
  64                 SSH_CMSG_AUTH_RHOSTS_RSA, "rhosts-rsa",
  65                 &options.rhosts_rsa_authentication, auth1_process_rhosts_rsa
  66         },
  67         {
  68                 SSH_CMSG_AUTH_TIS, "challenge-response",
  69                 &options.challenge_response_authentication,
  70                 auth1_process_tis_challenge
  71         },
  72         {
  73                 SSH_CMSG_AUTH_TIS_RESPONSE, "challenge-response",
  74                 &options.challenge_response_authentication,
  75                 auth1_process_tis_response
  76         },
  77         { -1, NULL, NULL, NULL}
  78 };
  79
  80 static const struct AuthMethod1
  81 *lookup_authmethod1(int type)
  82 {
  83         int i;
  84
  85         for (i = 0; auth1_methods[i].name != NULL; i++)
  86                 if (auth1_methods[i].type == type)
  87                         return (&(auth1_methods[i]));
  88
  89         return (NULL);
  90 }
  91
  92 static char *
  93 get_authname(int type)
  94 {
  95         const struct AuthMethod1 *a;
  96         static char buf[64];
  97
  98         if ((a = lookup_authmethod1(type)) != NULL)
  99                 return (a->name);
 100         snprintf(buf, sizeof(buf), "bad-auth-msg-%d", type);
 101         return (buf);
 102 }
 103
 104 /*ARGSUSED*/
 105 static int
 106 auth1_process_password(Authctxt *authctxt, char *info, size_t infolen)
 107 {
 108         int authenticated = 0;
 109         char *password;
 110         u_int dlen;
 111
 112         /*
 113          * Read user password.  It is in plain text, but was
 114          * transmitted over the encrypted channel so it is
 115          * not visible to an outside observer.
 116          */
 117         password = packet_get_string(&dlen);
 118         packet_check_eom();
 119
 120         /* Try authentication with the password. */
 121         authenticated = PRIVSEP(auth_password(authctxt, password));
 122
 123         memset(password, 0, dlen);
 124         xfree(password);
 125
 126         return (authenticated);
 127 }
 128
 129 /*ARGSUSED*/
 130 static int
 131 auth1_process_rsa(Authctxt *authctxt, char *info, size_t infolen)
 132 {
 133         int authenticated = 0;
 134         BIGNUM *n;
 135
 136         /* RSA authentication requested. */
 137         if ((n = BN_new()) == NULL)
 138                 fatal("do_authloop: BN_new failed");
 139         packet_get_bignum(n);
 140         packet_check_eom();
 141         authenticated = auth_rsa(authctxt, n);
 142         BN_clear_free(n);
 143
 144         return (authenticated);
 145 }
 146
 147 /*ARGSUSED*/
 148 static int
 149 auth1_process_rhosts_rsa(Authctxt *authctxt, char *info, size_t infolen)
 150 {
 151         int keybits, authenticated = 0;
 152         u_int bits;
 153         Key *client_host_key;
 154         u_int ulen;
 155
 156         /*
 157          * Get client user name.  Note that we just have to
 158          * trust the client; root on the client machine can
 159          * claim to be any user.
 160          */
 161         client_user = packet_get_string(&ulen);
 162
 163         /* Get the client host key. */
 164         client_host_key = key_new(KEY_RSA1);
 165         bits = packet_get_int();
 166         packet_get_bignum(client_host_key->rsa->e);
 167         packet_get_bignum(client_host_key->rsa->n);
 168
 169         keybits = BN_num_bits(client_host_key->rsa->n);
 170         if (keybits < 0 || bits != (u_int)keybits) {
 171                 verbose("Warning: keysize mismatch for client_host_key: "
 172                     "actual %d, announced %d",
 173                     BN_num_bits(client_host_key->rsa->n), bits);
 174         }
 175         packet_check_eom();
 176
 177         authenticated = auth_rhosts_rsa(authctxt, client_user,
 178             client_host_key);
 179         key_free(client_host_key);
 180
 181         snprintf(info, infolen, " ruser %.100s", client_user);
 182
 183         return (authenticated);
 184 }
 185
 186 /*ARGSUSED*/
 187 static int
 188 auth1_process_tis_challenge(Authctxt *authctxt, char *info, size_t infolen)
 189 {
 190         char *challenge;
 191
 192         if ((challenge = get_challenge(authctxt)) == NULL)
 193                 return (0);
 194
 195         debug("sending challenge '%s'", challenge);
 196         packet_start(SSH_SMSG_AUTH_TIS_CHALLENGE);
 197         packet_put_cstring(challenge);
 198         xfree(challenge);
 199         packet_send();
 200         packet_write_wait();
 201
 202         return (-1);
 203 }
 204
 205 /*ARGSUSED*/
 206 static int
 207 auth1_process_tis_response(Authctxt *authctxt, char *info, size_t infolen)
 208 {
 209         int authenticated = 0;
 210         char *response;
 211         u_int dlen;
 212
 213         response = packet_get_string(&dlen);
 214         packet_check_eom();
 215         authenticated = verify_response(authctxt, response);
 216         memset(response, 'r', dlen);
 217         xfree(response);
 218
 219         return (authenticated);
 220 }
 221
 222 /*
 223  * read packets, try to authenticate the user and
 224  * return only if authentication is successful
 225  */
 226 static void
 227 do_authloop(Authctxt *authctxt)
 228 {
 229         int authenticated = 0;
 230         char info[1024];
 231         int prev = 0, type = 0;
 232         const struct AuthMethod1 *meth;
 233
 234         debug("Attempting authentication for %s%.100s.",
 235             authctxt->valid ? "" : "invalid user ", authctxt->user);
 236
 237         /* If the user has no password, accept authentication immediately. */
 238         if (options.password_authentication &&
 239 #ifdef KRB5
 240             (!options.kerberos_authentication || options.kerberos_or_local_passwd) &&
 241 #endif
 242             PRIVSEP(auth_password(authctxt, ""))) {
 243 #ifdef USE_PAM
 244                 if (options.use_pam && (PRIVSEP(do_pam_account())))
 245 #endif
 246                 {
 247                         auth_log(authctxt, 1, "without authentication", "");
 248                         return;
 249                 }
 250         }
 251
 252         /* Indicate that authentication is needed. */
 253         packet_start(SSH_SMSG_FAILURE);
 254         packet_send();
 255         packet_write_wait();
 256
 257         for (;;) {
 258                 /* default to fail */
 259                 authenticated = 0;
 260
 261                 info[0] = '\0';
 262
 263                 /* Get a packet from the client. */
 264                 prev = type;
 265                 type = packet_read();
 266
 267                 /*
 268                  * If we started challenge-response authentication but the
 269                  * next packet is not a response to our challenge, release
 270                  * the resources allocated by get_challenge() (which would
 271                  * normally have been released by verify_response() had we
 272                  * received such a response)
 273                  */
 274                 if (prev == SSH_CMSG_AUTH_TIS &&
 275                     type != SSH_CMSG_AUTH_TIS_RESPONSE)
 276                         abandon_challenge_response(authctxt);
 277
 278                 if ((meth = lookup_authmethod1(type)) == NULL) {
 279                         logit("Unknown message during authentication: "
 280                             "type %d", type);
 281                         goto skip;
 282                 }
 283
 284                 if (!*(meth->enabled)) {
 285                         verbose("%s authentication disabled.", meth->name);
 286                         goto skip;
 287                 }
 288
 289                 authenticated = meth->method(authctxt, info, sizeof(info));
 290                 if (authenticated == -1)
 291                         continue; /* "postponed" */
 292
 293 #ifdef BSD_AUTH
 294                 if (authctxt->as) {
 295                         auth_close(authctxt->as);
 296                         authctxt->as = NULL;
 297                 }
 298 #endif
 299                 if (!authctxt->valid && authenticated)
 300                         fatal("INTERNAL ERROR: authenticated invalid user %s",
 301                             authctxt->user);
 302
 303 #ifdef _UNICOS
 304                 if (authenticated && cray_access_denied(authctxt->user)) {
 305                         authenticated = 0;
 306                         fatal("Access denied for user %s.",authctxt->user);
 307                 }
 308 #endif /* _UNICOS */
 309
 310 #ifdef HAVE_CYGWIN
 311                 if (authenticated &&
 312                     !check_nt_auth(type == SSH_CMSG_AUTH_PASSWORD,
 313                     authctxt->pw)) {
 314                         packet_disconnect("Authentication rejected for uid %d.",
 315                             authctxt->pw == NULL ? -1 : authctxt->pw->pw_uid);
 316                         authenticated = 0;
 317                 }
 318 #else
 319                 /* Special handling for root */
 320                 if (authenticated && authctxt->pw->pw_uid == 0 &&
 321                     !auth_root_allowed(meth->name)) {
 322                         authenticated = 0;
 323 # ifdef SSH_AUDIT_EVENTS
 324                         PRIVSEP(audit_event(SSH_LOGIN_ROOT_DENIED));
 325 # endif
 326                 }
 327 #endif
 328
 329 #ifdef USE_PAM
 330                 if (options.use_pam && authenticated &&
 331                     !PRIVSEP(do_pam_account())) {
 332                         char *msg;
 333                         size_t len;
 334
 335                         error("Access denied for user %s by PAM account "
 336                             "configuration", authctxt->user);
 337                         len = buffer_len(&loginmsg);
 338                         buffer_append(&loginmsg, "\0", 1);
 339                         msg = buffer_ptr(&loginmsg);
 340                         /* strip trailing newlines */
 341                         if (len > 0)
 342                                 while (len > 0 && msg[--len] == '\n')
 343                                         msg[len] = '\0';
 344                         else
 345                                 msg = "Access denied.";
 346                         packet_disconnect(msg);
 347                 }
 348 #endif
 349
 350  skip:
 351                 /* Log before sending the reply */
 352                 auth_log(authctxt, authenticated, get_authname(type), info);
 353
 354                 if (client_user != NULL) {
 355                         xfree(client_user);
 356                         client_user = NULL;
 357                 }
 358
 359                 if (authenticated)
 360                         return;
 361
 362                 if (authctxt->failures++ > options.max_authtries) {
 363 #ifdef SSH_AUDIT_EVENTS
 364                         PRIVSEP(audit_event(SSH_LOGIN_EXCEED_MAXTRIES));
 365 #endif
 366                         packet_disconnect(AUTH_FAIL_MSG, authctxt->user);
 367                 }
 368
 369                 packet_start(SSH_SMSG_FAILURE);
 370                 packet_send();
 371                 packet_write_wait();
 372         }
 373 }
 374
 375 /*
 376  * Performs authentication of an incoming connection.  Session key has already
 377  * been exchanged and encryption is enabled.
 378  */
 379 void
 380 do_authentication(Authctxt *authctxt)
 381 {
 382         u_int ulen;
 383         char *user, *style = NULL;
 384
 385         /* Get the name of the user that we wish to log in as. */
 386         packet_read_expect(SSH_CMSG_USER);
 387
 388         /* Get the user name. */
 389         user = packet_get_string(&ulen);
 390         packet_check_eom();
 391
 392         if ((style = strchr(user, ':')) != NULL)
 393                 *style++ = '\0';
 394
 395         authctxt->user = user;
 396         authctxt->style = style;
 397
 398         /* Verify that the user is a valid user. */
 399         if ((authctxt->pw = PRIVSEP(getpwnamallow(user))) != NULL)
 400                 authctxt->valid = 1;
 401         else {
 402                 debug("do_authentication: invalid user %s", user);
 403                 authctxt->pw = fakepw();
 404         }
 405
 406         setproctitle("%s%s", authctxt->valid ? user : "unknown",
 407             use_privsep ? " [net]" : "");
 408
 409 #ifdef USE_PAM
 410         if (options.use_pam)
 411                 PRIVSEP(start_pam(authctxt));
 412 #endif
 413
 414         /*
 415          * If we are not running as root, the user must have the same uid as
 416          * the server.
 417          */
 418 #ifndef HAVE_CYGWIN
 419         if (!use_privsep && getuid() != 0 && authctxt->pw &&
 420             authctxt->pw->pw_uid != getuid())
 421                 packet_disconnect("Cannot change user when server not running as root.");
 422 #endif
 423
 424         /*
 425          * Loop until the user has been authenticated or the connection is
 426          * closed, do_authloop() returns only if authentication is successful
 427          */
 428         do_authloop(authctxt);
 429
 430         /* The user has been authenticated and accepted. */
 431         packet_start(SSH_SMSG_SUCCESS);
 432         packet_send();
 433         packet_write_wait();
 434 }