auth1.c

   1 /* $OpenBSD: auth1.c,v 1.70 2006/08/03 03:34:41 deraadt 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 <stdio.h>
  18 #include <string.h>
  19 #include <unistd.h>
  20 #include <pwd.h>
  21
  22 #include "xmalloc.h"
  23 #include "rsa.h"
  24 #include "ssh1.h"
  25 #include "packet.h"
  26 #include "buffer.h"
  27 #include "log.h"
  28 #include "servconf.h"
  29 #include "compat.h"
  30 #include "key.h"
  31 #include "hostfile.h"
  32 #include "auth.h"
  33 #include "channels.h"
  34 #include "session.h"
  35 #include "uidswap.h"
  36 #ifdef GSSAPI
  37 #include "ssh-gss.h"
  38 #endif
  39 #include "monitor_wrap.h"
  40 #include "buffer.h"
  41
  42 /* import */
  43 extern ServerOptions options;
  44 extern Buffer loginmsg;
  45
  46 static int auth1_process_password(Authctxt *, char *, size_t);
  47 static int auth1_process_rsa(Authctxt *, char *, size_t);
  48 static int auth1_process_rhosts_rsa(Authctxt *, char *, size_t);
  49 static int auth1_process_tis_challenge(Authctxt *, char *, size_t);
  50 static int auth1_process_tis_response(Authctxt *, char *, size_t);
  51
  52 static char *client_user = NULL;    /* Used to fill in remote user for PAM */
  53
  54 struct AuthMethod1 {
  55         int type;
  56         char *name;
  57         int *enabled;
  58         int (*method)(Authctxt *, char *, size_t);
  59 };
  60
  61 const struct AuthMethod1 auth1_methods[] = {
  62         {
  63                 SSH_CMSG_AUTH_PASSWORD, "password",
  64                 &options.password_authentication, auth1_process_password
  65         },
  66         {
  67                 SSH_CMSG_AUTH_RSA, "rsa",
  68                 &options.rsa_authentication, auth1_process_rsa
  69         },
  70         {
  71                 SSH_CMSG_AUTH_RHOSTS_RSA, "rhosts-rsa",
  72                 &options.rhosts_rsa_authentication, auth1_process_rhosts_rsa
  73         },
  74         {
  75                 SSH_CMSG_AUTH_TIS, "challenge-response",
  76                 &options.challenge_response_authentication,
  77                 auth1_process_tis_challenge
  78         },
  79         {
  80                 SSH_CMSG_AUTH_TIS_RESPONSE, "challenge-response",
  81                 &options.challenge_response_authentication,
  82                 auth1_process_tis_response
  83         },
  84         { -1, NULL, NULL, NULL}
  85 };
  86
  87 static const struct AuthMethod1
  88 *lookup_authmethod1(int type)
  89 {
  90         int i;
  91
  92         for (i = 0; auth1_methods[i].name != NULL; i++)
  93                 if (auth1_methods[i].type == type)
  94                         return (&(auth1_methods[i]));
  95
  96         return (NULL);
  97 }
  98
  99 static char *
 100 get_authname(int type)
 101 {
 102         const struct AuthMethod1 *a;
 103         static char buf[64];
 104
 105         if ((a = lookup_authmethod1(type)) != NULL)
 106                 return (a->name);
 107         snprintf(buf, sizeof(buf), "bad-auth-msg-%d", type);
 108         return (buf);
 109 }
 110
 111 /*ARGSUSED*/
 112 static int
 113 auth1_process_password(Authctxt *authctxt, char *info, size_t infolen)
 114 {
 115         int authenticated = 0;
 116         char *password;
 117         u_int dlen;
 118
 119         /*
 120          * Read user password.  It is in plain text, but was
 121          * transmitted over the encrypted channel so it is
 122          * not visible to an outside observer.
 123          */
 124         password = packet_get_string(&dlen);
 125         packet_check_eom();
 126
 127         /* Try authentication with the password. */
 128         authenticated = PRIVSEP(auth_password(authctxt, password));
 129
 130         memset(password, 0, dlen);
 131         xfree(password);
 132
 133         return (authenticated);
 134 }
 135
 136 /*ARGSUSED*/
 137 static int
 138 auth1_process_rsa(Authctxt *authctxt, char *info, size_t infolen)
 139 {
 140         int authenticated = 0;
 141         BIGNUM *n;
 142
 143         /* RSA authentication requested. */
 144         if ((n = BN_new()) == NULL)
 145                 fatal("do_authloop: BN_new failed");
 146         packet_get_bignum(n);
 147         packet_check_eom();
 148         authenticated = auth_rsa(authctxt, n);
 149         BN_clear_free(n);
 150
 151         return (authenticated);
 152 }
 153
 154 /*ARGSUSED*/
 155 static int
 156 auth1_process_rhosts_rsa(Authctxt *authctxt, char *info, size_t infolen)
 157 {
 158         int keybits, authenticated = 0;
 159         u_int bits;
 160         Key *client_host_key;
 161         u_int ulen;
 162
 163         /*
 164          * Get client user name.  Note that we just have to
 165          * trust the client; root on the client machine can
 166          * claim to be any user.
 167          */
 168         client_user = packet_get_string(&ulen);
 169
 170         /* Get the client host key. */
 171         client_host_key = key_new(KEY_RSA1);
 172         bits = packet_get_int();
 173         packet_get_bignum(client_host_key->rsa->e);
 174         packet_get_bignum(client_host_key->rsa->n);
 175
 176         keybits = BN_num_bits(client_host_key->rsa->n);
 177         if (keybits < 0 || bits != (u_int)keybits) {
 178                 verbose("Warning: keysize mismatch for client_host_key: "
 179                     "actual %d, announced %d",
 180                     BN_num_bits(client_host_key->rsa->n), bits);
 181         }
 182         packet_check_eom();
 183
 184         authenticated = auth_rhosts_rsa(authctxt, client_user,
 185             client_host_key);
 186         key_free(client_host_key);
 187
 188         snprintf(info, infolen, " ruser %.100s", client_user);
 189
 190         return (authenticated);
 191 }
 192
 193 /*ARGSUSED*/
 194 static int
 195 auth1_process_tis_challenge(Authctxt *authctxt, char *info, size_t infolen)
 196 {
 197         char *challenge;
 198
 199         if ((challenge = get_challenge(authctxt)) == NULL)
 200                 return (0);
 201
 202         debug("sending challenge '%s'", challenge);
 203         packet_start(SSH_SMSG_AUTH_TIS_CHALLENGE);
 204         packet_put_cstring(challenge);
 205         xfree(challenge);
 206         packet_send();
 207         packet_write_wait();
 208
 209         return (-1);
 210 }
 211
 212 /*ARGSUSED*/
 213 static int
 214 auth1_process_tis_response(Authctxt *authctxt, char *info, size_t infolen)
 215 {
 216         int authenticated = 0;
 217         char *response;
 218         u_int dlen;
 219
 220         response = packet_get_string(&dlen);
 221         packet_check_eom();
 222         authenticated = verify_response(authctxt, response);
 223         memset(response, 'r', dlen);
 224         xfree(response);
 225
 226         return (authenticated);
 227 }
 228
 229 /*
 230  * read packets, try to authenticate the user and
 231  * return only if authentication is successful
 232  */
 233 static void
 234 do_authloop(Authctxt *authctxt)
 235 {
 236         int authenticated = 0;
 237         char info[1024];
 238         int prev = 0, type = 0;
 239         const struct AuthMethod1 *meth;
 240
 241         debug("Attempting authentication for %s%.100s.",
 242             authctxt->valid ? "" : "invalid user ", authctxt->user);
 243
 244         /* If the user has no password, accept authentication immediately. */
 245         if (options.password_authentication &&
 246 #ifdef KRB5
 247             (!options.kerberos_authentication || options.kerberos_or_local_passwd) &&
 248 #endif
 249             PRIVSEP(auth_password(authctxt, ""))) {
 250 #ifdef USE_PAM
 251                 if (options.use_pam && (PRIVSEP(do_pam_account())))
 252 #endif
 253                 {
 254                         auth_log(authctxt, 1, "without authentication", "");
 255                         return;
 256                 }
 257         }
 258
 259         /* Indicate that authentication is needed. */
 260         packet_start(SSH_SMSG_FAILURE);
 261         packet_send();
 262         packet_write_wait();
 263
 264         for (;;) {
 265                 /* default to fail */
 266                 authenticated = 0;
 267
 268                 info[0] = '\0';
 269
 270                 /* Get a packet from the client. */
 271                 prev = type;
 272                 type = packet_read();
 273
 274                 /*
 275                  * If we started challenge-response authentication but the
 276                  * next packet is not a response to our challenge, release
 277                  * the resources allocated by get_challenge() (which would
 278                  * normally have been released by verify_response() had we
 279                  * received such a response)
 280                  */
 281                 if (prev == SSH_CMSG_AUTH_TIS &&
 282                     type != SSH_CMSG_AUTH_TIS_RESPONSE)
 283                         abandon_challenge_response(authctxt);
 284
 285                 if ((meth = lookup_authmethod1(type)) == NULL) {
 286                         logit("Unknown message during authentication: "
 287                             "type %d", type);
 288                         goto skip;
 289                 }
 290
 291                 if (!*(meth->enabled)) {
 292                         verbose("%s authentication disabled.", meth->name);
 293                         goto skip;
 294                 }
 295
 296                 authenticated = meth->method(authctxt, info, sizeof(info));
 297                 if (authenticated == -1)
 298                         continue; /* "postponed" */
 299
 300 #ifdef BSD_AUTH
 301                 if (authctxt->as) {
 302                         auth_close(authctxt->as);
 303                         authctxt->as = NULL;
 304                 }
 305 #endif
 306                 if (!authctxt->valid && authenticated)
 307                         fatal("INTERNAL ERROR: authenticated invalid user %s",
 308                             authctxt->user);
 309
 310 #ifdef _UNICOS
 311                 if (authenticated && cray_access_denied(authctxt->user)) {
 312                         authenticated = 0;
 313                         fatal("Access denied for user %s.",authctxt->user);
 314                 }
 315 #endif /* _UNICOS */
 316
 317 #ifdef HAVE_CYGWIN
 318                 if (authenticated &&
 319                     !check_nt_auth(type == SSH_CMSG_AUTH_PASSWORD,
 320                     authctxt->pw)) {
 321                         packet_disconnect("Authentication rejected for uid %d.",
 322                             authctxt->pw == NULL ? -1 : authctxt->pw->pw_uid);
 323                         authenticated = 0;
 324                 }
 325 #else
 326                 /* Special handling for root */
 327                 if (authenticated && authctxt->pw->pw_uid == 0 &&
 328                     !auth_root_allowed(meth->name)) {
 329                         authenticated = 0;
 330 # ifdef SSH_AUDIT_EVENTS
 331                         PRIVSEP(audit_event(SSH_LOGIN_ROOT_DENIED));
 332 # endif
 333                 }
 334 #endif
 335
 336 #ifdef USE_PAM
 337                 if (options.use_pam && authenticated &&
 338                     !PRIVSEP(do_pam_account())) {
 339                         char *msg;
 340                         size_t len;
 341
 342                         error("Access denied for user %s by PAM account "
 343                             "configuration", authctxt->user);
 344                         len = buffer_len(&loginmsg);
 345                         buffer_append(&loginmsg, "\0", 1);
 346                         msg = buffer_ptr(&loginmsg);
 347                         /* strip trailing newlines */
 348                         if (len > 0)
 349                                 while (len > 0 && msg[--len] == '\n')
 350                                         msg[len] = '\0';
 351                         else
 352                                 msg = "Access denied.";
 353                         packet_disconnect(msg);
 354                 }
 355 #endif
 356
 357  skip:
 358                 /* Log before sending the reply */
 359                 auth_log(authctxt, authenticated, get_authname(type), info);
 360
 361                 if (client_user != NULL) {
 362                         xfree(client_user);
 363                         client_user = NULL;
 364                 }
 365
 366                 if (authenticated)
 367                         return;
 368
 369                 if (authctxt->failures++ > options.max_authtries) {
 370 #ifdef SSH_AUDIT_EVENTS
 371                         PRIVSEP(audit_event(SSH_LOGIN_EXCEED_MAXTRIES));
 372 #endif
 373                         packet_disconnect(AUTH_FAIL_MSG, authctxt->user);
 374                 }
 375
 376                 packet_start(SSH_SMSG_FAILURE);
 377                 packet_send();
 378                 packet_write_wait();
 379         }
 380 }
 381
 382 /*
 383  * Performs authentication of an incoming connection.  Session key has already
 384  * been exchanged and encryption is enabled.
 385  */
 386 void
 387 do_authentication(Authctxt *authctxt)
 388 {
 389         u_int ulen;
 390         char *user, *style = NULL;
 391
 392         /* Get the name of the user that we wish to log in as. */
 393         packet_read_expect(SSH_CMSG_USER);
 394
 395         /* Get the user name. */
 396         user = packet_get_string(&ulen);
 397         packet_check_eom();
 398
 399         if ((style = strchr(user, ':')) != NULL)
 400                 *style++ = '\0';
 401
 402         authctxt->user = user;
 403         authctxt->style = style;
 404
 405         /* Verify that the user is a valid user. */
 406         if ((authctxt->pw = PRIVSEP(getpwnamallow(user))) != NULL)
 407                 authctxt->valid = 1;
 408         else {
 409                 debug("do_authentication: invalid user %s", user);
 410                 authctxt->pw = fakepw();
 411         }
 412
 413         setproctitle("%s%s", authctxt->valid ? user : "unknown",
 414             use_privsep ? " [net]" : "");
 415
 416 #ifdef USE_PAM
 417         if (options.use_pam)
 418                 PRIVSEP(start_pam(authctxt));
 419 #endif
 420
 421         /*
 422          * If we are not running as root, the user must have the same uid as
 423          * the server.
 424          */
 425 #ifndef HAVE_CYGWIN
 426         if (!use_privsep && getuid() != 0 && authctxt->pw &&
 427             authctxt->pw->pw_uid != getuid())
 428                 packet_disconnect("Cannot change user when server not running as root.");
 429 #endif
 430
 431         /*
 432          * Loop until the user has been authenticated or the connection is
 433          * closed, do_authloop() returns only if authentication is successful
 434          */
 435         do_authloop(authctxt);
 436
 437         /* The user has been authenticated and accepted. */
 438         packet_start(SSH_SMSG_SUCCESS);
 439         packet_send();
 440         packet_write_wait();
 441 }