crypto/external/bsd/openssh/dist/auth1.c

   1 /*      $NetBSD$        */
   2 /* $OpenBSD: auth1.c,v 1.73 2008/07/04 23:30:16 djm Exp $ */
   3 /*
   4  * Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
   5  *                    All rights reserved
   6  *
   7  * As far as I am concerned, the code I have written for this software
   8  * can be used freely for any purpose.  Any derived versions of this
   9  * software must be clearly marked as such, and if the derived work is
  10  * incompatible with the protocol description in the RFC file, it must be
  11  * called by a name other than "ssh" or "Secure Shell".
  12  */
  13
  14 #include "includes.h"
  15 __RCSID("$NetBSD: auth1.c,v 1.33 2009/02/16 20:53:54 christos Exp $");
  16 #include <sys/types.h>
  17 #include <sys/queue.h>
  18
  19 #include <stdio.h>
  20 #include <string.h>
  21 #include <unistd.h>
  22 #include <pwd.h>
  23
  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 #if defined(KRB4) || defined(KRB5)
  54 static int auth1_process_kerberos(Authctxt *, char *, size_t);
  55 #endif
  56
  57 struct AuthMethod1 {
  58         int type;
  59         char *name;
  60         int *enabled;
  61         int (*method)(Authctxt *, char *, size_t);
  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 #if defined(KRB4) || defined(KRB5)
  88         {
  89                 SSH_CMSG_AUTH_KERBEROS, "kerberos",
  90                 &options.kerberos_authentication,
  91                 auth1_process_kerberos
  92         },
  93 #endif /* KRB4 || KRB5 */
  94         { -1, NULL, NULL, NULL}
  95 };
  96
  97 static const struct AuthMethod1
  98 *lookup_authmethod1(int type)
  99 {
 100         int i;
 101
 102         for (i = 0; auth1_methods[i].name != NULL; i++)
 103                 if (auth1_methods[i].type == type)
 104                         return (&(auth1_methods[i]));
 105
 106         return (NULL);
 107 }
 108
 109 static char *
 110 get_authname(int type)
 111 {
 112         const struct AuthMethod1 *a;
 113         static char buf[64];
 114
 115         if ((a = lookup_authmethod1(type)) != NULL)
 116                 return (a->name);
 117         snprintf(buf, sizeof(buf), "bad-auth-msg-%d", type);
 118         return (buf);
 119 }
 120
 121 /*ARGSUSED*/
 122 static int
 123 auth1_process_password(Authctxt *authctxt, char *info, size_t infolen)
 124 {
 125         int authenticated = 0;
 126         char *password;
 127         u_int dlen;
 128
 129         /*
 130          * Read user password.  It is in plain text, but was
 131          * transmitted over the encrypted channel so it is
 132          * not visible to an outside observer.
 133          */
 134         password = packet_get_string(&dlen);
 135         packet_check_eom();
 136
 137         /* Try authentication with the password. */
 138         authenticated = PRIVSEP(auth_password(authctxt, password));
 139
 140         memset(password, 0, dlen);
 141         xfree(password);
 142
 143         return (authenticated);
 144 }
 145
 146 #if defined(KRB4) || defined(KRB5)
 147 static int
 148 auth1_process_kerberos(Authctxt *authctxt, char *info, size_t infolen)
 149 {
 150         int authenticated = 0;
 151         u_int dlen;
 152         char *client_user;
 153         char *kdata = packet_get_string(&dlen);
 154         packet_check_eom();
 155
 156         if (kdata[0] == 4) { /* KRB_PROT_VERSION */
 157 #ifdef KRB4
 158                 KTEXT_ST tkt, reply;
 159                 tkt.length = dlen;
 160                 if (tkt.length < MAX_KTXT_LEN)
 161                         memcpy(tkt.dat, kdata, tkt.length);
 162
 163                 if (PRIVSEP(auth_krb4(authctxt, &tkt, &client_user, &reply))) {
 164                         authenticated = 1;
 165                         snprintf(info, sizeof(info), " tktuser %.100s",
 166                             client_user);
 167
 168                         packet_start(SSH_SMSG_AUTH_KERBEROS_RESPONSE);
 169                         packet_put_string((char *)
 170                             reply.dat, reply.length);
 171                         packet_send();
 172                         packet_write_wait();
 173
 174                         xfree(client_user);
 175                 }
 176 #endif /* KRB4 */
 177         } else {
 178 #ifdef KRB5
 179                 krb5_data tkt, reply;
 180                 tkt.length = dlen;
 181                 tkt.data = kdata;
 182
 183                 if (PRIVSEP(auth_krb5(authctxt, &tkt, &client_user, &reply))) {
 184                         authenticated = 1;
 185                         snprintf(info, sizeof(info), " tktuser %.100s",
 186                             client_user);
 187
 188                         /* Send response to client */
 189                         packet_start(SSH_SMSG_AUTH_KERBEROS_RESPONSE);
 190                         packet_put_string((char *)reply.data, reply.length);
 191                         packet_send();
 192                         packet_write_wait();
 193
 194                         if (reply.length)
 195                                 xfree(reply.data);
 196                         xfree(client_user);
 197                 }
 198 #endif /* KRB5 */
 199         }
 200         xfree(kdata);
 201         return authenticated;
 202 }
 203 #endif /* KRB4 || KRB5 */
 204
 205 /*ARGSUSED*/
 206 static int
 207 auth1_process_rhosts_rsa(Authctxt *authctxt, char *info, size_t infolen)
 208 {
 209         int keybits, authenticated = 0;
 210         u_int bits;
 211         char *client_user;
 212         Key *client_host_key;
 213         u_int ulen;
 214
 215         /*
 216          * Get client user name.  Note that we just have to
 217          * trust the client; root on the client machine can
 218          * claim to be any user.
 219          */
 220         client_user = packet_get_string(&ulen);
 221
 222         /* Get the client host key. */
 223         client_host_key = key_new(KEY_RSA1);
 224         bits = packet_get_int();
 225         packet_get_bignum(client_host_key->rsa->e);
 226         packet_get_bignum(client_host_key->rsa->n);
 227
 228         keybits = BN_num_bits(client_host_key->rsa->n);
 229         if (keybits < 0 || bits != (u_int)keybits) {
 230                 verbose("Warning: keysize mismatch for client_host_key: "
 231                     "actual %d, announced %d",
 232                     BN_num_bits(client_host_key->rsa->n), bits);
 233         }
 234         packet_check_eom();
 235
 236         authenticated = auth_rhosts_rsa(authctxt, client_user,
 237             client_host_key);
 238         key_free(client_host_key);
 239
 240         snprintf(info, infolen, " ruser %.100s", client_user);
 241         xfree(client_user);
 242
 243         return (authenticated);
 244 }
 245
 246 /*ARGSUSED*/
 247 static int
 248 auth1_process_rsa(Authctxt *authctxt, char *info, size_t infolen)
 249 {
 250         int authenticated = 0;
 251         BIGNUM *n;
 252
 253         /* RSA authentication requested. */
 254         if ((n = BN_new()) == NULL)
 255                 fatal("do_authloop: BN_new failed");
 256         packet_get_bignum(n);
 257         packet_check_eom();
 258         authenticated = auth_rsa(authctxt, n);
 259         BN_clear_free(n);
 260
 261         return (authenticated);
 262 }
 263
 264 /*ARGSUSED*/
 265 static int
 266 auth1_process_tis_challenge(Authctxt *authctxt, char *info, size_t infolen)
 267 {
 268         char *challenge;
 269
 270         if ((challenge = get_challenge(authctxt)) == NULL)
 271                 return (0);
 272
 273         debug("sending challenge '%s'", challenge);
 274         packet_start(SSH_SMSG_AUTH_TIS_CHALLENGE);
 275         packet_put_cstring(challenge);
 276         xfree(challenge);
 277         packet_send();
 278         packet_write_wait();
 279
 280         return (-1);
 281 }
 282
 283 /*ARGSUSED*/
 284 static int
 285 auth1_process_tis_response(Authctxt *authctxt, char *info, size_t infolen)
 286 {
 287         int authenticated = 0;
 288         char *response;
 289         u_int dlen;
 290
 291         response = packet_get_string(&dlen);
 292         packet_check_eom();
 293         authenticated = verify_response(authctxt, response);
 294         memset(response, 'r', dlen);
 295         xfree(response);
 296
 297         return (authenticated);
 298 }
 299
 300 /*
 301  * read packets, try to authenticate the user and
 302  * return only if authentication is successful
 303  */
 304 static void
 305 do_authloop(Authctxt *authctxt)
 306 {
 307         int authenticated = 0;
 308         char info[1024];
 309         int type = 0;
 310         const struct AuthMethod1 *meth;
 311
 312         debug("Attempting authentication for %s%.100s.",
 313             authctxt->valid ? "" : "invalid user ", authctxt->user);
 314
 315         /* If the user has no password, accept authentication immediately. */
 316         if (options.password_authentication &&
 317 #if defined(KRB4) || defined(KRB5)
 318             (!options.kerberos_authentication || options.kerberos_or_local_passwd) &&
 319 #endif
 320             PRIVSEP(auth_password(authctxt, ""))) {
 321 #ifdef USE_PAM
 322                 if (options.use_pam && PRIVSEP(do_pam_account()))
 323 #endif
 324                 {
 325                         auth_log(authctxt, 1, "without authentication", "");
 326                         return;
 327                 }
 328                 return;
 329         }
 330
 331         /* Indicate that authentication is needed. */
 332         packet_start(SSH_SMSG_FAILURE);
 333         packet_send();
 334         packet_write_wait();
 335
 336         for (;;) {
 337                 /* default to fail */
 338                 authenticated = 0;
 339
 340                 info[0] = '\0';
 341
 342                 /* Get a packet from the client. */
 343                 type = packet_read();
 344                 if (authctxt->failures >= options.max_authtries)
 345                         goto skip;
 346                 if ((meth = lookup_authmethod1(type)) == NULL) {
 347                         logit("Unknown message during authentication: "
 348                             "type %d", type);
 349                         goto skip;
 350                 }
 351
 352                 if (!*(meth->enabled)) {
 353                         verbose("%s authentication disabled.", meth->name);
 354                         goto skip;
 355                 }
 356
 357                 authenticated = meth->method(authctxt, info, sizeof(info));
 358                 if (authenticated == -1)
 359                         continue; /* "postponed" */
 360
 361 #ifdef BSD_AUTH
 362                 if (authctxt->as) {
 363                         auth_close(authctxt->as);
 364                         authctxt->as = NULL;
 365                 }
 366 #endif
 367                 if (!authctxt->valid && authenticated)
 368                         fatal("INTERNAL ERROR: authenticated invalid user %s",
 369                             authctxt->user);
 370
 371                 /* Special handling for root */
 372                 if (authenticated && authctxt->pw->pw_uid == 0 &&
 373                     !auth_root_allowed(meth->name))
 374                         authenticated = 0;
 375
 376 #ifdef USE_PAM
 377                 if (options.use_pam && authenticated &&
 378                     !PRIVSEP(do_pam_account())) {
 379                         char *msg;
 380                         size_t len;
 381
 382                         error("Access denied for user %s by PAM account "
 383                             "configuration", authctxt->user);
 384                         len = buffer_len(&loginmsg);
 385                         buffer_append(&loginmsg, "\0", 1);
 386                         msg = buffer_ptr(&loginmsg);
 387                         /* strip trailing newlines */
 388                         if (len > 0)
 389                                 while (len > 0 && msg[--len] == '\n')
 390                                         msg[len] = '\0';
 391                         else
 392                                 msg = "Access denied.";
 393                         packet_disconnect(msg);
 394                 }
 395 #endif
 396
 397  skip:
 398                 /* Log before sending the reply */
 399                 auth_log(authctxt, authenticated, get_authname(type), info);
 400
 401                 if (authenticated)
 402                         return;
 403
 404                 if (++authctxt->failures >= options.max_authtries)
 405                         packet_disconnect(AUTH_FAIL_MSG, authctxt->user);
 406
 407                 packet_start(SSH_SMSG_FAILURE);
 408                 packet_send();
 409                 packet_write_wait();
 410         }
 411 }
 412
 413 /*
 414  * Performs authentication of an incoming connection.  Session key has already
 415  * been exchanged and encryption is enabled.
 416  */
 417 void
 418 do_authentication(Authctxt *authctxt)
 419 {
 420         u_int ulen;
 421         char *user, *style = NULL;
 422
 423         /* Get the name of the user that we wish to log in as. */
 424         packet_read_expect(SSH_CMSG_USER);
 425
 426         /* Get the user name. */
 427         user = packet_get_string(&ulen);
 428         packet_check_eom();
 429
 430         if ((style = strchr(user, ':')) != NULL)
 431                 *style++ = '\0';
 432
 433 #ifdef KRB5
 434         /* XXX - SSH.com Kerberos v5 braindeath. */
 435         if ((datafellows & SSH_BUG_K5USER) &&
 436             options.kerberos_authentication) {
 437                 char *p;
 438                 if ((p = strchr(user, '@')) != NULL)
 439                         *p = '\0';
 440         }
 441 #endif
 442
 443         authctxt->user = user;
 444         authctxt->style = style;
 445
 446         /* Verify that the user is a valid user. */
 447         if ((authctxt->pw = PRIVSEP(getpwnamallow(user))) != NULL)
 448                 authctxt->valid = 1;
 449         else {
 450                 debug("do_authentication: invalid user %s", user);
 451                 authctxt->pw = fakepw();
 452         }
 453
 454         setproctitle("%s%s", authctxt->valid ? user : "unknown",
 455             use_privsep ? " [net]" : "");
 456
 457 #ifdef USE_PAM
 458         if (options.use_pam)
 459                 PRIVSEP(start_pam(authctxt));
 460 #endif
 461
 462         /*
 463          * If we are not running as root, the user must have the same uid as
 464          * the server.
 465          */
 466         if (!use_privsep && getuid() != 0 && authctxt->pw &&
 467             authctxt->pw->pw_uid != getuid())
 468                 packet_disconnect("Cannot change user when server not running as root.");
 469
 470         /*
 471          * Loop until the user has been authenticated or the connection is
 472          * closed, do_authloop() returns only if authentication is successful
 473          */
 474         do_authloop(authctxt);
 475
 476         /* The user has been authenticated and accepted. */
 477         packet_start(SSH_SMSG_SUCCESS);
 478         packet_send();
 479         packet_write_wait();
 480 }