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