auth1.c

   1 /* $OpenBSD: auth1.c,v 1.69 2006/08/01 23:22:47 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 <stdio.h>
  18 #include <string.h>
  19 #include <unistd.h>
  20
  21 #include "xmalloc.h"
  22 #include "rsa.h"
  23 #include "ssh1.h"
  24 #include "packet.h"
  25 #include "buffer.h"
  26 #include "log.h"
  27 #include "servconf.h"
  28 #include "compat.h"
  29 #include "auth.h"
  30 #include "channels.h"
  31 #include "session.h"
  32 #include "uidswap.h"
  33 #include "monitor_wrap.h"
  34 #include "buffer.h"
  35
  36 /* import */
  37 extern ServerOptions options;
  38 extern Buffer loginmsg;
  39
  40 static int auth1_process_password(Authctxt *, char *, size_t);
  41 static int auth1_process_rsa(Authctxt *, char *, size_t);
  42 static int auth1_process_rhosts_rsa(Authctxt *, char *, size_t);
  43 static int auth1_process_tis_challenge(Authctxt *, char *, size_t);
  44 static int auth1_process_tis_response(Authctxt *, char *, size_t);
  45
  46 static char *client_user = NULL;    /* Used to fill in remote user for PAM */
  47
  48 struct AuthMethod1 {
  49         int type;
  50         char *name;
  51         int *enabled;
  52         int (*method)(Authctxt *, char *, size_t);
  53 };
  54
  55 const struct AuthMethod1 auth1_methods[] = {
  56         {
  57                 SSH_CMSG_AUTH_PASSWORD, "password",
  58                 &options.password_authentication, auth1_process_password
  59         },
  60         {
  61                 SSH_CMSG_AUTH_RSA, "rsa",
  62                 &options.rsa_authentication, auth1_process_rsa
  63         },
  64         {
  65                 SSH_CMSG_AUTH_RHOSTS_RSA, "rhosts-rsa",
  66                 &options.rhosts_rsa_authentication, auth1_process_rhosts_rsa
  67         },
  68         {
  69                 SSH_CMSG_AUTH_TIS, "challenge-response",
  70                 &options.challenge_response_authentication,
  71                 auth1_process_tis_challenge
  72         },
  73         {
  74                 SSH_CMSG_AUTH_TIS_RESPONSE, "challenge-response",
  75                 &options.challenge_response_authentication,
  76                 auth1_process_tis_response
  77         },
  78         { -1, NULL, NULL, NULL}
  79 };
  80
  81 static const struct AuthMethod1
  82 *lookup_authmethod1(int type)
  83 {
  84         int i;
  85
  86         for (i = 0; auth1_methods[i].name != NULL; i++)
  87                 if (auth1_methods[i].type == type)
  88                         return (&(auth1_methods[i]));
  89
  90         return (NULL);
  91 }
  92
  93 static char *
  94 get_authname(int type)
  95 {
  96         const struct AuthMethod1 *a;
  97         static char buf[64];
  98
  99         if ((a = lookup_authmethod1(type)) != NULL)
 100                 return (a->name);
 101         snprintf(buf, sizeof(buf), "bad-auth-msg-%d", type);
 102         return (buf);
 103 }
 104
 105 /*ARGSUSED*/
 106 static int
 107 auth1_process_password(Authctxt *authctxt, char *info, size_t infolen)
 108 {
 109         int authenticated = 0;
 110         char *password;
 111         u_int dlen;
 112
 113         /*
 114          * Read user password.  It is in plain text, but was
 115          * transmitted over the encrypted channel so it is
 116          * not visible to an outside observer.
 117          */
 118         password = packet_get_string(&dlen);
 119         packet_check_eom();
 120
 121         /* Try authentication with the password. */
 122         authenticated = PRIVSEP(auth_password(authctxt, password));
 123
 124         memset(password, 0, dlen);
 125         xfree(password);
 126
 127         return (authenticated);
 128 }
 129
 130 /*ARGSUSED*/
 131 static int
 132 auth1_process_rsa(Authctxt *authctxt, char *info, size_t infolen)
 133 {
 134         int authenticated = 0;
 135         BIGNUM *n;
 136
 137         /* RSA authentication requested. */
 138         if ((n = BN_new()) == NULL)
 139                 fatal("do_authloop: BN_new failed");
 140         packet_get_bignum(n);
 141         packet_check_eom();
 142         authenticated = auth_rsa(authctxt, n);
 143         BN_clear_free(n);
 144
 145         return (authenticated);
 146 }
 147
 148 /*ARGSUSED*/
 149 static int
 150 auth1_process_rhosts_rsa(Authctxt *authctxt, char *info, size_t infolen)
 151 {
 152         int keybits, authenticated = 0;
 153         u_int bits;
 154         Key *client_host_key;
 155         u_int ulen;
 156
 157         /*
 158          * Get client user name.  Note that we just have to
 159          * trust the client; root on the client machine can
 160          * claim to be any user.
 161          */
 162         client_user = packet_get_string(&ulen);
 163
 164         /* Get the client host key. */
 165         client_host_key = key_new(KEY_RSA1);
 166         bits = packet_get_int();
 167         packet_get_bignum(client_host_key->rsa->e);
 168         packet_get_bignum(client_host_key->rsa->n);
 169
 170         keybits = BN_num_bits(client_host_key->rsa->n);
 171         if (keybits < 0 || bits != (u_int)keybits) {
 172                 verbose("Warning: keysize mismatch for client_host_key: "
 173                     "actual %d, announced %d",
 174                     BN_num_bits(client_host_key->rsa->n), bits);
 175         }
 176         packet_check_eom();
 177
 178         authenticated = auth_rhosts_rsa(authctxt, client_user,
 179             client_host_key);
 180         key_free(client_host_key);
 181
 182         snprintf(info, infolen, " ruser %.100s", client_user);
 183
 184         return (authenticated);
 185 }
 186
 187 /*ARGSUSED*/
 188 static int
 189 auth1_process_tis_challenge(Authctxt *authctxt, char *info, size_t infolen)
 190 {
 191         char *challenge;
 192
 193         if ((challenge = get_challenge(authctxt)) == NULL)
 194                 return (0);
 195
 196         debug("sending challenge '%s'", challenge);
 197         packet_start(SSH_SMSG_AUTH_TIS_CHALLENGE);
 198         packet_put_cstring(challenge);
 199         xfree(challenge);
 200         packet_send();
 201         packet_write_wait();
 202
 203         return (-1);
 204 }
 205
 206 /*ARGSUSED*/
 207 static int
 208 auth1_process_tis_response(Authctxt *authctxt, char *info, size_t infolen)
 209 {
 210         int authenticated = 0;
 211         char *response;
 212         u_int dlen;
 213
 214         response = packet_get_string(&dlen);
 215         packet_check_eom();
 216         authenticated = verify_response(authctxt, response);
 217         memset(response, 'r', dlen);
 218         xfree(response);
 219
 220         return (authenticated);
 221 }
 222
 223 /*
 224  * read packets, try to authenticate the user and
 225  * return only if authentication is successful
 226  */
 227 static void
 228 do_authloop(Authctxt *authctxt)
 229 {
 230         int authenticated = 0;
 231         char info[1024];
 232         int prev = 0, type = 0;
 233         const struct AuthMethod1 *meth;
 234
 235         debug("Attempting authentication for %s%.100s.",
 236             authctxt->valid ? "" : "invalid user ", authctxt->user);
 237
 238         /* If the user has no password, accept authentication immediately. */
 239         if (options.password_authentication &&
 240 #ifdef KRB5
 241             (!options.kerberos_authentication || options.kerberos_or_local_passwd) &&
 242 #endif
 243             PRIVSEP(auth_password(authctxt, ""))) {
 244 #ifdef USE_PAM
 245                 if (options.use_pam && (PRIVSEP(do_pam_account())))
 246 #endif
 247                 {
 248                         auth_log(authctxt, 1, "without authentication", "");
 249                         return;
 250                 }
 251         }
 252
 253         /* Indicate that authentication is needed. */
 254         packet_start(SSH_SMSG_FAILURE);
 255         packet_send();
 256         packet_write_wait();
 257
 258         for (;;) {
 259                 /* default to fail */
 260                 authenticated = 0;
 261
 262                 info[0] = '\0';
 263
 264                 /* Get a packet from the client. */
 265                 prev = type;
 266                 type = packet_read();
 267
 268                 /*
 269                  * If we started challenge-response authentication but the
 270                  * next packet is not a response to our challenge, release
 271                  * the resources allocated by get_challenge() (which would
 272                  * normally have been released by verify_response() had we
 273                  * received such a response)
 274                  */
 275                 if (prev == SSH_CMSG_AUTH_TIS &&
 276                     type != SSH_CMSG_AUTH_TIS_RESPONSE)
 277                         abandon_challenge_response(authctxt);
 278
 279                 if ((meth = lookup_authmethod1(type)) == NULL) {
 280                         logit("Unknown message during authentication: "
 281                             "type %d", type);
 282                         goto skip;
 283                 }
 284
 285                 if (!*(meth->enabled)) {
 286                         verbose("%s authentication disabled.", meth->name);
 287                         goto skip;
 288                 }
 289
 290                 authenticated = meth->method(authctxt, info, sizeof(info));
 291                 if (authenticated == -1)
 292                         continue; /* "postponed" */
 293
 294 #ifdef BSD_AUTH
 295                 if (authctxt->as) {
 296                         auth_close(authctxt->as);
 297                         authctxt->as = NULL;
 298                 }
 299 #endif
 300                 if (!authctxt->valid && authenticated)
 301                         fatal("INTERNAL ERROR: authenticated invalid user %s",
 302                             authctxt->user);
 303
 304 #ifdef _UNICOS
 305                 if (authenticated && cray_access_denied(authctxt->user)) {
 306                         authenticated = 0;
 307                         fatal("Access denied for user %s.",authctxt->user);
 308                 }
 309 #endif /* _UNICOS */
 310
 311 #ifdef HAVE_CYGWIN
 312                 if (authenticated &&
 313                     !check_nt_auth(type == SSH_CMSG_AUTH_PASSWORD,
 314                     authctxt->pw)) {
 315                         packet_disconnect("Authentication rejected for uid %d.",
 316                             authctxt->pw == NULL ? -1 : authctxt->pw->pw_uid);
 317                         authenticated = 0;
 318                 }
 319 #else
 320                 /* Special handling for root */
 321                 if (authenticated && authctxt->pw->pw_uid == 0 &&
 322                     !auth_root_allowed(meth->name)) {
 323                         authenticated = 0;
 324 # ifdef SSH_AUDIT_EVENTS
 325                         PRIVSEP(audit_event(SSH_LOGIN_ROOT_DENIED));
 326 # endif
 327                 }
 328 #endif
 329
 330 #ifdef USE_PAM
 331                 if (options.use_pam && authenticated &&
 332                     !PRIVSEP(do_pam_account())) {
 333                         char *msg;
 334                         size_t len;
 335
 336                         error("Access denied for user %s by PAM account "
 337                             "configuration", authctxt->user);
 338                         len = buffer_len(&loginmsg);
 339                         buffer_append(&loginmsg, "\0", 1);
 340                         msg = buffer_ptr(&loginmsg);
 341                         /* strip trailing newlines */
 342                         if (len > 0)
 343                                 while (len > 0 && msg[--len] == '\n')
 344                                         msg[len] = '\0';
 345                         else
 346                                 msg = "Access denied.";
 347                         packet_disconnect(msg);
 348                 }
 349 #endif
 350
 351  skip:
 352                 /* Log before sending the reply */
 353                 auth_log(authctxt, authenticated, get_authname(type), info);
 354
 355                 if (client_user != NULL) {
 356                         xfree(client_user);
 357                         client_user = NULL;
 358                 }
 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                         packet_disconnect(AUTH_FAIL_MSG, authctxt->user);
 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_string(&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         setproctitle("%s%s", authctxt->valid ? user : "unknown",
 408             use_privsep ? " [net]" : "");
 409
 410 #ifdef USE_PAM
 411         if (options.use_pam)
 412                 PRIVSEP(start_pam(authctxt));
 413 #endif
 414
 415         /*
 416          * If we are not running as root, the user must have the same uid as
 417          * the server.
 418          */
 419 #ifndef HAVE_CYGWIN
 420         if (!use_privsep && getuid() != 0 && authctxt->pw &&
 421             authctxt->pw->pw_uid != getuid())
 422                 packet_disconnect("Cannot change user when server not running as root.");
 423 #endif
 424
 425         /*
 426          * Loop until the user has been authenticated or the connection is
 427          * closed, do_authloop() returns only if authentication is successful
 428          */
 429         do_authloop(authctxt);
 430
 431         /* The user has been authenticated and accepted. */
 432         packet_start(SSH_SMSG_SUCCESS);
 433         packet_send();
 434         packet_write_wait();
 435 }