crypto/openssh-4/auth1.c

   1 /*
   2  * Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
   3  *                    All rights reserved
   4  *
   5  * As far as I am concerned, the code I have written for this software
   6  * can be used freely for any purpose.  Any derived versions of this
   7  * software must be clearly marked as such, and if the derived work is
   8  * incompatible with the protocol description in the RFC file, it must be
   9  * called by a name other than "ssh" or "Secure Shell".
  10  */
  11
  12 #include "includes.h"
  13 RCSID("$OpenBSD: auth1.c,v 1.62 2005/07/16 01:35:24 djm Exp $");
  14
  15 #include "xmalloc.h"
  16 #include "rsa.h"
  17 #include "ssh1.h"
  18 #include "packet.h"
  19 #include "buffer.h"
  20 #include "log.h"
  21 #include "servconf.h"
  22 #include "compat.h"
  23 #include "auth.h"
  24 #include "channels.h"
  25 #include "session.h"
  26 #include "uidswap.h"
  27 #include "monitor_wrap.h"
  28 #include "buffer.h"
  29
  30 /* import */
  31 extern ServerOptions options;
  32 extern Buffer loginmsg;
  33
  34 static int auth1_process_password(Authctxt *, char *, size_t);
  35 static int auth1_process_rsa(Authctxt *, char *, size_t);
  36 static int auth1_process_rhosts_rsa(Authctxt *, char *, size_t);
  37 static int auth1_process_tis_challenge(Authctxt *, char *, size_t);
  38 static int auth1_process_tis_response(Authctxt *, char *, size_t);
  39
  40 static char *client_user = NULL;    /* Used to fill in remote user for PAM */
  41
  42 struct AuthMethod1 {
  43         int type;
  44         char *name;
  45         int *enabled;
  46         int (*method)(Authctxt *, char *, size_t);
  47 };
  48
  49 const struct AuthMethod1 auth1_methods[] = {
  50         {
  51                 SSH_CMSG_AUTH_PASSWORD, "password",
  52                 &options.password_authentication, auth1_process_password
  53         },
  54         {
  55                 SSH_CMSG_AUTH_RSA, "rsa",
  56                 &options.rsa_authentication, auth1_process_rsa
  57         },
  58         {
  59                 SSH_CMSG_AUTH_RHOSTS_RSA, "rhosts-rsa",
  60                 &options.rhosts_rsa_authentication, auth1_process_rhosts_rsa
  61         },
  62         {
  63                 SSH_CMSG_AUTH_TIS, "challenge-response",
  64                 &options.challenge_response_authentication,
  65                 auth1_process_tis_challenge
  66         },
  67         {
  68                 SSH_CMSG_AUTH_TIS_RESPONSE, "challenge-response",
  69                 &options.challenge_response_authentication,
  70                 auth1_process_tis_response
  71         },
  72         { -1, NULL, NULL, NULL}
  73 };
  74
  75 static const struct AuthMethod1
  76 *lookup_authmethod1(int type)
  77 {
  78         int i;
  79
  80         for(i = 0; auth1_methods[i].name != NULL; i++)
  81                 if (auth1_methods[i].type == type)
  82                         return (&(auth1_methods[i]));
  83
  84         return (NULL);
  85 }
  86
  87 static char *
  88 get_authname(int type)
  89 {
  90         const struct AuthMethod1 *a;
  91         static char buf[64];
  92
  93         if ((a = lookup_authmethod1(type)) != NULL)
  94                 return (a->name);
  95         snprintf(buf, sizeof(buf), "bad-auth-msg-%d", type);
  96         return (buf);
  97 }
  98
  99 static int
 100 auth1_process_password(Authctxt *authctxt, char *info, size_t infolen)
 101 {
 102         int authenticated = 0;
 103         char *password;
 104         u_int dlen;
 105
 106         /*
 107          * Read user password.  It is in plain text, but was
 108          * transmitted over the encrypted channel so it is
 109          * not visible to an outside observer.
 110          */
 111         password = packet_get_string(&dlen);
 112         packet_check_eom();
 113
 114         /* Try authentication with the password. */
 115         authenticated = PRIVSEP(auth_password(authctxt, password));
 116
 117         memset(password, 0, dlen);
 118         xfree(password);
 119
 120         return (authenticated);
 121 }
 122
 123 static int
 124 auth1_process_rsa(Authctxt *authctxt, char *info, size_t infolen)
 125 {
 126         int authenticated = 0;
 127         BIGNUM *n;
 128
 129         /* RSA authentication requested. */
 130         if ((n = BN_new()) == NULL)
 131                 fatal("do_authloop: BN_new failed");
 132         packet_get_bignum(n);
 133         packet_check_eom();
 134         authenticated = auth_rsa(authctxt, n);
 135         BN_clear_free(n);
 136
 137         return (authenticated);
 138 }
 139
 140 static int
 141 auth1_process_rhosts_rsa(Authctxt *authctxt, char *info, size_t infolen)
 142 {
 143         int keybits, authenticated = 0;
 144         u_int bits;
 145         Key *client_host_key;
 146         u_int ulen;
 147
 148         /*
 149          * Get client user name.  Note that we just have to
 150          * trust the client; root on the client machine can
 151          * claim to be any user.
 152          */
 153         client_user = packet_get_string(&ulen);
 154
 155         /* Get the client host key. */
 156         client_host_key = key_new(KEY_RSA1);
 157         bits = packet_get_int();
 158         packet_get_bignum(client_host_key->rsa->e);
 159         packet_get_bignum(client_host_key->rsa->n);
 160
 161         keybits = BN_num_bits(client_host_key->rsa->n);
 162         if (keybits < 0 || bits != (u_int)keybits) {
 163                 verbose("Warning: keysize mismatch for client_host_key: "
 164                     "actual %d, announced %d",
 165                     BN_num_bits(client_host_key->rsa->n), bits);
 166         }
 167         packet_check_eom();
 168
 169         authenticated = auth_rhosts_rsa(authctxt, client_user,
 170             client_host_key);
 171         key_free(client_host_key);
 172
 173         snprintf(info, infolen, " ruser %.100s", client_user);
 174
 175         return (authenticated);
 176 }
 177
 178 static int
 179 auth1_process_tis_challenge(Authctxt *authctxt, char *info, size_t infolen)
 180 {
 181         char *challenge;
 182
 183         if ((challenge = get_challenge(authctxt)) == NULL)
 184                 return (0);
 185
 186         debug("sending challenge '%s'", challenge);
 187         packet_start(SSH_SMSG_AUTH_TIS_CHALLENGE);
 188         packet_put_cstring(challenge);
 189         xfree(challenge);
 190         packet_send();
 191         packet_write_wait();
 192
 193         return (-1);
 194 }
 195
 196 static int
 197 auth1_process_tis_response(Authctxt *authctxt, char *info, size_t infolen)
 198 {
 199         int authenticated = 0;
 200         char *response;
 201         u_int dlen;
 202
 203         response = packet_get_string(&dlen);
 204         packet_check_eom();
 205         authenticated = verify_response(authctxt, response);
 206         memset(response, 'r', dlen);
 207         xfree(response);
 208
 209         return (authenticated);
 210 }
 211
 212 /*
 213  * read packets, try to authenticate the user and
 214  * return only if authentication is successful
 215  */
 216 static void
 217 do_authloop(Authctxt *authctxt)
 218 {
 219         int authenticated = 0;
 220         char info[1024];
 221         int prev = 0, type = 0;
 222         const struct AuthMethod1 *meth;
 223
 224         debug("Attempting authentication for %s%.100s.",
 225             authctxt->valid ? "" : "invalid user ", authctxt->user);
 226
 227         /* If the user has no password, accept authentication immediately. */
 228         if (options.password_authentication &&
 229 #ifdef KRB5
 230             (!options.kerberos_authentication || options.kerberos_or_local_passwd) &&
 231 #endif
 232             PRIVSEP(auth_password(authctxt, ""))) {
 233 #ifdef USE_PAM
 234                 if (options.use_pam && (PRIVSEP(do_pam_account())))
 235 #endif
 236                 {
 237                         auth_log(authctxt, 1, "without authentication", "");
 238                         return;
 239                 }
 240         }
 241
 242         /* Indicate that authentication is needed. */
 243         packet_start(SSH_SMSG_FAILURE);
 244         packet_send();
 245         packet_write_wait();
 246
 247         for (;;) {
 248                 /* default to fail */
 249                 authenticated = 0;
 250
 251                 info[0] = '\0';
 252
 253                 /* Get a packet from the client. */
 254                 prev = type;
 255                 type = packet_read();
 256
 257                 /*
 258                  * If we started challenge-response authentication but the
 259                  * next packet is not a response to our challenge, release
 260                  * the resources allocated by get_challenge() (which would
 261                  * normally have been released by verify_response() had we
 262                  * received such a response)
 263                  */
 264                 if (prev == SSH_CMSG_AUTH_TIS &&
 265                     type != SSH_CMSG_AUTH_TIS_RESPONSE)
 266                         abandon_challenge_response(authctxt);
 267
 268                 if ((meth = lookup_authmethod1(type)) == NULL) {
 269                         logit("Unknown message during authentication: "
 270                             "type %d", type);
 271                         goto skip;
 272                 }
 273
 274                 if (!*(meth->enabled)) {
 275                         verbose("%s authentication disabled.", meth->name);
 276                         goto skip;
 277                 }
 278
 279                 authenticated = meth->method(authctxt, info, sizeof(info));
 280                 if (authenticated == -1)
 281                         continue; /* "postponed" */
 282
 283 #ifdef BSD_AUTH
 284                 if (authctxt->as) {
 285                         auth_close(authctxt->as);
 286                         authctxt->as = NULL;
 287                 }
 288 #endif
 289                 if (!authctxt->valid && authenticated)
 290                         fatal("INTERNAL ERROR: authenticated invalid user %s",
 291                             authctxt->user);
 292
 293 #ifdef _UNICOS
 294                 if (authenticated && cray_access_denied(authctxt->user)) {
 295                         authenticated = 0;
 296                         fatal("Access denied for user %s.",authctxt->user);
 297                 }
 298 #endif /* _UNICOS */
 299
 300 #ifdef HAVE_CYGWIN
 301                 if (authenticated &&
 302                     !check_nt_auth(type == SSH_CMSG_AUTH_PASSWORD,
 303                     authctxt->pw)) {
 304                         packet_disconnect("Authentication rejected for uid %d.",
 305                             authctxt->pw == NULL ? -1 : authctxt->pw->pw_uid);
 306                         authenticated = 0;
 307                 }
 308 #else
 309                 /* Special handling for root */
 310                 if (authenticated && authctxt->pw->pw_uid == 0 &&
 311                     !auth_root_allowed(meth->name)) {
 312                         authenticated = 0;
 313 # ifdef SSH_AUDIT_EVENTS
 314                         PRIVSEP(audit_event(SSH_LOGIN_ROOT_DENIED));
 315 # endif
 316                 }
 317 #endif
 318
 319 #ifdef USE_PAM
 320                 if (options.use_pam && authenticated &&
 321                     !PRIVSEP(do_pam_account())) {
 322                         char *msg;
 323                         size_t len;
 324
 325                         error("Access denied for user %s by PAM account "
 326                             "configuration", authctxt->user);
 327                         len = buffer_len(&loginmsg);
 328                         buffer_append(&loginmsg, "\0", 1);
 329                         msg = buffer_ptr(&loginmsg);
 330                         /* strip trailing newlines */
 331                         if (len > 0)
 332                                 while (len > 0 && msg[--len] == '\n')
 333                                         msg[len] = '\0';
 334                         else
 335                                 msg = "Access denied.";
 336                         packet_disconnect(msg);
 337                 }
 338 #endif
 339
 340  skip:
 341                 /* Log before sending the reply */
 342                 auth_log(authctxt, authenticated, get_authname(type), info);
 343
 344                 if (client_user != NULL) {
 345                         xfree(client_user);
 346                         client_user = NULL;
 347                 }
 348
 349                 if (authenticated)
 350                         return;
 351
 352                 if (authctxt->failures++ > options.max_authtries) {
 353 #ifdef SSH_AUDIT_EVENTS
 354                         PRIVSEP(audit_event(SSH_LOGIN_EXCEED_MAXTRIES));
 355 #endif
 356                         packet_disconnect(AUTH_FAIL_MSG, authctxt->user);
 357                 }
 358
 359                 packet_start(SSH_SMSG_FAILURE);
 360                 packet_send();
 361                 packet_write_wait();
 362         }
 363 }
 364
 365 /*
 366  * Performs authentication of an incoming connection.  Session key has already
 367  * been exchanged and encryption is enabled.
 368  */
 369 void
 370 do_authentication(Authctxt *authctxt)
 371 {
 372         u_int ulen;
 373         char *user, *style = NULL;
 374
 375         /* Get the name of the user that we wish to log in as. */
 376         packet_read_expect(SSH_CMSG_USER);
 377
 378         /* Get the user name. */
 379         user = packet_get_string(&ulen);
 380         packet_check_eom();
 381
 382         if ((style = strchr(user, ':')) != NULL)
 383                 *style++ = '\0';
 384
 385         authctxt->user = user;
 386         authctxt->style = style;
 387
 388         /* Verify that the user is a valid user. */
 389         if ((authctxt->pw = PRIVSEP(getpwnamallow(user))) != NULL)
 390                 authctxt->valid = 1;
 391         else {
 392                 debug("do_authentication: invalid user %s", user);
 393                 authctxt->pw = fakepw();
 394         }
 395
 396         setproctitle("%s%s", authctxt->valid ? user : "unknown",
 397             use_privsep ? " [net]" : "");
 398
 399 #ifdef USE_PAM
 400         if (options.use_pam)
 401                 PRIVSEP(start_pam(authctxt));
 402 #endif
 403
 404         /*
 405          * If we are not running as root, the user must have the same uid as
 406          * the server.
 407          */
 408 #ifndef HAVE_CYGWIN
 409         if (!use_privsep && getuid() != 0 && authctxt->pw &&
 410             authctxt->pw->pw_uid != getuid())
 411                 packet_disconnect("Cannot change user when server not running as root.");
 412 #endif
 413
 414         /*
 415          * Loop until the user has been authenticated or the connection is
 416          * closed, do_authloop() returns only if authentication is successful
 417          */
 418         do_authloop(authctxt);
 419
 420         /* The user has been authenticated and accepted. */
 421         packet_start(SSH_SMSG_SUCCESS);
 422         packet_send();
 423         packet_write_wait();
 424 }