1 /* $OpenBSD: auth1.c,v 1.82 2014/07/15 15:54:14 millert Exp $ */ 2 /* 3 * Copyright (c) 1995 Tatu Ylonen <ylo (at) 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 #ifdef WITH_SSH1 16 17 #include <sys/types.h> 18 19 #include <stdarg.h> 20 #include <stdio.h> 21 #include <string.h> 22 #include <unistd.h> 23 #include <pwd.h> 24 25 #include "openbsd-compat/sys-queue.h" 26 #include "xmalloc.h" 27 #include "rsa.h" 28 #include "ssh1.h" 29 #include "packet.h" 30 #include "buffer.h" 31 #include "log.h" 32 #include "misc.h" 33 #include "servconf.h" 34 #include "compat.h" 35 #include "key.h" 36 #include "hostfile.h" 37 #include "auth.h" 38 #include "channels.h" 39 #include "session.h" 40 #include "uidswap.h" 41 #ifdef GSSAPI 42 #include "ssh-gss.h" 43 #endif 44 #include "monitor_wrap.h" 45 #include "buffer.h" 46 47 /* import */ 48 extern ServerOptions options; 49 extern Buffer loginmsg; 50 51 static int auth1_process_password(Authctxt *); 52 static int auth1_process_rsa(Authctxt *); 53 static int auth1_process_rhosts_rsa(Authctxt *); 54 static int auth1_process_tis_challenge(Authctxt *); 55 static int auth1_process_tis_response(Authctxt *); 56 57 static char *client_user = NULL; /* Used to fill in remote user for PAM */ 58 59 struct AuthMethod1 { 60 int type; 61 char *name; 62 int *enabled; 63 int (*method)(Authctxt *); 64 }; 65 66 const struct AuthMethod1 auth1_methods[] = { 67 { 68 SSH_CMSG_AUTH_PASSWORD, "password", 69 &options.password_authentication, auth1_process_password 70 }, 71 { 72 SSH_CMSG_AUTH_RSA, "rsa", 73 &options.rsa_authentication, auth1_process_rsa 74 }, 75 { 76 SSH_CMSG_AUTH_RHOSTS_RSA, "rhosts-rsa", 77 &options.rhosts_rsa_authentication, auth1_process_rhosts_rsa 78 }, 79 { 80 SSH_CMSG_AUTH_TIS, "challenge-response", 81 &options.challenge_response_authentication, 82 auth1_process_tis_challenge 83 }, 84 { 85 SSH_CMSG_AUTH_TIS_RESPONSE, "challenge-response", 86 &options.challenge_response_authentication, 87 auth1_process_tis_response 88 }, 89 { -1, NULL, NULL, NULL} 90 }; 91 92 static const struct AuthMethod1 93 *lookup_authmethod1(int type) 94 { 95 int i; 96 97 for (i = 0; auth1_methods[i].name != NULL; i++) 98 if (auth1_methods[i].type == type) 99 return (&(auth1_methods[i])); 100 101 return (NULL); 102 } 103 104 static char * 105 get_authname(int type) 106 { 107 const struct AuthMethod1 *a; 108 static char buf[64]; 109 110 if ((a = lookup_authmethod1(type)) != NULL) 111 return (a->name); 112 snprintf(buf, sizeof(buf), "bad-auth-msg-%d", type); 113 return (buf); 114 } 115 116 /*ARGSUSED*/ 117 static int 118 auth1_process_password(Authctxt *authctxt) 119 { 120 int authenticated = 0; 121 char *password; 122 u_int dlen; 123 124 /* 125 * Read user password. It is in plain text, but was 126 * transmitted over the encrypted channel so it is 127 * not visible to an outside observer. 128 */ 129 password = packet_get_string(&dlen); 130 packet_check_eom(); 131 132 /* Try authentication with the password. */ 133 authenticated = PRIVSEP(auth_password(authctxt, password)); 134 135 explicit_bzero(password, dlen); 136 free(password); 137 138 return (authenticated); 139 } 140 141 /*ARGSUSED*/ 142 static int 143 auth1_process_rsa(Authctxt *authctxt) 144 { 145 int authenticated = 0; 146 BIGNUM *n; 147 148 /* RSA authentication requested. */ 149 if ((n = BN_new()) == NULL) 150 fatal("do_authloop: BN_new failed"); 151 packet_get_bignum(n); 152 packet_check_eom(); 153 authenticated = auth_rsa(authctxt, n); 154 BN_clear_free(n); 155 156 return (authenticated); 157 } 158 159 /*ARGSUSED*/ 160 static int 161 auth1_process_rhosts_rsa(Authctxt *authctxt) 162 { 163 int keybits, authenticated = 0; 164 u_int bits; 165 Key *client_host_key; 166 u_int ulen; 167 168 /* 169 * Get client user name. Note that we just have to 170 * trust the client; root on the client machine can 171 * claim to be any user. 172 */ 173 client_user = packet_get_cstring(&ulen); 174 175 /* Get the client host key. */ 176 client_host_key = key_new(KEY_RSA1); 177 bits = packet_get_int(); 178 packet_get_bignum(client_host_key->rsa->e); 179 packet_get_bignum(client_host_key->rsa->n); 180 181 keybits = BN_num_bits(client_host_key->rsa->n); 182 if (keybits < 0 || bits != (u_int)keybits) { 183 verbose("Warning: keysize mismatch for client_host_key: " 184 "actual %d, announced %d", 185 BN_num_bits(client_host_key->rsa->n), bits); 186 } 187 packet_check_eom(); 188 189 authenticated = auth_rhosts_rsa(authctxt, client_user, 190 client_host_key); 191 key_free(client_host_key); 192 193 auth_info(authctxt, "ruser %.100s", client_user); 194 195 return (authenticated); 196 } 197 198 /*ARGSUSED*/ 199 static int 200 auth1_process_tis_challenge(Authctxt *authctxt) 201 { 202 char *challenge; 203 204 if ((challenge = get_challenge(authctxt)) == NULL) 205 return (0); 206 207 debug("sending challenge '%s'", challenge); 208 packet_start(SSH_SMSG_AUTH_TIS_CHALLENGE); 209 packet_put_cstring(challenge); 210 free(challenge); 211 packet_send(); 212 packet_write_wait(); 213 214 return (-1); 215 } 216 217 /*ARGSUSED*/ 218 static int 219 auth1_process_tis_response(Authctxt *authctxt) 220 { 221 int authenticated = 0; 222 char *response; 223 u_int dlen; 224 225 response = packet_get_string(&dlen); 226 packet_check_eom(); 227 authenticated = verify_response(authctxt, response); 228 explicit_bzero(response, dlen); 229 free(response); 230 231 return (authenticated); 232 } 233 234 /* 235 * read packets, try to authenticate the user and 236 * return only if authentication is successful 237 */ 238 static void 239 do_authloop(Authctxt *authctxt) 240 { 241 int authenticated = 0; 242 int prev = 0, type = 0; 243 const struct AuthMethod1 *meth; 244 245 debug("Attempting authentication for %s%.100s.", 246 authctxt->valid ? "" : "invalid user ", authctxt->user); 247 248 /* If the user has no password, accept authentication immediately. */ 249 if (options.permit_empty_passwd && options.password_authentication && 250 #ifdef KRB5 251 (!options.kerberos_authentication || options.kerberos_or_local_passwd) && 252 #endif 253 PRIVSEP(auth_password(authctxt, ""))) { 254 #ifdef USE_PAM 255 if (options.use_pam && (PRIVSEP(do_pam_account()))) 256 #endif 257 { 258 auth_log(authctxt, 1, 0, "without authentication", 259 NULL); 260 return; 261 } 262 } 263 264 /* Indicate that authentication is needed. */ 265 packet_start(SSH_SMSG_FAILURE); 266 packet_send(); 267 packet_write_wait(); 268 269 for (;;) { 270 /* default to fail */ 271 authenticated = 0; 272 273 274 /* Get a packet from the client. */ 275 prev = type; 276 type = packet_read(); 277 278 /* 279 * If we started challenge-response authentication but the 280 * next packet is not a response to our challenge, release 281 * the resources allocated by get_challenge() (which would 282 * normally have been released by verify_response() had we 283 * received such a response) 284 */ 285 if (prev == SSH_CMSG_AUTH_TIS && 286 type != SSH_CMSG_AUTH_TIS_RESPONSE) 287 abandon_challenge_response(authctxt); 288 289 if (authctxt->failures >= options.max_authtries) 290 goto skip; 291 if ((meth = lookup_authmethod1(type)) == NULL) { 292 logit("Unknown message during authentication: " 293 "type %d", type); 294 goto skip; 295 } 296 297 if (!*(meth->enabled)) { 298 verbose("%s authentication disabled.", meth->name); 299 goto skip; 300 } 301 302 authenticated = meth->method(authctxt); 303 if (authenticated == -1) 304 continue; /* "postponed" */ 305 306 #ifdef BSD_AUTH 307 if (authctxt->as) { 308 auth_close(authctxt->as); 309 authctxt->as = NULL; 310 } 311 #endif 312 if (!authctxt->valid && authenticated) 313 fatal("INTERNAL ERROR: authenticated invalid user %s", 314 authctxt->user); 315 316 #ifdef _UNICOS 317 if (authenticated && cray_access_denied(authctxt->user)) { 318 authenticated = 0; 319 fatal("Access denied for user %s.",authctxt->user); 320 } 321 #endif /* _UNICOS */ 322 323 #ifndef HAVE_CYGWIN 324 /* Special handling for root */ 325 if (authenticated && authctxt->pw->pw_uid == 0 && 326 !auth_root_allowed(meth->name)) { 327 authenticated = 0; 328 # ifdef SSH_AUDIT_EVENTS 329 PRIVSEP(audit_event(SSH_LOGIN_ROOT_DENIED)); 330 # endif 331 } 332 #endif 333 334 #ifdef USE_PAM 335 if (options.use_pam && authenticated && 336 !PRIVSEP(do_pam_account())) { 337 char *msg; 338 size_t len; 339 340 error("Access denied for user %s by PAM account " 341 "configuration", authctxt->user); 342 len = buffer_len(&loginmsg); 343 buffer_append(&loginmsg, "\0", 1); 344 msg = buffer_ptr(&loginmsg); 345 /* strip trailing newlines */ 346 if (len > 0) 347 while (len > 0 && msg[--len] == '\n') 348 msg[len] = '\0'; 349 else 350 msg = "Access denied."; 351 packet_disconnect("%s", msg); 352 } 353 #endif 354 355 skip: 356 /* Log before sending the reply */ 357 auth_log(authctxt, authenticated, 0, get_authname(type), NULL); 358 359 free(client_user); 360 client_user = NULL; 361 362 if (authenticated) 363 return; 364 365 if (++authctxt->failures >= options.max_authtries) { 366 #ifdef SSH_AUDIT_EVENTS 367 PRIVSEP(audit_event(SSH_LOGIN_EXCEED_MAXTRIES)); 368 #endif 369 auth_maxtries_exceeded(authctxt); 370 } 371 372 packet_start(SSH_SMSG_FAILURE); 373 packet_send(); 374 packet_write_wait(); 375 } 376 } 377 378 /* 379 * Performs authentication of an incoming connection. Session key has already 380 * been exchanged and encryption is enabled. 381 */ 382 void 383 do_authentication(Authctxt *authctxt) 384 { 385 u_int ulen; 386 char *user, *style = NULL; 387 388 /* Get the name of the user that we wish to log in as. */ 389 packet_read_expect(SSH_CMSG_USER); 390 391 /* Get the user name. */ 392 user = packet_get_cstring(&ulen); 393 packet_check_eom(); 394 395 if ((style = strchr(user, ':')) != NULL) 396 *style++ = '\0'; 397 398 authctxt->user = user; 399 authctxt->style = style; 400 401 /* Verify that the user is a valid user. */ 402 if ((authctxt->pw = PRIVSEP(getpwnamallow(user))) != NULL) 403 authctxt->valid = 1; 404 else { 405 debug("do_authentication: invalid user %s", user); 406 authctxt->pw = fakepw(); 407 } 408 409 /* Configuration may have changed as a result of Match */ 410 if (options.num_auth_methods != 0) 411 fatal("AuthenticationMethods is not supported with SSH " 412 "protocol 1"); 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 } 443 444 #endif /* WITH_SSH1 */ 445
