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      1 /*
      2  * Copyright (c) 1995 Tatu Ylonen <ylo (at) 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  * Copyright 2007 Sun Microsystems, Inc.  All rights reserved.
     13  * Use is subject to license terms.
     14  */
     15 
     16 #include "includes.h"
     17 RCSID("$OpenBSD: auth1.c,v 1.44 2002/09/26 11:38:43 markus Exp $");
     18 
     19 #pragma ident	"%Z%%M%	%I%	%E% SMI"
     20 
     21 #include "xmalloc.h"
     22 #include "rsa.h"
     23 #include "ssh1.h"
     24 #include "packet.h"
     25 #include "buffer.h"
     26 #include "mpaux.h"
     27 #include "log.h"
     28 #include "servconf.h"
     29 #include "compat.h"
     30 #include "auth.h"
     31 #include "channels.h"
     32 #include "session.h"
     33 #include "uidswap.h"
     34 
     35 #ifdef HAVE_BSM
     36 #include "bsmaudit.h"
     37 extern adt_session_data_t *ah;
     38 #endif /* HAVE_BSM */
     39 
     40 /* import */
     41 extern ServerOptions options;
     42 
     43 /*
     44  * convert ssh auth msg type into description
     45  */
     46 static char *
     47 get_authname(int type)
     48 {
     49 	static char buf[1024];
     50 	switch (type) {
     51 	case SSH_CMSG_AUTH_PASSWORD:
     52 		return "password";
     53 	case SSH_CMSG_AUTH_RSA:
     54 		return "rsa";
     55 	case SSH_CMSG_AUTH_RHOSTS_RSA:
     56 		return "rhosts-rsa";
     57 	case SSH_CMSG_AUTH_RHOSTS:
     58 		return "rhosts";
     59 	case SSH_CMSG_AUTH_TIS:
     60 	case SSH_CMSG_AUTH_TIS_RESPONSE:
     61 		return "challenge-response";
     62 #if defined(KRB4) || defined(KRB5)
     63 	case SSH_CMSG_AUTH_KERBEROS:
     64 		return "kerberos";
     65 #endif
     66 	}
     67 	snprintf(buf, sizeof buf, "bad-auth-msg-%d", type);
     68 	return buf;
     69 }
     70 
     71 /*
     72  * read packets, try to authenticate the user and
     73  * return only if authentication is successful
     74  */
     75 static void
     76 do_authloop(Authctxt *authctxt)
     77 {
     78 	int authenticated = 0;
     79 	u_int bits;
     80 	Key *client_host_key;
     81 	BIGNUM *n;
     82 	char *client_user, *password;
     83 	char info[1024];
     84 	u_int dlen;
     85 	u_int ulen;
     86 	int type = 0;
     87 	struct passwd *pw = authctxt->pw;
     88 
     89 	debug("Attempting authentication for %s%.100s.",
     90 	    authctxt->valid ? "" : "illegal user ", authctxt->user);
     91 
     92 	/* If the user has no password, accept authentication immediately. */
     93 	if (options.password_authentication &&
     94 #if defined(KRB4) || defined(KRB5)
     95 	    (!options.kerberos_authentication || options.kerberos_or_local_passwd) &&
     96 #endif
     97 	    auth_password(authctxt, "")) {
     98 		auth_log(authctxt, 1, "without authentication", "");
     99 		return;
    100 	}
    101 
    102 	/* Indicate that authentication is needed. */
    103 	packet_start(SSH_SMSG_FAILURE);
    104 	packet_send();
    105 	packet_write_wait();
    106 
    107 	client_user = NULL;
    108 
    109 	for ( ;; ) {
    110 		/* default to fail */
    111 		authenticated = 0;
    112 
    113 		info[0] = '\0';
    114 
    115 		/* Get a packet from the client. */
    116 		authctxt->v1_auth_type = type = packet_read();
    117 		authctxt->v1_auth_name = get_authname(type);
    118 
    119 		authctxt->attempt++;
    120 
    121 		/* Process the packet. */
    122 		switch (type) {
    123 
    124 #if defined(KRB4) || defined(KRB5)
    125 		case SSH_CMSG_AUTH_KERBEROS:
    126 			if (!options.kerberos_authentication) {
    127 				verbose("Kerberos authentication disabled.");
    128 			} else {
    129 				char *kdata = packet_get_string(&dlen);
    130 				packet_check_eom();
    131 
    132 				if (kdata[0] == 4) { /* KRB_PROT_VERSION */
    133 #ifdef KRB4
    134 					KTEXT_ST tkt, reply;
    135 					tkt.length = dlen;
    136 					if (tkt.length < MAX_KTXT_LEN)
    137 						memcpy(tkt.dat, kdata, tkt.length);
    138 
    139 					if (auth_krb4(authctxt, &tkt,
    140 					    &client_user, &reply)) {
    141 						authenticated = 1;
    142 						snprintf(info, sizeof(info),
    143 						    " tktuser %.100s",
    144 						    client_user);
    145 
    146 						packet_start(
    147 						    SSH_SMSG_AUTH_KERBEROS_RESPONSE);
    148 						packet_put_string((char *)
    149 						    reply.dat, reply.length);
    150 						packet_send();
    151 						packet_write_wait();
    152 					}
    153 #endif /* KRB4 */
    154 				} else {
    155 #ifdef KRB5
    156 					krb5_data tkt, reply;
    157 					tkt.length = dlen;
    158 					tkt.data = kdata;
    159 
    160 					if (auth_krb5(authctxt, &tkt,
    161 					    &client_user, &reply)) {
    162 						authenticated = 1;
    163 						snprintf(info, sizeof(info),
    164 						    " tktuser %.100s",
    165 						    client_user);
    166 
    167  						/* Send response to client */
    168  						packet_start(
    169 						    SSH_SMSG_AUTH_KERBEROS_RESPONSE);
    170  						packet_put_string((char *)
    171 						    reply.data, reply.length);
    172  						packet_send();
    173  						packet_write_wait();
    174 
    175  						if (reply.length)
    176  							xfree(reply.data);
    177 					}
    178 #endif /* KRB5 */
    179 				}
    180 				xfree(kdata);
    181 			}
    182 			break;
    183 #endif /* KRB4 || KRB5 */
    184 
    185 #if defined(AFS) || defined(KRB5)
    186 			/* XXX - punt on backward compatibility here. */
    187 		case SSH_CMSG_HAVE_KERBEROS_TGT:
    188 			packet_send_debug("Kerberos TGT passing disabled before authentication.");
    189 			break;
    190 #ifdef AFS
    191 		case SSH_CMSG_HAVE_AFS_TOKEN:
    192 			packet_send_debug("AFS token passing disabled before authentication.");
    193 			break;
    194 #endif /* AFS */
    195 #endif /* AFS || KRB5 */
    196 
    197 		case SSH_CMSG_AUTH_RHOSTS:
    198 			if (!options.rhosts_authentication) {
    199 				verbose("Rhosts authentication disabled.");
    200 				break;
    201 			}
    202 			/*
    203 			 * Get client user name.  Note that we just have to
    204 			 * trust the client; this is one reason why rhosts
    205 			 * authentication is insecure. (Another is
    206 			 * IP-spoofing on a local network.)
    207 			 */
    208 			client_user = packet_get_string(&ulen);
    209 			packet_check_eom();
    210 
    211 			/* Try to authenticate using /etc/hosts.equiv and .rhosts. */
    212 			authenticated = auth_rhosts(pw, client_user);
    213 
    214 			snprintf(info, sizeof info, " ruser %.100s", client_user);
    215 			break;
    216 
    217 		case SSH_CMSG_AUTH_RHOSTS_RSA:
    218 			if (!options.rhosts_rsa_authentication) {
    219 				verbose("Rhosts with RSA authentication disabled.");
    220 				break;
    221 			}
    222 			/*
    223 			 * Get client user name.  Note that we just have to
    224 			 * trust the client; root on the client machine can
    225 			 * claim to be any user.
    226 			 */
    227 			client_user = packet_get_string(&ulen);
    228 
    229 			/* Get the client host key. */
    230 			client_host_key = key_new(KEY_RSA1);
    231 			bits = packet_get_int();
    232 			packet_get_bignum(client_host_key->rsa->e);
    233 			packet_get_bignum(client_host_key->rsa->n);
    234 
    235 			if (bits != BN_num_bits(client_host_key->rsa->n))
    236 				verbose("Warning: keysize mismatch for client_host_key: "
    237 				    "actual %d, announced %d",
    238 				    BN_num_bits(client_host_key->rsa->n), bits);
    239 			packet_check_eom();
    240 
    241 			authenticated = auth_rhosts_rsa(pw, client_user,
    242 			    client_host_key);
    243 			key_free(client_host_key);
    244 
    245 			snprintf(info, sizeof info, " ruser %.100s", client_user);
    246 			break;
    247 
    248 		case SSH_CMSG_AUTH_RSA:
    249 			if (!options.rsa_authentication) {
    250 				verbose("RSA authentication disabled.");
    251 				break;
    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(pw, n);
    259 			BN_clear_free(n);
    260 			break;
    261 
    262 		case SSH_CMSG_AUTH_PASSWORD:
    263 			authctxt->init_attempt++;
    264 
    265 			if (!options.password_authentication) {
    266 				verbose("Password authentication disabled.");
    267 				break;
    268 			}
    269 			/*
    270 			 * Read user password.  It is in plain text, but was
    271 			 * transmitted over the encrypted channel so it is
    272 			 * not visible to an outside observer.
    273 			 */
    274 			password = packet_get_string(&dlen);
    275 			packet_check_eom();
    276 
    277 			/* Try authentication with the password. */
    278 			if (authctxt->init_failures <
    279 				options.max_init_auth_tries)
    280 				authenticated =
    281 				    auth_password(authctxt, password);
    282 
    283 			memset(password, 0, strlen(password));
    284 			xfree(password);
    285 			break;
    286 
    287 		case SSH_CMSG_AUTH_TIS:
    288 			debug("rcvd SSH_CMSG_AUTH_TIS");
    289 			if (options.challenge_response_authentication == 1) {
    290 				char *challenge = get_challenge(authctxt);
    291 				if (challenge != NULL) {
    292 					debug("sending challenge '%s'", challenge);
    293 					packet_start(SSH_SMSG_AUTH_TIS_CHALLENGE);
    294 					packet_put_cstring(challenge);
    295 					xfree(challenge);
    296 					packet_send();
    297 					packet_write_wait();
    298 					continue;
    299 				}
    300 			}
    301 			break;
    302 		case SSH_CMSG_AUTH_TIS_RESPONSE:
    303 			debug("rcvd SSH_CMSG_AUTH_TIS_RESPONSE");
    304 			if (options.challenge_response_authentication == 1) {
    305 				char *response = packet_get_string(&dlen);
    306 				debug("got response '%s'", response);
    307 				packet_check_eom();
    308 				authenticated = verify_response(authctxt, response);
    309 				memset(response, 'r', dlen);
    310 				xfree(response);
    311 			}
    312 			break;
    313 
    314 		default:
    315 			/*
    316 			 * Any unknown messages will be ignored (and failure
    317 			 * returned) during authentication.
    318 			 */
    319 			log("Unknown message during authentication: type %d", type);
    320 			break;
    321 		}
    322 #ifdef BSD_AUTH
    323 		if (authctxt->as) {
    324 			auth_close(authctxt->as);
    325 			authctxt->as = NULL;
    326 		}
    327 #endif
    328 		if (!authctxt->valid && authenticated) {
    329 			authenticated = 0;
    330 			log("Ignoring authenticated invalid user %s",
    331 			    authctxt->user);
    332 		}
    333 
    334 #ifdef _UNICOS
    335 		if (type == SSH_CMSG_AUTH_PASSWORD && !authenticated)
    336 			cray_login_failure(authctxt->user, IA_UDBERR);
    337 		if (authenticated && cray_access_denied(authctxt->user)) {
    338 			authenticated = 0;
    339 			fatal("Access denied for user %s.",authctxt->user);
    340 		}
    341 #endif /* _UNICOS */
    342 
    343 #ifdef HAVE_CYGWIN
    344 		if (authenticated &&
    345 		    !check_nt_auth(type == SSH_CMSG_AUTH_PASSWORD, pw)) {
    346 			packet_disconnect("Authentication rejected for uid %d.",
    347 			pw == NULL ? -1 : pw->pw_uid);
    348 			authenticated = 0;
    349 		}
    350 #else
    351 		/* Special handling for root */
    352 		if (authenticated && authctxt->pw->pw_uid == 0 &&
    353 		    !auth_root_allowed(get_authname(type)))
    354 			authenticated = 0;
    355 #endif
    356 #ifdef USE_PAM
    357 		if (authenticated && type != SSH_CMSG_AUTH_PASSWORD)
    358 			authenticated = do_pam_non_initial_userauth(authctxt);
    359 		else if (authenticated && !AUTHPAM_DONE(authctxt))
    360 			authenticated = 0;
    361 
    362 		if (!authenticated)
    363 			authctxt->pam_retval = AUTHPAM_ERROR(authctxt,
    364 				PAM_PERM_DENIED);
    365 #endif /* USE_PAM */
    366 
    367 		/* Log before sending the reply */
    368 		auth_log(authctxt, authenticated, get_authname(type), info);
    369 
    370 		if (client_user != NULL) {
    371 			xfree(client_user);
    372 			client_user = NULL;
    373 		}
    374 
    375 		if (authenticated)
    376 			return;
    377 
    378 		if (type == SSH_CMSG_AUTH_PASSWORD)
    379 			authctxt->init_failures++;
    380 
    381 		if (authctxt->failures++ > options.max_auth_tries) {
    382 #ifdef HAVE_BSM
    383 			fatal_remove_cleanup(audit_failed_login_cleanup,
    384 				authctxt);
    385 			audit_sshd_login_failure(&ah, PAM_MAXTRIES);
    386 #endif /* HAVE_BSM */
    387 			packet_disconnect(AUTH_FAIL_MSG, authctxt->user);
    388 		}
    389 
    390 		packet_start(SSH_SMSG_FAILURE);
    391 		packet_send();
    392 		packet_write_wait();
    393 	}
    394 }
    395 
    396 /*
    397  * Performs authentication of an incoming connection.  Session key has already
    398  * been exchanged and encryption is enabled.
    399  */
    400 Authctxt *
    401 do_authentication(void)
    402 {
    403 	Authctxt *authctxt;
    404 	u_int ulen;
    405 	char *user, *style = NULL;
    406 
    407 	/* Get the name of the user that we wish to log in as. */
    408 	packet_read_expect(SSH_CMSG_USER);
    409 
    410 	/* Get the user name. */
    411 	user = packet_get_string(&ulen);
    412 	packet_check_eom();
    413 
    414 	if ((style = strchr(user, ':')) != NULL)
    415 		*style++ = '\0';
    416 
    417 #ifdef KRB5
    418 	/* XXX - SSH.com Kerberos v5 braindeath. */
    419 	if ((datafellows & SSH_BUG_K5USER) &&
    420 	    options.kerberos_authentication) {
    421 		char *p;
    422 		if ((p = strchr(user, '@')) != NULL)
    423 			*p = '\0';
    424 	}
    425 #endif
    426 
    427 	authctxt = authctxt_new();
    428 	authctxt->user = user;
    429 	authctxt->style = style;
    430 
    431 #ifdef HAVE_BSM
    432 	fatal_add_cleanup(audit_failed_login_cleanup, authctxt);
    433 #endif /* HAVE_BSM */
    434 
    435 	/* Verify that the user is a valid user. */
    436 	if ((authctxt->pw = getpwnamallow(user)) != NULL) {
    437 		authctxt->valid = 1;
    438 	} else {
    439 		authctxt->valid = 0;
    440 		debug("do_authentication: illegal user %s", user);
    441 	}
    442 
    443 	setproctitle("%s", authctxt->pw ? user : "unknown");
    444 
    445 	/*
    446 	 * If we are not running as root, the user must have the same uid as
    447 	 * the server. (Unless you are running Windows)
    448 	 */
    449 #ifndef HAVE_CYGWIN
    450 	if (getuid() != 0 && authctxt->pw &&
    451 	    authctxt->pw->pw_uid != getuid())
    452 		packet_disconnect("Cannot change user when server not running as root.");
    453 #endif
    454 
    455 	/*
    456 	 * Loop until the user has been authenticated or the connection is
    457 	 * closed, do_authloop() returns only if authentication is successful
    458 	 */
    459 	do_authloop(authctxt);
    460 
    461 	/* The user has been authenticated and accepted. */
    462 	packet_start(SSH_SMSG_SUCCESS);
    463 	packet_send();
    464 	packet_write_wait();
    465 
    466 	return (authctxt);
    467 }
    468