xref: /titanic_50/usr/src/cmd/ssh/libssh/common/kexgssc.c (revision 2654012f83cec5dc15b61dfe3e4a4915f186e7a6)
1 /*
2  * Copyright (c) 2001-2003 Simon Wilkinson. All rights reserved.
3  *
4  * Redistribution and use in source and binary forms, with or without
5  * modification, are permitted provided that the following conditions
6  * are met:
7  * 1. Redistributions of source code must retain the above copyright
8  *    notice, this list of conditions and the following disclaimer.
9  * 2. Redistributions in binary form must reproduce the above copyright
10  *    notice, this list of conditions and the following disclaimer in the
11  *    documentation and/or other materials provided with the distribution.
12  *
13  * THIS SOFTWARE IS PROVIDED BY THE AUTHOR `AS IS'' AND ANY EXPRESS OR
14  * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
15  * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
16  * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
17  * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
18  * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
19  * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
20  * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
21  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
22  * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
23  */
24 /*
25  * Copyright 2008 Sun Microsystems, Inc.  All rights reserved.
26  * Use is subject to license terms.
27  */
28 
29 #pragma ident	"%Z%%M%	%I%	%E% SMI"
30 
31 
32 #include "includes.h"
33 
34 #ifdef GSSAPI
35 
36 #include <openssl/crypto.h>
37 #include <openssl/bn.h>
38 
39 #include "xmalloc.h"
40 #include "buffer.h"
41 #include "bufaux.h"
42 #include "kex.h"
43 #include "log.h"
44 #include "packet.h"
45 #include "dh.h"
46 #include "canohost.h"
47 #include "ssh2.h"
48 #include "ssh-gss.h"
49 
50 extern char *xxx_host;
51 
52 Gssctxt *xxx_gssctxt;
53 
54 static void kexgss_verbose_cleanup(void *arg);
55 
56 void
57 kexgss_client(Kex *kex)
58 {
59 	gss_buffer_desc gssbuf, send_tok, recv_tok, msg_tok;
60 	gss_buffer_t token_ptr;
61 	gss_OID mech = GSS_C_NULL_OID;
62 	Gssctxt *ctxt = NULL;
63 	OM_uint32 maj_status, min_status, smaj_status, smin_status;
64 	unsigned int klen, kout;
65 	DH *dh;
66 	BIGNUM *dh_server_pub = 0;
67 	BIGNUM *shared_secret = 0;
68 	Key *server_host_key = NULL;
69 	unsigned char *kbuf;
70 	unsigned char *hash;
71 	unsigned char *server_host_key_blob = NULL;
72 	char *msg, *lang;
73 	int type = 0;
74 	int first = 1;
75 	uint_t sbloblen = 0;
76 	uint_t strlen;
77 
78 	/* Map the negotiated kex name to a mech OID */
79 	ssh_gssapi_oid_of_kexname(kex->name, &mech);
80 	if (mech == GSS_C_NULL_OID)
81 		fatal("Couldn't match the negotiated GSS key exchange");
82 
83 	ssh_gssapi_build_ctx(&ctxt, 1, mech);
84 
85 	/* This code should match that in ssh_dh1_client */
86 
87 	/* Step 1 - e is dh->pub_key */
88 	dh = dh_new_group1();
89 	dh_gen_key(dh, kex->we_need * 8);
90 
91 	/* This is f, we initialise it now to make life easier */
92 	dh_server_pub = BN_new();
93 	if (dh_server_pub == NULL) {
94 		fatal("dh_server_pub == NULL");
95 	}
96 
97 	token_ptr = GSS_C_NO_BUFFER;
98 
99 	recv_tok.value = NULL;
100 	recv_tok.length = 0;
101 
102 	do {
103 		debug("Calling gss_init_sec_context");
104 
105 		maj_status = ssh_gssapi_init_ctx(ctxt, xxx_host,
106 		    kex->options.gss_deleg_creds, token_ptr, &send_tok);
107 
108 		if (GSS_ERROR(maj_status)) {
109 			ssh_gssapi_error(ctxt, "performing GSS-API protected "
110 			    "SSHv2 key exchange");
111 			(void) gss_release_buffer(&min_status, &send_tok);
112 			packet_disconnect("A GSS-API error occurred during "
113 			    "GSS-API protected SSHv2 key exchange\n");
114 		}
115 
116 		/* If we've got an old receive buffer get rid of it */
117 		if (token_ptr != GSS_C_NO_BUFFER) {
118 			/* We allocated recv_tok */
119 			xfree(recv_tok.value);
120 			recv_tok.value = NULL;
121 			recv_tok.length = 0;
122 			token_ptr = GSS_C_NO_BUFFER;
123 		}
124 
125 		if (maj_status == GSS_S_COMPLETE) {
126 			/* If mutual state flag is not true, kex fails */
127 			if (!(ctxt->flags & GSS_C_MUTUAL_FLAG)) {
128 				fatal("Mutual authentication failed");
129 			}
130 			/* If integ avail flag is not true kex fails */
131 			if (!(ctxt->flags & GSS_C_INTEG_FLAG)) {
132 				fatal("Integrity check failed");
133 			}
134 		}
135 
136 		/*
137 		 * If we have data to send, then the last message that we
138 		 * received cannot have been a 'complete'.
139 		 */
140 		if (send_tok.length != 0) {
141 			if (first) {
142 				packet_start(SSH2_MSG_KEXGSS_INIT);
143 				packet_put_string(send_tok.value,
144 				    send_tok.length);
145 				packet_put_bignum2(dh->pub_key);
146 				first = 0;
147 			} else {
148 				packet_start(SSH2_MSG_KEXGSS_CONTINUE);
149 				packet_put_string(send_tok.value,
150 				    send_tok.length);
151 			}
152 			(void) gss_release_buffer(&min_status, &send_tok);
153 			packet_send();
154 			packet_write_wait();
155 
156 
157 			/*
158 			 * If we've sent them data, they'd better be polite and
159 			 * reply.
160 			 */
161 
162 next_packet:
163 			/*
164 			 * We need to catch connection closing w/o error
165 			 * tokens or messages so we can tell the user
166 			 * _something_ more useful than "Connection
167 			 * closed by ..."
168 			 *
169 			 * We use a fatal cleanup function as that's
170 			 * all, really, that we can do for now.
171 			 */
172 			fatal_add_cleanup(kexgss_verbose_cleanup, NULL);
173 			type = packet_read();
174 			fatal_remove_cleanup(kexgss_verbose_cleanup, NULL);
175 			switch (type) {
176 			case SSH2_MSG_KEXGSS_HOSTKEY:
177 				debug("Received KEXGSS_HOSTKEY");
178 				server_host_key_blob =
179 				    packet_get_string(&sbloblen);
180 				server_host_key =
181 				    key_from_blob(server_host_key_blob,
182 				    sbloblen);
183 				goto next_packet; /* there MUSt be another */
184 				break;
185 			case SSH2_MSG_KEXGSS_CONTINUE:
186 				debug("Received GSSAPI_CONTINUE");
187 				if (maj_status == GSS_S_COMPLETE)
188 					packet_disconnect("Protocol error: "
189 					    "received GSS-API context token "
190 					    "though the context was already "
191 					    "established");
192 				recv_tok.value = packet_get_string(&strlen);
193 				recv_tok.length = strlen; /* u_int vs. size_t */
194 				break;
195 			case SSH2_MSG_KEXGSS_COMPLETE:
196 				debug("Received GSSAPI_COMPLETE");
197 				packet_get_bignum2(dh_server_pub);
198 				msg_tok.value = packet_get_string(&strlen);
199 				msg_tok.length = strlen; /* u_int vs. size_t */
200 
201 				/* Is there a token included? */
202 				if (packet_get_char()) {
203 					recv_tok.value =
204 					    packet_get_string(&strlen);
205 					/* u_int/size_t */
206 					recv_tok.length = strlen;
207 				}
208 				if (recv_tok.length > 0 &&
209 				    maj_status == GSS_S_COMPLETE) {
210 					packet_disconnect("Protocol error: "
211 					    "received GSS-API context token "
212 					    "though the context was already "
213 					    "established");
214 				} else if (recv_tok.length == 0 &&
215 				    maj_status == GSS_S_CONTINUE_NEEDED) {
216 					/* No token included */
217 					packet_disconnect("Protocol error: "
218 					    "did not receive expected "
219 					    "GSS-API context token");
220 				}
221 				break;
222 			case SSH2_MSG_KEXGSS_ERROR:
223 				smaj_status = packet_get_int();
224 				smin_status = packet_get_int();
225 				msg = packet_get_string(NULL);
226 				lang = packet_get_string(NULL);
227 				xfree(lang);
228 				error("Server had a GSS-API error; the "
229 				    "connection will close (%d/%d):\n%s",
230 				    smaj_status, smin_status, msg);
231 				error("Use the GssKeyEx option to disable "
232 				    "GSS-API key exchange and try again.");
233 				packet_disconnect("The server had a GSS-API "
234 				    "error during GSS-API protected SSHv2 "
235 				    "key exchange\n");
236 				break;
237 			default:
238 				packet_disconnect("Protocol error: "
239 				    "didn't expect packet type %d", type);
240 			}
241 			if (recv_tok.value)
242 				token_ptr = &recv_tok;
243 		} else {
244 			/* No data, and not complete */
245 			if (maj_status != GSS_S_COMPLETE) {
246 				fatal("Not complete, and no token output");
247 			}
248 		}
249 	} while (maj_status == GSS_S_CONTINUE_NEEDED);
250 
251 	/*
252 	 * We _must_ have received a COMPLETE message in reply from the
253 	 * server, which will have set dh_server_pub and msg_tok.
254 	 */
255 	if (type != SSH2_MSG_KEXGSS_COMPLETE)
256 		fatal("Expected SSH2_MSG_KEXGSS_COMPLETE never arrived");
257 	if (maj_status != GSS_S_COMPLETE)
258 		fatal("Internal error in GSS-API protected SSHv2 key exchange");
259 
260 	/* Check f in range [1, p-1] */
261 	if (!dh_pub_is_valid(dh, dh_server_pub))
262 		packet_disconnect("bad server public DH value");
263 
264 	/* compute K=f^x mod p */
265 	klen = DH_size(dh);
266 	kbuf = xmalloc(klen);
267 	kout = DH_compute_key(kbuf, dh_server_pub, dh);
268 
269 	shared_secret = BN_new();
270 	BN_bin2bn(kbuf, kout, shared_secret);
271 	(void) memset(kbuf, 0, klen);
272 	xfree(kbuf);
273 
274 	/* The GSS hash is identical to the DH one */
275 	hash = kex_dh_hash(
276 	    kex->client_version_string,
277 	    kex->server_version_string,
278 	    buffer_ptr(&kex->my), buffer_len(&kex->my),
279 	    buffer_ptr(&kex->peer), buffer_len(&kex->peer),
280 	    server_host_key_blob, sbloblen, /* server host key */
281 	    dh->pub_key,	/* e */
282 	    dh_server_pub,	/* f */
283 	    shared_secret);	/* K */
284 
285 	gssbuf.value = hash;
286 	gssbuf.length = 20;
287 
288 	/* Verify that H matches the token we just got. */
289 	if ((maj_status = gss_verify_mic(&min_status, ctxt->context, &gssbuf,
290 	    &msg_tok, NULL))) {
291 		packet_disconnect("Hash's MIC didn't verify");
292 	}
293 
294 	if (server_host_key && kex->accept_host_key != NULL)
295 		(void) kex->accept_host_key(server_host_key);
296 
297 	DH_free(dh);
298 
299 	xxx_gssctxt = ctxt; /* for gss keyex w/ mic userauth */
300 
301 	/* save session id */
302 	if (kex->session_id == NULL) {
303 		kex->session_id_len = 20;
304 		kex->session_id = xmalloc(kex->session_id_len);
305 		(void) memcpy(kex->session_id, hash, kex->session_id_len);
306 	}
307 
308 	kex_derive_keys(kex, hash, shared_secret);
309 	BN_clear_free(shared_secret);
310 	kex_finish(kex);
311 }
312 
313 /* ARGSUSED */
314 static
315 void
316 kexgss_verbose_cleanup(void *arg)
317 {
318 	error("The GSS-API protected key exchange has failed without "
319 	    "indication\nfrom the server, possibly due to misconfiguration "
320 	    "of the server.");
321 	error("Use the GssKeyEx option to disable GSS-API key exchange "
322 	    "and try again.");
323 }
324 
325 #endif /* GSSAPI */
326