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1 /* $OpenBSD: auth2-gss.c,v 1.22 2015/01/19 20:07:45 markus Exp $ */
2 
3 /*
4  * Copyright (c) 2001-2003 Simon Wilkinson. All rights reserved.
5  *
6  * Redistribution and use in source and binary forms, with or without
7  * modification, are permitted provided that the following conditions
8  * are met:
9  * 1. Redistributions of source code must retain the above copyright
10  *    notice, this list of conditions and the following disclaimer.
11  * 2. Redistributions in binary form must reproduce the above copyright
12  *    notice, this list of conditions and the following disclaimer in the
13  *    documentation and/or other materials provided with the distribution.
14  *
15  * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AS IS'' AND ANY EXPRESS OR
16  * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
17  * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
18  * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
19  * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
20  * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
21  * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
22  * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
23  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
24  * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
25  */
26 
27 #include "includes.h"
28 
29 #ifdef GSSAPI
30 
31 #include <sys/types.h>
32 
33 #include <stdarg.h>
34 
35 #include "xmalloc.h"
36 #include "key.h"
37 #include "hostfile.h"
38 #include "auth.h"
39 #include "ssh2.h"
40 #include "log.h"
41 #include "dispatch.h"
42 #include "buffer.h"
43 #include "misc.h"
44 #include "servconf.h"
45 #include "packet.h"
46 #include "ssh-gss.h"
47 #include "monitor_wrap.h"
48 
49 extern ServerOptions options;
50 
51 static int input_gssapi_token(int type, u_int32_t plen, void *ctxt);
52 static int input_gssapi_mic(int type, u_int32_t plen, void *ctxt);
53 static int input_gssapi_exchange_complete(int type, u_int32_t plen, void *ctxt);
54 static int input_gssapi_errtok(int, u_int32_t, void *);
55 
56 /*
57  * We only support those mechanisms that we know about (ie ones that we know
58  * how to check local user kuserok and the like)
59  */
60 static int
userauth_gssapi(Authctxt * authctxt)61 userauth_gssapi(Authctxt *authctxt)
62 {
63 	gss_OID_desc goid = {0, NULL};
64 	Gssctxt *ctxt = NULL;
65 	int mechs;
66 	int present;
67 	OM_uint32 ms;
68 	u_int len;
69 	u_char *doid = NULL;
70 
71 	if (!authctxt->valid || authctxt->user == NULL)
72 		return (0);
73 
74 	mechs = packet_get_int();
75 	if (mechs == 0) {
76 		debug("Mechanism negotiation is not supported");
77 		return (0);
78 	}
79 
80 	do {
81 		mechs--;
82 
83 		free(doid);
84 
85 		present = 0;
86 		doid = packet_get_string(&len);
87 
88 		if (len > 2 && doid[0] == SSH_GSS_OIDTYPE &&
89 		    doid[1] == len - 2) {
90 			goid.elements = doid + 2;
91 			goid.length   = len - 2;
92 			ssh_gssapi_test_oid_supported(&ms, &goid, &present);
93 		} else {
94 			logit("Badly formed OID received");
95 		}
96 	} while (mechs > 0 && !present);
97 
98 	if (!present) {
99 		free(doid);
100 		authctxt->server_caused_failure = 1;
101 		return (0);
102 	}
103 
104 	if (GSS_ERROR(PRIVSEP(ssh_gssapi_server_ctx(&ctxt, &goid)))) {
105 		if (ctxt != NULL)
106 			ssh_gssapi_delete_ctx(&ctxt);
107 		free(doid);
108 		authctxt->server_caused_failure = 1;
109 		return (0);
110 	}
111 
112 	authctxt->methoddata = (void *)ctxt;
113 
114 	packet_start(SSH2_MSG_USERAUTH_GSSAPI_RESPONSE);
115 
116 	/* Return the OID that we received */
117 	packet_put_string(doid, len);
118 
119 	packet_send();
120 	free(doid);
121 
122 	dispatch_set(SSH2_MSG_USERAUTH_GSSAPI_TOKEN, &input_gssapi_token);
123 	dispatch_set(SSH2_MSG_USERAUTH_GSSAPI_ERRTOK, &input_gssapi_errtok);
124 	authctxt->postponed = 1;
125 
126 	return (0);
127 }
128 
129 static int
input_gssapi_token(int type,u_int32_t plen,void * ctxt)130 input_gssapi_token(int type, u_int32_t plen, void *ctxt)
131 {
132 	Authctxt *authctxt = ctxt;
133 	Gssctxt *gssctxt;
134 	gss_buffer_desc send_tok = GSS_C_EMPTY_BUFFER;
135 	gss_buffer_desc recv_tok;
136 	OM_uint32 maj_status, min_status, flags;
137 	u_int len;
138 
139 	if (authctxt == NULL || (authctxt->methoddata == NULL && !use_privsep))
140 		fatal("No authentication or GSSAPI context");
141 
142 	gssctxt = authctxt->methoddata;
143 	recv_tok.value = packet_get_string(&len);
144 	recv_tok.length = len; /* u_int vs. size_t */
145 
146 	packet_check_eom();
147 
148 	maj_status = PRIVSEP(ssh_gssapi_accept_ctx(gssctxt, &recv_tok,
149 	    &send_tok, &flags));
150 
151 	free(recv_tok.value);
152 
153 	if (GSS_ERROR(maj_status)) {
154 		if (send_tok.length != 0) {
155 			packet_start(SSH2_MSG_USERAUTH_GSSAPI_ERRTOK);
156 			packet_put_string(send_tok.value, send_tok.length);
157 			packet_send();
158 		}
159 		authctxt->postponed = 0;
160 		dispatch_set(SSH2_MSG_USERAUTH_GSSAPI_TOKEN, NULL);
161 		userauth_finish(authctxt, 0, "gssapi-with-mic", NULL);
162 	} else {
163 		if (send_tok.length != 0) {
164 			packet_start(SSH2_MSG_USERAUTH_GSSAPI_TOKEN);
165 			packet_put_string(send_tok.value, send_tok.length);
166 			packet_send();
167 		}
168 		if (maj_status == GSS_S_COMPLETE) {
169 			dispatch_set(SSH2_MSG_USERAUTH_GSSAPI_TOKEN, NULL);
170 			if (flags & GSS_C_INTEG_FLAG)
171 				dispatch_set(SSH2_MSG_USERAUTH_GSSAPI_MIC,
172 				    &input_gssapi_mic);
173 			else
174 				dispatch_set(
175 				    SSH2_MSG_USERAUTH_GSSAPI_EXCHANGE_COMPLETE,
176 				    &input_gssapi_exchange_complete);
177 		}
178 	}
179 
180 	gss_release_buffer(&min_status, &send_tok);
181 	return 0;
182 }
183 
184 static int
input_gssapi_errtok(int type,u_int32_t plen,void * ctxt)185 input_gssapi_errtok(int type, u_int32_t plen, void *ctxt)
186 {
187 	Authctxt *authctxt = ctxt;
188 	Gssctxt *gssctxt;
189 	gss_buffer_desc send_tok = GSS_C_EMPTY_BUFFER;
190 	gss_buffer_desc recv_tok;
191 	OM_uint32 maj_status;
192 	u_int len;
193 
194 	if (authctxt == NULL || (authctxt->methoddata == NULL && !use_privsep))
195 		fatal("No authentication or GSSAPI context");
196 
197 	gssctxt = authctxt->methoddata;
198 	recv_tok.value = packet_get_string(&len);
199 	recv_tok.length = len;
200 
201 	packet_check_eom();
202 
203 	/* Push the error token into GSSAPI to see what it says */
204 	maj_status = PRIVSEP(ssh_gssapi_accept_ctx(gssctxt, &recv_tok,
205 	    &send_tok, NULL));
206 
207 	free(recv_tok.value);
208 
209 	/* We can't return anything to the client, even if we wanted to */
210 	dispatch_set(SSH2_MSG_USERAUTH_GSSAPI_TOKEN, NULL);
211 	dispatch_set(SSH2_MSG_USERAUTH_GSSAPI_ERRTOK, NULL);
212 
213 	/* The client will have already moved on to the next auth */
214 
215 	gss_release_buffer(&maj_status, &send_tok);
216 	return 0;
217 }
218 
219 /*
220  * This is called when the client thinks we've completed authentication.
221  * It should only be enabled in the dispatch handler by the function above,
222  * which only enables it once the GSSAPI exchange is complete.
223  */
224 
225 static int
input_gssapi_exchange_complete(int type,u_int32_t plen,void * ctxt)226 input_gssapi_exchange_complete(int type, u_int32_t plen, void *ctxt)
227 {
228 	Authctxt *authctxt = ctxt;
229 	int authenticated;
230 
231 	if (authctxt == NULL || (authctxt->methoddata == NULL && !use_privsep))
232 		fatal("No authentication or GSSAPI context");
233 
234 	/*
235 	 * We don't need to check the status, because we're only enabled in
236 	 * the dispatcher once the exchange is complete
237 	 */
238 
239 	packet_check_eom();
240 
241 	authenticated = PRIVSEP(ssh_gssapi_userok(authctxt->user));
242 
243 	authctxt->postponed = 0;
244 	dispatch_set(SSH2_MSG_USERAUTH_GSSAPI_TOKEN, NULL);
245 	dispatch_set(SSH2_MSG_USERAUTH_GSSAPI_ERRTOK, NULL);
246 	dispatch_set(SSH2_MSG_USERAUTH_GSSAPI_MIC, NULL);
247 	dispatch_set(SSH2_MSG_USERAUTH_GSSAPI_EXCHANGE_COMPLETE, NULL);
248 	userauth_finish(authctxt, authenticated, "gssapi-with-mic", NULL);
249 	return 0;
250 }
251 
252 static int
input_gssapi_mic(int type,u_int32_t plen,void * ctxt)253 input_gssapi_mic(int type, u_int32_t plen, void *ctxt)
254 {
255 	Authctxt *authctxt = ctxt;
256 	Gssctxt *gssctxt;
257 	int authenticated = 0;
258 	Buffer b;
259 	gss_buffer_desc mic, gssbuf;
260 	u_int len;
261 
262 	if (authctxt == NULL || (authctxt->methoddata == NULL && !use_privsep))
263 		fatal("No authentication or GSSAPI context");
264 
265 	gssctxt = authctxt->methoddata;
266 
267 	mic.value = packet_get_string(&len);
268 	mic.length = len;
269 
270 	ssh_gssapi_buildmic(&b, authctxt->user, authctxt->service,
271 	    "gssapi-with-mic");
272 
273 	gssbuf.value = buffer_ptr(&b);
274 	gssbuf.length = buffer_len(&b);
275 
276 	if (!GSS_ERROR(PRIVSEP(ssh_gssapi_checkmic(gssctxt, &gssbuf, &mic))))
277 		authenticated = PRIVSEP(ssh_gssapi_userok(authctxt->user));
278 	else
279 		logit("GSSAPI MIC check failed");
280 
281 	buffer_free(&b);
282 	free(mic.value);
283 
284 	authctxt->postponed = 0;
285 	dispatch_set(SSH2_MSG_USERAUTH_GSSAPI_TOKEN, NULL);
286 	dispatch_set(SSH2_MSG_USERAUTH_GSSAPI_ERRTOK, NULL);
287 	dispatch_set(SSH2_MSG_USERAUTH_GSSAPI_MIC, NULL);
288 	dispatch_set(SSH2_MSG_USERAUTH_GSSAPI_EXCHANGE_COMPLETE, NULL);
289 	userauth_finish(authctxt, authenticated, "gssapi-with-mic", NULL);
290 	return 0;
291 }
292 
293 Authmethod method_gssapi = {
294 	"gssapi-with-mic",
295 	userauth_gssapi,
296 	&options.gss_authentication
297 };
298 
299 #endif /* GSSAPI */
300