xref: /openssh-portable/auth2-gss.c (revision 39be3dc2)
1 /* $OpenBSD: auth2-gss.c,v 1.31 2021/01/27 10:05:28 djm 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 "sshkey.h"
37 #include "hostfile.h"
38 #include "auth.h"
39 #include "ssh2.h"
40 #include "log.h"
41 #include "dispatch.h"
42 #include "sshbuf.h"
43 #include "ssherr.h"
44 #include "misc.h"
45 #include "servconf.h"
46 #include "packet.h"
47 #include "ssh-gss.h"
48 #include "monitor_wrap.h"
49 
50 extern ServerOptions options;
51 
52 static int input_gssapi_token(int type, u_int32_t plen, struct ssh *ssh);
53 static int input_gssapi_mic(int type, u_int32_t plen, struct ssh *ssh);
54 static int input_gssapi_exchange_complete(int type, u_int32_t plen, struct ssh *ssh);
55 static int input_gssapi_errtok(int, u_int32_t, struct ssh *);
56 
57 /*
58  * We only support those mechanisms that we know about (ie ones that we know
59  * how to check local user kuserok and the like)
60  */
61 static int
62 userauth_gssapi(struct ssh *ssh)
63 {
64 	Authctxt *authctxt = ssh->authctxt;
65 	gss_OID_desc goid = {0, NULL};
66 	Gssctxt *ctxt = NULL;
67 	int r, present;
68 	u_int mechs;
69 	OM_uint32 ms;
70 	size_t len;
71 	u_char *doid = NULL;
72 
73 	if ((r = sshpkt_get_u32(ssh, &mechs)) != 0)
74 		fatal_fr(r, "parse packet");
75 
76 	if (mechs == 0) {
77 		debug("Mechanism negotiation is not supported");
78 		return (0);
79 	}
80 
81 	do {
82 		mechs--;
83 
84 		free(doid);
85 
86 		present = 0;
87 		if ((r = sshpkt_get_string(ssh, &doid, &len)) != 0)
88 			fatal_fr(r, "parse oid");
89 
90 		if (len > 2 && doid[0] == SSH_GSS_OIDTYPE &&
91 		    doid[1] == len - 2) {
92 			goid.elements = doid + 2;
93 			goid.length   = len - 2;
94 			ssh_gssapi_test_oid_supported(&ms, &goid, &present);
95 		} else {
96 			logit("Badly formed OID received");
97 		}
98 	} while (mechs > 0 && !present);
99 
100 	if (!present) {
101 		free(doid);
102 		authctxt->server_caused_failure = 1;
103 		return (0);
104 	}
105 
106 	if (!authctxt->valid || authctxt->user == NULL) {
107 		debug2_f("disabled because of invalid user");
108 		free(doid);
109 		return (0);
110 	}
111 
112 	if (GSS_ERROR(PRIVSEP(ssh_gssapi_server_ctx(&ctxt, &goid)))) {
113 		if (ctxt != NULL)
114 			ssh_gssapi_delete_ctx(&ctxt);
115 		free(doid);
116 		authctxt->server_caused_failure = 1;
117 		return (0);
118 	}
119 
120 	authctxt->methoddata = (void *)ctxt;
121 
122 	/* Return the OID that we received */
123 	if ((r = sshpkt_start(ssh, SSH2_MSG_USERAUTH_GSSAPI_RESPONSE)) != 0 ||
124 	    (r = sshpkt_put_string(ssh, doid, len)) != 0 ||
125 	    (r = sshpkt_send(ssh)) != 0)
126 		fatal_fr(r, "send packet");
127 
128 	free(doid);
129 
130 	ssh_dispatch_set(ssh, SSH2_MSG_USERAUTH_GSSAPI_TOKEN, &input_gssapi_token);
131 	ssh_dispatch_set(ssh, SSH2_MSG_USERAUTH_GSSAPI_ERRTOK, &input_gssapi_errtok);
132 	authctxt->postponed = 1;
133 
134 	return (0);
135 }
136 
137 static int
138 input_gssapi_token(int type, u_int32_t plen, struct ssh *ssh)
139 {
140 	Authctxt *authctxt = ssh->authctxt;
141 	Gssctxt *gssctxt;
142 	gss_buffer_desc send_tok = GSS_C_EMPTY_BUFFER;
143 	gss_buffer_desc recv_tok;
144 	OM_uint32 maj_status, min_status, flags;
145 	u_char *p;
146 	size_t len;
147 	int r;
148 
149 	if (authctxt == NULL || (authctxt->methoddata == NULL && !use_privsep))
150 		fatal("No authentication or GSSAPI context");
151 
152 	gssctxt = authctxt->methoddata;
153 	if ((r = sshpkt_get_string(ssh, &p, &len)) != 0 ||
154 	    (r = sshpkt_get_end(ssh)) != 0)
155 		fatal_fr(r, "parse packet");
156 
157 	recv_tok.value = p;
158 	recv_tok.length = len;
159 	maj_status = PRIVSEP(ssh_gssapi_accept_ctx(gssctxt, &recv_tok,
160 	    &send_tok, &flags));
161 
162 	free(p);
163 
164 	if (GSS_ERROR(maj_status)) {
165 		if (send_tok.length != 0) {
166 			if ((r = sshpkt_start(ssh,
167 			    SSH2_MSG_USERAUTH_GSSAPI_ERRTOK)) != 0 ||
168 			    (r = sshpkt_put_string(ssh, send_tok.value,
169 			    send_tok.length)) != 0 ||
170 			    (r = sshpkt_send(ssh)) != 0)
171 				fatal_fr(r, "send ERRTOK packet");
172 		}
173 		authctxt->postponed = 0;
174 		ssh_dispatch_set(ssh, SSH2_MSG_USERAUTH_GSSAPI_TOKEN, NULL);
175 		userauth_finish(ssh, 0, "gssapi-with-mic", NULL);
176 	} else {
177 		if (send_tok.length != 0) {
178 			if ((r = sshpkt_start(ssh,
179 			    SSH2_MSG_USERAUTH_GSSAPI_TOKEN)) != 0 ||
180 			    (r = sshpkt_put_string(ssh, send_tok.value,
181 			    send_tok.length)) != 0 ||
182 			    (r = sshpkt_send(ssh)) != 0)
183 				fatal_fr(r, "send TOKEN packet");
184 		}
185 		if (maj_status == GSS_S_COMPLETE) {
186 			ssh_dispatch_set(ssh, SSH2_MSG_USERAUTH_GSSAPI_TOKEN, NULL);
187 			if (flags & GSS_C_INTEG_FLAG)
188 				ssh_dispatch_set(ssh, SSH2_MSG_USERAUTH_GSSAPI_MIC,
189 				    &input_gssapi_mic);
190 			else
191 				ssh_dispatch_set(ssh,
192 				    SSH2_MSG_USERAUTH_GSSAPI_EXCHANGE_COMPLETE,
193 				    &input_gssapi_exchange_complete);
194 		}
195 	}
196 
197 	gss_release_buffer(&min_status, &send_tok);
198 	return 0;
199 }
200 
201 static int
202 input_gssapi_errtok(int type, u_int32_t plen, struct ssh *ssh)
203 {
204 	Authctxt *authctxt = ssh->authctxt;
205 	Gssctxt *gssctxt;
206 	gss_buffer_desc send_tok = GSS_C_EMPTY_BUFFER;
207 	gss_buffer_desc recv_tok;
208 	OM_uint32 maj_status;
209 	int r;
210 	u_char *p;
211 	size_t len;
212 
213 	if (authctxt == NULL || (authctxt->methoddata == NULL && !use_privsep))
214 		fatal("No authentication or GSSAPI context");
215 
216 	gssctxt = authctxt->methoddata;
217 	if ((r = sshpkt_get_string(ssh, &p, &len)) != 0 ||
218 	    (r = sshpkt_get_end(ssh)) != 0)
219 		fatal_fr(r, "parse packet");
220 	recv_tok.value = p;
221 	recv_tok.length = len;
222 
223 	/* Push the error token into GSSAPI to see what it says */
224 	maj_status = PRIVSEP(ssh_gssapi_accept_ctx(gssctxt, &recv_tok,
225 	    &send_tok, NULL));
226 
227 	free(recv_tok.value);
228 
229 	/* We can't return anything to the client, even if we wanted to */
230 	ssh_dispatch_set(ssh, SSH2_MSG_USERAUTH_GSSAPI_TOKEN, NULL);
231 	ssh_dispatch_set(ssh, SSH2_MSG_USERAUTH_GSSAPI_ERRTOK, NULL);
232 
233 	/* The client will have already moved on to the next auth */
234 
235 	gss_release_buffer(&maj_status, &send_tok);
236 	return 0;
237 }
238 
239 /*
240  * This is called when the client thinks we've completed authentication.
241  * It should only be enabled in the dispatch handler by the function above,
242  * which only enables it once the GSSAPI exchange is complete.
243  */
244 
245 static int
246 input_gssapi_exchange_complete(int type, u_int32_t plen, struct ssh *ssh)
247 {
248 	Authctxt *authctxt = ssh->authctxt;
249 	int r, authenticated;
250 	const char *displayname;
251 
252 	if (authctxt == NULL || (authctxt->methoddata == NULL && !use_privsep))
253 		fatal("No authentication or GSSAPI context");
254 
255 	/*
256 	 * We don't need to check the status, because we're only enabled in
257 	 * the dispatcher once the exchange is complete
258 	 */
259 
260 	if ((r = sshpkt_get_end(ssh)) != 0)
261 		fatal_fr(r, "parse packet");
262 
263 	authenticated = PRIVSEP(ssh_gssapi_userok(authctxt->user));
264 
265 	if ((!use_privsep || mm_is_monitor()) &&
266 	    (displayname = ssh_gssapi_displayname()) != NULL)
267 		auth2_record_info(authctxt, "%s", displayname);
268 
269 	authctxt->postponed = 0;
270 	ssh_dispatch_set(ssh, SSH2_MSG_USERAUTH_GSSAPI_TOKEN, NULL);
271 	ssh_dispatch_set(ssh, SSH2_MSG_USERAUTH_GSSAPI_ERRTOK, NULL);
272 	ssh_dispatch_set(ssh, SSH2_MSG_USERAUTH_GSSAPI_MIC, NULL);
273 	ssh_dispatch_set(ssh, SSH2_MSG_USERAUTH_GSSAPI_EXCHANGE_COMPLETE, NULL);
274 	userauth_finish(ssh, authenticated, "gssapi-with-mic", NULL);
275 	return 0;
276 }
277 
278 static int
279 input_gssapi_mic(int type, u_int32_t plen, struct ssh *ssh)
280 {
281 	Authctxt *authctxt = ssh->authctxt;
282 	Gssctxt *gssctxt;
283 	int r, authenticated = 0;
284 	struct sshbuf *b;
285 	gss_buffer_desc mic, gssbuf;
286 	const char *displayname;
287 	u_char *p;
288 	size_t len;
289 
290 	if (authctxt == NULL || (authctxt->methoddata == NULL && !use_privsep))
291 		fatal("No authentication or GSSAPI context");
292 
293 	gssctxt = authctxt->methoddata;
294 
295 	if ((r = sshpkt_get_string(ssh, &p, &len)) != 0)
296 		fatal_fr(r, "parse packet");
297 	if ((b = sshbuf_new()) == NULL)
298 		fatal_f("sshbuf_new failed");
299 	mic.value = p;
300 	mic.length = len;
301 	ssh_gssapi_buildmic(b, authctxt->user, authctxt->service,
302 	    "gssapi-with-mic", ssh->kex->session_id);
303 
304 	if ((gssbuf.value = sshbuf_mutable_ptr(b)) == NULL)
305 		fatal_f("sshbuf_mutable_ptr failed");
306 	gssbuf.length = sshbuf_len(b);
307 
308 	if (!GSS_ERROR(PRIVSEP(ssh_gssapi_checkmic(gssctxt, &gssbuf, &mic))))
309 		authenticated = PRIVSEP(ssh_gssapi_userok(authctxt->user));
310 	else
311 		logit("GSSAPI MIC check failed");
312 
313 	sshbuf_free(b);
314 	free(mic.value);
315 
316 	if ((!use_privsep || mm_is_monitor()) &&
317 	    (displayname = ssh_gssapi_displayname()) != NULL)
318 		auth2_record_info(authctxt, "%s", displayname);
319 
320 	authctxt->postponed = 0;
321 	ssh_dispatch_set(ssh, SSH2_MSG_USERAUTH_GSSAPI_TOKEN, NULL);
322 	ssh_dispatch_set(ssh, SSH2_MSG_USERAUTH_GSSAPI_ERRTOK, NULL);
323 	ssh_dispatch_set(ssh, SSH2_MSG_USERAUTH_GSSAPI_MIC, NULL);
324 	ssh_dispatch_set(ssh, SSH2_MSG_USERAUTH_GSSAPI_EXCHANGE_COMPLETE, NULL);
325 	userauth_finish(ssh, authenticated, "gssapi-with-mic", NULL);
326 	return 0;
327 }
328 
329 Authmethod method_gssapi = {
330 	"gssapi-with-mic",
331 	userauth_gssapi,
332 	&options.gss_authentication
333 };
334 
335 #endif /* GSSAPI */
336