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1 /* $OpenBSD: gss-serv.c,v 1.29 2015/05/22 03:50:02 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 #include <string.h>
35 #include <unistd.h>
36 
37 #include "openbsd-compat/sys-queue.h"
38 #include "xmalloc.h"
39 #include "buffer.h"
40 #include "key.h"
41 #include "hostfile.h"
42 #include "auth.h"
43 #include "log.h"
44 #include "channels.h"
45 #include "session.h"
46 #include "misc.h"
47 #include "servconf.h"
48 
49 #include "ssh-gss.h"
50 
51 extern ServerOptions options;
52 
53 static ssh_gssapi_client gssapi_client =
54     { GSS_C_EMPTY_BUFFER, GSS_C_EMPTY_BUFFER,
55     GSS_C_NO_CREDENTIAL, NULL, {NULL, NULL, NULL, NULL}};
56 
57 ssh_gssapi_mech gssapi_null_mech =
58     { NULL, NULL, {0, NULL}, NULL, NULL, NULL, NULL};
59 
60 #ifdef KRB5
61 extern ssh_gssapi_mech gssapi_kerberos_mech;
62 #endif
63 
64 ssh_gssapi_mech* supported_mechs[]= {
65 #ifdef KRB5
66 	&gssapi_kerberos_mech,
67 #endif
68 	&gssapi_null_mech,
69 };
70 
71 /*
72  * ssh_gssapi_supported_oids() can cause sandbox violations, so prepare the
73  * list of supported mechanisms before privsep is set up.
74  */
75 static gss_OID_set supported_oids;
76 
77 void
ssh_gssapi_prepare_supported_oids(void)78 ssh_gssapi_prepare_supported_oids(void)
79 {
80 	ssh_gssapi_supported_oids(&supported_oids);
81 }
82 
83 OM_uint32
ssh_gssapi_test_oid_supported(OM_uint32 * ms,gss_OID member,int * present)84 ssh_gssapi_test_oid_supported(OM_uint32 *ms, gss_OID member, int *present)
85 {
86 	if (supported_oids == NULL)
87 		ssh_gssapi_prepare_supported_oids();
88 	return gss_test_oid_set_member(ms, member, supported_oids, present);
89 }
90 
91 /*
92  * Acquire credentials for a server running on the current host.
93  * Requires that the context structure contains a valid OID
94  */
95 
96 /* Returns a GSSAPI error code */
97 /* Privileged (called from ssh_gssapi_server_ctx) */
98 static OM_uint32
ssh_gssapi_acquire_cred(Gssctxt * ctx)99 ssh_gssapi_acquire_cred(Gssctxt *ctx)
100 {
101 	OM_uint32 status;
102 	char lname[NI_MAXHOST];
103 	gss_OID_set oidset;
104 
105 	if (options.gss_strict_acceptor) {
106 		gss_create_empty_oid_set(&status, &oidset);
107 		gss_add_oid_set_member(&status, ctx->oid, &oidset);
108 
109 		if (gethostname(lname, MAXHOSTNAMELEN)) {
110 			gss_release_oid_set(&status, &oidset);
111 			return (-1);
112 		}
113 
114 		if (GSS_ERROR(ssh_gssapi_import_name(ctx, lname))) {
115 			gss_release_oid_set(&status, &oidset);
116 			return (ctx->major);
117 		}
118 
119 		if ((ctx->major = gss_acquire_cred(&ctx->minor,
120 		    ctx->name, 0, oidset, GSS_C_ACCEPT, &ctx->creds,
121 		    NULL, NULL)))
122 			ssh_gssapi_error(ctx);
123 
124 		gss_release_oid_set(&status, &oidset);
125 		return (ctx->major);
126 	} else {
127 		ctx->name = GSS_C_NO_NAME;
128 		ctx->creds = GSS_C_NO_CREDENTIAL;
129 	}
130 	return GSS_S_COMPLETE;
131 }
132 
133 /* Privileged */
134 OM_uint32
ssh_gssapi_server_ctx(Gssctxt ** ctx,gss_OID oid)135 ssh_gssapi_server_ctx(Gssctxt **ctx, gss_OID oid)
136 {
137 	if (*ctx)
138 		ssh_gssapi_delete_ctx(ctx);
139 	ssh_gssapi_build_ctx(ctx);
140 	ssh_gssapi_set_oid(*ctx, oid);
141 	return (ssh_gssapi_acquire_cred(*ctx));
142 }
143 
144 /* Unprivileged */
145 void
ssh_gssapi_supported_oids(gss_OID_set * oidset)146 ssh_gssapi_supported_oids(gss_OID_set *oidset)
147 {
148 	int i = 0;
149 	OM_uint32 min_status;
150 	int present;
151 	gss_OID_set supported;
152 
153 	gss_create_empty_oid_set(&min_status, oidset);
154 	gss_indicate_mechs(&min_status, &supported);
155 
156 	while (supported_mechs[i]->name != NULL) {
157 		if (GSS_ERROR(gss_test_oid_set_member(&min_status,
158 		    &supported_mechs[i]->oid, supported, &present)))
159 			present = 0;
160 		if (present)
161 			gss_add_oid_set_member(&min_status,
162 			    &supported_mechs[i]->oid, oidset);
163 		i++;
164 	}
165 
166 	gss_release_oid_set(&min_status, &supported);
167 }
168 
169 
170 /* Wrapper around accept_sec_context
171  * Requires that the context contains:
172  *    oid
173  *    credentials	(from ssh_gssapi_acquire_cred)
174  */
175 /* Privileged */
176 OM_uint32
ssh_gssapi_accept_ctx(Gssctxt * ctx,gss_buffer_desc * recv_tok,gss_buffer_desc * send_tok,OM_uint32 * flags)177 ssh_gssapi_accept_ctx(Gssctxt *ctx, gss_buffer_desc *recv_tok,
178     gss_buffer_desc *send_tok, OM_uint32 *flags)
179 {
180 	OM_uint32 status;
181 	gss_OID mech;
182 
183 	ctx->major = gss_accept_sec_context(&ctx->minor,
184 	    &ctx->context, ctx->creds, recv_tok,
185 	    GSS_C_NO_CHANNEL_BINDINGS, &ctx->client, &mech,
186 	    send_tok, flags, NULL, &ctx->client_creds);
187 
188 	if (GSS_ERROR(ctx->major))
189 		ssh_gssapi_error(ctx);
190 
191 	if (ctx->client_creds)
192 		debug("Received some client credentials");
193 	else
194 		debug("Got no client credentials");
195 
196 	status = ctx->major;
197 
198 	/* Now, if we're complete and we have the right flags, then
199 	 * we flag the user as also having been authenticated
200 	 */
201 
202 	if (((flags == NULL) || ((*flags & GSS_C_MUTUAL_FLAG) &&
203 	    (*flags & GSS_C_INTEG_FLAG))) && (ctx->major == GSS_S_COMPLETE)) {
204 		if (ssh_gssapi_getclient(ctx, &gssapi_client))
205 			fatal("Couldn't convert client name");
206 	}
207 
208 	return (status);
209 }
210 
211 /*
212  * This parses an exported name, extracting the mechanism specific portion
213  * to use for ACL checking. It verifies that the name belongs the mechanism
214  * originally selected.
215  */
216 static OM_uint32
ssh_gssapi_parse_ename(Gssctxt * ctx,gss_buffer_t ename,gss_buffer_t name)217 ssh_gssapi_parse_ename(Gssctxt *ctx, gss_buffer_t ename, gss_buffer_t name)
218 {
219 	u_char *tok;
220 	OM_uint32 offset;
221 	OM_uint32 oidl;
222 
223 	tok = ename->value;
224 
225 	/*
226 	 * Check that ename is long enough for all of the fixed length
227 	 * header, and that the initial ID bytes are correct
228 	 */
229 
230 	if (ename->length < 6 || memcmp(tok, "\x04\x01", 2) != 0)
231 		return GSS_S_FAILURE;
232 
233 	/*
234 	 * Extract the OID, and check it. Here GSSAPI breaks with tradition
235 	 * and does use the OID type and length bytes. To confuse things
236 	 * there are two lengths - the first including these, and the
237 	 * second without.
238 	 */
239 
240 	oidl = get_u16(tok+2); /* length including next two bytes */
241 	oidl = oidl-2; /* turn it into the _real_ length of the variable OID */
242 
243 	/*
244 	 * Check the BER encoding for correct type and length, that the
245 	 * string is long enough and that the OID matches that in our context
246 	 */
247 	if (tok[4] != 0x06 || tok[5] != oidl ||
248 	    ename->length < oidl+6 ||
249 	    !ssh_gssapi_check_oid(ctx, tok+6, oidl))
250 		return GSS_S_FAILURE;
251 
252 	offset = oidl+6;
253 
254 	if (ename->length < offset+4)
255 		return GSS_S_FAILURE;
256 
257 	name->length = get_u32(tok+offset);
258 	offset += 4;
259 
260 	if (UINT_MAX - offset < name->length)
261 		return GSS_S_FAILURE;
262 	if (ename->length < offset+name->length)
263 		return GSS_S_FAILURE;
264 
265 	name->value = xmalloc(name->length+1);
266 	memcpy(name->value, tok+offset, name->length);
267 	((char *)name->value)[name->length] = 0;
268 
269 	return GSS_S_COMPLETE;
270 }
271 
272 /* Extract the client details from a given context. This can only reliably
273  * be called once for a context */
274 
275 /* Privileged (called from accept_secure_ctx) */
276 OM_uint32
ssh_gssapi_getclient(Gssctxt * ctx,ssh_gssapi_client * client)277 ssh_gssapi_getclient(Gssctxt *ctx, ssh_gssapi_client *client)
278 {
279 	int i = 0;
280 
281 	gss_buffer_desc ename;
282 
283 	client->mech = NULL;
284 
285 	while (supported_mechs[i]->name != NULL) {
286 		if (supported_mechs[i]->oid.length == ctx->oid->length &&
287 		    (memcmp(supported_mechs[i]->oid.elements,
288 		    ctx->oid->elements, ctx->oid->length) == 0))
289 			client->mech = supported_mechs[i];
290 		i++;
291 	}
292 
293 	if (client->mech == NULL)
294 		return GSS_S_FAILURE;
295 
296 	if ((ctx->major = gss_display_name(&ctx->minor, ctx->client,
297 	    &client->displayname, NULL))) {
298 		ssh_gssapi_error(ctx);
299 		return (ctx->major);
300 	}
301 
302 	if ((ctx->major = gss_export_name(&ctx->minor, ctx->client,
303 	    &ename))) {
304 		ssh_gssapi_error(ctx);
305 		return (ctx->major);
306 	}
307 
308 	if ((ctx->major = ssh_gssapi_parse_ename(ctx,&ename,
309 	    &client->exportedname))) {
310 		return (ctx->major);
311 	}
312 
313 	/* We can't copy this structure, so we just move the pointer to it */
314 	client->creds = ctx->client_creds;
315 	ctx->client_creds = GSS_C_NO_CREDENTIAL;
316 	return (ctx->major);
317 }
318 
319 /* As user - called on fatal/exit */
320 void
ssh_gssapi_cleanup_creds(void)321 ssh_gssapi_cleanup_creds(void)
322 {
323 	if (gssapi_client.store.filename != NULL) {
324 		/* Unlink probably isn't sufficient */
325 		debug("removing gssapi cred file\"%s\"",
326 		    gssapi_client.store.filename);
327 		unlink(gssapi_client.store.filename);
328 	}
329 }
330 
331 /* As user */
332 void
ssh_gssapi_storecreds(void)333 ssh_gssapi_storecreds(void)
334 {
335 	if (gssapi_client.mech && gssapi_client.mech->storecreds) {
336 		(*gssapi_client.mech->storecreds)(&gssapi_client);
337 	} else
338 		debug("ssh_gssapi_storecreds: Not a GSSAPI mechanism");
339 }
340 
341 /* This allows GSSAPI methods to do things to the childs environment based
342  * on the passed authentication process and credentials.
343  */
344 /* As user */
345 void
ssh_gssapi_do_child(char *** envp,u_int * envsizep)346 ssh_gssapi_do_child(char ***envp, u_int *envsizep)
347 {
348 
349 	if (gssapi_client.store.envvar != NULL &&
350 	    gssapi_client.store.envval != NULL) {
351 		debug("Setting %s to %s", gssapi_client.store.envvar,
352 		    gssapi_client.store.envval);
353 		child_set_env(envp, envsizep, gssapi_client.store.envvar,
354 		    gssapi_client.store.envval);
355 	}
356 }
357 
358 /* Privileged */
359 int
ssh_gssapi_userok(char * user)360 ssh_gssapi_userok(char *user)
361 {
362 	OM_uint32 lmin;
363 
364 	if (gssapi_client.exportedname.length == 0 ||
365 	    gssapi_client.exportedname.value == NULL) {
366 		debug("No suitable client data");
367 		return 0;
368 	}
369 	if (gssapi_client.mech && gssapi_client.mech->userok)
370 		if ((*gssapi_client.mech->userok)(&gssapi_client, user))
371 			return 1;
372 		else {
373 			/* Destroy delegated credentials if userok fails */
374 			gss_release_buffer(&lmin, &gssapi_client.displayname);
375 			gss_release_buffer(&lmin, &gssapi_client.exportedname);
376 			gss_release_cred(&lmin, &gssapi_client.creds);
377 			explicit_bzero(&gssapi_client,
378 			    sizeof(ssh_gssapi_client));
379 			return 0;
380 		}
381 	else
382 		debug("ssh_gssapi_userok: Unknown GSSAPI mechanism");
383 	return (0);
384 }
385 
386 /* Privileged */
387 OM_uint32
ssh_gssapi_checkmic(Gssctxt * ctx,gss_buffer_t gssbuf,gss_buffer_t gssmic)388 ssh_gssapi_checkmic(Gssctxt *ctx, gss_buffer_t gssbuf, gss_buffer_t gssmic)
389 {
390 	ctx->major = gss_verify_mic(&ctx->minor, ctx->context,
391 	    gssbuf, gssmic, NULL);
392 
393 	return (ctx->major);
394 }
395 
396 #endif
397