xref: /openssh-portable/gss-serv.c (revision b8d9214d)
1 /* $OpenBSD: gss-serv.c,v 1.31 2018/07/09 21:37:55 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 #include <string.h>
35 #include <unistd.h>
36 
37 #include "openbsd-compat/sys-queue.h"
38 #include "xmalloc.h"
39 #include "sshkey.h"
40 #include "hostfile.h"
41 #include "auth.h"
42 #include "log.h"
43 #include "channels.h"
44 #include "session.h"
45 #include "misc.h"
46 #include "servconf.h"
47 
48 #include "ssh-gss.h"
49 
50 extern ServerOptions options;
51 
52 static ssh_gssapi_client gssapi_client =
53     { GSS_C_EMPTY_BUFFER, GSS_C_EMPTY_BUFFER,
54     GSS_C_NO_CREDENTIAL, NULL, {NULL, NULL, NULL, NULL}};
55 
56 ssh_gssapi_mech gssapi_null_mech =
57     { NULL, NULL, {0, NULL}, NULL, NULL, NULL, NULL};
58 
59 #ifdef KRB5
60 extern ssh_gssapi_mech gssapi_kerberos_mech;
61 #endif
62 
63 ssh_gssapi_mech* supported_mechs[]= {
64 #ifdef KRB5
65 	&gssapi_kerberos_mech,
66 #endif
67 	&gssapi_null_mech,
68 };
69 
70 /*
71  * ssh_gssapi_supported_oids() can cause sandbox violations, so prepare the
72  * list of supported mechanisms before privsep is set up.
73  */
74 static gss_OID_set supported_oids;
75 
76 void
ssh_gssapi_prepare_supported_oids(void)77 ssh_gssapi_prepare_supported_oids(void)
78 {
79 	ssh_gssapi_supported_oids(&supported_oids);
80 }
81 
82 OM_uint32
ssh_gssapi_test_oid_supported(OM_uint32 * ms,gss_OID member,int * present)83 ssh_gssapi_test_oid_supported(OM_uint32 *ms, gss_OID member, int *present)
84 {
85 	if (supported_oids == NULL)
86 		ssh_gssapi_prepare_supported_oids();
87 	return gss_test_oid_set_member(ms, member, supported_oids, present);
88 }
89 
90 /*
91  * Acquire credentials for a server running on the current host.
92  * Requires that the context structure contains a valid OID
93  */
94 
95 /* Returns a GSSAPI error code */
96 /* Privileged (called from ssh_gssapi_server_ctx) */
97 static OM_uint32
ssh_gssapi_acquire_cred(Gssctxt * ctx)98 ssh_gssapi_acquire_cred(Gssctxt *ctx)
99 {
100 	OM_uint32 status;
101 	char lname[NI_MAXHOST];
102 	gss_OID_set oidset;
103 
104 	if (options.gss_strict_acceptor) {
105 		gss_create_empty_oid_set(&status, &oidset);
106 		gss_add_oid_set_member(&status, ctx->oid, &oidset);
107 
108 		if (gethostname(lname, MAXHOSTNAMELEN)) {
109 			gss_release_oid_set(&status, &oidset);
110 			return (-1);
111 		}
112 
113 		if (GSS_ERROR(ssh_gssapi_import_name(ctx, lname))) {
114 			gss_release_oid_set(&status, &oidset);
115 			return (ctx->major);
116 		}
117 
118 		if ((ctx->major = gss_acquire_cred(&ctx->minor,
119 		    ctx->name, 0, oidset, GSS_C_ACCEPT, &ctx->creds,
120 		    NULL, NULL)))
121 			ssh_gssapi_error(ctx);
122 
123 		gss_release_oid_set(&status, &oidset);
124 		return (ctx->major);
125 	} else {
126 		ctx->name = GSS_C_NO_NAME;
127 		ctx->creds = GSS_C_NO_CREDENTIAL;
128 	}
129 	return GSS_S_COMPLETE;
130 }
131 
132 /* Privileged */
133 OM_uint32
ssh_gssapi_server_ctx(Gssctxt ** ctx,gss_OID oid)134 ssh_gssapi_server_ctx(Gssctxt **ctx, gss_OID oid)
135 {
136 	if (*ctx)
137 		ssh_gssapi_delete_ctx(ctx);
138 	ssh_gssapi_build_ctx(ctx);
139 	ssh_gssapi_set_oid(*ctx, oid);
140 	return (ssh_gssapi_acquire_cred(*ctx));
141 }
142 
143 /* Unprivileged */
144 void
ssh_gssapi_supported_oids(gss_OID_set * oidset)145 ssh_gssapi_supported_oids(gss_OID_set *oidset)
146 {
147 	int i = 0;
148 	OM_uint32 min_status;
149 	int present;
150 	gss_OID_set supported;
151 
152 	gss_create_empty_oid_set(&min_status, oidset);
153 	gss_indicate_mechs(&min_status, &supported);
154 
155 	while (supported_mechs[i]->name != NULL) {
156 		if (GSS_ERROR(gss_test_oid_set_member(&min_status,
157 		    &supported_mechs[i]->oid, supported, &present)))
158 			present = 0;
159 		if (present)
160 			gss_add_oid_set_member(&min_status,
161 			    &supported_mechs[i]->oid, oidset);
162 		i++;
163 	}
164 
165 	gss_release_oid_set(&min_status, &supported);
166 }
167 
168 
169 /* Wrapper around accept_sec_context
170  * Requires that the context contains:
171  *    oid
172  *    credentials	(from ssh_gssapi_acquire_cred)
173  */
174 /* Privileged */
175 OM_uint32
ssh_gssapi_accept_ctx(Gssctxt * ctx,gss_buffer_desc * recv_tok,gss_buffer_desc * send_tok,OM_uint32 * flags)176 ssh_gssapi_accept_ctx(Gssctxt *ctx, gss_buffer_desc *recv_tok,
177     gss_buffer_desc *send_tok, OM_uint32 *flags)
178 {
179 	OM_uint32 status;
180 	gss_OID mech;
181 
182 	ctx->major = gss_accept_sec_context(&ctx->minor,
183 	    &ctx->context, ctx->creds, recv_tok,
184 	    GSS_C_NO_CHANNEL_BINDINGS, &ctx->client, &mech,
185 	    send_tok, flags, NULL, &ctx->client_creds);
186 
187 	if (GSS_ERROR(ctx->major))
188 		ssh_gssapi_error(ctx);
189 
190 	if (ctx->client_creds)
191 		debug("Received some client credentials");
192 	else
193 		debug("Got no client credentials");
194 
195 	status = ctx->major;
196 
197 	/* Now, if we're complete and we have the right flags, then
198 	 * we flag the user as also having been authenticated
199 	 */
200 
201 	if (((flags == NULL) || ((*flags & GSS_C_MUTUAL_FLAG) &&
202 	    (*flags & GSS_C_INTEG_FLAG))) && (ctx->major == GSS_S_COMPLETE)) {
203 		if (ssh_gssapi_getclient(ctx, &gssapi_client))
204 			fatal("Couldn't convert client name");
205 	}
206 
207 	return (status);
208 }
209 
210 /*
211  * This parses an exported name, extracting the mechanism specific portion
212  * to use for ACL checking. It verifies that the name belongs the mechanism
213  * originally selected.
214  */
215 static OM_uint32
ssh_gssapi_parse_ename(Gssctxt * ctx,gss_buffer_t ename,gss_buffer_t name)216 ssh_gssapi_parse_ename(Gssctxt *ctx, gss_buffer_t ename, gss_buffer_t name)
217 {
218 	u_char *tok;
219 	OM_uint32 offset;
220 	OM_uint32 oidl;
221 
222 	tok = ename->value;
223 
224 	/*
225 	 * Check that ename is long enough for all of the fixed length
226 	 * header, and that the initial ID bytes are correct
227 	 */
228 
229 	if (ename->length < 6 || memcmp(tok, "\x04\x01", 2) != 0)
230 		return GSS_S_FAILURE;
231 
232 	/*
233 	 * Extract the OID, and check it. Here GSSAPI breaks with tradition
234 	 * and does use the OID type and length bytes. To confuse things
235 	 * there are two lengths - the first including these, and the
236 	 * second without.
237 	 */
238 
239 	oidl = get_u16(tok+2); /* length including next two bytes */
240 	oidl = oidl-2; /* turn it into the _real_ length of the variable OID */
241 
242 	/*
243 	 * Check the BER encoding for correct type and length, that the
244 	 * string is long enough and that the OID matches that in our context
245 	 */
246 	if (tok[4] != 0x06 || tok[5] != oidl ||
247 	    ename->length < oidl+6 ||
248 	    !ssh_gssapi_check_oid(ctx, tok+6, oidl))
249 		return GSS_S_FAILURE;
250 
251 	offset = oidl+6;
252 
253 	if (ename->length < offset+4)
254 		return GSS_S_FAILURE;
255 
256 	name->length = get_u32(tok+offset);
257 	offset += 4;
258 
259 	if (UINT_MAX - offset < name->length)
260 		return GSS_S_FAILURE;
261 	if (ename->length < offset+name->length)
262 		return GSS_S_FAILURE;
263 
264 	name->value = xmalloc(name->length+1);
265 	memcpy(name->value, tok+offset, name->length);
266 	((char *)name->value)[name->length] = 0;
267 
268 	return GSS_S_COMPLETE;
269 }
270 
271 /* Extract the client details from a given context. This can only reliably
272  * be called once for a context */
273 
274 /* Privileged (called from accept_secure_ctx) */
275 OM_uint32
ssh_gssapi_getclient(Gssctxt * ctx,ssh_gssapi_client * client)276 ssh_gssapi_getclient(Gssctxt *ctx, ssh_gssapi_client *client)
277 {
278 	int i = 0;
279 
280 	gss_buffer_desc ename;
281 
282 	client->mech = NULL;
283 
284 	while (supported_mechs[i]->name != NULL) {
285 		if (supported_mechs[i]->oid.length == ctx->oid->length &&
286 		    (memcmp(supported_mechs[i]->oid.elements,
287 		    ctx->oid->elements, ctx->oid->length) == 0))
288 			client->mech = supported_mechs[i];
289 		i++;
290 	}
291 
292 	if (client->mech == NULL)
293 		return GSS_S_FAILURE;
294 
295 	if ((ctx->major = gss_display_name(&ctx->minor, ctx->client,
296 	    &client->displayname, NULL))) {
297 		ssh_gssapi_error(ctx);
298 		return (ctx->major);
299 	}
300 
301 	if ((ctx->major = gss_export_name(&ctx->minor, ctx->client,
302 	    &ename))) {
303 		ssh_gssapi_error(ctx);
304 		return (ctx->major);
305 	}
306 
307 	if ((ctx->major = ssh_gssapi_parse_ename(ctx,&ename,
308 	    &client->exportedname))) {
309 		return (ctx->major);
310 	}
311 
312 	/* We can't copy this structure, so we just move the pointer to it */
313 	client->creds = ctx->client_creds;
314 	ctx->client_creds = GSS_C_NO_CREDENTIAL;
315 	return (ctx->major);
316 }
317 
318 /* As user - called on fatal/exit */
319 void
ssh_gssapi_cleanup_creds(void)320 ssh_gssapi_cleanup_creds(void)
321 {
322 	if (gssapi_client.store.filename != NULL) {
323 		/* Unlink probably isn't sufficient */
324 		debug("removing gssapi cred file\"%s\"",
325 		    gssapi_client.store.filename);
326 		unlink(gssapi_client.store.filename);
327 	}
328 }
329 
330 /* As user */
331 void
ssh_gssapi_storecreds(void)332 ssh_gssapi_storecreds(void)
333 {
334 	if (gssapi_client.mech && gssapi_client.mech->storecreds) {
335 		(*gssapi_client.mech->storecreds)(&gssapi_client);
336 	} else
337 		debug("ssh_gssapi_storecreds: Not a GSSAPI mechanism");
338 }
339 
340 /* This allows GSSAPI methods to do things to the childs environment based
341  * on the passed authentication process and credentials.
342  */
343 /* As user */
344 void
ssh_gssapi_do_child(char *** envp,u_int * envsizep)345 ssh_gssapi_do_child(char ***envp, u_int *envsizep)
346 {
347 
348 	if (gssapi_client.store.envvar != NULL &&
349 	    gssapi_client.store.envval != NULL) {
350 		debug("Setting %s to %s", gssapi_client.store.envvar,
351 		    gssapi_client.store.envval);
352 		child_set_env(envp, envsizep, gssapi_client.store.envvar,
353 		    gssapi_client.store.envval);
354 	}
355 }
356 
357 /* Privileged */
358 int
ssh_gssapi_userok(char * user)359 ssh_gssapi_userok(char *user)
360 {
361 	OM_uint32 lmin;
362 
363 	if (gssapi_client.exportedname.length == 0 ||
364 	    gssapi_client.exportedname.value == NULL) {
365 		debug("No suitable client data");
366 		return 0;
367 	}
368 	if (gssapi_client.mech && gssapi_client.mech->userok)
369 		if ((*gssapi_client.mech->userok)(&gssapi_client, user))
370 			return 1;
371 		else {
372 			/* Destroy delegated credentials if userok fails */
373 			gss_release_buffer(&lmin, &gssapi_client.displayname);
374 			gss_release_buffer(&lmin, &gssapi_client.exportedname);
375 			gss_release_cred(&lmin, &gssapi_client.creds);
376 			explicit_bzero(&gssapi_client,
377 			    sizeof(ssh_gssapi_client));
378 			return 0;
379 		}
380 	else
381 		debug("ssh_gssapi_userok: Unknown GSSAPI mechanism");
382 	return (0);
383 }
384 
385 /* Privileged */
386 OM_uint32
ssh_gssapi_checkmic(Gssctxt * ctx,gss_buffer_t gssbuf,gss_buffer_t gssmic)387 ssh_gssapi_checkmic(Gssctxt *ctx, gss_buffer_t gssbuf, gss_buffer_t gssmic)
388 {
389 	ctx->major = gss_verify_mic(&ctx->minor, ctx->context,
390 	    gssbuf, gssmic, NULL);
391 
392 	return (ctx->major);
393 }
394 
395 /* Privileged */
ssh_gssapi_displayname(void)396 const char *ssh_gssapi_displayname(void)
397 {
398 	if (gssapi_client.displayname.length == 0 ||
399 	    gssapi_client.displayname.value == NULL)
400 		return NULL;
401 	return (char *)gssapi_client.displayname.value;
402 }
403 
404 #endif
405