1/* $OpenBSD: gss-serv.c,v 1.23 2011/08/01 19:18:15 markus Exp $ */
2
3/*
4 * Copyright (c) 2001-2009 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#include <sys/param.h>
33
34#include <stdarg.h>
35#include <string.h>
36#include <unistd.h>
37
38#include "openbsd-compat/sys-queue.h"
39#include "xmalloc.h"
40#include "buffer.h"
41#include "key.h"
42#include "hostfile.h"
43#include "auth.h"
44#include "log.h"
45#include "channels.h"
46#include "session.h"
47#include "misc.h"
48#include "servconf.h"
49#include "uidswap.h"
50
51#include "ssh-gss.h"
52#include "monitor_wrap.h"
53
54extern ServerOptions options;
55
56static ssh_gssapi_client gssapi_client =
57    { GSS_C_EMPTY_BUFFER, GSS_C_EMPTY_BUFFER,
58    GSS_C_NO_CREDENTIAL, GSS_C_NO_NAME,  NULL, {NULL, NULL, NULL}, 0, 0};
59
60ssh_gssapi_mech gssapi_null_mech =
61    { NULL, NULL, {0, NULL}, NULL, NULL, NULL, NULL, NULL};
62
63#ifdef KRB5
64extern ssh_gssapi_mech gssapi_kerberos_mech;
65#endif
66
67ssh_gssapi_mech* supported_mechs[]= {
68#ifdef KRB5
69	&gssapi_kerberos_mech,
70#endif
71	&gssapi_null_mech,
72};
73
74
75/*
76 * Acquire credentials for a server running on the current host.
77 * Requires that the context structure contains a valid OID
78 */
79
80/* Returns a GSSAPI error code */
81/* Privileged (called from ssh_gssapi_server_ctx) */
82static OM_uint32
83ssh_gssapi_acquire_cred(Gssctxt *ctx)
84{
85	OM_uint32 status;
86	char lname[MAXHOSTNAMELEN];
87	gss_OID_set oidset;
88
89	if (options.gss_strict_acceptor) {
90		gss_create_empty_oid_set(&status, &oidset);
91		gss_add_oid_set_member(&status, ctx->oid, &oidset);
92
93		if (gethostname(lname, MAXHOSTNAMELEN)) {
94			gss_release_oid_set(&status, &oidset);
95			return (-1);
96		}
97
98		if (GSS_ERROR(ssh_gssapi_import_name(ctx, lname))) {
99			gss_release_oid_set(&status, &oidset);
100			return (ctx->major);
101		}
102
103		if ((ctx->major = gss_acquire_cred(&ctx->minor,
104		    ctx->name, 0, oidset, GSS_C_ACCEPT, &ctx->creds,
105		    NULL, NULL)))
106			ssh_gssapi_error(ctx);
107
108		gss_release_oid_set(&status, &oidset);
109		return (ctx->major);
110	} else {
111		ctx->name = GSS_C_NO_NAME;
112		ctx->creds = GSS_C_NO_CREDENTIAL;
113	}
114	return GSS_S_COMPLETE;
115}
116
117/* Privileged */
118OM_uint32
119ssh_gssapi_server_ctx(Gssctxt **ctx, gss_OID oid)
120{
121	if (*ctx)
122		ssh_gssapi_delete_ctx(ctx);
123	ssh_gssapi_build_ctx(ctx);
124	ssh_gssapi_set_oid(*ctx, oid);
125	return (ssh_gssapi_acquire_cred(*ctx));
126}
127
128/* Unprivileged */
129char *
130ssh_gssapi_server_mechanisms() {
131	gss_OID_set	supported;
132
133	ssh_gssapi_supported_oids(&supported);
134	return (ssh_gssapi_kex_mechs(supported, &ssh_gssapi_server_check_mech,
135	    NULL, NULL));
136}
137
138/* Unprivileged */
139int
140ssh_gssapi_server_check_mech(Gssctxt **dum, gss_OID oid, const char *data,
141    const char *dummy) {
142	Gssctxt *ctx = NULL;
143	int res;
144
145	res = !GSS_ERROR(PRIVSEP(ssh_gssapi_server_ctx(&ctx, oid)));
146	ssh_gssapi_delete_ctx(&ctx);
147
148	return (res);
149}
150
151/* Unprivileged */
152void
153ssh_gssapi_supported_oids(gss_OID_set *oidset)
154{
155	int i = 0;
156	OM_uint32 min_status;
157	int present;
158	gss_OID_set supported;
159
160	gss_create_empty_oid_set(&min_status, oidset);
161
162	if (GSS_ERROR(gss_indicate_mechs(&min_status, &supported)))
163		return;
164
165	while (supported_mechs[i]->name != NULL) {
166		if (GSS_ERROR(gss_test_oid_set_member(&min_status,
167		    &supported_mechs[i]->oid, supported, &present)))
168			present = 0;
169		if (present)
170			gss_add_oid_set_member(&min_status,
171			    &supported_mechs[i]->oid, oidset);
172		i++;
173	}
174
175	gss_release_oid_set(&min_status, &supported);
176}
177
178
179/* Wrapper around accept_sec_context
180 * Requires that the context contains:
181 *    oid
182 *    credentials	(from ssh_gssapi_acquire_cred)
183 */
184/* Privileged */
185OM_uint32
186ssh_gssapi_accept_ctx(Gssctxt *ctx, gss_buffer_desc *recv_tok,
187    gss_buffer_desc *send_tok, OM_uint32 *flags)
188{
189	OM_uint32 status;
190	gss_OID mech;
191
192	ctx->major = gss_accept_sec_context(&ctx->minor,
193	    &ctx->context, ctx->creds, recv_tok,
194	    GSS_C_NO_CHANNEL_BINDINGS, &ctx->client, &mech,
195	    send_tok, flags, NULL, &ctx->client_creds);
196
197	if (GSS_ERROR(ctx->major))
198		ssh_gssapi_error(ctx);
199
200	if (ctx->client_creds)
201		debug("Received some client credentials");
202	else
203		debug("Got no client credentials");
204
205	status = ctx->major;
206
207	/* Now, if we're complete and we have the right flags, then
208	 * we flag the user as also having been authenticated
209	 */
210
211	if (((flags == NULL) || ((*flags & GSS_C_MUTUAL_FLAG) &&
212	    (*flags & GSS_C_INTEG_FLAG))) && (ctx->major == GSS_S_COMPLETE)) {
213		if (ssh_gssapi_getclient(ctx, &gssapi_client))
214			fatal("Couldn't convert client name");
215	}
216
217	return (status);
218}
219
220/*
221 * This parses an exported name, extracting the mechanism specific portion
222 * to use for ACL checking. It verifies that the name belongs the mechanism
223 * originally selected.
224 */
225static OM_uint32
226ssh_gssapi_parse_ename(Gssctxt *ctx, gss_buffer_t ename, gss_buffer_t name)
227{
228	u_char *tok;
229	OM_uint32 offset;
230	OM_uint32 oidl;
231
232	tok = ename->value;
233
234	/*
235	 * Check that ename is long enough for all of the fixed length
236	 * header, and that the initial ID bytes are correct
237	 */
238
239	if (ename->length < 6 || memcmp(tok, "\x04\x01", 2) != 0)
240		return GSS_S_FAILURE;
241
242	/*
243	 * Extract the OID, and check it. Here GSSAPI breaks with tradition
244	 * and does use the OID type and length bytes. To confuse things
245	 * there are two lengths - the first including these, and the
246	 * second without.
247	 */
248
249	oidl = get_u16(tok+2); /* length including next two bytes */
250	oidl = oidl-2; /* turn it into the _real_ length of the variable OID */
251
252	/*
253	 * Check the BER encoding for correct type and length, that the
254	 * string is long enough and that the OID matches that in our context
255	 */
256	if (tok[4] != 0x06 || tok[5] != oidl ||
257	    ename->length < oidl+6 ||
258	    !ssh_gssapi_check_oid(ctx, tok+6, oidl))
259		return GSS_S_FAILURE;
260
261	offset = oidl+6;
262
263	if (ename->length < offset+4)
264		return GSS_S_FAILURE;
265
266	name->length = get_u32(tok+offset);
267	offset += 4;
268
269	if (UINT_MAX - offset < name->length)
270		return GSS_S_FAILURE;
271	if (ename->length < offset+name->length)
272		return GSS_S_FAILURE;
273
274	name->value = xmalloc(name->length+1);
275	memcpy(name->value, tok+offset, name->length);
276	((char *)name->value)[name->length] = 0;
277
278	return GSS_S_COMPLETE;
279}
280
281/* Extract the client details from a given context. This can only reliably
282 * be called once for a context */
283
284/* Privileged (called from accept_secure_ctx) */
285OM_uint32
286ssh_gssapi_getclient(Gssctxt *ctx, ssh_gssapi_client *client)
287{
288	int i = 0;
289	int equal = 0;
290	gss_name_t new_name = GSS_C_NO_NAME;
291	gss_buffer_desc ename = GSS_C_EMPTY_BUFFER;
292
293	if (options.gss_store_rekey && client->used && ctx->client_creds) {
294		if (client->mech->oid.length != ctx->oid->length ||
295		    (memcmp(client->mech->oid.elements,
296		     ctx->oid->elements, ctx->oid->length) !=0)) {
297			debug("Rekeyed credentials have different mechanism");
298			return GSS_S_COMPLETE;
299		}
300
301		if ((ctx->major = gss_inquire_cred_by_mech(&ctx->minor,
302		    ctx->client_creds, ctx->oid, &new_name,
303		    NULL, NULL, NULL))) {
304			ssh_gssapi_error(ctx);
305			return (ctx->major);
306		}
307
308		ctx->major = gss_compare_name(&ctx->minor, client->name,
309		    new_name, &equal);
310
311		if (GSS_ERROR(ctx->major)) {
312			ssh_gssapi_error(ctx);
313			return (ctx->major);
314		}
315
316		if (!equal) {
317			debug("Rekeyed credentials have different name");
318			return GSS_S_COMPLETE;
319		}
320
321		debug("Marking rekeyed credentials for export");
322
323		gss_release_name(&ctx->minor, &client->name);
324		gss_release_cred(&ctx->minor, &client->creds);
325		client->name = new_name;
326		client->creds = ctx->client_creds;
327        	ctx->client_creds = GSS_C_NO_CREDENTIAL;
328		client->updated = 1;
329		return GSS_S_COMPLETE;
330	}
331
332	client->mech = NULL;
333
334	while (supported_mechs[i]->name != NULL) {
335		if (supported_mechs[i]->oid.length == ctx->oid->length &&
336		    (memcmp(supported_mechs[i]->oid.elements,
337		    ctx->oid->elements, ctx->oid->length) == 0))
338			client->mech = supported_mechs[i];
339		i++;
340	}
341
342	if (client->mech == NULL)
343		return GSS_S_FAILURE;
344
345	if (ctx->client_creds &&
346	    (ctx->major = gss_inquire_cred_by_mech(&ctx->minor,
347	     ctx->client_creds, ctx->oid, &client->name, NULL, NULL, NULL))) {
348		ssh_gssapi_error(ctx);
349		return (ctx->major);
350	}
351
352	if ((ctx->major = gss_display_name(&ctx->minor, ctx->client,
353	    &client->displayname, NULL))) {
354		ssh_gssapi_error(ctx);
355		return (ctx->major);
356	}
357
358	if ((ctx->major = gss_export_name(&ctx->minor, ctx->client,
359	    &ename))) {
360		ssh_gssapi_error(ctx);
361		return (ctx->major);
362	}
363
364	if ((ctx->major = ssh_gssapi_parse_ename(ctx,&ename,
365	    &client->exportedname))) {
366		return (ctx->major);
367	}
368
369	gss_release_buffer(&ctx->minor, &ename);
370
371	/* We can't copy this structure, so we just move the pointer to it */
372	client->creds = ctx->client_creds;
373	ctx->client_creds = GSS_C_NO_CREDENTIAL;
374	return (ctx->major);
375}
376
377/* As user - called on fatal/exit */
378void
379ssh_gssapi_cleanup_creds(void)
380{
381	if (gssapi_client.store.filename != NULL) {
382		/* Unlink probably isn't sufficient */
383		debug("removing gssapi cred file\"%s\"",
384		    gssapi_client.store.filename);
385		unlink(gssapi_client.store.filename);
386	}
387}
388
389/* As user */
390void
391ssh_gssapi_storecreds(void)
392{
393	if (gssapi_client.mech && gssapi_client.mech->storecreds) {
394		(*gssapi_client.mech->storecreds)(&gssapi_client);
395	} else
396		debug("ssh_gssapi_storecreds: Not a GSSAPI mechanism");
397}
398
399/* This allows GSSAPI methods to do things to the childs environment based
400 * on the passed authentication process and credentials.
401 */
402/* As user */
403void
404ssh_gssapi_do_child(char ***envp, u_int *envsizep)
405{
406
407	if (gssapi_client.store.envvar != NULL &&
408	    gssapi_client.store.envval != NULL) {
409		debug("Setting %s to %s", gssapi_client.store.envvar,
410		    gssapi_client.store.envval);
411		child_set_env(envp, envsizep, gssapi_client.store.envvar,
412		    gssapi_client.store.envval);
413	}
414}
415
416/* Privileged */
417int
418ssh_gssapi_userok(char *user, struct passwd *pw)
419{
420	OM_uint32 lmin;
421
422	if (gssapi_client.exportedname.length == 0 ||
423	    gssapi_client.exportedname.value == NULL) {
424		debug("No suitable client data");
425		return 0;
426	}
427	if (gssapi_client.mech && gssapi_client.mech->userok)
428		if ((*gssapi_client.mech->userok)(&gssapi_client, user)) {
429			gssapi_client.used = 1;
430			gssapi_client.store.owner = pw;
431			return 1;
432		} else {
433			/* Destroy delegated credentials if userok fails */
434			gss_release_buffer(&lmin, &gssapi_client.displayname);
435			gss_release_buffer(&lmin, &gssapi_client.exportedname);
436			gss_release_cred(&lmin, &gssapi_client.creds);
437			memset(&gssapi_client, 0, sizeof(ssh_gssapi_client));
438			return 0;
439		}
440	else
441		debug("ssh_gssapi_userok: Unknown GSSAPI mechanism");
442	return (0);
443}
444
445/* These bits are only used for rekeying. The unpriviledged child is running
446 * as the user, the monitor is root.
447 *
448 * In the child, we want to :
449 *    *) Ask the monitor to store our credentials into the store we specify
450 *    *) If it succeeds, maybe do a PAM update
451 */
452
453/* Stuff for PAM */
454
455#ifdef USE_PAM
456static int ssh_gssapi_simple_conv(int n, const struct pam_message **msg,
457    struct pam_response **resp, void *data)
458{
459	return (PAM_CONV_ERR);
460}
461#endif
462
463void
464ssh_gssapi_rekey_creds() {
465	int ok;
466	int ret;
467#ifdef USE_PAM
468	pam_handle_t *pamh = NULL;
469	struct pam_conv pamconv = {ssh_gssapi_simple_conv, NULL};
470	char *envstr;
471#endif
472
473	if (gssapi_client.store.filename == NULL &&
474	    gssapi_client.store.envval == NULL &&
475	    gssapi_client.store.envvar == NULL)
476		return;
477
478	ok = PRIVSEP(ssh_gssapi_update_creds(&gssapi_client.store));
479
480	if (!ok)
481		return;
482
483	debug("Rekeyed credentials stored successfully");
484
485	/* Actually managing to play with the ssh pam stack from here will
486	 * be next to impossible. In any case, we may want different options
487	 * for rekeying. So, use our own :)
488	 */
489#ifdef USE_PAM
490	if (!use_privsep) {
491		debug("Not even going to try and do PAM with privsep disabled");
492		return;
493	}
494
495	ret = pam_start("sshd-rekey", gssapi_client.store.owner->pw_name,
496 	    &pamconv, &pamh);
497	if (ret)
498		return;
499
500	xasprintf(&envstr, "%s=%s", gssapi_client.store.envvar,
501	    gssapi_client.store.envval);
502
503	ret = pam_putenv(pamh, envstr);
504	if (!ret)
505		pam_setcred(pamh, PAM_REINITIALIZE_CRED);
506	pam_end(pamh, PAM_SUCCESS);
507#endif
508}
509
510int
511ssh_gssapi_update_creds(ssh_gssapi_ccache *store) {
512	int ok = 0;
513
514	/* Check we've got credentials to store */
515	if (!gssapi_client.updated)
516		return 0;
517
518	gssapi_client.updated = 0;
519
520	temporarily_use_uid(gssapi_client.store.owner);
521	if (gssapi_client.mech && gssapi_client.mech->updatecreds)
522		ok = (*gssapi_client.mech->updatecreds)(store, &gssapi_client);
523	else
524		debug("No update function for this mechanism");
525
526	restore_uid();
527
528	return ok;
529}
530
531#endif
532