1/* $OpenBSD: gss-serv.c,v 1.28 2015/01/20 23:14:00 deraadt 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
48#include "ssh-gss.h"
49
50static ssh_gssapi_client gssapi_client =
51    { GSS_C_EMPTY_BUFFER, GSS_C_EMPTY_BUFFER,
52    GSS_C_NO_CREDENTIAL, NULL, {NULL, NULL, NULL, NULL}};
53
54ssh_gssapi_mech gssapi_null_mech =
55    { NULL, NULL, {0, NULL}, NULL, NULL, NULL, NULL};
56
57#ifdef KRB5
58extern ssh_gssapi_mech gssapi_kerberos_mech;
59#endif
60
61ssh_gssapi_mech* supported_mechs[]= {
62#ifdef KRB5
63	&gssapi_kerberos_mech,
64#endif
65	&gssapi_null_mech,
66};
67
68/*
69 * ssh_gssapi_supported_oids() can cause sandbox violations, so prepare the
70 * list of supported mechanisms before privsep is set up.
71 */
72static gss_OID_set supported_oids;
73
74void
75ssh_gssapi_prepare_supported_oids(void)
76{
77	ssh_gssapi_supported_oids(&supported_oids);
78}
79
80OM_uint32
81ssh_gssapi_test_oid_supported(OM_uint32 *ms, gss_OID member, int *present)
82{
83	if (supported_oids == NULL)
84		ssh_gssapi_prepare_supported_oids();
85	return gss_test_oid_set_member(ms, member, supported_oids, present);
86}
87
88/*
89 * Acquire credentials for a server running on the current host.
90 * Requires that the context structure contains a valid OID
91 */
92
93/* Returns a GSSAPI error code */
94/* Privileged (called from ssh_gssapi_server_ctx) */
95static OM_uint32
96ssh_gssapi_acquire_cred(Gssctxt *ctx)
97{
98	OM_uint32 status;
99	char lname[NI_MAXHOST];
100	gss_OID_set oidset;
101
102	gss_create_empty_oid_set(&status, &oidset);
103	gss_add_oid_set_member(&status, ctx->oid, &oidset);
104
105	if (gethostname(lname, sizeof(lname))) {
106		gss_release_oid_set(&status, &oidset);
107		return (-1);
108	}
109
110	if (GSS_ERROR(ssh_gssapi_import_name(ctx, lname))) {
111		gss_release_oid_set(&status, &oidset);
112		return (ctx->major);
113	}
114
115	if ((ctx->major = gss_acquire_cred(&ctx->minor,
116	    ctx->name, 0, oidset, GSS_C_ACCEPT, &ctx->creds, NULL, NULL)))
117		ssh_gssapi_error(ctx);
118
119	gss_release_oid_set(&status, &oidset);
120	return (ctx->major);
121}
122
123/* Privileged */
124OM_uint32
125ssh_gssapi_server_ctx(Gssctxt **ctx, gss_OID oid)
126{
127	if (*ctx)
128		ssh_gssapi_delete_ctx(ctx);
129	ssh_gssapi_build_ctx(ctx);
130	ssh_gssapi_set_oid(*ctx, oid);
131	return (ssh_gssapi_acquire_cred(*ctx));
132}
133
134/* Unprivileged */
135void
136ssh_gssapi_supported_oids(gss_OID_set *oidset)
137{
138	int i = 0;
139	OM_uint32 min_status;
140	int present;
141	gss_OID_set supported;
142
143	gss_create_empty_oid_set(&min_status, oidset);
144	gss_indicate_mechs(&min_status, &supported);
145
146	while (supported_mechs[i]->name != NULL) {
147		if (GSS_ERROR(gss_test_oid_set_member(&min_status,
148		    &supported_mechs[i]->oid, supported, &present)))
149			present = 0;
150		if (present)
151			gss_add_oid_set_member(&min_status,
152			    &supported_mechs[i]->oid, oidset);
153		i++;
154	}
155
156	gss_release_oid_set(&min_status, &supported);
157}
158
159
160/* Wrapper around accept_sec_context
161 * Requires that the context contains:
162 *    oid
163 *    credentials	(from ssh_gssapi_acquire_cred)
164 */
165/* Privileged */
166OM_uint32
167ssh_gssapi_accept_ctx(Gssctxt *ctx, gss_buffer_desc *recv_tok,
168    gss_buffer_desc *send_tok, OM_uint32 *flags)
169{
170	OM_uint32 status;
171	gss_OID mech;
172
173	ctx->major = gss_accept_sec_context(&ctx->minor,
174	    &ctx->context, ctx->creds, recv_tok,
175	    GSS_C_NO_CHANNEL_BINDINGS, &ctx->client, &mech,
176	    send_tok, flags, NULL, &ctx->client_creds);
177
178	if (GSS_ERROR(ctx->major))
179		ssh_gssapi_error(ctx);
180
181	if (ctx->client_creds)
182		debug("Received some client credentials");
183	else
184		debug("Got no client credentials");
185
186	status = ctx->major;
187
188	/* Now, if we're complete and we have the right flags, then
189	 * we flag the user as also having been authenticated
190	 */
191
192	if (((flags == NULL) || ((*flags & GSS_C_MUTUAL_FLAG) &&
193	    (*flags & GSS_C_INTEG_FLAG))) && (ctx->major == GSS_S_COMPLETE)) {
194		if (ssh_gssapi_getclient(ctx, &gssapi_client))
195			fatal("Couldn't convert client name");
196	}
197
198	return (status);
199}
200
201/*
202 * This parses an exported name, extracting the mechanism specific portion
203 * to use for ACL checking. It verifies that the name belongs the mechanism
204 * originally selected.
205 */
206static OM_uint32
207ssh_gssapi_parse_ename(Gssctxt *ctx, gss_buffer_t ename, gss_buffer_t name)
208{
209	u_char *tok;
210	OM_uint32 offset;
211	OM_uint32 oidl;
212
213	tok = ename->value;
214
215	/*
216	 * Check that ename is long enough for all of the fixed length
217	 * header, and that the initial ID bytes are correct
218	 */
219
220	if (ename->length < 6 || memcmp(tok, "\x04\x01", 2) != 0)
221		return GSS_S_FAILURE;
222
223	/*
224	 * Extract the OID, and check it. Here GSSAPI breaks with tradition
225	 * and does use the OID type and length bytes. To confuse things
226	 * there are two lengths - the first including these, and the
227	 * second without.
228	 */
229
230	oidl = get_u16(tok+2); /* length including next two bytes */
231	oidl = oidl-2; /* turn it into the _real_ length of the variable OID */
232
233	/*
234	 * Check the BER encoding for correct type and length, that the
235	 * string is long enough and that the OID matches that in our context
236	 */
237	if (tok[4] != 0x06 || tok[5] != oidl ||
238	    ename->length < oidl+6 ||
239	    !ssh_gssapi_check_oid(ctx, tok+6, oidl))
240		return GSS_S_FAILURE;
241
242	offset = oidl+6;
243
244	if (ename->length < offset+4)
245		return GSS_S_FAILURE;
246
247	name->length = get_u32(tok+offset);
248	offset += 4;
249
250	if (UINT_MAX - offset < name->length)
251		return GSS_S_FAILURE;
252	if (ename->length < offset+name->length)
253		return GSS_S_FAILURE;
254
255	name->value = xmalloc(name->length+1);
256	memcpy(name->value, tok+offset, name->length);
257	((char *)name->value)[name->length] = 0;
258
259	return GSS_S_COMPLETE;
260}
261
262/* Extract the client details from a given context. This can only reliably
263 * be called once for a context */
264
265/* Privileged (called from accept_secure_ctx) */
266OM_uint32
267ssh_gssapi_getclient(Gssctxt *ctx, ssh_gssapi_client *client)
268{
269	int i = 0;
270
271	gss_buffer_desc ename;
272
273	client->mech = NULL;
274
275	while (supported_mechs[i]->name != NULL) {
276		if (supported_mechs[i]->oid.length == ctx->oid->length &&
277		    (memcmp(supported_mechs[i]->oid.elements,
278		    ctx->oid->elements, ctx->oid->length) == 0))
279			client->mech = supported_mechs[i];
280		i++;
281	}
282
283	if (client->mech == NULL)
284		return GSS_S_FAILURE;
285
286	if ((ctx->major = gss_display_name(&ctx->minor, ctx->client,
287	    &client->displayname, NULL))) {
288		ssh_gssapi_error(ctx);
289		return (ctx->major);
290	}
291
292	if ((ctx->major = gss_export_name(&ctx->minor, ctx->client,
293	    &ename))) {
294		ssh_gssapi_error(ctx);
295		return (ctx->major);
296	}
297
298	if ((ctx->major = ssh_gssapi_parse_ename(ctx,&ename,
299	    &client->exportedname))) {
300		return (ctx->major);
301	}
302
303	/* We can't copy this structure, so we just move the pointer to it */
304	client->creds = ctx->client_creds;
305	ctx->client_creds = GSS_C_NO_CREDENTIAL;
306	return (ctx->major);
307}
308
309/* As user - called on fatal/exit */
310void
311ssh_gssapi_cleanup_creds(void)
312{
313	if (gssapi_client.store.filename != NULL) {
314		/* Unlink probably isn't sufficient */
315		debug("removing gssapi cred file\"%s\"",
316		    gssapi_client.store.filename);
317		unlink(gssapi_client.store.filename);
318	}
319}
320
321/* As user */
322void
323ssh_gssapi_storecreds(void)
324{
325	if (gssapi_client.mech && gssapi_client.mech->storecreds) {
326		(*gssapi_client.mech->storecreds)(&gssapi_client);
327	} else
328		debug("ssh_gssapi_storecreds: Not a GSSAPI mechanism");
329}
330
331/* This allows GSSAPI methods to do things to the childs environment based
332 * on the passed authentication process and credentials.
333 */
334/* As user */
335void
336ssh_gssapi_do_child(char ***envp, u_int *envsizep)
337{
338
339	if (gssapi_client.store.envvar != NULL &&
340	    gssapi_client.store.envval != NULL) {
341		debug("Setting %s to %s", gssapi_client.store.envvar,
342		    gssapi_client.store.envval);
343		child_set_env(envp, envsizep, gssapi_client.store.envvar,
344		    gssapi_client.store.envval);
345	}
346}
347
348/* Privileged */
349int
350ssh_gssapi_userok(char *user)
351{
352	OM_uint32 lmin;
353
354	if (gssapi_client.exportedname.length == 0 ||
355	    gssapi_client.exportedname.value == NULL) {
356		debug("No suitable client data");
357		return 0;
358	}
359	if (gssapi_client.mech && gssapi_client.mech->userok)
360		if ((*gssapi_client.mech->userok)(&gssapi_client, user))
361			return 1;
362		else {
363			/* Destroy delegated credentials if userok fails */
364			gss_release_buffer(&lmin, &gssapi_client.displayname);
365			gss_release_buffer(&lmin, &gssapi_client.exportedname);
366			gss_release_cred(&lmin, &gssapi_client.creds);
367			explicit_bzero(&gssapi_client,
368			    sizeof(ssh_gssapi_client));
369			return 0;
370		}
371	else
372		debug("ssh_gssapi_userok: Unknown GSSAPI mechanism");
373	return (0);
374}
375
376/* Privileged */
377OM_uint32
378ssh_gssapi_checkmic(Gssctxt *ctx, gss_buffer_t gssbuf, gss_buffer_t gssmic)
379{
380	ctx->major = gss_verify_mic(&ctx->minor, ctx->context,
381	    gssbuf, gssmic, NULL);
382
383	return (ctx->major);
384}
385
386#endif
387