1/* $OpenBSD: gss-serv.c,v 1.32 2020/03/13 03:17:07 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 "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
50extern ServerOptions options;
51
52static 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
56ssh_gssapi_mech gssapi_null_mech =
57    { NULL, NULL, {0, NULL}, NULL, NULL, NULL, NULL};
58
59#ifdef KRB5
60extern ssh_gssapi_mech gssapi_kerberos_mech;
61#endif
62
63ssh_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 */
74static gss_OID_set supported_oids;
75
76void
77ssh_gssapi_prepare_supported_oids(void)
78{
79	ssh_gssapi_supported_oids(&supported_oids);
80}
81
82OM_uint32
83ssh_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) */
97static OM_uint32
98ssh_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, HOST_NAME_MAX)) {
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 */
133OM_uint32
134ssh_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 */
144void
145ssh_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 */
175OM_uint32
176ssh_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 */
215static OM_uint32
216ssh_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) */
275OM_uint32
276ssh_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 */
319void
320ssh_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 */
331void
332ssh_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 child's environment based
341 * on the passed authentication process and credentials.
342 */
343/* As user */
344void
345ssh_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 */
358int
359ssh_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 */
386OM_uint32
387ssh_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 */
396const 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