1/*	$NetBSD: gss-serv.c,v 1.15 2020/05/28 17:05:49 christos Exp $	*/
2/* $OpenBSD: gss-serv.c,v 1.32 2020/03/13 03:17:07 djm Exp $ */
3
4/*
5 * Copyright (c) 2001-2003 Simon Wilkinson. All rights reserved.
6 *
7 * Redistribution and use in source and binary forms, with or without
8 * modification, are permitted provided that the following conditions
9 * are met:
10 * 1. Redistributions of source code must retain the above copyright
11 *    notice, this list of conditions and the following disclaimer.
12 * 2. Redistributions in binary form must reproduce the above copyright
13 *    notice, this list of conditions and the following disclaimer in the
14 *    documentation and/or other materials provided with the distribution.
15 *
16 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR `AS IS'' AND ANY EXPRESS OR
17 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
18 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
19 * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
20 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
21 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
22 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
23 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
24 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
25 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
26 */
27
28#include "includes.h"
29__RCSID("$NetBSD: gss-serv.c,v 1.15 2020/05/28 17:05:49 christos Exp $");
30
31#include <sys/param.h>
32#include <sys/types.h>
33#include <sys/queue.h>
34
35#ifdef GSSAPI
36
37#include <string.h>
38#include <unistd.h>
39#include <netdb.h>
40#include <limits.h>
41#include <stdarg.h>
42
43#include "xmalloc.h"
44#include "sshkey.h"
45#include "hostfile.h"
46#include "auth.h"
47#include "log.h"
48#include "channels.h"
49#include "session.h"
50#include "misc.h"
51#include "servconf.h"
52
53#include "ssh-gss.h"
54
55extern ServerOptions options;
56
57static ssh_gssapi_client gssapi_client =
58    { GSS_C_EMPTY_BUFFER, GSS_C_EMPTY_BUFFER,
59    GSS_C_NO_CREDENTIAL, NULL, {NULL, NULL, NULL, NULL}};
60
61ssh_gssapi_mech gssapi_null_mech =
62    { NULL, NULL, {0, NULL}, NULL, NULL, NULL, NULL};
63
64#ifdef KRB5
65extern ssh_gssapi_mech gssapi_kerberos_mech;
66#endif
67
68ssh_gssapi_mech* supported_mechs[]= {
69#ifdef KRB5
70	&gssapi_kerberos_mech,
71#endif
72	&gssapi_null_mech,
73};
74
75/*
76 * ssh_gssapi_supported_oids() can cause sandbox violations, so prepare the
77 * list of supported mechanisms before privsep is set up.
78 */
79static gss_OID_set supported_oids;
80
81void
82ssh_gssapi_prepare_supported_oids(void)
83{
84	ssh_gssapi_supported_oids(&supported_oids);
85}
86
87OM_uint32
88ssh_gssapi_test_oid_supported(OM_uint32 *ms, gss_OID member, int *present)
89{
90	if (supported_oids == NULL)
91		ssh_gssapi_prepare_supported_oids();
92	return gss_test_oid_set_member(ms, member, supported_oids, present);
93}
94
95/*
96 * Acquire credentials for a server running on the current host.
97 * Requires that the context structure contains a valid OID
98 */
99
100/* Returns a GSSAPI error code */
101/* Privileged (called from ssh_gssapi_server_ctx) */
102static OM_uint32
103ssh_gssapi_acquire_cred(Gssctxt *ctx)
104{
105	OM_uint32 status;
106	char lname[NI_MAXHOST];
107	gss_OID_set oidset;
108
109	if (options.gss_strict_acceptor) {
110		gss_create_empty_oid_set(&status, &oidset);
111		gss_add_oid_set_member(&status, ctx->oid, &oidset);
112
113		if (gethostname(lname, MAXHOSTNAMELEN)) {
114			gss_release_oid_set(&status, &oidset);
115			return (-1);
116		}
117
118		if (GSS_ERROR(ssh_gssapi_import_name(ctx, lname))) {
119			gss_release_oid_set(&status, &oidset);
120			return (ctx->major);
121		}
122
123		if ((ctx->major = gss_acquire_cred(&ctx->minor,
124		    ctx->name, 0, oidset, GSS_C_ACCEPT, &ctx->creds,
125		    NULL, NULL)))
126			ssh_gssapi_error(ctx);
127
128		gss_release_oid_set(&status, &oidset);
129		return (ctx->major);
130	} else {
131		ctx->name = GSS_C_NO_NAME;
132		ctx->creds = GSS_C_NO_CREDENTIAL;
133	}
134	return GSS_S_COMPLETE;
135}
136
137/* Privileged */
138OM_uint32
139ssh_gssapi_server_ctx(Gssctxt **ctx, gss_OID oid)
140{
141	if (*ctx)
142		ssh_gssapi_delete_ctx(ctx);
143	ssh_gssapi_build_ctx(ctx);
144	ssh_gssapi_set_oid(*ctx, oid);
145	return (ssh_gssapi_acquire_cred(*ctx));
146}
147
148/* Unprivileged */
149void
150ssh_gssapi_supported_oids(gss_OID_set *oidset)
151{
152	int i = 0;
153	OM_uint32 min_status;
154	int present;
155	gss_OID_set supported;
156
157	gss_create_empty_oid_set(&min_status, oidset);
158	gss_indicate_mechs(&min_status, &supported);
159
160	while (supported_mechs[i]->name != NULL) {
161		if (GSS_ERROR(gss_test_oid_set_member(&min_status,
162		    &supported_mechs[i]->oid, supported, &present)))
163			present = 0;
164		if (present)
165			gss_add_oid_set_member(&min_status,
166			    &supported_mechs[i]->oid, oidset);
167		i++;
168	}
169
170	gss_release_oid_set(&min_status, &supported);
171}
172
173
174/* Wrapper around accept_sec_context
175 * Requires that the context contains:
176 *    oid
177 *    credentials	(from ssh_gssapi_acquire_cred)
178 */
179/* Privileged */
180OM_uint32
181ssh_gssapi_accept_ctx(Gssctxt *ctx, gss_buffer_desc *recv_tok,
182    gss_buffer_desc *send_tok, OM_uint32 *flags)
183{
184	OM_uint32 status;
185	gss_OID mech;
186
187	ctx->major = gss_accept_sec_context(&ctx->minor,
188	    &ctx->context, ctx->creds, recv_tok,
189	    GSS_C_NO_CHANNEL_BINDINGS, &ctx->client, &mech,
190	    send_tok, flags, NULL, &ctx->client_creds);
191
192	if (GSS_ERROR(ctx->major))
193		ssh_gssapi_error(ctx);
194
195	if (ctx->client_creds)
196		debug("Received some client credentials");
197	else
198		debug("Got no client credentials");
199
200	status = ctx->major;
201
202	/* Now, if we're complete and we have the right flags, then
203	 * we flag the user as also having been authenticated
204	 */
205
206	if (((flags == NULL) || ((*flags & GSS_C_MUTUAL_FLAG) &&
207	    (*flags & GSS_C_INTEG_FLAG))) && (ctx->major == GSS_S_COMPLETE)) {
208		if (ssh_gssapi_getclient(ctx, &gssapi_client))
209			fatal("Couldn't convert client name");
210	}
211
212	return (status);
213}
214
215/*
216 * This parses an exported name, extracting the mechanism specific portion
217 * to use for ACL checking. It verifies that the name belongs the mechanism
218 * originally selected.
219 */
220static OM_uint32
221ssh_gssapi_parse_ename(Gssctxt *ctx, gss_buffer_t ename, gss_buffer_t name)
222{
223	u_char *tok;
224	OM_uint32 offset;
225	OM_uint32 oidl;
226
227	tok = ename->value;
228
229	/*
230	 * Check that ename is long enough for all of the fixed length
231	 * header, and that the initial ID bytes are correct
232	 */
233
234	if (ename->length < 6 || memcmp(tok, "\x04\x01", 2) != 0)
235		return GSS_S_FAILURE;
236
237	/*
238	 * Extract the OID, and check it. Here GSSAPI breaks with tradition
239	 * and does use the OID type and length bytes. To confuse things
240	 * there are two lengths - the first including these, and the
241	 * second without.
242	 */
243
244	oidl = get_u16(tok+2); /* length including next two bytes */
245	oidl = oidl-2; /* turn it into the _real_ length of the variable OID */
246
247	/*
248	 * Check the BER encoding for correct type and length, that the
249	 * string is long enough and that the OID matches that in our context
250	 */
251	if (tok[4] != 0x06 || tok[5] != oidl ||
252	    ename->length < oidl+6 ||
253	    !ssh_gssapi_check_oid(ctx, tok+6, oidl))
254		return GSS_S_FAILURE;
255
256	offset = oidl+6;
257
258	if (ename->length < offset+4)
259		return GSS_S_FAILURE;
260
261	name->length = get_u32(tok+offset);
262	offset += 4;
263
264	if (UINT_MAX - offset < name->length)
265		return GSS_S_FAILURE;
266	if (ename->length < offset+name->length)
267		return GSS_S_FAILURE;
268
269	name->value = xmalloc(name->length+1);
270	memcpy(name->value, tok+offset, name->length);
271	((char *)name->value)[name->length] = 0;
272
273	return GSS_S_COMPLETE;
274}
275
276/* Extract the client details from a given context. This can only reliably
277 * be called once for a context */
278
279/* Privileged (called from accept_secure_ctx) */
280OM_uint32
281ssh_gssapi_getclient(Gssctxt *ctx, ssh_gssapi_client *client)
282{
283	int i = 0;
284
285	gss_buffer_desc ename;
286
287	client->mech = NULL;
288
289	while (supported_mechs[i]->name != NULL) {
290		if (supported_mechs[i]->oid.length == ctx->oid->length &&
291		    (memcmp(supported_mechs[i]->oid.elements,
292		    ctx->oid->elements, ctx->oid->length) == 0))
293			client->mech = supported_mechs[i];
294		i++;
295	}
296
297	if (client->mech == NULL)
298		return GSS_S_FAILURE;
299
300	if ((ctx->major = gss_display_name(&ctx->minor, ctx->client,
301	    &client->displayname, NULL))) {
302		ssh_gssapi_error(ctx);
303		return (ctx->major);
304	}
305
306	if ((ctx->major = gss_export_name(&ctx->minor, ctx->client,
307	    &ename))) {
308		ssh_gssapi_error(ctx);
309		return (ctx->major);
310	}
311
312	if ((ctx->major = ssh_gssapi_parse_ename(ctx,&ename,
313	    &client->exportedname))) {
314		return (ctx->major);
315	}
316
317	/* We can't copy this structure, so we just move the pointer to it */
318	client->creds = ctx->client_creds;
319	ctx->client_creds = GSS_C_NO_CREDENTIAL;
320	return (ctx->major);
321}
322
323/* As user - called on fatal/exit */
324void
325ssh_gssapi_cleanup_creds(void)
326{
327	if (gssapi_client.store.filename != NULL) {
328		/* Unlink probably isn't sufficient */
329		debug("removing gssapi cred file\"%s\"",
330		    gssapi_client.store.filename);
331		unlink(gssapi_client.store.filename);
332	}
333}
334
335/* As user */
336void
337ssh_gssapi_storecreds(void)
338{
339	if (gssapi_client.mech && gssapi_client.mech->storecreds) {
340		(*gssapi_client.mech->storecreds)(&gssapi_client);
341	} else
342		debug("ssh_gssapi_storecreds: Not a GSSAPI mechanism");
343}
344
345/* This allows GSSAPI methods to do things to the child's environment based
346 * on the passed authentication process and credentials.
347 */
348/* As user */
349void
350ssh_gssapi_do_child(char ***envp, u_int *envsizep)
351{
352
353	if (gssapi_client.store.envvar != NULL &&
354	    gssapi_client.store.envval != NULL) {
355		debug("Setting %s to %s", gssapi_client.store.envvar,
356		    gssapi_client.store.envval);
357		child_set_env(envp, envsizep, gssapi_client.store.envvar,
358		    gssapi_client.store.envval);
359	}
360}
361
362/* Privileged */
363int
364ssh_gssapi_userok(char *user)
365{
366	OM_uint32 lmin;
367
368	if (gssapi_client.exportedname.length == 0 ||
369	    gssapi_client.exportedname.value == NULL) {
370		debug("No suitable client data");
371		return 0;
372	}
373	if (gssapi_client.mech && gssapi_client.mech->userok)
374		if ((*gssapi_client.mech->userok)(&gssapi_client, user))
375			return 1;
376		else {
377			/* Destroy delegated credentials if userok fails */
378			gss_release_buffer(&lmin, &gssapi_client.displayname);
379			gss_release_buffer(&lmin, &gssapi_client.exportedname);
380			gss_release_cred(&lmin, &gssapi_client.creds);
381			explicit_bzero(&gssapi_client,
382			    sizeof(ssh_gssapi_client));
383			return 0;
384		}
385	else
386		debug("ssh_gssapi_userok: Unknown GSSAPI mechanism");
387	return (0);
388}
389
390/* Privileged */
391OM_uint32
392ssh_gssapi_checkmic(Gssctxt *ctx, gss_buffer_t gssbuf, gss_buffer_t gssmic)
393{
394	ctx->major = gss_verify_mic(&ctx->minor, ctx->context,
395	    gssbuf, gssmic, NULL);
396
397	return (ctx->major);
398}
399
400/* Privileged */
401const char *ssh_gssapi_displayname(void)
402{
403	if (gssapi_client.displayname.length == 0 ||
404	    gssapi_client.displayname.value == NULL)
405		return NULL;
406	return (char *)gssapi_client.displayname.value;
407}
408
409#endif
410