1/* $OpenBSD: auth2-pubkey.c,v 1.29 2011/05/23 03:30:07 djm Exp $ */
2/*
3 * Copyright (c) 2000 Markus Friedl.  All rights reserved.
4 *
5 * Redistribution and use in source and binary forms, with or without
6 * modification, are permitted provided that the following conditions
7 * are met:
8 * 1. Redistributions of source code must retain the above copyright
9 *    notice, this list of conditions and the following disclaimer.
10 * 2. Redistributions in binary form must reproduce the above copyright
11 *    notice, this list of conditions and the following disclaimer in the
12 *    documentation and/or other materials provided with the distribution.
13 *
14 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
15 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
16 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
17 * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
18 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
19 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
20 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
21 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
22 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
23 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
24 */
25
26#include "includes.h"
27
28#include <sys/types.h>
29#include <sys/stat.h>
30
31#include <fcntl.h>
32#include <pwd.h>
33#include <stdio.h>
34#include <stdarg.h>
35#include <string.h>
36#include <time.h>
37#include <unistd.h>
38
39#include "xmalloc.h"
40#include "ssh.h"
41#include "ssh2.h"
42#include "packet.h"
43#include "buffer.h"
44#include "log.h"
45#include "servconf.h"
46#include "compat.h"
47#include "key.h"
48#include "hostfile.h"
49#include "auth.h"
50#include "pathnames.h"
51#include "uidswap.h"
52#include "auth-options.h"
53#include "canohost.h"
54#ifdef GSSAPI
55#include "ssh-gss.h"
56#endif
57#include "monitor_wrap.h"
58#include "misc.h"
59#include "authfile.h"
60#include "match.h"
61
62/* import */
63extern ServerOptions options;
64extern u_char *session_id2;
65extern u_int session_id2_len;
66
67static int
68userauth_pubkey(Authctxt *authctxt)
69{
70	Buffer b;
71	Key *key = NULL;
72	char *pkalg;
73	u_char *pkblob, *sig;
74	u_int alen, blen, slen;
75	int have_sig, pktype;
76	int authenticated = 0;
77
78	if (!authctxt->valid) {
79		debug2("userauth_pubkey: disabled because of invalid user");
80		return 0;
81	}
82	have_sig = packet_get_char();
83	if (datafellows & SSH_BUG_PKAUTH) {
84		debug2("userauth_pubkey: SSH_BUG_PKAUTH");
85		/* no explicit pkalg given */
86		pkblob = packet_get_string(&blen);
87		buffer_init(&b);
88		buffer_append(&b, pkblob, blen);
89		/* so we have to extract the pkalg from the pkblob */
90		pkalg = buffer_get_string(&b, &alen);
91		buffer_free(&b);
92	} else {
93		pkalg = packet_get_string(&alen);
94		pkblob = packet_get_string(&blen);
95	}
96	pktype = key_type_from_name(pkalg);
97	if (pktype == KEY_UNSPEC) {
98		/* this is perfectly legal */
99		logit("userauth_pubkey: unsupported public key algorithm: %s",
100		    pkalg);
101		goto done;
102	}
103	key = key_from_blob(pkblob, blen);
104	if (key == NULL) {
105		error("userauth_pubkey: cannot decode key: %s", pkalg);
106		goto done;
107	}
108	if (key->type != pktype) {
109		error("userauth_pubkey: type mismatch for decoded key "
110		    "(received %d, expected %d)", key->type, pktype);
111		goto done;
112	}
113	if (have_sig) {
114		sig = packet_get_string(&slen);
115		packet_check_eom();
116		buffer_init(&b);
117		if (datafellows & SSH_OLD_SESSIONID) {
118			buffer_append(&b, session_id2, session_id2_len);
119		} else {
120			buffer_put_string(&b, session_id2, session_id2_len);
121		}
122		/* reconstruct packet */
123		buffer_put_char(&b, SSH2_MSG_USERAUTH_REQUEST);
124		buffer_put_cstring(&b, authctxt->user);
125		buffer_put_cstring(&b,
126		    datafellows & SSH_BUG_PKSERVICE ?
127		    "ssh-userauth" :
128		    authctxt->service);
129		if (datafellows & SSH_BUG_PKAUTH) {
130			buffer_put_char(&b, have_sig);
131		} else {
132			buffer_put_cstring(&b, "publickey");
133			buffer_put_char(&b, have_sig);
134			buffer_put_cstring(&b, pkalg);
135		}
136		buffer_put_string(&b, pkblob, blen);
137#ifdef DEBUG_PK
138		buffer_dump(&b);
139#endif
140		/* test for correct signature */
141		authenticated = 0;
142		if (PRIVSEP(user_key_allowed(authctxt->pw, key)) &&
143		    PRIVSEP(key_verify(key, sig, slen, buffer_ptr(&b),
144		    buffer_len(&b))) == 1)
145			authenticated = 1;
146		buffer_free(&b);
147		xfree(sig);
148	} else {
149		debug("test whether pkalg/pkblob are acceptable");
150		packet_check_eom();
151
152		/* XXX fake reply and always send PK_OK ? */
153		/*
154		 * XXX this allows testing whether a user is allowed
155		 * to login: if you happen to have a valid pubkey this
156		 * message is sent. the message is NEVER sent at all
157		 * if a user is not allowed to login. is this an
158		 * issue? -markus
159		 */
160		if (PRIVSEP(user_key_allowed(authctxt->pw, key))) {
161			packet_start(SSH2_MSG_USERAUTH_PK_OK);
162			packet_put_string(pkalg, alen);
163			packet_put_string(pkblob, blen);
164			packet_send();
165			packet_write_wait();
166			authctxt->postponed = 1;
167		}
168	}
169	if (authenticated != 1)
170		auth_clear_options();
171done:
172	debug2("userauth_pubkey: authenticated %d pkalg %s", authenticated, pkalg);
173	if (key != NULL)
174		key_free(key);
175	xfree(pkalg);
176	xfree(pkblob);
177	return authenticated;
178}
179
180static int
181match_principals_option(const char *principal_list, struct KeyCert *cert)
182{
183	char *result;
184	u_int i;
185
186	/* XXX percent_expand() sequences for authorized_principals? */
187
188	for (i = 0; i < cert->nprincipals; i++) {
189		if ((result = match_list(cert->principals[i],
190		    principal_list, NULL)) != NULL) {
191			debug3("matched principal from key options \"%.100s\"",
192			    result);
193			xfree(result);
194			return 1;
195		}
196	}
197	return 0;
198}
199
200static int
201match_principals_file(char *file, struct passwd *pw, struct KeyCert *cert)
202{
203	FILE *f;
204	char line[SSH_MAX_PUBKEY_BYTES], *cp, *ep, *line_opts;
205	u_long linenum = 0;
206	u_int i;
207
208	temporarily_use_uid(pw);
209	debug("trying authorized principals file %s", file);
210	if ((f = auth_openprincipals(file, pw, options.strict_modes)) == NULL) {
211		restore_uid();
212		return 0;
213	}
214	while (read_keyfile_line(f, file, line, sizeof(line), &linenum) != -1) {
215		/* Skip leading whitespace. */
216		for (cp = line; *cp == ' ' || *cp == '\t'; cp++)
217			;
218		/* Skip blank and comment lines. */
219		if ((ep = strchr(cp, '#')) != NULL)
220			*ep = '\0';
221		if (!*cp || *cp == '\n')
222			continue;
223		/* Trim trailing whitespace. */
224		ep = cp + strlen(cp) - 1;
225		while (ep > cp && (*ep == '\n' || *ep == ' ' || *ep == '\t'))
226			*ep-- = '\0';
227		/*
228		 * If the line has internal whitespace then assume it has
229		 * key options.
230		 */
231		line_opts = NULL;
232		if ((ep = strrchr(cp, ' ')) != NULL ||
233		    (ep = strrchr(cp, '\t')) != NULL) {
234			for (; *ep == ' ' || *ep == '\t'; ep++)
235				;
236			line_opts = cp;
237			cp = ep;
238		}
239		for (i = 0; i < cert->nprincipals; i++) {
240			if (strcmp(cp, cert->principals[i]) == 0) {
241				debug3("matched principal from file \"%.100s\"",
242			    	    cert->principals[i]);
243				if (auth_parse_options(pw, line_opts,
244				    file, linenum) != 1)
245					continue;
246				fclose(f);
247				restore_uid();
248				return 1;
249			}
250		}
251	}
252	fclose(f);
253	restore_uid();
254	return 0;
255}
256
257/* return 1 if user allows given key */
258static int
259user_key_allowed2(struct passwd *pw, Key *key, char *file)
260{
261	char line[SSH_MAX_PUBKEY_BYTES];
262	const char *reason;
263	int found_key = 0;
264	FILE *f;
265	u_long linenum = 0;
266	Key *found;
267	char *fp;
268
269	/* Temporarily use the user's uid. */
270	temporarily_use_uid(pw);
271
272	debug("trying public key file %s", file);
273	f = auth_openkeyfile(file, pw, options.strict_modes);
274
275	if (!f) {
276		restore_uid();
277		return 0;
278	}
279
280	found_key = 0;
281	found = key_new(key_is_cert(key) ? KEY_UNSPEC : key->type);
282
283	while (read_keyfile_line(f, file, line, sizeof(line), &linenum) != -1) {
284		char *cp, *key_options = NULL;
285
286		auth_clear_options();
287
288		/* Skip leading whitespace, empty and comment lines. */
289		for (cp = line; *cp == ' ' || *cp == '\t'; cp++)
290			;
291		if (!*cp || *cp == '\n' || *cp == '#')
292			continue;
293
294		if (key_read(found, &cp) != 1) {
295			/* no key?  check if there are options for this key */
296			int quoted = 0;
297			debug2("user_key_allowed: check options: '%s'", cp);
298			key_options = cp;
299			for (; *cp && (quoted || (*cp != ' ' && *cp != '\t')); cp++) {
300				if (*cp == '\\' && cp[1] == '"')
301					cp++;	/* Skip both */
302				else if (*cp == '"')
303					quoted = !quoted;
304			}
305			/* Skip remaining whitespace. */
306			for (; *cp == ' ' || *cp == '\t'; cp++)
307				;
308			if (key_read(found, &cp) != 1) {
309				debug2("user_key_allowed: advance: '%s'", cp);
310				/* still no key?  advance to next line*/
311				continue;
312			}
313		}
314		if (key_is_cert(key)) {
315			if (!key_equal(found, key->cert->signature_key))
316				continue;
317			if (auth_parse_options(pw, key_options, file,
318			    linenum) != 1)
319				continue;
320			if (!key_is_cert_authority)
321				continue;
322			fp = key_fingerprint(found, SSH_FP_MD5,
323			    SSH_FP_HEX);
324			debug("matching CA found: file %s, line %lu, %s %s",
325			    file, linenum, key_type(found), fp);
326			/*
327			 * If the user has specified a list of principals as
328			 * a key option, then prefer that list to matching
329			 * their username in the certificate principals list.
330			 */
331			if (authorized_principals != NULL &&
332			    !match_principals_option(authorized_principals,
333			    key->cert)) {
334				reason = "Certificate does not contain an "
335				    "authorized principal";
336 fail_reason:
337				xfree(fp);
338				error("%s", reason);
339				auth_debug_add("%s", reason);
340				continue;
341			}
342			if (key_cert_check_authority(key, 0, 0,
343			    authorized_principals == NULL ? pw->pw_name : NULL,
344			    &reason) != 0)
345				goto fail_reason;
346			if (auth_cert_options(key, pw) != 0) {
347				xfree(fp);
348				continue;
349			}
350			verbose("Accepted certificate ID \"%s\" "
351			    "signed by %s CA %s via %s", key->cert->key_id,
352			    key_type(found), fp, file);
353			xfree(fp);
354			found_key = 1;
355			break;
356		} else if (key_equal(found, key)) {
357			if (auth_parse_options(pw, key_options, file,
358			    linenum) != 1)
359				continue;
360			if (key_is_cert_authority)
361				continue;
362			found_key = 1;
363			debug("matching key found: file %s, line %lu",
364			    file, linenum);
365			fp = key_fingerprint(found, SSH_FP_MD5, SSH_FP_HEX);
366			verbose("Found matching %s key: %s",
367			    key_type(found), fp);
368			xfree(fp);
369			break;
370		}
371	}
372	restore_uid();
373	fclose(f);
374	key_free(found);
375	if (!found_key)
376		debug2("key not found");
377	return found_key;
378}
379
380/* Authenticate a certificate key against TrustedUserCAKeys */
381static int
382user_cert_trusted_ca(struct passwd *pw, Key *key)
383{
384	char *ca_fp, *principals_file = NULL;
385	const char *reason;
386	int ret = 0;
387
388	if (!key_is_cert(key) || options.trusted_user_ca_keys == NULL)
389		return 0;
390
391	ca_fp = key_fingerprint(key->cert->signature_key,
392	    SSH_FP_MD5, SSH_FP_HEX);
393
394	if (key_in_file(key->cert->signature_key,
395	    options.trusted_user_ca_keys, 1) != 1) {
396		debug2("%s: CA %s %s is not listed in %s", __func__,
397		    key_type(key->cert->signature_key), ca_fp,
398		    options.trusted_user_ca_keys);
399		goto out;
400	}
401	/*
402	 * If AuthorizedPrincipals is in use, then compare the certificate
403	 * principals against the names in that file rather than matching
404	 * against the username.
405	 */
406	if ((principals_file = authorized_principals_file(pw)) != NULL) {
407		if (!match_principals_file(principals_file, pw, key->cert)) {
408			reason = "Certificate does not contain an "
409			    "authorized principal";
410 fail_reason:
411			error("%s", reason);
412			auth_debug_add("%s", reason);
413			goto out;
414		}
415	}
416	if (key_cert_check_authority(key, 0, 1,
417	    principals_file == NULL ? pw->pw_name : NULL, &reason) != 0)
418		goto fail_reason;
419	if (auth_cert_options(key, pw) != 0)
420		goto out;
421
422	verbose("Accepted certificate ID \"%s\" signed by %s CA %s via %s",
423	    key->cert->key_id, key_type(key->cert->signature_key), ca_fp,
424	    options.trusted_user_ca_keys);
425	ret = 1;
426
427 out:
428	if (principals_file != NULL)
429		xfree(principals_file);
430	if (ca_fp != NULL)
431		xfree(ca_fp);
432	return ret;
433}
434
435/* check whether given key is in .ssh/authorized_keys* */
436int
437user_key_allowed(struct passwd *pw, Key *key)
438{
439	u_int success, i;
440	char *file;
441
442	if (auth_key_is_revoked(key))
443		return 0;
444	if (key_is_cert(key) && auth_key_is_revoked(key->cert->signature_key))
445		return 0;
446
447	success = user_cert_trusted_ca(pw, key);
448	if (success)
449		return success;
450
451	for (i = 0; !success && i < options.num_authkeys_files; i++) {
452		file = expand_authorized_keys(
453		    options.authorized_keys_files[i], pw);
454		success = user_key_allowed2(pw, key, file);
455		xfree(file);
456	}
457
458	return success;
459}
460
461Authmethod method_pubkey = {
462	"publickey",
463	userauth_pubkey,
464	&options.pubkey_authentication
465};
466