[openssh.git] / auth2-pubkey.c

/*
 * Copyright (c) 2000 Markus Friedl.  All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
 * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */

#include "includes.h"
RCSID("$OpenBSD: auth2-pubkey.c,v 1.7 2004/06/21 17:36:31 avsm Exp $");

#include "ssh2.h"
#include "xmalloc.h"
#include "packet.h"
#include "buffer.h"
#include "log.h"
#include "servconf.h"
#include "compat.h"
#include "bufaux.h"
#include "auth.h"
#include "key.h"
#include "pathnames.h"
#include "uidswap.h"
#include "auth-options.h"
#include "canohost.h"
#include "monitor_wrap.h"

/* import */
extern ServerOptions options;
extern u_char *session_id2;
extern u_int session_id2_len;

static int
userauth_pubkey(Authctxt *authctxt)
{
	Buffer b;
	Key *key = NULL;
	char *pkalg;
	u_char *pkblob, *sig;
	u_int alen, blen, slen;
	int have_sig, pktype;
	int authenticated = 0;

	if (!authctxt->valid) {
		debug2("userauth_pubkey: disabled because of invalid user");
		return 0;
	}
	have_sig = packet_get_char();
	if (datafellows & SSH_BUG_PKAUTH) {
		debug2("userauth_pubkey: SSH_BUG_PKAUTH");
		/* no explicit pkalg given */
		pkblob = packet_get_string(&blen);
		buffer_init(&b);
		buffer_append(&b, pkblob, blen);
		/* so we have to extract the pkalg from the pkblob */
		pkalg = buffer_get_string(&b, &alen);
		buffer_free(&b);
	} else {
		pkalg = packet_get_string(&alen);
		pkblob = packet_get_string(&blen);
	}
	pktype = key_type_from_name(pkalg);
	if (pktype == KEY_UNSPEC) {
		/* this is perfectly legal */
		logit("userauth_pubkey: unsupported public key algorithm: %s",
		    pkalg);
		goto done;
	}
	key = key_from_blob(pkblob, blen);
	if (key == NULL) {
		error("userauth_pubkey: cannot decode key: %s", pkalg);
		goto done;
	}
	if (key->type != pktype) {
		error("userauth_pubkey: type mismatch for decoded key "
		    "(received %d, expected %d)", key->type, pktype);
		goto done;
	}
	if (have_sig) {
		sig = packet_get_string(&slen);
		packet_check_eom();
		buffer_init(&b);
		if (datafellows & SSH_OLD_SESSIONID) {
			buffer_append(&b, session_id2, session_id2_len);
		} else {
			buffer_put_string(&b, session_id2, session_id2_len);
		}
		/* reconstruct packet */
		buffer_put_char(&b, SSH2_MSG_USERAUTH_REQUEST);
		buffer_put_cstring(&b, authctxt->user);
		buffer_put_cstring(&b,
		    datafellows & SSH_BUG_PKSERVICE ?
		    "ssh-userauth" :
		    authctxt->service);
		if (datafellows & SSH_BUG_PKAUTH) {
			buffer_put_char(&b, have_sig);
		} else {
			buffer_put_cstring(&b, "publickey");
			buffer_put_char(&b, have_sig);
			buffer_put_cstring(&b, pkalg);
		}
		buffer_put_string(&b, pkblob, blen);
#ifdef DEBUG_PK
		buffer_dump(&b);
#endif
		/* test for correct signature */
		authenticated = 0;
		if (PRIVSEP(user_key_allowed(authctxt->pw, key)) &&
		    PRIVSEP(key_verify(key, sig, slen, buffer_ptr(&b),
		    buffer_len(&b))) == 1)
			authenticated = 1;
		buffer_free(&b);
		xfree(sig);
	} else {
		debug("test whether pkalg/pkblob are acceptable");
		packet_check_eom();

		/* XXX fake reply and always send PK_OK ? */
		/*
		 * XXX this allows testing whether a user is allowed
		 * to login: if you happen to have a valid pubkey this
		 * message is sent. the message is NEVER sent at all
		 * if a user is not allowed to login. is this an
		 * issue? -markus
		 */
		if (PRIVSEP(user_key_allowed(authctxt->pw, key))) {
			packet_start(SSH2_MSG_USERAUTH_PK_OK);
			packet_put_string(pkalg, alen);
			packet_put_string(pkblob, blen);
			packet_send();
			packet_write_wait();
			authctxt->postponed = 1;
		}
	}
	if (authenticated != 1)
		auth_clear_options();
done:
	debug2("userauth_pubkey: authenticated %d pkalg %s", authenticated, pkalg);
	if (key != NULL)
		key_free(key);
	xfree(pkalg);
	xfree(pkblob);
#ifdef HAVE_CYGWIN
	if (check_nt_auth(0, authctxt->pw) == 0)
		authenticated = 0;
#endif
	return authenticated;
}

/* return 1 if user allows given key */
static int
user_key_allowed2(struct passwd *pw, Key *key, char *file)
{
	char line[8192];
	int found_key = 0;
	FILE *f;
	u_long linenum = 0;
	struct stat st;
	Key *found;
	char *fp;

	/* Temporarily use the user's uid. */
	temporarily_use_uid(pw);

	debug("trying public key file %s", file);

	/* Fail quietly if file does not exist */
	if (stat(file, &st) < 0) {
		/* Restore the privileged uid. */
		restore_uid();
		return 0;
	}
	/* Open the file containing the authorized keys. */
	f = fopen(file, "r");
	if (!f) {
		/* Restore the privileged uid. */
		restore_uid();
		return 0;
	}
	if (options.strict_modes &&
	    secure_filename(f, file, pw, line, sizeof(line)) != 0) {
		fclose(f);
		logit("Authentication refused: %s", line);
		restore_uid();
		return 0;
	}

	found_key = 0;
	found = key_new(key->type);

	while (fgets(line, sizeof(line), f)) {
		char *cp, *key_options = NULL;
		linenum++;
		/* Skip leading whitespace, empty and comment lines. */
		for (cp = line; *cp == ' ' || *cp == '\t'; cp++)
			;
		if (!*cp || *cp == '\n' || *cp == '#')
			continue;

		if (key_read(found, &cp) != 1) {
			/* no key?  check if there are options for this key */
			int quoted = 0;
			debug2("user_key_allowed: check options: '%s'", cp);
			key_options = cp;
			for (; *cp && (quoted || (*cp != ' ' && *cp != '\t')); cp++) {
				if (*cp == '\\' && cp[1] == '"')
					cp++;	/* Skip both */
				else if (*cp == '"')
					quoted = !quoted;
			}
			/* Skip remaining whitespace. */
			for (; *cp == ' ' || *cp == '\t'; cp++)
				;
			if (key_read(found, &cp) != 1) {
				debug2("user_key_allowed: advance: '%s'", cp);
				/* still no key?  advance to next line*/
				continue;
			}
		}
		if (key_equal(found, key) &&
		    auth_parse_options(pw, key_options, file, linenum) == 1) {
			found_key = 1;
			debug("matching key found: file %s, line %lu",
			    file, linenum);
			fp = key_fingerprint(found, SSH_FP_MD5, SSH_FP_HEX);
			verbose("Found matching %s key: %s",
			    key_type(found), fp);
			xfree(fp);
			break;
		}
	}
	restore_uid();
	fclose(f);
	key_free(found);
	if (!found_key)
		debug2("key not found");
	return found_key;
}

/* check whether given key is in .ssh/authorized_keys* */
int
user_key_allowed(struct passwd *pw, Key *key)
{
	int success;
	char *file;

	file = authorized_keys_file(pw);
	success = user_key_allowed2(pw, key, file);
	xfree(file);
	if (success)
		return success;

	/* try suffix "2" for backward compat, too */
	file = authorized_keys_file2(pw);
	success = user_key_allowed2(pw, key, file);
	xfree(file);
	return success;
}

Authmethod method_pubkey = {
	"publickey",
	userauth_pubkey,
	&options.pubkey_authentication
};
Commit	Line	Data
013eab17	1	/*
	2	* Copyright (c) 2000 Markus Friedl. All rights reserved.
	3	*
	4	* Redistribution and use in source and binary forms, with or without
	5	* modification, are permitted provided that the following conditions
	6	* are met:
	7	* 1. Redistributions of source code must retain the above copyright
	8	* notice, this list of conditions and the following disclaimer.
	9	* 2. Redistributions in binary form must reproduce the above copyright
	10	* notice, this list of conditions and the following disclaimer in the
	11	* documentation and/or other materials provided with the distribution.
	12	*
	13	* THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
	14	* IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
	15	* OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
	16	* IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
	17	* INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
	18	* NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
	19	* DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
	20	* THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
	21	* (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
	22	* THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
	23	*/
	24
	25	#include "includes.h"
ca75d7de	26	RCSID("$OpenBSD: auth2-pubkey.c,v 1.7 2004/06/21 17:36:31 avsm Exp $");
013eab17	27
	28	#include "ssh2.h"
	29	#include "xmalloc.h"
	30	#include "packet.h"
	31	#include "buffer.h"
	32	#include "log.h"
	33	#include "servconf.h"
	34	#include "compat.h"
	35	#include "bufaux.h"
	36	#include "auth.h"
	37	#include "key.h"
	38	#include "pathnames.h"
	39	#include "uidswap.h"
	40	#include "auth-options.h"
	41	#include "canohost.h"
	42	#include "monitor_wrap.h"
	43
	44	/* import */
	45	extern ServerOptions options;
	46	extern u_char *session_id2;
a27002e5	47	extern u_int session_id2_len;
013eab17	48
	49	static int
	50	userauth_pubkey(Authctxt *authctxt)
	51	{
	52	Buffer b;
	53	Key *key = NULL;
	54	char *pkalg;
	55	u_char pkblob, sig;
	56	u_int alen, blen, slen;
	57	int have_sig, pktype;
	58	int authenticated = 0;
	59
	60	if (!authctxt->valid) {
	61	debug2("userauth_pubkey: disabled because of invalid user");
	62	return 0;
	63	}
	64	have_sig = packet_get_char();
	65	if (datafellows & SSH_BUG_PKAUTH) {
	66	debug2("userauth_pubkey: SSH_BUG_PKAUTH");
	67	/* no explicit pkalg given */
	68	pkblob = packet_get_string(&blen);
	69	buffer_init(&b);
	70	buffer_append(&b, pkblob, blen);
	71	/* so we have to extract the pkalg from the pkblob */
	72	pkalg = buffer_get_string(&b, &alen);
	73	buffer_free(&b);
	74	} else {
	75	pkalg = packet_get_string(&alen);
	76	pkblob = packet_get_string(&blen);
	77	}
	78	pktype = key_type_from_name(pkalg);
	79	if (pktype == KEY_UNSPEC) {
	80	/* this is perfectly legal */
bbe88b6d	81	logit("userauth_pubkey: unsupported public key algorithm: %s",
013eab17	82	pkalg);
	83	goto done;
	84	}
	85	key = key_from_blob(pkblob, blen);
	86	if (key == NULL) {
	87	error("userauth_pubkey: cannot decode key: %s", pkalg);
	88	goto done;
	89	}
	90	if (key->type != pktype) {
	91	error("userauth_pubkey: type mismatch for decoded key "
	92	"(received %d, expected %d)", key->type, pktype);
	93	goto done;
	94	}
	95	if (have_sig) {
	96	sig = packet_get_string(&slen);
	97	packet_check_eom();
	98	buffer_init(&b);
	99	if (datafellows & SSH_OLD_SESSIONID) {
	100	buffer_append(&b, session_id2, session_id2_len);
	101	} else {
	102	buffer_put_string(&b, session_id2, session_id2_len);
	103	}
	104	/* reconstruct packet */
	105	buffer_put_char(&b, SSH2_MSG_USERAUTH_REQUEST);
	106	buffer_put_cstring(&b, authctxt->user);
	107	buffer_put_cstring(&b,
	108	datafellows & SSH_BUG_PKSERVICE ?
	109	"ssh-userauth" :
	110	authctxt->service);
	111	if (datafellows & SSH_BUG_PKAUTH) {
	112	buffer_put_char(&b, have_sig);
	113	} else {
	114	buffer_put_cstring(&b, "publickey");
	115	buffer_put_char(&b, have_sig);
	116	buffer_put_cstring(&b, pkalg);
	117	}
	118	buffer_put_string(&b, pkblob, blen);
	119	#ifdef DEBUG_PK
	120	buffer_dump(&b);
	121	#endif
	122	/* test for correct signature */
	123	authenticated = 0;
	124	if (PRIVSEP(user_key_allowed(authctxt->pw, key)) &&
	125	PRIVSEP(key_verify(key, sig, slen, buffer_ptr(&b),
43f7a4b8	126	buffer_len(&b))) == 1)
013eab17	127	authenticated = 1;
43f7a4b8	128	buffer_free(&b);
013eab17	129	xfree(sig);
	130	} else {
	131	debug("test whether pkalg/pkblob are acceptable");
	132	packet_check_eom();
	133
	134	/* XXX fake reply and always send PK_OK ? */
	135	/*
	136	* XXX this allows testing whether a user is allowed
	137	* to login: if you happen to have a valid pubkey this
	138	* message is sent. the message is NEVER sent at all
	139	* if a user is not allowed to login. is this an
	140	* issue? -markus
	141	*/
	142	if (PRIVSEP(user_key_allowed(authctxt->pw, key))) {
	143	packet_start(SSH2_MSG_USERAUTH_PK_OK);
	144	packet_put_string(pkalg, alen);
	145	packet_put_string(pkblob, blen);
	146	packet_send();
	147	packet_write_wait();
	148	authctxt->postponed = 1;
	149	}
	150	}
	151	if (authenticated != 1)
	152	auth_clear_options();
	153	done:
	154	debug2("userauth_pubkey: authenticated %d pkalg %s", authenticated, pkalg);
	155	if (key != NULL)
	156	key_free(key);
	157	xfree(pkalg);
	158	xfree(pkblob);
	159	#ifdef HAVE_CYGWIN
	160	if (check_nt_auth(0, authctxt->pw) == 0)
73b1ee82	161	authenticated = 0;
013eab17	162	#endif
	163	return authenticated;
	164	}
	165
	166	/* return 1 if user allows given key */
	167	static int
	168	user_key_allowed2(struct passwd pw, Key key, char *file)
	169	{
	170	char line[8192];
	171	int found_key = 0;
	172	FILE *f;
	173	u_long linenum = 0;
	174	struct stat st;
	175	Key *found;
	176	char *fp;
	177
013eab17	178	/* Temporarily use the user's uid. */
	179	temporarily_use_uid(pw);
	180
	181	debug("trying public key file %s", file);
	182
	183	/* Fail quietly if file does not exist */
	184	if (stat(file, &st) < 0) {
	185	/* Restore the privileged uid. */
	186	restore_uid();
	187	return 0;
	188	}
	189	/* Open the file containing the authorized keys. */
	190	f = fopen(file, "r");
	191	if (!f) {
	192	/* Restore the privileged uid. */
	193	restore_uid();
	194	return 0;
	195	}
	196	if (options.strict_modes &&
	197	secure_filename(f, file, pw, line, sizeof(line)) != 0) {
	198	fclose(f);
bbe88b6d	199	logit("Authentication refused: %s", line);
013eab17	200	restore_uid();
	201	return 0;
	202	}
	203
	204	found_key = 0;
	205	found = key_new(key->type);
	206
	207	while (fgets(line, sizeof(line), f)) {
ca75d7de	208	char cp, key_options = NULL;
013eab17	209	linenum++;
	210	/* Skip leading whitespace, empty and comment lines. */
	211	for (cp = line; cp == ' ' \|\| cp == '\t'; cp++)
	212	;
	213	if (!cp \|\| cp == '\n' \|\| *cp == '#')
	214	continue;
	215
	216	if (key_read(found, &cp) != 1) {
	217	/* no key? check if there are options for this key */
	218	int quoted = 0;
	219	debug2("user_key_allowed: check options: '%s'", cp);
ca75d7de	220	key_options = cp;
013eab17	221	for (; cp && (quoted \|\| (cp != ' ' && *cp != '\t')); cp++) {
	222	if (*cp == '\\' && cp[1] == '"')
	223	cp++; /* Skip both */
	224	else if (*cp == '"')
	225	quoted = !quoted;
	226	}
	227	/* Skip remaining whitespace. */
	228	for (; cp == ' ' \|\| cp == '\t'; cp++)
	229	;
	230	if (key_read(found, &cp) != 1) {
	231	debug2("user_key_allowed: advance: '%s'", cp);
	232	/* still no key? advance to next line*/
	233	continue;
	234	}
	235	}
	236	if (key_equal(found, key) &&
ca75d7de	237	auth_parse_options(pw, key_options, file, linenum) == 1) {
013eab17	238	found_key = 1;
	239	debug("matching key found: file %s, line %lu",
	240	file, linenum);
	241	fp = key_fingerprint(found, SSH_FP_MD5, SSH_FP_HEX);
	242	verbose("Found matching %s key: %s",
	243	key_type(found), fp);
	244	xfree(fp);
	245	break;
	246	}
	247	}
	248	restore_uid();
	249	fclose(f);
	250	key_free(found);
	251	if (!found_key)
	252	debug2("key not found");
	253	return found_key;
	254	}
	255
	256	/* check whether given key is in .ssh/authorized_keys* */
	257	int
	258	user_key_allowed(struct passwd pw, Key key)
	259	{
	260	int success;
	261	char *file;
	262
	263	file = authorized_keys_file(pw);
	264	success = user_key_allowed2(pw, key, file);
	265	xfree(file);
	266	if (success)
	267	return success;
	268
	269	/* try suffix "2" for backward compat, too */
	270	file = authorized_keys_file2(pw);
	271	success = user_key_allowed2(pw, key, file);
	272	xfree(file);
	273	return success;
	274	}
	275
	276	Authmethod method_pubkey = {
	277	"publickey",
	278	userauth_pubkey,
	279	&options.pubkey_authentication
	280	};