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1 /* $OpenBSD: auth2-hostbased.c,v 1.26 2016/03/07 19:02:43 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 
30 #include <pwd.h>
31 #include <string.h>
32 #include <stdarg.h>
33 
34 #include "xmalloc.h"
35 #include "ssh2.h"
36 #include "packet.h"
37 #include "buffer.h"
38 #include "log.h"
39 #include "misc.h"
40 #include "servconf.h"
41 #include "compat.h"
42 #include "key.h"
43 #include "hostfile.h"
44 #include "auth.h"
45 #include "canohost.h"
46 #ifdef GSSAPI
47 #include "ssh-gss.h"
48 #endif
49 #include "monitor_wrap.h"
50 #include "pathnames.h"
51 #include "match.h"
52 
53 /* import */
54 extern ServerOptions options;
55 extern u_char *session_id2;
56 extern u_int session_id2_len;
57 
58 static int
userauth_hostbased(Authctxt * authctxt)59 userauth_hostbased(Authctxt *authctxt)
60 {
61 	Buffer b;
62 	Key *key = NULL;
63 	char *pkalg, *cuser, *chost, *service;
64 	u_char *pkblob, *sig;
65 	u_int alen, blen, slen;
66 	int pktype;
67 	int authenticated = 0;
68 
69 	if (!authctxt->valid) {
70 		debug2("userauth_hostbased: disabled because of invalid user");
71 		return 0;
72 	}
73 	pkalg = packet_get_string(&alen);
74 	pkblob = packet_get_string(&blen);
75 	chost = packet_get_string(NULL);
76 	cuser = packet_get_string(NULL);
77 	sig = packet_get_string(&slen);
78 
79 	debug("userauth_hostbased: cuser %s chost %s pkalg %s slen %d",
80 	    cuser, chost, pkalg, slen);
81 #ifdef DEBUG_PK
82 	debug("signature:");
83 	buffer_init(&b);
84 	buffer_append(&b, sig, slen);
85 	buffer_dump(&b);
86 	buffer_free(&b);
87 #endif
88 	pktype = key_type_from_name(pkalg);
89 	if (pktype == KEY_UNSPEC) {
90 		/* this is perfectly legal */
91 		logit("userauth_hostbased: unsupported "
92 		    "public key algorithm: %s", pkalg);
93 		goto done;
94 	}
95 	key = key_from_blob(pkblob, blen);
96 	if (key == NULL) {
97 		error("userauth_hostbased: cannot decode key: %s", pkalg);
98 		goto done;
99 	}
100 	if (key->type != pktype) {
101 		error("userauth_hostbased: type mismatch for decoded key "
102 		    "(received %d, expected %d)", key->type, pktype);
103 		goto done;
104 	}
105 	if (key_type_plain(key->type) == KEY_RSA &&
106 	    (datafellows & SSH_BUG_RSASIGMD5) != 0) {
107 		error("Refusing RSA key because peer uses unsafe "
108 		    "signature format");
109 		goto done;
110 	}
111 	if (match_pattern_list(sshkey_ssh_name(key),
112 	    options.hostbased_key_types, 0) != 1) {
113 		logit("%s: key type %s not in HostbasedAcceptedKeyTypes",
114 		    __func__, sshkey_type(key));
115 		goto done;
116 	}
117 
118 	service = datafellows & SSH_BUG_HBSERVICE ? "ssh-userauth" :
119 	    authctxt->service;
120 	buffer_init(&b);
121 	buffer_put_string(&b, session_id2, session_id2_len);
122 	/* reconstruct packet */
123 	buffer_put_char(&b, SSH2_MSG_USERAUTH_REQUEST);
124 	buffer_put_cstring(&b, authctxt->user);
125 	buffer_put_cstring(&b, service);
126 	buffer_put_cstring(&b, "hostbased");
127 	buffer_put_string(&b, pkalg, alen);
128 	buffer_put_string(&b, pkblob, blen);
129 	buffer_put_cstring(&b, chost);
130 	buffer_put_cstring(&b, cuser);
131 #ifdef DEBUG_PK
132 	buffer_dump(&b);
133 #endif
134 
135 	pubkey_auth_info(authctxt, key,
136 	    "client user \"%.100s\", client host \"%.100s\"", cuser, chost);
137 
138 	/* test for allowed key and correct signature */
139 	authenticated = 0;
140 	if (PRIVSEP(hostbased_key_allowed(authctxt->pw, cuser, chost, key)) &&
141 	    PRIVSEP(key_verify(key, sig, slen, buffer_ptr(&b),
142 			buffer_len(&b))) == 1)
143 		authenticated = 1;
144 
145 	buffer_free(&b);
146 done:
147 	debug2("userauth_hostbased: authenticated %d", authenticated);
148 	if (key != NULL)
149 		key_free(key);
150 	free(pkalg);
151 	free(pkblob);
152 	free(cuser);
153 	free(chost);
154 	free(sig);
155 	return authenticated;
156 }
157 
158 /* return 1 if given hostkey is allowed */
159 int
hostbased_key_allowed(struct passwd * pw,const char * cuser,char * chost,Key * key)160 hostbased_key_allowed(struct passwd *pw, const char *cuser, char *chost,
161     Key *key)
162 {
163 	struct ssh *ssh = active_state; /* XXX */
164 	const char *resolvedname, *ipaddr, *lookup, *reason;
165 	HostStatus host_status;
166 	int len;
167 	char *fp;
168 
169 	if (auth_key_is_revoked(key))
170 		return 0;
171 
172 	resolvedname = auth_get_canonical_hostname(ssh, options.use_dns);
173 	ipaddr = ssh_remote_ipaddr(ssh);
174 
175 	debug2("%s: chost %s resolvedname %s ipaddr %s", __func__,
176 	    chost, resolvedname, ipaddr);
177 
178 	if (((len = strlen(chost)) > 0) && chost[len - 1] == '.') {
179 		debug2("stripping trailing dot from chost %s", chost);
180 		chost[len - 1] = '\0';
181 	}
182 
183 	if (options.hostbased_uses_name_from_packet_only) {
184 		if (auth_rhosts2(pw, cuser, chost, chost) == 0) {
185 			debug2("%s: auth_rhosts2 refused "
186 			    "user \"%.100s\" host \"%.100s\" (from packet)",
187 			    __func__, cuser, chost);
188 			return 0;
189 		}
190 		lookup = chost;
191 	} else {
192 		if (strcasecmp(resolvedname, chost) != 0)
193 			logit("userauth_hostbased mismatch: "
194 			    "client sends %s, but we resolve %s to %s",
195 			    chost, ipaddr, resolvedname);
196 		if (auth_rhosts2(pw, cuser, resolvedname, ipaddr) == 0) {
197 			debug2("%s: auth_rhosts2 refused "
198 			    "user \"%.100s\" host \"%.100s\" addr \"%.100s\"",
199 			    __func__, cuser, resolvedname, ipaddr);
200 			return 0;
201 		}
202 		lookup = resolvedname;
203 	}
204 	debug2("%s: access allowed by auth_rhosts2", __func__);
205 
206 	if (key_is_cert(key) &&
207 	    key_cert_check_authority(key, 1, 0, lookup, &reason)) {
208 		error("%s", reason);
209 		auth_debug_add("%s", reason);
210 		return 0;
211 	}
212 
213 	host_status = check_key_in_hostfiles(pw, key, lookup,
214 	    _PATH_SSH_SYSTEM_HOSTFILE,
215 	    options.ignore_user_known_hosts ? NULL : _PATH_SSH_USER_HOSTFILE);
216 
217 	/* backward compat if no key has been found. */
218 	if (host_status == HOST_NEW) {
219 		host_status = check_key_in_hostfiles(pw, key, lookup,
220 		    _PATH_SSH_SYSTEM_HOSTFILE2,
221 		    options.ignore_user_known_hosts ? NULL :
222 		    _PATH_SSH_USER_HOSTFILE2);
223 	}
224 
225 	if (host_status == HOST_OK) {
226 		if (key_is_cert(key)) {
227 			if ((fp = sshkey_fingerprint(key->cert->signature_key,
228 			    options.fingerprint_hash, SSH_FP_DEFAULT)) == NULL)
229 				fatal("%s: sshkey_fingerprint fail", __func__);
230 			verbose("Accepted certificate ID \"%s\" signed by "
231 			    "%s CA %s from %s@%s", key->cert->key_id,
232 			    key_type(key->cert->signature_key), fp,
233 			    cuser, lookup);
234 		} else {
235 			if ((fp = sshkey_fingerprint(key,
236 			    options.fingerprint_hash, SSH_FP_DEFAULT)) == NULL)
237 				fatal("%s: sshkey_fingerprint fail", __func__);
238 			verbose("Accepted %s public key %s from %s@%s",
239 			    key_type(key), fp, cuser, lookup);
240 		}
241 		free(fp);
242 	}
243 
244 	return (host_status == HOST_OK);
245 }
246 
247 Authmethod method_hostbased = {
248 	"hostbased",
249 	userauth_hostbased,
250 	&options.hostbased_authentication
251 };
252