xref: /freebsd/crypto/openssh/auth2-hostbased.c (revision 4d3fc8b0)
1 /* $OpenBSD: auth2-hostbased.c,v 1.52 2023/03/05 05:34:09 dtucker 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 <stdlib.h>
31 #include <pwd.h>
32 #include <string.h>
33 #include <stdarg.h>
34 
35 #include "xmalloc.h"
36 #include "ssh2.h"
37 #include "packet.h"
38 #include "kex.h"
39 #include "sshbuf.h"
40 #include "log.h"
41 #include "misc.h"
42 #include "servconf.h"
43 #include "sshkey.h"
44 #include "hostfile.h"
45 #include "auth.h"
46 #include "canohost.h"
47 #ifdef GSSAPI
48 #include "ssh-gss.h"
49 #endif
50 #include "monitor_wrap.h"
51 #include "pathnames.h"
52 #include "ssherr.h"
53 #include "match.h"
54 
55 /* import */
56 extern ServerOptions options;
57 
58 static int
userauth_hostbased(struct ssh * ssh,const char * method)59 userauth_hostbased(struct ssh *ssh, const char *method)
60 {
61 	Authctxt *authctxt = ssh->authctxt;
62 	struct sshbuf *b;
63 	struct sshkey *key = NULL;
64 	char *pkalg, *cuser, *chost;
65 	u_char *pkblob, *sig;
66 	size_t alen, blen, slen;
67 	int r, pktype, authenticated = 0;
68 
69 	/* XXX use sshkey_froms() */
70 	if ((r = sshpkt_get_cstring(ssh, &pkalg, &alen)) != 0 ||
71 	    (r = sshpkt_get_string(ssh, &pkblob, &blen)) != 0 ||
72 	    (r = sshpkt_get_cstring(ssh, &chost, NULL)) != 0 ||
73 	    (r = sshpkt_get_cstring(ssh, &cuser, NULL)) != 0 ||
74 	    (r = sshpkt_get_string(ssh, &sig, &slen)) != 0)
75 		fatal_fr(r, "parse packet");
76 
77 	debug_f("cuser %s chost %s pkalg %s slen %zu",
78 	    cuser, chost, pkalg, slen);
79 #ifdef DEBUG_PK
80 	debug("signature:");
81 	sshbuf_dump_data(sig, slen, stderr);
82 #endif
83 	pktype = sshkey_type_from_name(pkalg);
84 	if (pktype == KEY_UNSPEC) {
85 		/* this is perfectly legal */
86 		logit_f("unsupported public key algorithm: %s",
87 		    pkalg);
88 		goto done;
89 	}
90 	if ((r = sshkey_from_blob(pkblob, blen, &key)) != 0) {
91 		error_fr(r, "key_from_blob");
92 		goto done;
93 	}
94 	if (key == NULL) {
95 		error_f("cannot decode key: %s", pkalg);
96 		goto done;
97 	}
98 	if (key->type != pktype) {
99 		error_f("type mismatch for decoded key "
100 		    "(received %d, expected %d)", key->type, pktype);
101 		goto done;
102 	}
103 	if (match_pattern_list(pkalg, options.hostbased_accepted_algos, 0) != 1) {
104 		logit_f("signature algorithm %s not in "
105 		    "HostbasedAcceptedAlgorithms", pkalg);
106 		goto done;
107 	}
108 	if ((r = sshkey_check_cert_sigtype(key,
109 	    options.ca_sign_algorithms)) != 0) {
110 		logit_fr(r, "certificate signature algorithm %s",
111 		    (key->cert == NULL || key->cert->signature_type == NULL) ?
112 		    "(null)" : key->cert->signature_type);
113 		goto done;
114 	}
115 	if ((r = sshkey_check_rsa_length(key,
116 	    options.required_rsa_size)) != 0) {
117 		logit_r(r, "refusing %s key", sshkey_type(key));
118 		goto done;
119 	}
120 
121 	if (!authctxt->valid || authctxt->user == NULL) {
122 		debug2_f("disabled because of invalid user");
123 		goto done;
124 	}
125 
126 	if ((b = sshbuf_new()) == NULL)
127 		fatal_f("sshbuf_new failed");
128 	/* reconstruct packet */
129 	if ((r = sshbuf_put_stringb(b, ssh->kex->session_id)) != 0 ||
130 	    (r = sshbuf_put_u8(b, SSH2_MSG_USERAUTH_REQUEST)) != 0 ||
131 	    (r = sshbuf_put_cstring(b, authctxt->user)) != 0 ||
132 	    (r = sshbuf_put_cstring(b, authctxt->service)) != 0 ||
133 	    (r = sshbuf_put_cstring(b, method)) != 0 ||
134 	    (r = sshbuf_put_string(b, pkalg, alen)) != 0 ||
135 	    (r = sshbuf_put_string(b, pkblob, blen)) != 0 ||
136 	    (r = sshbuf_put_cstring(b, chost)) != 0 ||
137 	    (r = sshbuf_put_cstring(b, cuser)) != 0)
138 		fatal_fr(r, "reconstruct packet");
139 #ifdef DEBUG_PK
140 	sshbuf_dump(b, stderr);
141 #endif
142 
143 	auth2_record_info(authctxt,
144 	    "client user \"%.100s\", client host \"%.100s\"", cuser, chost);
145 
146 	/* test for allowed key and correct signature */
147 	authenticated = 0;
148 	if (PRIVSEP(hostbased_key_allowed(ssh, authctxt->pw, cuser,
149 	    chost, key)) &&
150 	    PRIVSEP(sshkey_verify(key, sig, slen,
151 	    sshbuf_ptr(b), sshbuf_len(b), pkalg, ssh->compat, NULL)) == 0)
152 		authenticated = 1;
153 
154 	auth2_record_key(authctxt, authenticated, key);
155 	sshbuf_free(b);
156 done:
157 	debug2_f("authenticated %d", authenticated);
158 	sshkey_free(key);
159 	free(pkalg);
160 	free(pkblob);
161 	free(cuser);
162 	free(chost);
163 	free(sig);
164 	return authenticated;
165 }
166 
167 /* return 1 if given hostkey is allowed */
168 int
hostbased_key_allowed(struct ssh * ssh,struct passwd * pw,const char * cuser,char * chost,struct sshkey * key)169 hostbased_key_allowed(struct ssh *ssh, struct passwd *pw,
170     const char *cuser, char *chost, struct sshkey *key)
171 {
172 	const char *resolvedname, *ipaddr, *lookup, *reason;
173 	HostStatus host_status;
174 	int len;
175 	char *fp;
176 
177 	if (auth_key_is_revoked(key))
178 		return 0;
179 
180 	resolvedname = auth_get_canonical_hostname(ssh, options.use_dns);
181 	ipaddr = ssh_remote_ipaddr(ssh);
182 
183 	debug2_f("chost %s resolvedname %s ipaddr %s",
184 	    chost, resolvedname, ipaddr);
185 
186 	if (((len = strlen(chost)) > 0) && chost[len - 1] == '.') {
187 		debug2("stripping trailing dot from chost %s", chost);
188 		chost[len - 1] = '\0';
189 	}
190 
191 	if (options.hostbased_uses_name_from_packet_only) {
192 		if (auth_rhosts2(pw, cuser, chost, chost) == 0) {
193 			debug2_f("auth_rhosts2 refused user \"%.100s\" "
194 			    "host \"%.100s\" (from packet)", cuser, chost);
195 			return 0;
196 		}
197 		lookup = chost;
198 	} else {
199 		if (strcasecmp(resolvedname, chost) != 0)
200 			logit("userauth_hostbased mismatch: "
201 			    "client sends %s, but we resolve %s to %s",
202 			    chost, ipaddr, resolvedname);
203 		if (auth_rhosts2(pw, cuser, resolvedname, ipaddr) == 0) {
204 			debug2_f("auth_rhosts2 refused "
205 			    "user \"%.100s\" host \"%.100s\" addr \"%.100s\"",
206 			    cuser, resolvedname, ipaddr);
207 			return 0;
208 		}
209 		lookup = resolvedname;
210 	}
211 	debug2_f("access allowed by auth_rhosts2");
212 
213 	if (sshkey_is_cert(key) &&
214 	    sshkey_cert_check_authority_now(key, 1, 0, 0, lookup, &reason)) {
215 		error("%s", reason);
216 		auth_debug_add("%s", reason);
217 		return 0;
218 	}
219 
220 	host_status = check_key_in_hostfiles(pw, key, lookup,
221 	    _PATH_SSH_SYSTEM_HOSTFILE,
222 	    options.ignore_user_known_hosts ? NULL : _PATH_SSH_USER_HOSTFILE);
223 
224 	/* backward compat if no key has been found. */
225 	if (host_status == HOST_NEW) {
226 		host_status = check_key_in_hostfiles(pw, key, lookup,
227 		    _PATH_SSH_SYSTEM_HOSTFILE2,
228 		    options.ignore_user_known_hosts ? NULL :
229 		    _PATH_SSH_USER_HOSTFILE2);
230 	}
231 
232 	if (host_status == HOST_OK) {
233 		if (sshkey_is_cert(key)) {
234 			if ((fp = sshkey_fingerprint(key->cert->signature_key,
235 			    options.fingerprint_hash, SSH_FP_DEFAULT)) == NULL)
236 				fatal_f("sshkey_fingerprint fail");
237 			verbose("Accepted certificate ID \"%s\" signed by "
238 			    "%s CA %s from %s@%s", key->cert->key_id,
239 			    sshkey_type(key->cert->signature_key), fp,
240 			    cuser, lookup);
241 		} else {
242 			if ((fp = sshkey_fingerprint(key,
243 			    options.fingerprint_hash, SSH_FP_DEFAULT)) == NULL)
244 				fatal_f("sshkey_fingerprint fail");
245 			verbose("Accepted %s public key %s from %s@%s",
246 			    sshkey_type(key), fp, cuser, lookup);
247 		}
248 		free(fp);
249 	}
250 
251 	return (host_status == HOST_OK);
252 }
253 
254 Authmethod method_hostbased = {
255 	"hostbased",
256 	NULL,
257 	userauth_hostbased,
258 	&options.hostbased_authentication
259 };
260