1 /* $OpenBSD: auth2-hostbased.c,v 1.42 2019/11/25 00:51:37 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 <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 "sshbuf.h" 39 #include "log.h" 40 #include "misc.h" 41 #include "servconf.h" 42 #include "compat.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 extern u_char *session_id2; 58 extern u_int session_id2_len; 59 60 static int 61 userauth_hostbased(struct ssh *ssh) 62 { 63 Authctxt *authctxt = ssh->authctxt; 64 struct sshbuf *b; 65 struct sshkey *key = NULL; 66 char *pkalg, *cuser, *chost; 67 u_char *pkblob, *sig; 68 size_t alen, blen, slen; 69 int r, pktype, authenticated = 0; 70 71 /* XXX use sshkey_froms() */ 72 if ((r = sshpkt_get_cstring(ssh, &pkalg, &alen)) != 0 || 73 (r = sshpkt_get_string(ssh, &pkblob, &blen)) != 0 || 74 (r = sshpkt_get_cstring(ssh, &chost, NULL)) != 0 || 75 (r = sshpkt_get_cstring(ssh, &cuser, NULL)) != 0 || 76 (r = sshpkt_get_string(ssh, &sig, &slen)) != 0) 77 fatal("%s: packet parsing: %s", __func__, ssh_err(r)); 78 79 debug("%s: cuser %s chost %s pkalg %s slen %zu", __func__, 80 cuser, chost, pkalg, slen); 81 #ifdef DEBUG_PK 82 debug("signature:"); 83 sshbuf_dump_data(sig, slen, stderr); 84 #endif 85 pktype = sshkey_type_from_name(pkalg); 86 if (pktype == KEY_UNSPEC) { 87 /* this is perfectly legal */ 88 logit("%s: unsupported public key algorithm: %s", 89 __func__, pkalg); 90 goto done; 91 } 92 if ((r = sshkey_from_blob(pkblob, blen, &key)) != 0) { 93 error("%s: key_from_blob: %s", __func__, ssh_err(r)); 94 goto done; 95 } 96 if (key == NULL) { 97 error("%s: cannot decode key: %s", __func__, pkalg); 98 goto done; 99 } 100 if (key->type != pktype) { 101 error("%s: type mismatch for decoded key " 102 "(received %d, expected %d)", __func__, key->type, pktype); 103 goto done; 104 } 105 if (sshkey_type_plain(key->type) == KEY_RSA && 106 (ssh->compat & 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(pkalg, options.hostbased_key_types, 0) != 1) { 112 logit("%s: key type %s not in HostbasedAcceptedKeyTypes", 113 __func__, sshkey_type(key)); 114 goto done; 115 } 116 if ((r = sshkey_check_cert_sigtype(key, 117 options.ca_sign_algorithms)) != 0) { 118 logit("%s: certificate signature algorithm %s: %s", __func__, 119 (key->cert == NULL || key->cert->signature_type == NULL) ? 120 "(null)" : key->cert->signature_type, ssh_err(r)); 121 goto done; 122 } 123 124 if (!authctxt->valid || authctxt->user == NULL) { 125 debug2("%s: disabled because of invalid user", __func__); 126 goto done; 127 } 128 129 if ((b = sshbuf_new()) == NULL) 130 fatal("%s: sshbuf_new failed", __func__); 131 /* reconstruct packet */ 132 if ((r = sshbuf_put_string(b, session_id2, session_id2_len)) != 0 || 133 (r = sshbuf_put_u8(b, SSH2_MSG_USERAUTH_REQUEST)) != 0 || 134 (r = sshbuf_put_cstring(b, authctxt->user)) != 0 || 135 (r = sshbuf_put_cstring(b, authctxt->service)) != 0 || 136 (r = sshbuf_put_cstring(b, "hostbased")) != 0 || 137 (r = sshbuf_put_string(b, pkalg, alen)) != 0 || 138 (r = sshbuf_put_string(b, pkblob, blen)) != 0 || 139 (r = sshbuf_put_cstring(b, chost)) != 0 || 140 (r = sshbuf_put_cstring(b, cuser)) != 0) 141 fatal("%s: buffer error: %s", __func__, ssh_err(r)); 142 #ifdef DEBUG_PK 143 sshbuf_dump(b, stderr); 144 #endif 145 146 auth2_record_info(authctxt, 147 "client user \"%.100s\", client host \"%.100s\"", cuser, chost); 148 149 /* test for allowed key and correct signature */ 150 authenticated = 0; 151 if (PRIVSEP(hostbased_key_allowed(ssh, authctxt->pw, cuser, 152 chost, key)) && 153 PRIVSEP(sshkey_verify(key, sig, slen, 154 sshbuf_ptr(b), sshbuf_len(b), pkalg, ssh->compat, NULL)) == 0) 155 authenticated = 1; 156 157 auth2_record_key(authctxt, authenticated, key); 158 sshbuf_free(b); 159 done: 160 debug2("%s: authenticated %d", __func__, authenticated); 161 sshkey_free(key); 162 free(pkalg); 163 free(pkblob); 164 free(cuser); 165 free(chost); 166 free(sig); 167 return authenticated; 168 } 169 170 /* return 1 if given hostkey is allowed */ 171 int 172 hostbased_key_allowed(struct ssh *ssh, struct passwd *pw, 173 const char *cuser, char *chost, struct sshkey *key) 174 { 175 const char *resolvedname, *ipaddr, *lookup, *reason; 176 HostStatus host_status; 177 int len; 178 char *fp; 179 180 if (auth_key_is_revoked(key)) 181 return 0; 182 183 resolvedname = auth_get_canonical_hostname(ssh, options.use_dns); 184 ipaddr = ssh_remote_ipaddr(ssh); 185 186 debug2("%s: chost %s resolvedname %s ipaddr %s", __func__, 187 chost, resolvedname, ipaddr); 188 189 if (((len = strlen(chost)) > 0) && chost[len - 1] == '.') { 190 debug2("stripping trailing dot from chost %s", chost); 191 chost[len - 1] = '\0'; 192 } 193 194 if (options.hostbased_uses_name_from_packet_only) { 195 if (auth_rhosts2(pw, cuser, chost, chost) == 0) { 196 debug2("%s: auth_rhosts2 refused " 197 "user \"%.100s\" host \"%.100s\" (from packet)", 198 __func__, cuser, chost); 199 return 0; 200 } 201 lookup = chost; 202 } else { 203 if (strcasecmp(resolvedname, chost) != 0) 204 logit("userauth_hostbased mismatch: " 205 "client sends %s, but we resolve %s to %s", 206 chost, ipaddr, resolvedname); 207 if (auth_rhosts2(pw, cuser, resolvedname, ipaddr) == 0) { 208 debug2("%s: auth_rhosts2 refused " 209 "user \"%.100s\" host \"%.100s\" addr \"%.100s\"", 210 __func__, cuser, resolvedname, ipaddr); 211 return 0; 212 } 213 lookup = resolvedname; 214 } 215 debug2("%s: access allowed by auth_rhosts2", __func__); 216 217 if (sshkey_is_cert(key) && 218 sshkey_cert_check_authority(key, 1, 0, lookup, &reason)) { 219 error("%s", reason); 220 auth_debug_add("%s", reason); 221 return 0; 222 } 223 224 host_status = check_key_in_hostfiles(pw, key, lookup, 225 _PATH_SSH_SYSTEM_HOSTFILE, 226 options.ignore_user_known_hosts ? NULL : _PATH_SSH_USER_HOSTFILE); 227 228 /* backward compat if no key has been found. */ 229 if (host_status == HOST_NEW) { 230 host_status = check_key_in_hostfiles(pw, key, lookup, 231 _PATH_SSH_SYSTEM_HOSTFILE2, 232 options.ignore_user_known_hosts ? NULL : 233 _PATH_SSH_USER_HOSTFILE2); 234 } 235 236 if (host_status == HOST_OK) { 237 if (sshkey_is_cert(key)) { 238 if ((fp = sshkey_fingerprint(key->cert->signature_key, 239 options.fingerprint_hash, SSH_FP_DEFAULT)) == NULL) 240 fatal("%s: sshkey_fingerprint fail", __func__); 241 verbose("Accepted certificate ID \"%s\" signed by " 242 "%s CA %s from %s@%s", key->cert->key_id, 243 sshkey_type(key->cert->signature_key), fp, 244 cuser, lookup); 245 } else { 246 if ((fp = sshkey_fingerprint(key, 247 options.fingerprint_hash, SSH_FP_DEFAULT)) == NULL) 248 fatal("%s: sshkey_fingerprint fail", __func__); 249 verbose("Accepted %s public key %s from %s@%s", 250 sshkey_type(key), fp, cuser, lookup); 251 } 252 free(fp); 253 } 254 255 return (host_status == HOST_OK); 256 } 257 258 Authmethod method_hostbased = { 259 "hostbased", 260 userauth_hostbased, 261 &options.hostbased_authentication 262 }; 263