1 /* $OpenBSD: auth2-hostbased.c,v 1.38 2018/09/20 03:28:06 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 "sshbuf.h" 38 #include "log.h" 39 #include "misc.h" 40 #include "servconf.h" 41 #include "compat.h" 42 #include "sshkey.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 "ssherr.h" 52 #include "match.h" 53 54 /* import */ 55 extern ServerOptions options; 56 extern u_char *session_id2; 57 extern u_int session_id2_len; 58 59 static int 60 userauth_hostbased(struct ssh *ssh) 61 { 62 Authctxt *authctxt = ssh->authctxt; 63 struct sshbuf *b; 64 struct sshkey *key = NULL; 65 char *pkalg, *cuser, *chost; 66 u_char *pkblob, *sig; 67 size_t alen, blen, slen; 68 int r, pktype, authenticated = 0; 69 70 /* XXX use sshkey_froms() */ 71 if ((r = sshpkt_get_cstring(ssh, &pkalg, &alen)) != 0 || 72 (r = sshpkt_get_string(ssh, &pkblob, &blen)) != 0 || 73 (r = sshpkt_get_cstring(ssh, &chost, NULL)) != 0 || 74 (r = sshpkt_get_cstring(ssh, &cuser, NULL)) != 0 || 75 (r = sshpkt_get_string(ssh, &sig, &slen)) != 0) 76 fatal("%s: packet parsing: %s", __func__, ssh_err(r)); 77 78 debug("%s: cuser %s chost %s pkalg %s slen %zu", __func__, 79 cuser, chost, pkalg, slen); 80 #ifdef DEBUG_PK 81 debug("signature:"); 82 sshbuf_dump_data(sig, slen, stderr); 83 #endif 84 pktype = sshkey_type_from_name(pkalg); 85 if (pktype == KEY_UNSPEC) { 86 /* this is perfectly legal */ 87 logit("%s: unsupported public key algorithm: %s", 88 __func__, pkalg); 89 goto done; 90 } 91 if ((r = sshkey_from_blob(pkblob, blen, &key)) != 0) { 92 error("%s: key_from_blob: %s", __func__, ssh_err(r)); 93 goto done; 94 } 95 if (key == NULL) { 96 error("%s: cannot decode key: %s", __func__, pkalg); 97 goto done; 98 } 99 if (key->type != pktype) { 100 error("%s: type mismatch for decoded key " 101 "(received %d, expected %d)", __func__, key->type, pktype); 102 goto done; 103 } 104 if (sshkey_type_plain(key->type) == KEY_RSA && 105 (ssh->compat & SSH_BUG_RSASIGMD5) != 0) { 106 error("Refusing RSA key because peer uses unsafe " 107 "signature format"); 108 goto done; 109 } 110 if (match_pattern_list(pkalg, options.hostbased_key_types, 0) != 1) { 111 logit("%s: key type %s not in HostbasedAcceptedKeyTypes", 112 __func__, sshkey_type(key)); 113 goto done; 114 } 115 if ((r = sshkey_check_cert_sigtype(key, 116 options.ca_sign_algorithms)) != 0) { 117 logit("%s: certificate signature algorithm %s: %s", __func__, 118 (key->cert == NULL || key->cert->signature_type == NULL) ? 119 "(null)" : key->cert->signature_type, ssh_err(r)); 120 goto done; 121 } 122 123 if (!authctxt->valid || authctxt->user == NULL) { 124 debug2("%s: disabled because of invalid user", __func__); 125 goto done; 126 } 127 128 if ((b = sshbuf_new()) == NULL) 129 fatal("%s: sshbuf_new failed", __func__); 130 /* reconstruct packet */ 131 if ((r = sshbuf_put_string(b, session_id2, session_id2_len)) != 0 || 132 (r = sshbuf_put_u8(b, SSH2_MSG_USERAUTH_REQUEST)) != 0 || 133 (r = sshbuf_put_cstring(b, authctxt->user)) != 0 || 134 (r = sshbuf_put_cstring(b, authctxt->service)) != 0 || 135 (r = sshbuf_put_cstring(b, "hostbased")) != 0 || 136 (r = sshbuf_put_string(b, pkalg, alen)) != 0 || 137 (r = sshbuf_put_string(b, pkblob, blen)) != 0 || 138 (r = sshbuf_put_cstring(b, chost)) != 0 || 139 (r = sshbuf_put_cstring(b, cuser)) != 0) 140 fatal("%s: buffer error: %s", __func__, ssh_err(r)); 141 #ifdef DEBUG_PK 142 sshbuf_dump(b, stderr); 143 #endif 144 145 auth2_record_info(authctxt, 146 "client user \"%.100s\", client host \"%.100s\"", cuser, chost); 147 148 /* test for allowed key and correct signature */ 149 authenticated = 0; 150 if (PRIVSEP(hostbased_key_allowed(authctxt->pw, cuser, chost, key)) && 151 PRIVSEP(sshkey_verify(key, sig, slen, 152 sshbuf_ptr(b), sshbuf_len(b), pkalg, ssh->compat)) == 0) 153 authenticated = 1; 154 155 auth2_record_key(authctxt, authenticated, key); 156 sshbuf_free(b); 157 done: 158 debug2("%s: authenticated %d", __func__, authenticated); 159 sshkey_free(key); 160 free(pkalg); 161 free(pkblob); 162 free(cuser); 163 free(chost); 164 free(sig); 165 return authenticated; 166 } 167 168 /* return 1 if given hostkey is allowed */ 169 int 170 hostbased_key_allowed(struct passwd *pw, const char *cuser, char *chost, 171 struct sshkey *key) 172 { 173 struct ssh *ssh = active_state; /* XXX */ 174 const char *resolvedname, *ipaddr, *lookup, *reason; 175 HostStatus host_status; 176 int len; 177 char *fp; 178 179 if (auth_key_is_revoked(key)) 180 return 0; 181 182 resolvedname = auth_get_canonical_hostname(ssh, options.use_dns); 183 ipaddr = ssh_remote_ipaddr(ssh); 184 185 debug2("%s: chost %s resolvedname %s ipaddr %s", __func__, 186 chost, resolvedname, ipaddr); 187 188 if (((len = strlen(chost)) > 0) && chost[len - 1] == '.') { 189 debug2("stripping trailing dot from chost %s", chost); 190 chost[len - 1] = '\0'; 191 } 192 193 if (options.hostbased_uses_name_from_packet_only) { 194 if (auth_rhosts2(pw, cuser, chost, chost) == 0) { 195 debug2("%s: auth_rhosts2 refused " 196 "user \"%.100s\" host \"%.100s\" (from packet)", 197 __func__, cuser, chost); 198 return 0; 199 } 200 lookup = chost; 201 } else { 202 if (strcasecmp(resolvedname, chost) != 0) 203 logit("userauth_hostbased mismatch: " 204 "client sends %s, but we resolve %s to %s", 205 chost, ipaddr, resolvedname); 206 if (auth_rhosts2(pw, cuser, resolvedname, ipaddr) == 0) { 207 debug2("%s: auth_rhosts2 refused " 208 "user \"%.100s\" host \"%.100s\" addr \"%.100s\"", 209 __func__, cuser, resolvedname, ipaddr); 210 return 0; 211 } 212 lookup = resolvedname; 213 } 214 debug2("%s: access allowed by auth_rhosts2", __func__); 215 216 if (sshkey_is_cert(key) && 217 sshkey_cert_check_authority(key, 1, 0, lookup, &reason)) { 218 error("%s", reason); 219 auth_debug_add("%s", reason); 220 return 0; 221 } 222 223 host_status = check_key_in_hostfiles(pw, key, lookup, 224 _PATH_SSH_SYSTEM_HOSTFILE, 225 options.ignore_user_known_hosts ? NULL : _PATH_SSH_USER_HOSTFILE); 226 227 /* backward compat if no key has been found. */ 228 if (host_status == HOST_NEW) { 229 host_status = check_key_in_hostfiles(pw, key, lookup, 230 _PATH_SSH_SYSTEM_HOSTFILE2, 231 options.ignore_user_known_hosts ? NULL : 232 _PATH_SSH_USER_HOSTFILE2); 233 } 234 235 if (host_status == HOST_OK) { 236 if (sshkey_is_cert(key)) { 237 if ((fp = sshkey_fingerprint(key->cert->signature_key, 238 options.fingerprint_hash, SSH_FP_DEFAULT)) == NULL) 239 fatal("%s: sshkey_fingerprint fail", __func__); 240 verbose("Accepted certificate ID \"%s\" signed by " 241 "%s CA %s from %s@%s", key->cert->key_id, 242 sshkey_type(key->cert->signature_key), fp, 243 cuser, lookup); 244 } else { 245 if ((fp = sshkey_fingerprint(key, 246 options.fingerprint_hash, SSH_FP_DEFAULT)) == NULL) 247 fatal("%s: sshkey_fingerprint fail", __func__); 248 verbose("Accepted %s public key %s from %s@%s", 249 sshkey_type(key), fp, cuser, lookup); 250 } 251 free(fp); 252 } 253 254 return (host_status == HOST_OK); 255 } 256 257 Authmethod method_hostbased = { 258 "hostbased", 259 userauth_hostbased, 260 &options.hostbased_authentication 261 }; 262