1 /* $OpenBSD: auth2-hostbased.c,v 1.32 2017/12/18 02:25:15 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 27 #include <sys/types.h> 28 29 #include <pwd.h> 30 #include <string.h> 31 #include <stdarg.h> 32 33 #include "xmalloc.h" 34 #include "ssh2.h" 35 #include "packet.h" 36 #include "buffer.h" 37 #include "log.h" 38 #include "misc.h" 39 #include "servconf.h" 40 #include "compat.h" 41 #include "sshkey.h" 42 #include "hostfile.h" 43 #include "auth.h" 44 #include "canohost.h" 45 #ifdef GSSAPI 46 #include "ssh-gss.h" 47 #endif 48 #include "monitor_wrap.h" 49 #include "pathnames.h" 50 #include "ssherr.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 59 userauth_hostbased(struct ssh *ssh) 60 { 61 Authctxt *authctxt = ssh->authctxt; 62 struct sshbuf *b; 63 struct sshkey *key = NULL; 64 char *pkalg, *cuser, *chost, *service; 65 u_char *pkblob, *sig; 66 size_t alen, blen, slen; 67 int r, pktype, authenticated = 0; 68 69 if (!authctxt->valid) { 70 debug2("%s: disabled because of invalid user", __func__); 71 return 0; 72 } 73 /* XXX use sshkey_froms() */ 74 if ((r = sshpkt_get_cstring(ssh, &pkalg, &alen)) != 0 || 75 (r = sshpkt_get_string(ssh, &pkblob, &blen)) != 0 || 76 (r = sshpkt_get_cstring(ssh, &chost, NULL)) != 0 || 77 (r = sshpkt_get_cstring(ssh, &cuser, NULL)) != 0 || 78 (r = sshpkt_get_string(ssh, &sig, &slen)) != 0) 79 fatal("%s: packet parsing: %s", __func__, ssh_err(r)); 80 81 debug("%s: cuser %s chost %s pkalg %s slen %zu", __func__, 82 cuser, chost, pkalg, slen); 83 #ifdef DEBUG_PK 84 debug("signature:"); 85 sshbuf_dump_data(sig, siglen, stderr); 86 #endif 87 pktype = sshkey_type_from_name(pkalg); 88 if (pktype == KEY_UNSPEC) { 89 /* this is perfectly legal */ 90 logit("%s: unsupported public key algorithm: %s", 91 __func__, pkalg); 92 goto done; 93 } 94 if ((r = sshkey_from_blob(pkblob, blen, &key)) != 0) { 95 error("%s: key_from_blob: %s", __func__, ssh_err(r)); 96 goto done; 97 } 98 if (key == NULL) { 99 error("%s: cannot decode key: %s", __func__, pkalg); 100 goto done; 101 } 102 if (key->type != pktype) { 103 error("%s: type mismatch for decoded key " 104 "(received %d, expected %d)", __func__, key->type, pktype); 105 goto done; 106 } 107 if (sshkey_type_plain(key->type) == KEY_RSA && 108 (ssh->compat & SSH_BUG_RSASIGMD5) != 0) { 109 error("Refusing RSA key because peer uses unsafe " 110 "signature format"); 111 goto done; 112 } 113 if (match_pattern_list(sshkey_ssh_name(key), 114 options.hostbased_key_types, 0) != 1) { 115 logit("%s: key type %s not in HostbasedAcceptedKeyTypes", 116 __func__, sshkey_type(key)); 117 goto done; 118 } 119 120 service = ssh->compat & SSH_BUG_HBSERVICE ? "ssh-userauth" : 121 authctxt->service; 122 if ((b = sshbuf_new()) == NULL) 123 fatal("%s: sshbuf_new failed", __func__); 124 /* reconstruct packet */ 125 if ((r = sshbuf_put_string(b, session_id2, session_id2_len)) != 0 || 126 (r = sshbuf_put_u8(b, SSH2_MSG_USERAUTH_REQUEST)) != 0 || 127 (r = sshbuf_put_cstring(b, authctxt->user)) != 0 || 128 (r = sshbuf_put_cstring(b, service)) != 0 || 129 (r = sshbuf_put_cstring(b, "hostbased")) != 0 || 130 (r = sshbuf_put_string(b, pkalg, alen)) != 0 || 131 (r = sshbuf_put_string(b, pkblob, blen)) != 0 || 132 (r = sshbuf_put_cstring(b, chost)) != 0 || 133 (r = sshbuf_put_cstring(b, cuser)) != 0) 134 fatal("%s: buffer error: %s", __func__, ssh_err(r)); 135 #ifdef DEBUG_PK 136 sshbuf_dump(b, stderr); 137 #endif 138 139 auth2_record_info(authctxt, 140 "client user \"%.100s\", client host \"%.100s\"", cuser, chost); 141 142 /* test for allowed key and correct signature */ 143 authenticated = 0; 144 if (PRIVSEP(hostbased_key_allowed(authctxt->pw, cuser, chost, key)) && 145 PRIVSEP(sshkey_verify(key, sig, slen, 146 sshbuf_ptr(b), sshbuf_len(b), pkalg, ssh->compat)) == 0) 147 authenticated = 1; 148 149 auth2_record_key(authctxt, authenticated, key); 150 sshbuf_free(b); 151 done: 152 debug2("%s: authenticated %d", __func__, authenticated); 153 sshkey_free(key); 154 free(pkalg); 155 free(pkblob); 156 free(cuser); 157 free(chost); 158 free(sig); 159 return authenticated; 160 } 161 162 /* return 1 if given hostkey is allowed */ 163 int 164 hostbased_key_allowed(struct passwd *pw, const char *cuser, char *chost, 165 struct sshkey *key) 166 { 167 struct ssh *ssh = active_state; /* XXX */ 168 const char *resolvedname, *ipaddr, *lookup, *reason; 169 HostStatus host_status; 170 int len; 171 char *fp; 172 173 if (auth_key_is_revoked(key)) 174 return 0; 175 176 resolvedname = auth_get_canonical_hostname(ssh, options.use_dns); 177 ipaddr = ssh_remote_ipaddr(ssh); 178 179 debug2("%s: chost %s resolvedname %s ipaddr %s", __func__, 180 chost, resolvedname, ipaddr); 181 182 if (((len = strlen(chost)) > 0) && chost[len - 1] == '.') { 183 debug2("stripping trailing dot from chost %s", chost); 184 chost[len - 1] = '\0'; 185 } 186 187 if (options.hostbased_uses_name_from_packet_only) { 188 if (auth_rhosts2(pw, cuser, chost, chost) == 0) { 189 debug2("%s: auth_rhosts2 refused " 190 "user \"%.100s\" host \"%.100s\" (from packet)", 191 __func__, cuser, chost); 192 return 0; 193 } 194 lookup = chost; 195 } else { 196 if (strcasecmp(resolvedname, chost) != 0) 197 logit("userauth_hostbased mismatch: " 198 "client sends %s, but we resolve %s to %s", 199 chost, ipaddr, resolvedname); 200 if (auth_rhosts2(pw, cuser, resolvedname, ipaddr) == 0) { 201 debug2("%s: auth_rhosts2 refused " 202 "user \"%.100s\" host \"%.100s\" addr \"%.100s\"", 203 __func__, cuser, resolvedname, ipaddr); 204 return 0; 205 } 206 lookup = resolvedname; 207 } 208 debug2("%s: access allowed by auth_rhosts2", __func__); 209 210 if (sshkey_is_cert(key) && 211 sshkey_cert_check_authority(key, 1, 0, lookup, &reason)) { 212 error("%s", reason); 213 auth_debug_add("%s", reason); 214 return 0; 215 } 216 217 host_status = check_key_in_hostfiles(pw, key, lookup, 218 _PATH_SSH_SYSTEM_HOSTFILE, 219 options.ignore_user_known_hosts ? NULL : _PATH_SSH_USER_HOSTFILE); 220 221 /* backward compat if no key has been found. */ 222 if (host_status == HOST_NEW) { 223 host_status = check_key_in_hostfiles(pw, key, lookup, 224 _PATH_SSH_SYSTEM_HOSTFILE2, 225 options.ignore_user_known_hosts ? NULL : 226 _PATH_SSH_USER_HOSTFILE2); 227 } 228 229 if (host_status == HOST_OK) { 230 if (sshkey_is_cert(key)) { 231 if ((fp = sshkey_fingerprint(key->cert->signature_key, 232 options.fingerprint_hash, SSH_FP_DEFAULT)) == NULL) 233 fatal("%s: sshkey_fingerprint fail", __func__); 234 verbose("Accepted certificate ID \"%s\" signed by " 235 "%s CA %s from %s@%s", key->cert->key_id, 236 sshkey_type(key->cert->signature_key), fp, 237 cuser, lookup); 238 } else { 239 if ((fp = sshkey_fingerprint(key, 240 options.fingerprint_hash, SSH_FP_DEFAULT)) == NULL) 241 fatal("%s: sshkey_fingerprint fail", __func__); 242 verbose("Accepted %s public key %s from %s@%s", 243 sshkey_type(key), fp, cuser, lookup); 244 } 245 free(fp); 246 } 247 248 return (host_status == HOST_OK); 249 } 250 251 Authmethod method_hostbased = { 252 "hostbased", 253 userauth_hostbased, 254 &options.hostbased_authentication 255 }; 256