1 /* $OpenBSD: auth2-hostbased.c,v 1.33 2018/01/23 05:27:21 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 "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 if (!authctxt->valid) { 71 debug2("%s: disabled because of invalid user", __func__); 72 return 0; 73 } 74 /* XXX use sshkey_froms() */ 75 if ((r = sshpkt_get_cstring(ssh, &pkalg, &alen)) != 0 || 76 (r = sshpkt_get_string(ssh, &pkblob, &blen)) != 0 || 77 (r = sshpkt_get_cstring(ssh, &chost, NULL)) != 0 || 78 (r = sshpkt_get_cstring(ssh, &cuser, NULL)) != 0 || 79 (r = sshpkt_get_string(ssh, &sig, &slen)) != 0) 80 fatal("%s: packet parsing: %s", __func__, ssh_err(r)); 81 82 debug("%s: cuser %s chost %s pkalg %s slen %zu", __func__, 83 cuser, chost, pkalg, slen); 84 #ifdef DEBUG_PK 85 debug("signature:"); 86 sshbuf_dump_data(sig, siglen, stderr); 87 #endif 88 pktype = sshkey_type_from_name(pkalg); 89 if (pktype == KEY_UNSPEC) { 90 /* this is perfectly legal */ 91 logit("%s: unsupported public key algorithm: %s", 92 __func__, pkalg); 93 goto done; 94 } 95 if ((r = sshkey_from_blob(pkblob, blen, &key)) != 0) { 96 error("%s: key_from_blob: %s", __func__, ssh_err(r)); 97 goto done; 98 } 99 if (key == NULL) { 100 error("%s: cannot decode key: %s", __func__, pkalg); 101 goto done; 102 } 103 if (key->type != pktype) { 104 error("%s: type mismatch for decoded key " 105 "(received %d, expected %d)", __func__, key->type, pktype); 106 goto done; 107 } 108 if (sshkey_type_plain(key->type) == KEY_RSA && 109 (ssh->compat & SSH_BUG_RSASIGMD5) != 0) { 110 error("Refusing RSA key because peer uses unsafe " 111 "signature format"); 112 goto done; 113 } 114 if (match_pattern_list(sshkey_ssh_name(key), 115 options.hostbased_key_types, 0) != 1) { 116 logit("%s: key type %s not in HostbasedAcceptedKeyTypes", 117 __func__, sshkey_type(key)); 118 goto done; 119 } 120 121 if ((b = sshbuf_new()) == NULL) 122 fatal("%s: sshbuf_new failed", __func__); 123 /* reconstruct packet */ 124 if ((r = sshbuf_put_string(b, session_id2, session_id2_len)) != 0 || 125 (r = sshbuf_put_u8(b, SSH2_MSG_USERAUTH_REQUEST)) != 0 || 126 (r = sshbuf_put_cstring(b, authctxt->user)) != 0 || 127 (r = sshbuf_put_cstring(b, authctxt->service)) != 0 || 128 (r = sshbuf_put_cstring(b, "hostbased")) != 0 || 129 (r = sshbuf_put_string(b, pkalg, alen)) != 0 || 130 (r = sshbuf_put_string(b, pkblob, blen)) != 0 || 131 (r = sshbuf_put_cstring(b, chost)) != 0 || 132 (r = sshbuf_put_cstring(b, cuser)) != 0) 133 fatal("%s: buffer error: %s", __func__, ssh_err(r)); 134 #ifdef DEBUG_PK 135 sshbuf_dump(b, stderr); 136 #endif 137 138 auth2_record_info(authctxt, 139 "client user \"%.100s\", client host \"%.100s\"", cuser, chost); 140 141 /* test for allowed key and correct signature */ 142 authenticated = 0; 143 if (PRIVSEP(hostbased_key_allowed(authctxt->pw, cuser, chost, key)) && 144 PRIVSEP(sshkey_verify(key, sig, slen, 145 sshbuf_ptr(b), sshbuf_len(b), pkalg, ssh->compat)) == 0) 146 authenticated = 1; 147 148 auth2_record_key(authctxt, authenticated, key); 149 sshbuf_free(b); 150 done: 151 debug2("%s: authenticated %d", __func__, authenticated); 152 sshkey_free(key); 153 free(pkalg); 154 free(pkblob); 155 free(cuser); 156 free(chost); 157 free(sig); 158 return authenticated; 159 } 160 161 /* return 1 if given hostkey is allowed */ 162 int 163 hostbased_key_allowed(struct passwd *pw, const char *cuser, char *chost, 164 struct sshkey *key) 165 { 166 struct ssh *ssh = active_state; /* XXX */ 167 const char *resolvedname, *ipaddr, *lookup, *reason; 168 HostStatus host_status; 169 int len; 170 char *fp; 171 172 if (auth_key_is_revoked(key)) 173 return 0; 174 175 resolvedname = auth_get_canonical_hostname(ssh, options.use_dns); 176 ipaddr = ssh_remote_ipaddr(ssh); 177 178 debug2("%s: chost %s resolvedname %s ipaddr %s", __func__, 179 chost, resolvedname, ipaddr); 180 181 if (((len = strlen(chost)) > 0) && chost[len - 1] == '.') { 182 debug2("stripping trailing dot from chost %s", chost); 183 chost[len - 1] = '\0'; 184 } 185 186 if (options.hostbased_uses_name_from_packet_only) { 187 if (auth_rhosts2(pw, cuser, chost, chost) == 0) { 188 debug2("%s: auth_rhosts2 refused " 189 "user \"%.100s\" host \"%.100s\" (from packet)", 190 __func__, cuser, chost); 191 return 0; 192 } 193 lookup = chost; 194 } else { 195 if (strcasecmp(resolvedname, chost) != 0) 196 logit("userauth_hostbased mismatch: " 197 "client sends %s, but we resolve %s to %s", 198 chost, ipaddr, resolvedname); 199 if (auth_rhosts2(pw, cuser, resolvedname, ipaddr) == 0) { 200 debug2("%s: auth_rhosts2 refused " 201 "user \"%.100s\" host \"%.100s\" addr \"%.100s\"", 202 __func__, cuser, resolvedname, ipaddr); 203 return 0; 204 } 205 lookup = resolvedname; 206 } 207 debug2("%s: access allowed by auth_rhosts2", __func__); 208 209 if (sshkey_is_cert(key) && 210 sshkey_cert_check_authority(key, 1, 0, lookup, &reason)) { 211 error("%s", reason); 212 auth_debug_add("%s", reason); 213 return 0; 214 } 215 216 host_status = check_key_in_hostfiles(pw, key, lookup, 217 _PATH_SSH_SYSTEM_HOSTFILE, 218 options.ignore_user_known_hosts ? NULL : _PATH_SSH_USER_HOSTFILE); 219 220 /* backward compat if no key has been found. */ 221 if (host_status == HOST_NEW) { 222 host_status = check_key_in_hostfiles(pw, key, lookup, 223 _PATH_SSH_SYSTEM_HOSTFILE2, 224 options.ignore_user_known_hosts ? NULL : 225 _PATH_SSH_USER_HOSTFILE2); 226 } 227 228 if (host_status == HOST_OK) { 229 if (sshkey_is_cert(key)) { 230 if ((fp = sshkey_fingerprint(key->cert->signature_key, 231 options.fingerprint_hash, SSH_FP_DEFAULT)) == NULL) 232 fatal("%s: sshkey_fingerprint fail", __func__); 233 verbose("Accepted certificate ID \"%s\" signed by " 234 "%s CA %s from %s@%s", key->cert->key_id, 235 sshkey_type(key->cert->signature_key), fp, 236 cuser, lookup); 237 } else { 238 if ((fp = sshkey_fingerprint(key, 239 options.fingerprint_hash, SSH_FP_DEFAULT)) == NULL) 240 fatal("%s: sshkey_fingerprint fail", __func__); 241 verbose("Accepted %s public key %s from %s@%s", 242 sshkey_type(key), fp, cuser, lookup); 243 } 244 free(fp); 245 } 246 247 return (host_status == HOST_OK); 248 } 249 250 Authmethod method_hostbased = { 251 "hostbased", 252 userauth_hostbased, 253 &options.hostbased_authentication 254 }; 255