1 /* $OpenBSD: auth2-hostbased.c,v 1.31 2017/06/24 06:34:38 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, *service; 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 service = ssh->compat & SSH_BUG_HBSERVICE ? "ssh-userauth" : 122 authctxt->service; 123 if ((b = sshbuf_new()) == NULL) 124 fatal("%s: sshbuf_new failed", __func__); 125 /* reconstruct packet */ 126 if ((r = sshbuf_put_string(b, session_id2, session_id2_len)) != 0 || 127 (r = sshbuf_put_u8(b, SSH2_MSG_USERAUTH_REQUEST)) != 0 || 128 (r = sshbuf_put_cstring(b, authctxt->user)) != 0 || 129 (r = sshbuf_put_cstring(b, service)) != 0 || 130 (r = sshbuf_put_cstring(b, "hostbased")) != 0 || 131 (r = sshbuf_put_string(b, pkalg, alen)) != 0 || 132 (r = sshbuf_put_string(b, pkblob, blen)) != 0 || 133 (r = sshbuf_put_cstring(b, chost)) != 0 || 134 (r = sshbuf_put_cstring(b, cuser)) != 0) 135 fatal("%s: buffer error: %s", __func__, ssh_err(r)); 136 #ifdef DEBUG_PK 137 sshbuf_dump(b, stderr); 138 #endif 139 140 auth2_record_info(authctxt, 141 "client user \"%.100s\", client host \"%.100s\"", cuser, chost); 142 143 /* test for allowed key and correct signature */ 144 authenticated = 0; 145 if (PRIVSEP(hostbased_key_allowed(authctxt->pw, cuser, chost, key)) && 146 PRIVSEP(sshkey_verify(key, sig, slen, 147 sshbuf_ptr(b), sshbuf_len(b), ssh->compat)) == 0) 148 authenticated = 1; 149 150 auth2_record_key(authctxt, authenticated, key); 151 sshbuf_free(b); 152 done: 153 debug2("%s: authenticated %d", __func__, authenticated); 154 sshkey_free(key); 155 free(pkalg); 156 free(pkblob); 157 free(cuser); 158 free(chost); 159 free(sig); 160 return authenticated; 161 } 162 163 /* return 1 if given hostkey is allowed */ 164 int 165 hostbased_key_allowed(struct passwd *pw, const char *cuser, char *chost, 166 struct sshkey *key) 167 { 168 struct ssh *ssh = active_state; /* XXX */ 169 const char *resolvedname, *ipaddr, *lookup, *reason; 170 HostStatus host_status; 171 int len; 172 char *fp; 173 174 if (auth_key_is_revoked(key)) 175 return 0; 176 177 resolvedname = auth_get_canonical_hostname(ssh, options.use_dns); 178 ipaddr = ssh_remote_ipaddr(ssh); 179 180 debug2("%s: chost %s resolvedname %s ipaddr %s", __func__, 181 chost, resolvedname, ipaddr); 182 183 if (((len = strlen(chost)) > 0) && chost[len - 1] == '.') { 184 debug2("stripping trailing dot from chost %s", chost); 185 chost[len - 1] = '\0'; 186 } 187 188 if (options.hostbased_uses_name_from_packet_only) { 189 if (auth_rhosts2(pw, cuser, chost, chost) == 0) { 190 debug2("%s: auth_rhosts2 refused " 191 "user \"%.100s\" host \"%.100s\" (from packet)", 192 __func__, cuser, chost); 193 return 0; 194 } 195 lookup = chost; 196 } else { 197 if (strcasecmp(resolvedname, chost) != 0) 198 logit("userauth_hostbased mismatch: " 199 "client sends %s, but we resolve %s to %s", 200 chost, ipaddr, resolvedname); 201 if (auth_rhosts2(pw, cuser, resolvedname, ipaddr) == 0) { 202 debug2("%s: auth_rhosts2 refused " 203 "user \"%.100s\" host \"%.100s\" addr \"%.100s\"", 204 __func__, cuser, resolvedname, ipaddr); 205 return 0; 206 } 207 lookup = resolvedname; 208 } 209 debug2("%s: access allowed by auth_rhosts2", __func__); 210 211 if (sshkey_is_cert(key) && 212 sshkey_cert_check_authority(key, 1, 0, lookup, &reason)) { 213 error("%s", reason); 214 auth_debug_add("%s", reason); 215 return 0; 216 } 217 218 host_status = check_key_in_hostfiles(pw, key, lookup, 219 _PATH_SSH_SYSTEM_HOSTFILE, 220 options.ignore_user_known_hosts ? NULL : _PATH_SSH_USER_HOSTFILE); 221 222 /* backward compat if no key has been found. */ 223 if (host_status == HOST_NEW) { 224 host_status = check_key_in_hostfiles(pw, key, lookup, 225 _PATH_SSH_SYSTEM_HOSTFILE2, 226 options.ignore_user_known_hosts ? NULL : 227 _PATH_SSH_USER_HOSTFILE2); 228 } 229 230 if (host_status == HOST_OK) { 231 if (sshkey_is_cert(key)) { 232 if ((fp = sshkey_fingerprint(key->cert->signature_key, 233 options.fingerprint_hash, SSH_FP_DEFAULT)) == NULL) 234 fatal("%s: sshkey_fingerprint fail", __func__); 235 verbose("Accepted certificate ID \"%s\" signed by " 236 "%s CA %s from %s@%s", key->cert->key_id, 237 sshkey_type(key->cert->signature_key), fp, 238 cuser, lookup); 239 } else { 240 if ((fp = sshkey_fingerprint(key, 241 options.fingerprint_hash, SSH_FP_DEFAULT)) == NULL) 242 fatal("%s: sshkey_fingerprint fail", __func__); 243 verbose("Accepted %s public key %s from %s@%s", 244 sshkey_type(key), fp, cuser, lookup); 245 } 246 free(fp); 247 } 248 249 return (host_status == HOST_OK); 250 } 251 252 Authmethod method_hostbased = { 253 "hostbased", 254 userauth_hostbased, 255 &options.hostbased_authentication 256 }; 257