1 /* $OpenBSD: auth2-hostbased.c,v 1.26 2016/03/07 19:02:43 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 "key.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 "match.h" 51 52 /* import */ 53 extern ServerOptions options; 54 extern u_char *session_id2; 55 extern u_int session_id2_len; 56 57 static int 58 userauth_hostbased(Authctxt *authctxt) 59 { 60 Buffer b; 61 Key *key = NULL; 62 char *pkalg, *cuser, *chost, *service; 63 u_char *pkblob, *sig; 64 u_int alen, blen, slen; 65 int pktype; 66 int authenticated = 0; 67 68 if (!authctxt->valid) { 69 debug2("userauth_hostbased: disabled because of invalid user"); 70 return 0; 71 } 72 pkalg = packet_get_string(&alen); 73 pkblob = packet_get_string(&blen); 74 chost = packet_get_string(NULL); 75 cuser = packet_get_string(NULL); 76 sig = packet_get_string(&slen); 77 78 debug("userauth_hostbased: cuser %s chost %s pkalg %s slen %d", 79 cuser, chost, pkalg, slen); 80 #ifdef DEBUG_PK 81 debug("signature:"); 82 buffer_init(&b); 83 buffer_append(&b, sig, slen); 84 buffer_dump(&b); 85 buffer_free(&b); 86 #endif 87 pktype = key_type_from_name(pkalg); 88 if (pktype == KEY_UNSPEC) { 89 /* this is perfectly legal */ 90 logit("userauth_hostbased: unsupported " 91 "public key algorithm: %s", pkalg); 92 goto done; 93 } 94 key = key_from_blob(pkblob, blen); 95 if (key == NULL) { 96 error("userauth_hostbased: cannot decode key: %s", pkalg); 97 goto done; 98 } 99 if (key->type != pktype) { 100 error("userauth_hostbased: type mismatch for decoded key " 101 "(received %d, expected %d)", key->type, pktype); 102 goto done; 103 } 104 if (key_type_plain(key->type) == KEY_RSA && 105 (datafellows & 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(sshkey_ssh_name(key), 111 options.hostbased_key_types, 0) != 1) { 112 logit("%s: key type %s not in HostbasedAcceptedKeyTypes", 113 __func__, sshkey_type(key)); 114 goto done; 115 } 116 117 service = datafellows & SSH_BUG_HBSERVICE ? "ssh-userauth" : 118 authctxt->service; 119 buffer_init(&b); 120 buffer_put_string(&b, session_id2, session_id2_len); 121 /* reconstruct packet */ 122 buffer_put_char(&b, SSH2_MSG_USERAUTH_REQUEST); 123 buffer_put_cstring(&b, authctxt->user); 124 buffer_put_cstring(&b, service); 125 buffer_put_cstring(&b, "hostbased"); 126 buffer_put_string(&b, pkalg, alen); 127 buffer_put_string(&b, pkblob, blen); 128 buffer_put_cstring(&b, chost); 129 buffer_put_cstring(&b, cuser); 130 #ifdef DEBUG_PK 131 buffer_dump(&b); 132 #endif 133 134 pubkey_auth_info(authctxt, key, 135 "client user \"%.100s\", client host \"%.100s\"", cuser, chost); 136 137 /* test for allowed key and correct signature */ 138 authenticated = 0; 139 if (PRIVSEP(hostbased_key_allowed(authctxt->pw, cuser, chost, key)) && 140 PRIVSEP(key_verify(key, sig, slen, buffer_ptr(&b), 141 buffer_len(&b))) == 1) 142 authenticated = 1; 143 144 buffer_free(&b); 145 done: 146 debug2("userauth_hostbased: authenticated %d", authenticated); 147 if (key != NULL) 148 key_free(key); 149 free(pkalg); 150 free(pkblob); 151 free(cuser); 152 free(chost); 153 free(sig); 154 return authenticated; 155 } 156 157 /* return 1 if given hostkey is allowed */ 158 int 159 hostbased_key_allowed(struct passwd *pw, const char *cuser, char *chost, 160 Key *key) 161 { 162 struct ssh *ssh = active_state; /* XXX */ 163 const char *resolvedname, *ipaddr, *lookup, *reason; 164 HostStatus host_status; 165 int len; 166 char *fp; 167 168 if (auth_key_is_revoked(key)) 169 return 0; 170 171 resolvedname = auth_get_canonical_hostname(ssh, options.use_dns); 172 ipaddr = ssh_remote_ipaddr(ssh); 173 174 debug2("%s: chost %s resolvedname %s ipaddr %s", __func__, 175 chost, resolvedname, ipaddr); 176 177 if (((len = strlen(chost)) > 0) && chost[len - 1] == '.') { 178 debug2("stripping trailing dot from chost %s", chost); 179 chost[len - 1] = '\0'; 180 } 181 182 if (options.hostbased_uses_name_from_packet_only) { 183 if (auth_rhosts2(pw, cuser, chost, chost) == 0) { 184 debug2("%s: auth_rhosts2 refused " 185 "user \"%.100s\" host \"%.100s\" (from packet)", 186 __func__, cuser, chost); 187 return 0; 188 } 189 lookup = chost; 190 } else { 191 if (strcasecmp(resolvedname, chost) != 0) 192 logit("userauth_hostbased mismatch: " 193 "client sends %s, but we resolve %s to %s", 194 chost, ipaddr, resolvedname); 195 if (auth_rhosts2(pw, cuser, resolvedname, ipaddr) == 0) { 196 debug2("%s: auth_rhosts2 refused " 197 "user \"%.100s\" host \"%.100s\" addr \"%.100s\"", 198 __func__, cuser, resolvedname, ipaddr); 199 return 0; 200 } 201 lookup = resolvedname; 202 } 203 debug2("%s: access allowed by auth_rhosts2", __func__); 204 205 if (key_is_cert(key) && 206 key_cert_check_authority(key, 1, 0, lookup, &reason)) { 207 error("%s", reason); 208 auth_debug_add("%s", reason); 209 return 0; 210 } 211 212 host_status = check_key_in_hostfiles(pw, key, lookup, 213 _PATH_SSH_SYSTEM_HOSTFILE, 214 options.ignore_user_known_hosts ? NULL : _PATH_SSH_USER_HOSTFILE); 215 216 /* backward compat if no key has been found. */ 217 if (host_status == HOST_NEW) { 218 host_status = check_key_in_hostfiles(pw, key, lookup, 219 _PATH_SSH_SYSTEM_HOSTFILE2, 220 options.ignore_user_known_hosts ? NULL : 221 _PATH_SSH_USER_HOSTFILE2); 222 } 223 224 if (host_status == HOST_OK) { 225 if (key_is_cert(key)) { 226 if ((fp = sshkey_fingerprint(key->cert->signature_key, 227 options.fingerprint_hash, SSH_FP_DEFAULT)) == NULL) 228 fatal("%s: sshkey_fingerprint fail", __func__); 229 verbose("Accepted certificate ID \"%s\" signed by " 230 "%s CA %s from %s@%s", key->cert->key_id, 231 key_type(key->cert->signature_key), fp, 232 cuser, lookup); 233 } else { 234 if ((fp = sshkey_fingerprint(key, 235 options.fingerprint_hash, SSH_FP_DEFAULT)) == NULL) 236 fatal("%s: sshkey_fingerprint fail", __func__); 237 verbose("Accepted %s public key %s from %s@%s", 238 key_type(key), fp, cuser, lookup); 239 } 240 free(fp); 241 } 242 243 return (host_status == HOST_OK); 244 } 245 246 Authmethod method_hostbased = { 247 "hostbased", 248 userauth_hostbased, 249 &options.hostbased_authentication 250 }; 251