1 /* $OpenBSD: auth2-hostbased.c,v 1.17 2013/12/30 23:52:27 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 "servconf.h" 39 #include "compat.h" 40 #include "key.h" 41 #include "hostfile.h" 42 #include "auth.h" 43 #include "canohost.h" 44 #ifdef GSSAPI 45 #include "ssh-gss.h" 46 #endif 47 #include "monitor_wrap.h" 48 #include "pathnames.h" 49 50 /* import */ 51 extern ServerOptions options; 52 extern u_char *session_id2; 53 extern u_int session_id2_len; 54 55 static int 56 userauth_hostbased(Authctxt *authctxt) 57 { 58 Buffer b; 59 Key *key = NULL; 60 char *pkalg, *cuser, *chost, *service; 61 u_char *pkblob, *sig; 62 u_int alen, blen, slen; 63 int pktype; 64 int authenticated = 0; 65 66 if (!authctxt->valid) { 67 debug2("userauth_hostbased: disabled because of invalid user"); 68 return 0; 69 } 70 pkalg = packet_get_string(&alen); 71 pkblob = packet_get_string(&blen); 72 chost = packet_get_string(NULL); 73 cuser = packet_get_string(NULL); 74 sig = packet_get_string(&slen); 75 76 debug("userauth_hostbased: cuser %s chost %s pkalg %s slen %d", 77 cuser, chost, pkalg, slen); 78 #ifdef DEBUG_PK 79 debug("signature:"); 80 buffer_init(&b); 81 buffer_append(&b, sig, slen); 82 buffer_dump(&b); 83 buffer_free(&b); 84 #endif 85 pktype = key_type_from_name(pkalg); 86 if (pktype == KEY_UNSPEC) { 87 /* this is perfectly legal */ 88 logit("userauth_hostbased: unsupported " 89 "public key algorithm: %s", pkalg); 90 goto done; 91 } 92 key = key_from_blob(pkblob, blen); 93 if (key == NULL) { 94 error("userauth_hostbased: cannot decode key: %s", pkalg); 95 goto done; 96 } 97 if (key->type != pktype) { 98 error("userauth_hostbased: type mismatch for decoded key " 99 "(received %d, expected %d)", key->type, pktype); 100 goto done; 101 } 102 if (key_type_plain(key->type) == KEY_RSA && 103 (datafellows & SSH_BUG_RSASIGMD5) != 0) { 104 error("Refusing RSA key because peer uses unsafe " 105 "signature format"); 106 goto done; 107 } 108 service = datafellows & SSH_BUG_HBSERVICE ? "ssh-userauth" : 109 authctxt->service; 110 buffer_init(&b); 111 buffer_put_string(&b, session_id2, session_id2_len); 112 /* reconstruct packet */ 113 buffer_put_char(&b, SSH2_MSG_USERAUTH_REQUEST); 114 buffer_put_cstring(&b, authctxt->user); 115 buffer_put_cstring(&b, service); 116 buffer_put_cstring(&b, "hostbased"); 117 buffer_put_string(&b, pkalg, alen); 118 buffer_put_string(&b, pkblob, blen); 119 buffer_put_cstring(&b, chost); 120 buffer_put_cstring(&b, cuser); 121 #ifdef DEBUG_PK 122 buffer_dump(&b); 123 #endif 124 125 pubkey_auth_info(authctxt, key, 126 "client user \"%.100s\", client host \"%.100s\"", cuser, chost); 127 128 /* test for allowed key and correct signature */ 129 authenticated = 0; 130 if (PRIVSEP(hostbased_key_allowed(authctxt->pw, cuser, chost, key)) && 131 PRIVSEP(key_verify(key, sig, slen, buffer_ptr(&b), 132 buffer_len(&b))) == 1) 133 authenticated = 1; 134 135 buffer_free(&b); 136 done: 137 debug2("userauth_hostbased: authenticated %d", authenticated); 138 if (key != NULL) 139 key_free(key); 140 free(pkalg); 141 free(pkblob); 142 free(cuser); 143 free(chost); 144 free(sig); 145 return authenticated; 146 } 147 148 /* return 1 if given hostkey is allowed */ 149 int 150 hostbased_key_allowed(struct passwd *pw, const char *cuser, char *chost, 151 Key *key) 152 { 153 const char *resolvedname, *ipaddr, *lookup, *reason; 154 HostStatus host_status; 155 int len; 156 char *fp; 157 158 if (auth_key_is_revoked(key)) 159 return 0; 160 161 resolvedname = get_canonical_hostname(options.use_dns); 162 ipaddr = get_remote_ipaddr(); 163 164 debug2("userauth_hostbased: chost %s resolvedname %s ipaddr %s", 165 chost, resolvedname, ipaddr); 166 167 if (((len = strlen(chost)) > 0) && chost[len - 1] == '.') { 168 debug2("stripping trailing dot from chost %s", chost); 169 chost[len - 1] = '\0'; 170 } 171 172 if (options.hostbased_uses_name_from_packet_only) { 173 if (auth_rhosts2(pw, cuser, chost, chost) == 0) 174 return 0; 175 lookup = chost; 176 } else { 177 if (strcasecmp(resolvedname, chost) != 0) 178 logit("userauth_hostbased mismatch: " 179 "client sends %s, but we resolve %s to %s", 180 chost, ipaddr, resolvedname); 181 if (auth_rhosts2(pw, cuser, resolvedname, ipaddr) == 0) 182 return 0; 183 lookup = resolvedname; 184 } 185 debug2("userauth_hostbased: access allowed by auth_rhosts2"); 186 187 if (key_is_cert(key) && 188 key_cert_check_authority(key, 1, 0, lookup, &reason)) { 189 error("%s", reason); 190 auth_debug_add("%s", reason); 191 return 0; 192 } 193 194 host_status = check_key_in_hostfiles(pw, key, lookup, 195 _PATH_SSH_SYSTEM_HOSTFILE, 196 options.ignore_user_known_hosts ? NULL : _PATH_SSH_USER_HOSTFILE); 197 198 /* backward compat if no key has been found. */ 199 if (host_status == HOST_NEW) { 200 host_status = check_key_in_hostfiles(pw, key, lookup, 201 _PATH_SSH_SYSTEM_HOSTFILE2, 202 options.ignore_user_known_hosts ? NULL : 203 _PATH_SSH_USER_HOSTFILE2); 204 } 205 206 if (host_status == HOST_OK) { 207 if (key_is_cert(key)) { 208 fp = key_fingerprint(key->cert->signature_key, 209 SSH_FP_MD5, SSH_FP_HEX); 210 verbose("Accepted certificate ID \"%s\" signed by " 211 "%s CA %s from %s@%s", key->cert->key_id, 212 key_type(key->cert->signature_key), fp, 213 cuser, lookup); 214 } else { 215 fp = key_fingerprint(key, SSH_FP_MD5, SSH_FP_HEX); 216 verbose("Accepted %s public key %s from %s@%s", 217 key_type(key), fp, cuser, lookup); 218 } 219 free(fp); 220 } 221 222 return (host_status == HOST_OK); 223 } 224 225 Authmethod method_hostbased = { 226 "hostbased", 227 userauth_hostbased, 228 &options.hostbased_authentication 229 }; 230