auth2-hostbased.c revision 323129
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#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 "key.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 "match.h" 52 53/* import */ 54extern ServerOptions options; 55extern u_char *session_id2; 56extern u_int session_id2_len; 57 58static int 59userauth_hostbased(Authctxt *authctxt) 60{ 61 Buffer b; 62 Key *key = NULL; 63 char *pkalg, *cuser, *chost, *service; 64 u_char *pkblob, *sig; 65 u_int alen, blen, slen; 66 int pktype; 67 int authenticated = 0; 68 69 if (!authctxt->valid) { 70 debug2("userauth_hostbased: disabled because of invalid user"); 71 return 0; 72 } 73 pkalg = packet_get_string(&alen); 74 pkblob = packet_get_string(&blen); 75 chost = packet_get_string(NULL); 76 cuser = packet_get_string(NULL); 77 sig = packet_get_string(&slen); 78 79 debug("userauth_hostbased: cuser %s chost %s pkalg %s slen %d", 80 cuser, chost, pkalg, slen); 81#ifdef DEBUG_PK 82 debug("signature:"); 83 buffer_init(&b); 84 buffer_append(&b, sig, slen); 85 buffer_dump(&b); 86 buffer_free(&b); 87#endif 88 pktype = key_type_from_name(pkalg); 89 if (pktype == KEY_UNSPEC) { 90 /* this is perfectly legal */ 91 logit("userauth_hostbased: unsupported " 92 "public key algorithm: %s", pkalg); 93 goto done; 94 } 95 key = key_from_blob(pkblob, blen); 96 if (key == NULL) { 97 error("userauth_hostbased: cannot decode key: %s", pkalg); 98 goto done; 99 } 100 if (key->type != pktype) { 101 error("userauth_hostbased: type mismatch for decoded key " 102 "(received %d, expected %d)", key->type, pktype); 103 goto done; 104 } 105 if (key_type_plain(key->type) == KEY_RSA && 106 (datafellows & SSH_BUG_RSASIGMD5) != 0) { 107 error("Refusing RSA key because peer uses unsafe " 108 "signature format"); 109 goto done; 110 } 111 if (match_pattern_list(sshkey_ssh_name(key), 112 options.hostbased_key_types, 0) != 1) { 113 logit("%s: key type %s not in HostbasedAcceptedKeyTypes", 114 __func__, sshkey_type(key)); 115 goto done; 116 } 117 118 service = datafellows & SSH_BUG_HBSERVICE ? "ssh-userauth" : 119 authctxt->service; 120 buffer_init(&b); 121 buffer_put_string(&b, session_id2, session_id2_len); 122 /* reconstruct packet */ 123 buffer_put_char(&b, SSH2_MSG_USERAUTH_REQUEST); 124 buffer_put_cstring(&b, authctxt->user); 125 buffer_put_cstring(&b, service); 126 buffer_put_cstring(&b, "hostbased"); 127 buffer_put_string(&b, pkalg, alen); 128 buffer_put_string(&b, pkblob, blen); 129 buffer_put_cstring(&b, chost); 130 buffer_put_cstring(&b, cuser); 131#ifdef DEBUG_PK 132 buffer_dump(&b); 133#endif 134 135 pubkey_auth_info(authctxt, key, 136 "client user \"%.100s\", client host \"%.100s\"", cuser, chost); 137 138 /* test for allowed key and correct signature */ 139 authenticated = 0; 140 if (PRIVSEP(hostbased_key_allowed(authctxt->pw, cuser, chost, key)) && 141 PRIVSEP(key_verify(key, sig, slen, buffer_ptr(&b), 142 buffer_len(&b))) == 1) 143 authenticated = 1; 144 145 buffer_free(&b); 146done: 147 debug2("userauth_hostbased: authenticated %d", authenticated); 148 if (key != NULL) 149 key_free(key); 150 free(pkalg); 151 free(pkblob); 152 free(cuser); 153 free(chost); 154 free(sig); 155 return authenticated; 156} 157 158/* return 1 if given hostkey is allowed */ 159int 160hostbased_key_allowed(struct passwd *pw, const char *cuser, char *chost, 161 Key *key) 162{ 163 struct ssh *ssh = active_state; /* XXX */ 164 const char *resolvedname, *ipaddr, *lookup, *reason; 165 HostStatus host_status; 166 int len; 167 char *fp; 168 169 if (auth_key_is_revoked(key)) 170 return 0; 171 172 resolvedname = auth_get_canonical_hostname(ssh, options.use_dns); 173 ipaddr = ssh_remote_ipaddr(ssh); 174 175 debug2("%s: chost %s resolvedname %s ipaddr %s", __func__, 176 chost, resolvedname, ipaddr); 177 178 if (((len = strlen(chost)) > 0) && chost[len - 1] == '.') { 179 debug2("stripping trailing dot from chost %s", chost); 180 chost[len - 1] = '\0'; 181 } 182 183 if (options.hostbased_uses_name_from_packet_only) { 184 if (auth_rhosts2(pw, cuser, chost, chost) == 0) { 185 debug2("%s: auth_rhosts2 refused " 186 "user \"%.100s\" host \"%.100s\" (from packet)", 187 __func__, cuser, chost); 188 return 0; 189 } 190 lookup = chost; 191 } else { 192 if (strcasecmp(resolvedname, chost) != 0) 193 logit("userauth_hostbased mismatch: " 194 "client sends %s, but we resolve %s to %s", 195 chost, ipaddr, resolvedname); 196 if (auth_rhosts2(pw, cuser, resolvedname, ipaddr) == 0) { 197 debug2("%s: auth_rhosts2 refused " 198 "user \"%.100s\" host \"%.100s\" addr \"%.100s\"", 199 __func__, cuser, resolvedname, ipaddr); 200 return 0; 201 } 202 lookup = resolvedname; 203 } 204 debug2("%s: access allowed by auth_rhosts2", __func__); 205 206 if (key_is_cert(key) && 207 key_cert_check_authority(key, 1, 0, lookup, &reason)) { 208 error("%s", reason); 209 auth_debug_add("%s", reason); 210 return 0; 211 } 212 213 host_status = check_key_in_hostfiles(pw, key, lookup, 214 _PATH_SSH_SYSTEM_HOSTFILE, 215 options.ignore_user_known_hosts ? NULL : _PATH_SSH_USER_HOSTFILE); 216 217 /* backward compat if no key has been found. */ 218 if (host_status == HOST_NEW) { 219 host_status = check_key_in_hostfiles(pw, key, lookup, 220 _PATH_SSH_SYSTEM_HOSTFILE2, 221 options.ignore_user_known_hosts ? NULL : 222 _PATH_SSH_USER_HOSTFILE2); 223 } 224 225 if (host_status == HOST_OK) { 226 if (key_is_cert(key)) { 227 if ((fp = sshkey_fingerprint(key->cert->signature_key, 228 options.fingerprint_hash, SSH_FP_DEFAULT)) == NULL) 229 fatal("%s: sshkey_fingerprint fail", __func__); 230 verbose("Accepted certificate ID \"%s\" signed by " 231 "%s CA %s from %s@%s", key->cert->key_id, 232 key_type(key->cert->signature_key), fp, 233 cuser, lookup); 234 } else { 235 if ((fp = sshkey_fingerprint(key, 236 options.fingerprint_hash, SSH_FP_DEFAULT)) == NULL) 237 fatal("%s: sshkey_fingerprint fail", __func__); 238 verbose("Accepted %s public key %s from %s@%s", 239 key_type(key), fp, cuser, lookup); 240 } 241 free(fp); 242 } 243 244 return (host_status == HOST_OK); 245} 246 247Authmethod method_hostbased = { 248 "hostbased", 249 userauth_hostbased, 250 &options.hostbased_authentication 251}; 252