auth2-hostbased.c revision 262566
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#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 "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 51/* import */ 52extern ServerOptions options; 53extern u_char *session_id2; 54extern u_int session_id2_len; 55 56static int 57userauth_hostbased(Authctxt *authctxt) 58{ 59 Buffer b; 60 Key *key = NULL; 61 char *pkalg, *cuser, *chost, *service; 62 u_char *pkblob, *sig; 63 u_int alen, blen, slen; 64 int pktype; 65 int authenticated = 0; 66 67 if (!authctxt->valid) { 68 debug2("userauth_hostbased: disabled because of invalid user"); 69 return 0; 70 } 71 pkalg = packet_get_string(&alen); 72 pkblob = packet_get_string(&blen); 73 chost = packet_get_string(NULL); 74 cuser = packet_get_string(NULL); 75 sig = packet_get_string(&slen); 76 77 debug("userauth_hostbased: cuser %s chost %s pkalg %s slen %d", 78 cuser, chost, pkalg, slen); 79#ifdef DEBUG_PK 80 debug("signature:"); 81 buffer_init(&b); 82 buffer_append(&b, sig, slen); 83 buffer_dump(&b); 84 buffer_free(&b); 85#endif 86 pktype = key_type_from_name(pkalg); 87 if (pktype == KEY_UNSPEC) { 88 /* this is perfectly legal */ 89 logit("userauth_hostbased: unsupported " 90 "public key algorithm: %s", pkalg); 91 goto done; 92 } 93 key = key_from_blob(pkblob, blen); 94 if (key == NULL) { 95 error("userauth_hostbased: cannot decode key: %s", pkalg); 96 goto done; 97 } 98 if (key->type != pktype) { 99 error("userauth_hostbased: type mismatch for decoded key " 100 "(received %d, expected %d)", key->type, pktype); 101 goto done; 102 } 103 if (key_type_plain(key->type) == KEY_RSA && 104 (datafellows & SSH_BUG_RSASIGMD5) != 0) { 105 error("Refusing RSA key because peer uses unsafe " 106 "signature format"); 107 goto done; 108 } 109 service = datafellows & SSH_BUG_HBSERVICE ? "ssh-userauth" : 110 authctxt->service; 111 buffer_init(&b); 112 buffer_put_string(&b, session_id2, session_id2_len); 113 /* reconstruct packet */ 114 buffer_put_char(&b, SSH2_MSG_USERAUTH_REQUEST); 115 buffer_put_cstring(&b, authctxt->user); 116 buffer_put_cstring(&b, service); 117 buffer_put_cstring(&b, "hostbased"); 118 buffer_put_string(&b, pkalg, alen); 119 buffer_put_string(&b, pkblob, blen); 120 buffer_put_cstring(&b, chost); 121 buffer_put_cstring(&b, cuser); 122#ifdef DEBUG_PK 123 buffer_dump(&b); 124#endif 125 126 pubkey_auth_info(authctxt, key, 127 "client user \"%.100s\", client host \"%.100s\"", cuser, chost); 128 129 /* test for allowed key and correct signature */ 130 authenticated = 0; 131 if (PRIVSEP(hostbased_key_allowed(authctxt->pw, cuser, chost, key)) && 132 PRIVSEP(key_verify(key, sig, slen, buffer_ptr(&b), 133 buffer_len(&b))) == 1) 134 authenticated = 1; 135 136 buffer_free(&b); 137done: 138 debug2("userauth_hostbased: authenticated %d", authenticated); 139 if (key != NULL) 140 key_free(key); 141 free(pkalg); 142 free(pkblob); 143 free(cuser); 144 free(chost); 145 free(sig); 146 return authenticated; 147} 148 149/* return 1 if given hostkey is allowed */ 150int 151hostbased_key_allowed(struct passwd *pw, const char *cuser, char *chost, 152 Key *key) 153{ 154 const char *resolvedname, *ipaddr, *lookup, *reason; 155 HostStatus host_status; 156 int len; 157 char *fp; 158 159 if (auth_key_is_revoked(key)) 160 return 0; 161 162 resolvedname = get_canonical_hostname(options.use_dns); 163 ipaddr = get_remote_ipaddr(); 164 165 debug2("userauth_hostbased: chost %s resolvedname %s ipaddr %s", 166 chost, resolvedname, ipaddr); 167 168 if (((len = strlen(chost)) > 0) && chost[len - 1] == '.') { 169 debug2("stripping trailing dot from chost %s", chost); 170 chost[len - 1] = '\0'; 171 } 172 173 if (options.hostbased_uses_name_from_packet_only) { 174 if (auth_rhosts2(pw, cuser, chost, chost) == 0) 175 return 0; 176 lookup = chost; 177 } else { 178 if (strcasecmp(resolvedname, chost) != 0) 179 logit("userauth_hostbased mismatch: " 180 "client sends %s, but we resolve %s to %s", 181 chost, ipaddr, resolvedname); 182 if (auth_rhosts2(pw, cuser, resolvedname, ipaddr) == 0) 183 return 0; 184 lookup = resolvedname; 185 } 186 debug2("userauth_hostbased: access allowed by auth_rhosts2"); 187 188 if (key_is_cert(key) && 189 key_cert_check_authority(key, 1, 0, lookup, &reason)) { 190 error("%s", reason); 191 auth_debug_add("%s", reason); 192 return 0; 193 } 194 195 host_status = check_key_in_hostfiles(pw, key, lookup, 196 _PATH_SSH_SYSTEM_HOSTFILE, 197 options.ignore_user_known_hosts ? NULL : _PATH_SSH_USER_HOSTFILE); 198 199 /* backward compat if no key has been found. */ 200 if (host_status == HOST_NEW) { 201 host_status = check_key_in_hostfiles(pw, key, lookup, 202 _PATH_SSH_SYSTEM_HOSTFILE2, 203 options.ignore_user_known_hosts ? NULL : 204 _PATH_SSH_USER_HOSTFILE2); 205 } 206 207 if (host_status == HOST_OK) { 208 if (key_is_cert(key)) { 209 fp = key_fingerprint(key->cert->signature_key, 210 SSH_FP_MD5, SSH_FP_HEX); 211 verbose("Accepted certificate ID \"%s\" signed by " 212 "%s CA %s from %s@%s", key->cert->key_id, 213 key_type(key->cert->signature_key), fp, 214 cuser, lookup); 215 } else { 216 fp = key_fingerprint(key, SSH_FP_MD5, SSH_FP_HEX); 217 verbose("Accepted %s public key %s from %s@%s", 218 key_type(key), fp, cuser, lookup); 219 } 220 free(fp); 221 } 222 223 return (host_status == HOST_OK); 224} 225 226Authmethod method_hostbased = { 227 "hostbased", 228 userauth_hostbased, 229 &options.hostbased_authentication 230}; 231