1 /* $OpenBSD: auth2-hostbased.c,v 1.47 2021/07/23 03:37:52 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 <stdlib.h> 31 #include <pwd.h> 32 #include <string.h> 33 #include <stdarg.h> 34 35 #include "xmalloc.h" 36 #include "ssh2.h" 37 #include "packet.h" 38 #include "kex.h" 39 #include "sshbuf.h" 40 #include "log.h" 41 #include "misc.h" 42 #include "servconf.h" 43 #include "compat.h" 44 #include "sshkey.h" 45 #include "hostfile.h" 46 #include "auth.h" 47 #include "canohost.h" 48 #ifdef GSSAPI 49 #include "ssh-gss.h" 50 #endif 51 #include "monitor_wrap.h" 52 #include "pathnames.h" 53 #include "ssherr.h" 54 #include "match.h" 55 56 /* import */ 57 extern ServerOptions options; 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; 66 u_char *pkblob, *sig; 67 size_t alen, blen, slen; 68 int r, pktype, authenticated = 0; 69 70 /* XXX use sshkey_froms() */ 71 if ((r = sshpkt_get_cstring(ssh, &pkalg, &alen)) != 0 || 72 (r = sshpkt_get_string(ssh, &pkblob, &blen)) != 0 || 73 (r = sshpkt_get_cstring(ssh, &chost, NULL)) != 0 || 74 (r = sshpkt_get_cstring(ssh, &cuser, NULL)) != 0 || 75 (r = sshpkt_get_string(ssh, &sig, &slen)) != 0) 76 fatal_fr(r, "parse packet"); 77 78 debug_f("cuser %s chost %s pkalg %s slen %zu", 79 cuser, chost, pkalg, slen); 80 #ifdef DEBUG_PK 81 debug("signature:"); 82 sshbuf_dump_data(sig, slen, stderr); 83 #endif 84 pktype = sshkey_type_from_name(pkalg); 85 if (pktype == KEY_UNSPEC) { 86 /* this is perfectly legal */ 87 logit_f("unsupported public key algorithm: %s", 88 pkalg); 89 goto done; 90 } 91 if ((r = sshkey_from_blob(pkblob, blen, &key)) != 0) { 92 error_fr(r, "key_from_blob"); 93 goto done; 94 } 95 if (key == NULL) { 96 error_f("cannot decode key: %s", pkalg); 97 goto done; 98 } 99 if (key->type != pktype) { 100 error_f("type mismatch for decoded key " 101 "(received %d, expected %d)", key->type, pktype); 102 goto done; 103 } 104 if (sshkey_type_plain(key->type) == KEY_RSA && 105 (ssh->compat & 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(pkalg, options.hostbased_accepted_algos, 0) != 1) { 111 logit_f("key type %s not in HostbasedAcceptedAlgorithms", 112 sshkey_type(key)); 113 goto done; 114 } 115 if ((r = sshkey_check_cert_sigtype(key, 116 options.ca_sign_algorithms)) != 0) { 117 logit_fr(r, "certificate signature algorithm %s", 118 (key->cert == NULL || key->cert->signature_type == NULL) ? 119 "(null)" : key->cert->signature_type); 120 goto done; 121 } 122 123 if (!authctxt->valid || authctxt->user == NULL) { 124 debug2_f("disabled because of invalid user"); 125 goto done; 126 } 127 128 if ((b = sshbuf_new()) == NULL) 129 fatal_f("sshbuf_new failed"); 130 /* reconstruct packet */ 131 if ((r = sshbuf_put_stringb(b, ssh->kex->session_id)) != 0 || 132 (r = sshbuf_put_u8(b, SSH2_MSG_USERAUTH_REQUEST)) != 0 || 133 (r = sshbuf_put_cstring(b, authctxt->user)) != 0 || 134 (r = sshbuf_put_cstring(b, authctxt->service)) != 0 || 135 (r = sshbuf_put_cstring(b, "hostbased")) != 0 || 136 (r = sshbuf_put_string(b, pkalg, alen)) != 0 || 137 (r = sshbuf_put_string(b, pkblob, blen)) != 0 || 138 (r = sshbuf_put_cstring(b, chost)) != 0 || 139 (r = sshbuf_put_cstring(b, cuser)) != 0) 140 fatal_fr(r, "reconstruct packet"); 141 #ifdef DEBUG_PK 142 sshbuf_dump(b, stderr); 143 #endif 144 145 auth2_record_info(authctxt, 146 "client user \"%.100s\", client host \"%.100s\"", cuser, chost); 147 148 /* test for allowed key and correct signature */ 149 authenticated = 0; 150 if (PRIVSEP(hostbased_key_allowed(ssh, authctxt->pw, cuser, 151 chost, key)) && 152 PRIVSEP(sshkey_verify(key, sig, slen, 153 sshbuf_ptr(b), sshbuf_len(b), pkalg, ssh->compat, NULL)) == 0) 154 authenticated = 1; 155 156 auth2_record_key(authctxt, authenticated, key); 157 sshbuf_free(b); 158 done: 159 debug2_f("authenticated %d", authenticated); 160 sshkey_free(key); 161 free(pkalg); 162 free(pkblob); 163 free(cuser); 164 free(chost); 165 free(sig); 166 return authenticated; 167 } 168 169 /* return 1 if given hostkey is allowed */ 170 int 171 hostbased_key_allowed(struct ssh *ssh, struct passwd *pw, 172 const char *cuser, char *chost, struct sshkey *key) 173 { 174 const char *resolvedname, *ipaddr, *lookup, *reason; 175 HostStatus host_status; 176 int len; 177 char *fp; 178 179 if (auth_key_is_revoked(key)) 180 return 0; 181 182 resolvedname = auth_get_canonical_hostname(ssh, options.use_dns); 183 ipaddr = ssh_remote_ipaddr(ssh); 184 185 debug2_f("chost %s resolvedname %s ipaddr %s", 186 chost, resolvedname, ipaddr); 187 188 if (((len = strlen(chost)) > 0) && chost[len - 1] == '.') { 189 debug2("stripping trailing dot from chost %s", chost); 190 chost[len - 1] = '\0'; 191 } 192 193 if (options.hostbased_uses_name_from_packet_only) { 194 if (auth_rhosts2(pw, cuser, chost, chost) == 0) { 195 debug2_f("auth_rhosts2 refused user \"%.100s\" " 196 "host \"%.100s\" (from packet)", cuser, chost); 197 return 0; 198 } 199 lookup = chost; 200 } else { 201 if (strcasecmp(resolvedname, chost) != 0) 202 logit("userauth_hostbased mismatch: " 203 "client sends %s, but we resolve %s to %s", 204 chost, ipaddr, resolvedname); 205 if (auth_rhosts2(pw, cuser, resolvedname, ipaddr) == 0) { 206 debug2_f("auth_rhosts2 refused " 207 "user \"%.100s\" host \"%.100s\" addr \"%.100s\"", 208 cuser, resolvedname, ipaddr); 209 return 0; 210 } 211 lookup = resolvedname; 212 } 213 debug2_f("access allowed by auth_rhosts2"); 214 215 if (sshkey_is_cert(key) && 216 sshkey_cert_check_authority_now(key, 1, 0, 0, lookup, &reason)) { 217 error("%s", reason); 218 auth_debug_add("%s", reason); 219 return 0; 220 } 221 222 host_status = check_key_in_hostfiles(pw, key, lookup, 223 _PATH_SSH_SYSTEM_HOSTFILE, 224 options.ignore_user_known_hosts ? NULL : _PATH_SSH_USER_HOSTFILE); 225 226 /* backward compat if no key has been found. */ 227 if (host_status == HOST_NEW) { 228 host_status = check_key_in_hostfiles(pw, key, lookup, 229 _PATH_SSH_SYSTEM_HOSTFILE2, 230 options.ignore_user_known_hosts ? NULL : 231 _PATH_SSH_USER_HOSTFILE2); 232 } 233 234 if (host_status == HOST_OK) { 235 if (sshkey_is_cert(key)) { 236 if ((fp = sshkey_fingerprint(key->cert->signature_key, 237 options.fingerprint_hash, SSH_FP_DEFAULT)) == NULL) 238 fatal_f("sshkey_fingerprint fail"); 239 verbose("Accepted certificate ID \"%s\" signed by " 240 "%s CA %s from %s@%s", key->cert->key_id, 241 sshkey_type(key->cert->signature_key), fp, 242 cuser, lookup); 243 } else { 244 if ((fp = sshkey_fingerprint(key, 245 options.fingerprint_hash, SSH_FP_DEFAULT)) == NULL) 246 fatal_f("sshkey_fingerprint fail"); 247 verbose("Accepted %s public key %s from %s@%s", 248 sshkey_type(key), fp, cuser, lookup); 249 } 250 free(fp); 251 } 252 253 return (host_status == HOST_OK); 254 } 255 256 Authmethod method_hostbased = { 257 "hostbased", 258 userauth_hostbased, 259 &options.hostbased_authentication 260 }; 261