162321Salfred/* $NetBSD: auth2-hostbased.c,v 1.23 2023/07/26 17:58:15 christos Exp $ */ 262321Salfred/* $OpenBSD: auth2-hostbased.c,v 1.52 2023/03/05 05:34:09 dtucker Exp $ */ 362321Salfred/* 462321Salfred * Copyright (c) 2000 Markus Friedl. All rights reserved. 562321Salfred * 662321Salfred * Redistribution and use in source and binary forms, with or without 762321Salfred * modification, are permitted provided that the following conditions 862321Salfred * are met: 962321Salfred * 1. Redistributions of source code must retain the above copyright 1062321Salfred * notice, this list of conditions and the following disclaimer. 1162321Salfred * 2. Redistributions in binary form must reproduce the above copyright 1262321Salfred * notice, this list of conditions and the following disclaimer in the 1362321Salfred * documentation and/or other materials provided with the distribution. 1462321Salfred * 1562321Salfred * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR 1662321Salfred * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES 1762321Salfred * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. 1862321Salfred * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT, 1962321Salfred * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT 2062321Salfred * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, 2162321Salfred * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY 2262321Salfred * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT 2362321Salfred * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF 2462321Salfred * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. 2562321Salfred */ 2662321Salfred 2779754Sdd#include "includes.h" 2862321Salfred__RCSID("$NetBSD: auth2-hostbased.c,v 1.23 2023/07/26 17:58:15 christos Exp $"); 2962321Salfred#include <sys/types.h> 3062321Salfred 3162321Salfred#include <stdlib.h> 3262321Salfred#include <pwd.h> 3362321Salfred#include <string.h> 3471895Sru#include <stdarg.h> 3562321Salfred 3662321Salfred#include "xmalloc.h" 3783206Sasmodai#include "ssh2.h" 3862321Salfred#include "packet.h" 39103012Stjr#include "kex.h" 4062321Salfred#include "sshbuf.h" 41104400Smike#include "log.h" 4262321Salfred#include "misc.h" 4370482Sru#include "servconf.h" 4462321Salfred#include "sshkey.h" 45159879Skeramida#include "hostfile.h" 4662321Salfred#include "auth.h" 4762321Salfred#include "canohost.h" 4862321Salfred#ifdef GSSAPI 4962321Salfred#include "ssh-gss.h" 5062321Salfred#endif 5162321Salfred#include "monitor_wrap.h" 5262321Salfred#include "pathnames.h" 5362321Salfred#include "ssherr.h" 54131504Sru#include "match.h" 55131504Sru 5662321Salfred/* import */ 5762321Salfredextern ServerOptions options; 5862321Salfred 59108037Srustatic int 60108037Sruuserauth_hostbased(struct ssh *ssh, const char *method) 61108037Sru{ 6262321Salfred Authctxt *authctxt = ssh->authctxt; 6362321Salfred struct sshbuf *b; 6462321Salfred struct sshkey *key = NULL; 6562321Salfred char *pkalg, *cuser, *chost; 6662321Salfred u_char *pkblob, *sig; 6762321Salfred size_t alen, blen, slen; 6862321Salfred int r, pktype, authenticated = 0; 69108037Sru 70108037Sru /* XXX use sshkey_froms() */ 71108037Sru if ((r = sshpkt_get_cstring(ssh, &pkalg, &alen)) != 0 || 7262321Salfred (r = sshpkt_get_string(ssh, &pkblob, &blen)) != 0 || 7362321Salfred (r = sshpkt_get_cstring(ssh, &chost, NULL)) != 0 || 7462321Salfred (r = sshpkt_get_cstring(ssh, &cuser, NULL)) != 0 || 7562321Salfred (r = sshpkt_get_string(ssh, &sig, &slen)) != 0) 76131504Sru fatal_fr(r, "parse packet"); 77131504Sru 7862321Salfred debug_f("cuser %s chost %s pkalg %s slen %zu", 7962321Salfred cuser, chost, pkalg, slen); 8062321Salfred#ifdef DEBUG_PK 81108037Sru debug("signature:"); 82108037Sru sshbuf_dump_data(sig, slen, stderr); 83108037Sru#endif 8462321Salfred pktype = sshkey_type_from_name(pkalg); 8562321Salfred if (pktype == KEY_UNSPEC) { 8662321Salfred /* this is perfectly legal */ 8762321Salfred logit_f("unsupported public key algorithm: %s", 8862321Salfred pkalg); 8962321Salfred goto done; 9062321Salfred } 9162321Salfred if ((r = sshkey_from_blob(pkblob, blen, &key)) != 0) { 9262321Salfred error_fr(r, "key_from_blob"); 9362321Salfred goto done; 94108037Sru } 95108037Sru if (key == NULL) { 96108037Sru error_f("cannot decode key: %s", pkalg); 9762321Salfred goto done; 9868395Sru } 9962321Salfred if (key->type != pktype) { 10062321Salfred error_f("type mismatch for decoded key " 10162321Salfred "(received %d, expected %d)", key->type, pktype); 102108087Sru goto done; 103108087Sru } 104108087Sru if (match_pattern_list(pkalg, options.hostbased_accepted_algos, 0) != 1) { 10562321Salfred logit_f("signature algorithm %s not in " 10679754Sdd "HostbasedAcceptedAlgorithms", pkalg); 10762321Salfred goto done; 10862321Salfred } 10962321Salfred if ((r = sshkey_check_cert_sigtype(key, 11062321Salfred options.ca_sign_algorithms)) != 0) { 11162321Salfred logit_fr(r, "certificate signature algorithm %s", 11262321Salfred (key->cert == NULL || key->cert->signature_type == NULL) ? 11362321Salfred "(null)" : key->cert->signature_type); 11462321Salfred goto done; 11562321Salfred } 116108037Sru if ((r = sshkey_check_rsa_length(key, 117108037Sru options.required_rsa_size)) != 0) { 11862321Salfred logit_r(r, "refusing %s key", sshkey_type(key)); 11962321Salfred goto done; 12062321Salfred } 121108037Sru 12262321Salfred if (!authctxt->valid || authctxt->user == NULL) { 12362321Salfred debug2_f("disabled because of invalid user"); 12462321Salfred goto done; 12562321Salfred } 12662321Salfred 12762321Salfred if ((b = sshbuf_new()) == NULL) 12862321Salfred fatal_f("sshbuf_new failed"); 129140505Sru /* reconstruct packet */ 130140505Sru if ((r = sshbuf_put_stringb(b, ssh->kex->session_id)) != 0 || 131140505Sru (r = sshbuf_put_u8(b, SSH2_MSG_USERAUTH_REQUEST)) != 0 || 132140505Sru (r = sshbuf_put_cstring(b, authctxt->user)) != 0 || 133 (r = sshbuf_put_cstring(b, authctxt->service)) != 0 || 134 (r = sshbuf_put_cstring(b, method)) != 0 || 135 (r = sshbuf_put_string(b, pkalg, alen)) != 0 || 136 (r = sshbuf_put_string(b, pkblob, blen)) != 0 || 137 (r = sshbuf_put_cstring(b, chost)) != 0 || 138 (r = sshbuf_put_cstring(b, cuser)) != 0) 139 fatal_fr(r, "reconstruct packet"); 140#ifdef DEBUG_PK 141 sshbuf_dump(b, stderr); 142#endif 143 144 auth2_record_info(authctxt, 145 "client user \"%.100s\", client host \"%.100s\"", cuser, chost); 146 147 /* test for allowed key and correct signature */ 148 authenticated = 0; 149 if (PRIVSEP(hostbased_key_allowed(ssh, authctxt->pw, cuser, 150 chost, key)) && 151 PRIVSEP(sshkey_verify(key, sig, slen, 152 sshbuf_ptr(b), sshbuf_len(b), pkalg, ssh->compat, NULL)) == 0) 153 authenticated = 1; 154 155 auth2_record_key(authctxt, authenticated, key); 156 sshbuf_free(b); 157done: 158 debug2_f("authenticated %d", authenticated); 159 sshkey_free(key); 160 free(pkalg); 161 free(pkblob); 162 free(cuser); 163 free(chost); 164 free(sig); 165 return authenticated; 166} 167 168/* return 1 if given hostkey is allowed */ 169int 170hostbased_key_allowed(struct ssh *ssh, struct passwd *pw, 171 const char *cuser, char *chost, struct sshkey *key) 172{ 173 const char *resolvedname, *ipaddr, *lookup, *reason; 174 HostStatus host_status; 175 int len; 176 char *fp; 177 178 if (auth_key_is_revoked(key)) 179 return 0; 180 181 resolvedname = auth_get_canonical_hostname(ssh, options.use_dns); 182 ipaddr = ssh_remote_ipaddr(ssh); 183 184 debug2_f("chost %s resolvedname %s ipaddr %s", 185 chost, resolvedname, ipaddr); 186 187 if (((len = strlen(chost)) > 0) && chost[len - 1] == '.') { 188 debug2("stripping trailing dot from chost %s", chost); 189 chost[len - 1] = '\0'; 190 } 191 192 if (options.hostbased_uses_name_from_packet_only) { 193 if (auth_rhosts2(pw, cuser, chost, chost) == 0) { 194 debug2_f("auth_rhosts2 refused user \"%.100s\" " 195 "host \"%.100s\" (from packet)", cuser, chost); 196 return 0; 197 } 198 lookup = chost; 199 } else { 200 if (strcasecmp(resolvedname, chost) != 0) 201 logit("userauth_hostbased mismatch: " 202 "client sends %s, but we resolve %s to %s", 203 chost, ipaddr, resolvedname); 204 if (auth_rhosts2(pw, cuser, resolvedname, ipaddr) == 0) { 205 debug2_f("auth_rhosts2 refused " 206 "user \"%.100s\" host \"%.100s\" addr \"%.100s\"", 207 cuser, resolvedname, ipaddr); 208 return 0; 209 } 210 lookup = resolvedname; 211 } 212 debug2_f("access allowed by auth_rhosts2"); 213 214 if (sshkey_is_cert(key) && 215 sshkey_cert_check_authority_now(key, 1, 0, 0, lookup, &reason)) { 216 error("%s", reason); 217 auth_debug_add("%s", reason); 218 return 0; 219 } 220 221 host_status = check_key_in_hostfiles(pw, key, lookup, 222 _PATH_SSH_SYSTEM_HOSTFILE, 223 options.ignore_user_known_hosts ? NULL : _PATH_SSH_USER_HOSTFILE); 224 225 /* backward compat if no key has been found. */ 226 if (host_status == HOST_NEW) { 227 host_status = check_key_in_hostfiles(pw, key, lookup, 228 _PATH_SSH_SYSTEM_HOSTFILE2, 229 options.ignore_user_known_hosts ? NULL : 230 _PATH_SSH_USER_HOSTFILE2); 231 } 232 233 if (host_status == HOST_OK) { 234 if (sshkey_is_cert(key)) { 235 if ((fp = sshkey_fingerprint(key->cert->signature_key, 236 options.fingerprint_hash, SSH_FP_DEFAULT)) == NULL) 237 fatal_f("sshkey_fingerprint fail"); 238 verbose("Accepted certificate ID \"%s\" signed by " 239 "%s CA %s from %s@%s", key->cert->key_id, 240 sshkey_type(key->cert->signature_key), fp, 241 cuser, lookup); 242 } else { 243 if ((fp = sshkey_fingerprint(key, 244 options.fingerprint_hash, SSH_FP_DEFAULT)) == NULL) 245 fatal_f("sshkey_fingerprint fail"); 246 verbose("Accepted %s public key %s from %s@%s", 247 sshkey_type(key), fp, cuser, lookup); 248 } 249 free(fp); 250 } 251 252 return (host_status == HOST_OK); 253} 254 255Authmethod method_hostbased = { 256 "hostbased", 257 NULL, 258 userauth_hostbased, 259 &options.hostbased_authentication 260}; 261