1 /* $OpenBSD: auth2-hostbased.c,v 1.52 2023/03/05 05:34:09 dtucker 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 <stdlib.h> 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 "kex.h" 38 #include "sshbuf.h" 39 #include "log.h" 40 #include "misc.h" 41 #include "servconf.h" 42 #include "sshkey.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 "ssherr.h" 52 #include "match.h" 53 54 /* import */ 55 extern ServerOptions options; 56 57 static int 58 userauth_hostbased(struct ssh *ssh, const char *method) 59 { 60 Authctxt *authctxt = ssh->authctxt; 61 struct sshbuf *b; 62 struct sshkey *key = NULL; 63 char *pkalg, *cuser, *chost; 64 u_char *pkblob, *sig; 65 size_t alen, blen, slen; 66 int r, pktype, authenticated = 0; 67 68 /* XXX use sshkey_froms() */ 69 if ((r = sshpkt_get_cstring(ssh, &pkalg, &alen)) != 0 || 70 (r = sshpkt_get_string(ssh, &pkblob, &blen)) != 0 || 71 (r = sshpkt_get_cstring(ssh, &chost, NULL)) != 0 || 72 (r = sshpkt_get_cstring(ssh, &cuser, NULL)) != 0 || 73 (r = sshpkt_get_string(ssh, &sig, &slen)) != 0) 74 fatal_fr(r, "parse packet"); 75 76 debug_f("cuser %s chost %s pkalg %s slen %zu", 77 cuser, chost, pkalg, slen); 78 #ifdef DEBUG_PK 79 debug("signature:"); 80 sshbuf_dump_data(sig, slen, stderr); 81 #endif 82 pktype = sshkey_type_from_name(pkalg); 83 if (pktype == KEY_UNSPEC) { 84 /* this is perfectly legal */ 85 logit_f("unsupported public key algorithm: %s", 86 pkalg); 87 goto done; 88 } 89 if ((r = sshkey_from_blob(pkblob, blen, &key)) != 0) { 90 error_fr(r, "key_from_blob"); 91 goto done; 92 } 93 if (key == NULL) { 94 error_f("cannot decode key: %s", pkalg); 95 goto done; 96 } 97 if (key->type != pktype) { 98 error_f("type mismatch for decoded key " 99 "(received %d, expected %d)", key->type, pktype); 100 goto done; 101 } 102 if (match_pattern_list(pkalg, options.hostbased_accepted_algos, 0) != 1) { 103 logit_f("signature algorithm %s not in " 104 "HostbasedAcceptedAlgorithms", pkalg); 105 goto done; 106 } 107 if ((r = sshkey_check_cert_sigtype(key, 108 options.ca_sign_algorithms)) != 0) { 109 logit_fr(r, "certificate signature algorithm %s", 110 (key->cert == NULL || key->cert->signature_type == NULL) ? 111 "(null)" : key->cert->signature_type); 112 goto done; 113 } 114 if ((r = sshkey_check_rsa_length(key, 115 options.required_rsa_size)) != 0) { 116 logit_r(r, "refusing %s key", sshkey_type(key)); 117 goto done; 118 } 119 120 if (!authctxt->valid || authctxt->user == NULL) { 121 debug2_f("disabled because of invalid user"); 122 goto done; 123 } 124 125 if ((b = sshbuf_new()) == NULL) 126 fatal_f("sshbuf_new failed"); 127 /* reconstruct packet */ 128 if ((r = sshbuf_put_stringb(b, ssh->kex->session_id)) != 0 || 129 (r = sshbuf_put_u8(b, SSH2_MSG_USERAUTH_REQUEST)) != 0 || 130 (r = sshbuf_put_cstring(b, authctxt->user)) != 0 || 131 (r = sshbuf_put_cstring(b, authctxt->service)) != 0 || 132 (r = sshbuf_put_cstring(b, method)) != 0 || 133 (r = sshbuf_put_string(b, pkalg, alen)) != 0 || 134 (r = sshbuf_put_string(b, pkblob, blen)) != 0 || 135 (r = sshbuf_put_cstring(b, chost)) != 0 || 136 (r = sshbuf_put_cstring(b, cuser)) != 0) 137 fatal_fr(r, "reconstruct packet"); 138 #ifdef DEBUG_PK 139 sshbuf_dump(b, stderr); 140 #endif 141 142 auth2_record_info(authctxt, 143 "client user \"%.100s\", client host \"%.100s\"", cuser, chost); 144 145 /* test for allowed key and correct signature */ 146 authenticated = 0; 147 if (PRIVSEP(hostbased_key_allowed(ssh, authctxt->pw, cuser, 148 chost, key)) && 149 PRIVSEP(sshkey_verify(key, sig, slen, 150 sshbuf_ptr(b), sshbuf_len(b), pkalg, ssh->compat, NULL)) == 0) 151 authenticated = 1; 152 153 auth2_record_key(authctxt, authenticated, key); 154 sshbuf_free(b); 155 done: 156 debug2_f("authenticated %d", authenticated); 157 sshkey_free(key); 158 free(pkalg); 159 free(pkblob); 160 free(cuser); 161 free(chost); 162 free(sig); 163 return authenticated; 164 } 165 166 /* return 1 if given hostkey is allowed */ 167 int 168 hostbased_key_allowed(struct ssh *ssh, struct passwd *pw, 169 const char *cuser, char *chost, struct sshkey *key) 170 { 171 const char *resolvedname, *ipaddr, *lookup, *reason; 172 HostStatus host_status; 173 int len; 174 char *fp; 175 176 if (auth_key_is_revoked(key)) 177 return 0; 178 179 resolvedname = auth_get_canonical_hostname(ssh, options.use_dns); 180 ipaddr = ssh_remote_ipaddr(ssh); 181 182 debug2_f("chost %s resolvedname %s ipaddr %s", 183 chost, resolvedname, ipaddr); 184 185 if (((len = strlen(chost)) > 0) && chost[len - 1] == '.') { 186 debug2("stripping trailing dot from chost %s", chost); 187 chost[len - 1] = '\0'; 188 } 189 190 if (options.hostbased_uses_name_from_packet_only) { 191 if (auth_rhosts2(pw, cuser, chost, chost) == 0) { 192 debug2_f("auth_rhosts2 refused user \"%.100s\" " 193 "host \"%.100s\" (from packet)", cuser, chost); 194 return 0; 195 } 196 lookup = chost; 197 } else { 198 if (strcasecmp(resolvedname, chost) != 0) 199 logit("userauth_hostbased mismatch: " 200 "client sends %s, but we resolve %s to %s", 201 chost, ipaddr, resolvedname); 202 if (auth_rhosts2(pw, cuser, resolvedname, ipaddr) == 0) { 203 debug2_f("auth_rhosts2 refused " 204 "user \"%.100s\" host \"%.100s\" addr \"%.100s\"", 205 cuser, resolvedname, ipaddr); 206 return 0; 207 } 208 lookup = resolvedname; 209 } 210 debug2_f("access allowed by auth_rhosts2"); 211 212 if (sshkey_is_cert(key) && 213 sshkey_cert_check_authority_now(key, 1, 0, 0, lookup, &reason)) { 214 error("%s", reason); 215 auth_debug_add("%s", reason); 216 return 0; 217 } 218 219 host_status = check_key_in_hostfiles(pw, key, lookup, 220 _PATH_SSH_SYSTEM_HOSTFILE, 221 options.ignore_user_known_hosts ? NULL : _PATH_SSH_USER_HOSTFILE); 222 223 /* backward compat if no key has been found. */ 224 if (host_status == HOST_NEW) { 225 host_status = check_key_in_hostfiles(pw, key, lookup, 226 _PATH_SSH_SYSTEM_HOSTFILE2, 227 options.ignore_user_known_hosts ? NULL : 228 _PATH_SSH_USER_HOSTFILE2); 229 } 230 231 if (host_status == HOST_OK) { 232 if (sshkey_is_cert(key)) { 233 if ((fp = sshkey_fingerprint(key->cert->signature_key, 234 options.fingerprint_hash, SSH_FP_DEFAULT)) == NULL) 235 fatal_f("sshkey_fingerprint fail"); 236 verbose("Accepted certificate ID \"%s\" signed by " 237 "%s CA %s from %s@%s", key->cert->key_id, 238 sshkey_type(key->cert->signature_key), fp, 239 cuser, lookup); 240 } else { 241 if ((fp = sshkey_fingerprint(key, 242 options.fingerprint_hash, SSH_FP_DEFAULT)) == NULL) 243 fatal_f("sshkey_fingerprint fail"); 244 verbose("Accepted %s public key %s from %s@%s", 245 sshkey_type(key), fp, cuser, lookup); 246 } 247 free(fp); 248 } 249 250 return (host_status == HOST_OK); 251 } 252 253 Authmethod method_hostbased = { 254 "hostbased", 255 NULL, 256 userauth_hostbased, 257 &options.hostbased_authentication 258 }; 259