1 /* $OpenBSD: auth2-hostbased.c,v 1.50 2022/09/17 10:34:29 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 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 "compat.h" 43 #include "sshkey.h" 44 #include "hostfile.h" 45 #include "auth.h" 46 #include "canohost.h" 47 #ifdef GSSAPI 48 #include "ssh-gss.h" 49 #endif 50 #include "monitor_wrap.h" 51 #include "pathnames.h" 52 #include "ssherr.h" 53 #include "match.h" 54 55 /* import */ 56 extern ServerOptions options; 57 58 static int 59 userauth_hostbased(struct ssh *ssh, const char *method) 60 { 61 Authctxt *authctxt = ssh->authctxt; 62 struct sshbuf *b; 63 struct sshkey *key = NULL; 64 char *pkalg, *cuser, *chost; 65 u_char *pkblob, *sig; 66 size_t alen, blen, slen; 67 int r, pktype, authenticated = 0; 68 69 /* XXX use sshkey_froms() */ 70 if ((r = sshpkt_get_cstring(ssh, &pkalg, &alen)) != 0 || 71 (r = sshpkt_get_string(ssh, &pkblob, &blen)) != 0 || 72 (r = sshpkt_get_cstring(ssh, &chost, NULL)) != 0 || 73 (r = sshpkt_get_cstring(ssh, &cuser, NULL)) != 0 || 74 (r = sshpkt_get_string(ssh, &sig, &slen)) != 0) 75 fatal_fr(r, "parse packet"); 76 77 debug_f("cuser %s chost %s pkalg %s slen %zu", 78 cuser, chost, pkalg, slen); 79 #ifdef DEBUG_PK 80 debug("signature:"); 81 sshbuf_dump_data(sig, slen, stderr); 82 #endif 83 pktype = sshkey_type_from_name(pkalg); 84 if (pktype == KEY_UNSPEC) { 85 /* this is perfectly legal */ 86 logit_f("unsupported public key algorithm: %s", 87 pkalg); 88 goto done; 89 } 90 if ((r = sshkey_from_blob(pkblob, blen, &key)) != 0) { 91 error_fr(r, "key_from_blob"); 92 goto done; 93 } 94 if (key == NULL) { 95 error_f("cannot decode key: %s", pkalg); 96 goto done; 97 } 98 if (key->type != pktype) { 99 error_f("type mismatch for decoded key " 100 "(received %d, expected %d)", key->type, pktype); 101 goto done; 102 } 103 if (sshkey_type_plain(key->type) == KEY_RSA && 104 (ssh->compat & SSH_BUG_RSASIGMD5) != 0) { 105 error("Refusing RSA key because peer uses unsafe " 106 "signature format"); 107 goto done; 108 } 109 if (match_pattern_list(pkalg, options.hostbased_accepted_algos, 0) != 1) { 110 logit_f("signature algorithm %s not in " 111 "HostbasedAcceptedAlgorithms", pkalg); 112 goto done; 113 } 114 if ((r = sshkey_check_cert_sigtype(key, 115 options.ca_sign_algorithms)) != 0) { 116 logit_fr(r, "certificate signature algorithm %s", 117 (key->cert == NULL || key->cert->signature_type == NULL) ? 118 "(null)" : key->cert->signature_type); 119 goto done; 120 } 121 if ((r = sshkey_check_rsa_length(key, 122 options.required_rsa_size)) != 0) { 123 logit_r(r, "refusing %s key", sshkey_type(key)); 124 goto done; 125 } 126 127 if (!authctxt->valid || authctxt->user == NULL) { 128 debug2_f("disabled because of invalid user"); 129 goto done; 130 } 131 132 if ((b = sshbuf_new()) == NULL) 133 fatal_f("sshbuf_new failed"); 134 /* reconstruct packet */ 135 if ((r = sshbuf_put_stringb(b, ssh->kex->session_id)) != 0 || 136 (r = sshbuf_put_u8(b, SSH2_MSG_USERAUTH_REQUEST)) != 0 || 137 (r = sshbuf_put_cstring(b, authctxt->user)) != 0 || 138 (r = sshbuf_put_cstring(b, authctxt->service)) != 0 || 139 (r = sshbuf_put_cstring(b, method)) != 0 || 140 (r = sshbuf_put_string(b, pkalg, alen)) != 0 || 141 (r = sshbuf_put_string(b, pkblob, blen)) != 0 || 142 (r = sshbuf_put_cstring(b, chost)) != 0 || 143 (r = sshbuf_put_cstring(b, cuser)) != 0) 144 fatal_fr(r, "reconstruct packet"); 145 #ifdef DEBUG_PK 146 sshbuf_dump(b, stderr); 147 #endif 148 149 auth2_record_info(authctxt, 150 "client user \"%.100s\", client host \"%.100s\"", cuser, chost); 151 152 /* test for allowed key and correct signature */ 153 authenticated = 0; 154 if (PRIVSEP(hostbased_key_allowed(ssh, authctxt->pw, cuser, 155 chost, key)) && 156 PRIVSEP(sshkey_verify(key, sig, slen, 157 sshbuf_ptr(b), sshbuf_len(b), pkalg, ssh->compat, NULL)) == 0) 158 authenticated = 1; 159 160 auth2_record_key(authctxt, authenticated, key); 161 sshbuf_free(b); 162 done: 163 debug2_f("authenticated %d", authenticated); 164 sshkey_free(key); 165 free(pkalg); 166 free(pkblob); 167 free(cuser); 168 free(chost); 169 free(sig); 170 return authenticated; 171 } 172 173 /* return 1 if given hostkey is allowed */ 174 int 175 hostbased_key_allowed(struct ssh *ssh, struct passwd *pw, 176 const char *cuser, char *chost, struct sshkey *key) 177 { 178 const char *resolvedname, *ipaddr, *lookup, *reason; 179 HostStatus host_status; 180 int len; 181 char *fp; 182 183 if (auth_key_is_revoked(key)) 184 return 0; 185 186 resolvedname = auth_get_canonical_hostname(ssh, options.use_dns); 187 ipaddr = ssh_remote_ipaddr(ssh); 188 189 debug2_f("chost %s resolvedname %s ipaddr %s", 190 chost, resolvedname, ipaddr); 191 192 if (((len = strlen(chost)) > 0) && chost[len - 1] == '.') { 193 debug2("stripping trailing dot from chost %s", chost); 194 chost[len - 1] = '\0'; 195 } 196 197 if (options.hostbased_uses_name_from_packet_only) { 198 if (auth_rhosts2(pw, cuser, chost, chost) == 0) { 199 debug2_f("auth_rhosts2 refused user \"%.100s\" " 200 "host \"%.100s\" (from packet)", cuser, chost); 201 return 0; 202 } 203 lookup = chost; 204 } else { 205 if (strcasecmp(resolvedname, chost) != 0) 206 logit("userauth_hostbased mismatch: " 207 "client sends %s, but we resolve %s to %s", 208 chost, ipaddr, resolvedname); 209 if (auth_rhosts2(pw, cuser, resolvedname, ipaddr) == 0) { 210 debug2_f("auth_rhosts2 refused " 211 "user \"%.100s\" host \"%.100s\" addr \"%.100s\"", 212 cuser, resolvedname, ipaddr); 213 return 0; 214 } 215 lookup = resolvedname; 216 } 217 debug2_f("access allowed by auth_rhosts2"); 218 219 if (sshkey_is_cert(key) && 220 sshkey_cert_check_authority_now(key, 1, 0, 0, lookup, &reason)) { 221 error("%s", reason); 222 auth_debug_add("%s", reason); 223 return 0; 224 } 225 226 host_status = check_key_in_hostfiles(pw, key, lookup, 227 _PATH_SSH_SYSTEM_HOSTFILE, 228 options.ignore_user_known_hosts ? NULL : _PATH_SSH_USER_HOSTFILE); 229 230 /* backward compat if no key has been found. */ 231 if (host_status == HOST_NEW) { 232 host_status = check_key_in_hostfiles(pw, key, lookup, 233 _PATH_SSH_SYSTEM_HOSTFILE2, 234 options.ignore_user_known_hosts ? NULL : 235 _PATH_SSH_USER_HOSTFILE2); 236 } 237 238 if (host_status == HOST_OK) { 239 if (sshkey_is_cert(key)) { 240 if ((fp = sshkey_fingerprint(key->cert->signature_key, 241 options.fingerprint_hash, SSH_FP_DEFAULT)) == NULL) 242 fatal_f("sshkey_fingerprint fail"); 243 verbose("Accepted certificate ID \"%s\" signed by " 244 "%s CA %s from %s@%s", key->cert->key_id, 245 sshkey_type(key->cert->signature_key), fp, 246 cuser, lookup); 247 } else { 248 if ((fp = sshkey_fingerprint(key, 249 options.fingerprint_hash, SSH_FP_DEFAULT)) == NULL) 250 fatal_f("sshkey_fingerprint fail"); 251 verbose("Accepted %s public key %s from %s@%s", 252 sshkey_type(key), fp, cuser, lookup); 253 } 254 free(fp); 255 } 256 257 return (host_status == HOST_OK); 258 } 259 260 Authmethod method_hostbased = { 261 "hostbased", 262 NULL, 263 userauth_hostbased, 264 &options.hostbased_authentication 265 }; 266