1 /* $NetBSD: auth2-hostbased.c,v 1.26 2026/04/08 18:58:40 christos Exp $ */ 2 /* $OpenBSD: auth2-hostbased.c,v 1.57 2026/04/02 07:48:13 djm Exp $ */ 3 4 /* 5 * Copyright (c) 2000 Markus Friedl. All rights reserved. 6 * 7 * Redistribution and use in source and binary forms, with or without 8 * modification, are permitted provided that the following conditions 9 * are met: 10 * 1. Redistributions of source code must retain the above copyright 11 * notice, this list of conditions and the following disclaimer. 12 * 2. Redistributions in binary form must reproduce the above copyright 13 * notice, this list of conditions and the following disclaimer in the 14 * documentation and/or other materials provided with the distribution. 15 * 16 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR 17 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES 18 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. 19 * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT, 20 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT 21 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, 22 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY 23 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT 24 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF 25 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. 26 */ 27 28 #include "includes.h" 29 __RCSID("$NetBSD: auth2-hostbased.c,v 1.26 2026/04/08 18:58:40 christos Exp $"); 30 #include <sys/types.h> 31 32 #include <stdlib.h> 33 #include <pwd.h> 34 #include <string.h> 35 #include <stdarg.h> 36 37 #include "xmalloc.h" 38 #include "ssh2.h" 39 #include "packet.h" 40 #include "kex.h" 41 #include "sshbuf.h" 42 #include "log.h" 43 #include "misc.h" 44 #include "servconf.h" 45 #include "sshkey.h" 46 #include "hostfile.h" 47 #include "auth.h" 48 #include "canohost.h" 49 #ifdef GSSAPI 50 #include "ssh-gss.h" 51 #endif 52 #include "monitor_wrap.h" 53 #include "pathnames.h" 54 #include "ssherr.h" 55 #include "match.h" 56 57 /* import */ 58 extern ServerOptions options; 59 extern struct authmethod_cfg methodcfg_hostbased; 60 61 static int 62 userauth_hostbased(struct ssh *ssh, const char *method) 63 { 64 Authctxt *authctxt = ssh->authctxt; 65 struct sshbuf *b; 66 struct sshkey *key = NULL; 67 char *pkalg, *cuser, *chost; 68 u_char *pkblob, *sig; 69 size_t alen, blen, slen; 70 int r, pktype, authenticated = 0; 71 72 /* XXX use sshkey_froms() */ 73 if ((r = sshpkt_get_cstring(ssh, &pkalg, &alen)) != 0 || 74 (r = sshpkt_get_string(ssh, &pkblob, &blen)) != 0 || 75 (r = sshpkt_get_cstring(ssh, &chost, NULL)) != 0 || 76 (r = sshpkt_get_cstring(ssh, &cuser, NULL)) != 0 || 77 (r = sshpkt_get_string(ssh, &sig, &slen)) != 0) 78 fatal_fr(r, "parse packet"); 79 80 debug_f("cuser %s chost %s pkalg %s slen %zu", 81 cuser, chost, pkalg, slen); 82 #ifdef DEBUG_PK 83 debug("signature:"); 84 sshbuf_dump_data(sig, slen, stderr); 85 #endif 86 pktype = sshkey_type_from_name(pkalg); 87 if (pktype == KEY_UNSPEC) { 88 /* this is perfectly legal */ 89 logit_f("unsupported public key algorithm: %s", 90 pkalg); 91 goto done; 92 } 93 if ((r = sshkey_from_blob(pkblob, blen, &key)) != 0) { 94 error_fr(r, "key_from_blob"); 95 goto done; 96 } 97 if (key == NULL) { 98 error_f("cannot decode key: %s", pkalg); 99 goto done; 100 } 101 if (key->type != pktype || (sshkey_type_plain(pktype) == KEY_ECDSA && 102 sshkey_ecdsa_nid_from_name(pkalg) != key->ecdsa_nid)) { 103 error_f("key type mismatch for decoded key " 104 "(received %s, expected %s)", sshkey_ssh_name(key), pkalg); 105 goto done; 106 } 107 if (match_pattern_list(pkalg, options.hostbased_accepted_algos, 0) != 1) { 108 logit_f("signature algorithm %s not in " 109 "HostbasedAcceptedAlgorithms", pkalg); 110 goto done; 111 } 112 if ((r = sshkey_check_cert_sigtype(key, 113 options.ca_sign_algorithms)) != 0) { 114 logit_fr(r, "certificate signature algorithm %s", 115 (key->cert == NULL || key->cert->signature_type == NULL) ? 116 "(null)" : key->cert->signature_type); 117 goto done; 118 } 119 if ((r = sshkey_check_rsa_length(key, 120 options.required_rsa_size)) != 0) { 121 logit_r(r, "refusing %s key", sshkey_type(key)); 122 goto done; 123 } 124 125 if (!authctxt->valid || authctxt->user == NULL) { 126 debug2_f("disabled because of invalid user"); 127 goto done; 128 } 129 130 if ((b = sshbuf_new()) == NULL) 131 fatal_f("sshbuf_new failed"); 132 /* reconstruct packet */ 133 if ((r = sshbuf_put_stringb(b, ssh->kex->session_id)) != 0 || 134 (r = sshbuf_put_u8(b, SSH2_MSG_USERAUTH_REQUEST)) != 0 || 135 (r = sshbuf_put_cstring(b, authctxt->user)) != 0 || 136 (r = sshbuf_put_cstring(b, authctxt->service)) != 0 || 137 (r = sshbuf_put_cstring(b, method)) != 0 || 138 (r = sshbuf_put_string(b, pkalg, alen)) != 0 || 139 (r = sshbuf_put_string(b, pkblob, blen)) != 0 || 140 (r = sshbuf_put_cstring(b, chost)) != 0 || 141 (r = sshbuf_put_cstring(b, cuser)) != 0) 142 fatal_fr(r, "reconstruct packet"); 143 #ifdef DEBUG_PK 144 sshbuf_dump(b, stderr); 145 #endif 146 147 auth2_record_info(authctxt, 148 "client user \"%.100s\", client host \"%.100s\"", cuser, chost); 149 150 /* test for allowed key and correct signature */ 151 authenticated = 0; 152 if (mm_hostbased_key_allowed(ssh, authctxt->pw, cuser, 153 chost, key) && 154 mm_sshkey_verify(key, sig, slen, 155 sshbuf_ptr(b), sshbuf_len(b), pkalg, ssh->compat, NULL) == 0) 156 authenticated = 1; 157 158 auth2_record_key(authctxt, authenticated, key); 159 sshbuf_free(b); 160 done: 161 debug2_f("authenticated %d", authenticated); 162 sshkey_free(key); 163 free(pkalg); 164 free(pkblob); 165 free(cuser); 166 free(chost); 167 free(sig); 168 return authenticated; 169 } 170 171 /* return 1 if given hostkey is allowed */ 172 int 173 hostbased_key_allowed(struct ssh *ssh, struct passwd *pw, 174 const char *cuser, char *chost, struct sshkey *key) 175 { 176 const char *resolvedname, *ipaddr, *lookup, *reason; 177 HostStatus host_status; 178 int len; 179 char *fp; 180 181 if (auth_key_is_revoked(key)) 182 return 0; 183 184 resolvedname = auth_get_canonical_hostname(ssh, options.use_dns); 185 ipaddr = ssh_remote_ipaddr(ssh); 186 187 debug2_f("chost %s resolvedname %s ipaddr %s", 188 chost, resolvedname, ipaddr); 189 190 if (((len = strlen(chost)) > 0) && chost[len - 1] == '.') { 191 debug2("stripping trailing dot from chost %s", chost); 192 chost[len - 1] = '\0'; 193 } 194 195 if (options.hostbased_uses_name_from_packet_only) { 196 if (auth_rhosts2(pw, cuser, chost, chost) == 0) { 197 debug2_f("auth_rhosts2 refused user \"%.100s\" " 198 "host \"%.100s\" (from packet)", cuser, chost); 199 return 0; 200 } 201 lookup = chost; 202 } else { 203 if (strcasecmp(resolvedname, chost) != 0) 204 logit("userauth_hostbased mismatch: " 205 "client sends %s, but we resolve %s to %s", 206 chost, ipaddr, resolvedname); 207 if (auth_rhosts2(pw, cuser, resolvedname, ipaddr) == 0) { 208 debug2_f("auth_rhosts2 refused " 209 "user \"%.100s\" host \"%.100s\" addr \"%.100s\"", 210 cuser, resolvedname, ipaddr); 211 return 0; 212 } 213 lookup = resolvedname; 214 } 215 debug2_f("access allowed by auth_rhosts2"); 216 217 if (sshkey_is_cert(key) && sshkey_cert_check_host(key, lookup, 218 options.ca_sign_algorithms, &reason) != 0) { 219 if ((fp = sshkey_fingerprint(key->cert->signature_key, 220 options.fingerprint_hash, SSH_FP_DEFAULT)) == NULL) 221 fatal_f("sshkey_fingerprint fail"); 222 error("Refusing certificate ID \"%s\" serial=%llu signed by " 223 "%s CA %s: %s", key->cert->key_id, 224 (unsigned long long)key->cert->serial, 225 sshkey_type(key->cert->signature_key), fp, reason); 226 auth_debug_add("Refused Certificate ID \"%s\" serial=%llu: %s", 227 key->cert->key_id, (unsigned long long)key->cert->serial, 228 reason); 229 free(fp); 230 return 0; 231 } 232 233 host_status = check_key_in_hostfiles(pw, key, lookup, 234 _PATH_SSH_SYSTEM_HOSTFILE, 235 options.ignore_user_known_hosts ? NULL : _PATH_SSH_USER_HOSTFILE); 236 237 /* backward compat if no key has been found. */ 238 if (host_status == HOST_NEW) { 239 host_status = check_key_in_hostfiles(pw, key, lookup, 240 _PATH_SSH_SYSTEM_HOSTFILE2, 241 options.ignore_user_known_hosts ? NULL : 242 _PATH_SSH_USER_HOSTFILE2); 243 } 244 245 if (host_status == HOST_OK) { 246 if (sshkey_is_cert(key)) { 247 if ((fp = sshkey_fingerprint(key->cert->signature_key, 248 options.fingerprint_hash, SSH_FP_DEFAULT)) == NULL) 249 fatal_f("sshkey_fingerprint fail"); 250 verbose("Accepted certificate ID \"%s\" signed by " 251 "%s CA %s from %s@%s", key->cert->key_id, 252 sshkey_type(key->cert->signature_key), fp, 253 cuser, lookup); 254 } else { 255 if ((fp = sshkey_fingerprint(key, 256 options.fingerprint_hash, SSH_FP_DEFAULT)) == NULL) 257 fatal_f("sshkey_fingerprint fail"); 258 verbose("Accepted %s public key %s from %s@%s", 259 sshkey_type(key), fp, cuser, lookup); 260 } 261 free(fp); 262 } 263 264 return (host_status == HOST_OK); 265 } 266 267 Authmethod method_hostbased = { 268 &methodcfg_hostbased, 269 userauth_hostbased, 270 }; 271
Indexes created Fri Sep 18 00:27:12 UTC 2026