1 /* $NetBSD: auth2-hostbased.c,v 1.24 2024/07/08 22:33:43 christos Exp $ */ 2 /* $OpenBSD: auth2-hostbased.c,v 1.53 2024/05/17 00:30:23 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 1.24 2024/07/08 22:33:43 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) { 102 error_f("type mismatch for decoded key " 103 "(received %d, expected %d)", key->type, pktype); 104 goto done; 105 } 106 if (match_pattern_list(pkalg, options.hostbased_accepted_algos, 0) != 1) { 107 logit_f("signature algorithm %s not in " 108 "HostbasedAcceptedAlgorithms", pkalg); 109 goto done; 110 } 111 if ((r = sshkey_check_cert_sigtype(key, 112 options.ca_sign_algorithms)) != 0) { 113 logit_fr(r, "certificate signature algorithm %s", 114 (key->cert == NULL || key->cert->signature_type == NULL) ? 115 "(null)" : key->cert->signature_type); 116 goto done; 117 } 118 if ((r = sshkey_check_rsa_length(key, 119 options.required_rsa_size)) != 0) { 120 logit_r(r, "refusing %s key", sshkey_type(key)); 121 goto done; 122 } 123 124 if (!authctxt->valid || authctxt->user == NULL) { 125 debug2_f("disabled because of invalid user"); 126 goto done; 127 } 128 129 if ((b = sshbuf_new()) == NULL) 130 fatal_f("sshbuf_new failed"); 131 /* reconstruct packet */ 132 if ((r = sshbuf_put_stringb(b, ssh->kex->session_id)) != 0 || 133 (r = sshbuf_put_u8(b, SSH2_MSG_USERAUTH_REQUEST)) != 0 || 134 (r = sshbuf_put_cstring(b, authctxt->user)) != 0 || 135 (r = sshbuf_put_cstring(b, authctxt->service)) != 0 || 136 (r = sshbuf_put_cstring(b, method)) != 0 || 137 (r = sshbuf_put_string(b, pkalg, alen)) != 0 || 138 (r = sshbuf_put_string(b, pkblob, blen)) != 0 || 139 (r = sshbuf_put_cstring(b, chost)) != 0 || 140 (r = sshbuf_put_cstring(b, cuser)) != 0) 141 fatal_fr(r, "reconstruct packet"); 142 #ifdef DEBUG_PK 143 sshbuf_dump(b, stderr); 144 #endif 145 146 auth2_record_info(authctxt, 147 "client user \"%.100s\", client host \"%.100s\"", cuser, chost); 148 149 /* test for allowed key and correct signature */ 150 authenticated = 0; 151 if (mm_hostbased_key_allowed(ssh, authctxt->pw, cuser, 152 chost, key) && 153 mm_sshkey_verify(key, sig, slen, 154 sshbuf_ptr(b), sshbuf_len(b), pkalg, ssh->compat, NULL) == 0) 155 authenticated = 1; 156 157 auth2_record_key(authctxt, authenticated, key); 158 sshbuf_free(b); 159 done: 160 debug2_f("authenticated %d", authenticated); 161 sshkey_free(key); 162 free(pkalg); 163 free(pkblob); 164 free(cuser); 165 free(chost); 166 free(sig); 167 return authenticated; 168 } 169 170 /* return 1 if given hostkey is allowed */ 171 int 172 hostbased_key_allowed(struct ssh *ssh, struct passwd *pw, 173 const char *cuser, char *chost, struct sshkey *key) 174 { 175 const char *resolvedname, *ipaddr, *lookup, *reason; 176 HostStatus host_status; 177 int len; 178 char *fp; 179 180 if (auth_key_is_revoked(key)) 181 return 0; 182 183 resolvedname = auth_get_canonical_hostname(ssh, options.use_dns); 184 ipaddr = ssh_remote_ipaddr(ssh); 185 186 debug2_f("chost %s resolvedname %s ipaddr %s", 187 chost, resolvedname, ipaddr); 188 189 if (((len = strlen(chost)) > 0) && chost[len - 1] == '.') { 190 debug2("stripping trailing dot from chost %s", chost); 191 chost[len - 1] = '\0'; 192 } 193 194 if (options.hostbased_uses_name_from_packet_only) { 195 if (auth_rhosts2(pw, cuser, chost, chost) == 0) { 196 debug2_f("auth_rhosts2 refused user \"%.100s\" " 197 "host \"%.100s\" (from packet)", cuser, chost); 198 return 0; 199 } 200 lookup = chost; 201 } else { 202 if (strcasecmp(resolvedname, chost) != 0) 203 logit("userauth_hostbased mismatch: " 204 "client sends %s, but we resolve %s to %s", 205 chost, ipaddr, resolvedname); 206 if (auth_rhosts2(pw, cuser, resolvedname, ipaddr) == 0) { 207 debug2_f("auth_rhosts2 refused " 208 "user \"%.100s\" host \"%.100s\" addr \"%.100s\"", 209 cuser, resolvedname, ipaddr); 210 return 0; 211 } 212 lookup = resolvedname; 213 } 214 debug2_f("access allowed by auth_rhosts2"); 215 216 if (sshkey_is_cert(key) && 217 sshkey_cert_check_authority_now(key, 1, 0, 0, lookup, &reason)) { 218 error("%s", reason); 219 auth_debug_add("%s", reason); 220 return 0; 221 } 222 223 host_status = check_key_in_hostfiles(pw, key, lookup, 224 _PATH_SSH_SYSTEM_HOSTFILE, 225 options.ignore_user_known_hosts ? NULL : _PATH_SSH_USER_HOSTFILE); 226 227 /* backward compat if no key has been found. */ 228 if (host_status == HOST_NEW) { 229 host_status = check_key_in_hostfiles(pw, key, lookup, 230 _PATH_SSH_SYSTEM_HOSTFILE2, 231 options.ignore_user_known_hosts ? NULL : 232 _PATH_SSH_USER_HOSTFILE2); 233 } 234 235 if (host_status == HOST_OK) { 236 if (sshkey_is_cert(key)) { 237 if ((fp = sshkey_fingerprint(key->cert->signature_key, 238 options.fingerprint_hash, SSH_FP_DEFAULT)) == NULL) 239 fatal_f("sshkey_fingerprint fail"); 240 verbose("Accepted certificate ID \"%s\" signed by " 241 "%s CA %s from %s@%s", key->cert->key_id, 242 sshkey_type(key->cert->signature_key), fp, 243 cuser, lookup); 244 } else { 245 if ((fp = sshkey_fingerprint(key, 246 options.fingerprint_hash, SSH_FP_DEFAULT)) == NULL) 247 fatal_f("sshkey_fingerprint fail"); 248 verbose("Accepted %s public key %s from %s@%s", 249 sshkey_type(key), fp, cuser, lookup); 250 } 251 free(fp); 252 } 253 254 return (host_status == HOST_OK); 255 } 256 257 Authmethod method_hostbased = { 258 &methodcfg_hostbased, 259 userauth_hostbased, 260 }; 261