auth2-hostbased.c

   1 /* $OpenBSD: auth2-hostbased.c,v 1.53 2024/05/17 00:30:23 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 #include "includes.h"
  27
  28 #include <sys/types.h>
  29
  30 #include <stdlib.h>
  31 #include <pwd.h>
  32 #include <string.h>
  33 #include <stdarg.h>
  34
  35 #include "xmalloc.h"
  36 #include "ssh2.h"
  37 #include "packet.h"
  38 #include "kex.h"
  39 #include "sshbuf.h"
  40 #include "log.h"
  41 #include "misc.h"
  42 #include "servconf.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 extern struct authmethod_cfg methodcfg_hostbased;
  58
  59 static int
  60 userauth_hostbased(struct ssh *ssh, const char *method)
  61 {
  62         Authctxt *authctxt = ssh->authctxt;
  63         struct sshbuf *b;
  64         struct sshkey *key = NULL;
  65         char *pkalg, *cuser, *chost;
  66         u_char *pkblob, *sig;
  67         size_t alen, blen, slen;
  68         int r, pktype, authenticated = 0;
  69
  70         /* XXX use sshkey_froms() */
  71         if ((r = sshpkt_get_cstring(ssh, &pkalg, &alen)) != 0 ||
  72             (r = sshpkt_get_string(ssh, &pkblob, &blen)) != 0 ||
  73             (r = sshpkt_get_cstring(ssh, &chost, NULL)) != 0 ||
  74             (r = sshpkt_get_cstring(ssh, &cuser, NULL)) != 0 ||
  75             (r = sshpkt_get_string(ssh, &sig, &slen)) != 0)
  76                 fatal_fr(r, "parse packet");
  77
  78         debug_f("cuser %s chost %s pkalg %s slen %zu",
  79             cuser, chost, pkalg, slen);
  80 #ifdef DEBUG_PK
  81         debug("signature:");
  82         sshbuf_dump_data(sig, slen, stderr);
  83 #endif
  84         pktype = sshkey_type_from_name(pkalg);
  85         if (pktype == KEY_UNSPEC) {
  86                 /* this is perfectly legal */
  87                 logit_f("unsupported public key algorithm: %s",
  88                     pkalg);
  89                 goto done;
  90         }
  91         if ((r = sshkey_from_blob(pkblob, blen, &key)) != 0) {
  92                 error_fr(r, "key_from_blob");
  93                 goto done;
  94         }
  95         if (key == NULL) {
  96                 error_f("cannot decode key: %s", pkalg);
  97                 goto done;
  98         }
  99         if (key->type != pktype) {
 100                 error_f("type mismatch for decoded key "
 101                     "(received %d, expected %d)", key->type, pktype);
 102                 goto done;
 103         }
 104         if (match_pattern_list(pkalg, options.hostbased_accepted_algos, 0) != 1) {
 105                 logit_f("signature algorithm %s not in "
 106                     "HostbasedAcceptedAlgorithms", pkalg);
 107                 goto done;
 108         }
 109         if ((r = sshkey_check_cert_sigtype(key,
 110             options.ca_sign_algorithms)) != 0) {
 111                 logit_fr(r, "certificate signature algorithm %s",
 112                     (key->cert == NULL || key->cert->signature_type == NULL) ?
 113                     "(null)" : key->cert->signature_type);
 114                 goto done;
 115         }
 116         if ((r = sshkey_check_rsa_length(key,
 117             options.required_rsa_size)) != 0) {
 118                 logit_r(r, "refusing %s key", sshkey_type(key));
 119                 goto done;
 120         }
 121
 122         if (!authctxt->valid || authctxt->user == NULL) {
 123                 debug2_f("disabled because of invalid user");
 124                 goto done;
 125         }
 126
 127         if ((b = sshbuf_new()) == NULL)
 128                 fatal_f("sshbuf_new failed");
 129         /* reconstruct packet */
 130         if ((r = sshbuf_put_stringb(b, ssh->kex->session_id)) != 0 ||
 131             (r = sshbuf_put_u8(b, SSH2_MSG_USERAUTH_REQUEST)) != 0 ||
 132             (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 (mm_hostbased_key_allowed(ssh, authctxt->pw, cuser,
 150             chost, key) &&
 151             mm_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);
 157 done:
 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 */
 169 int
 170 hostbased_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
 255 Authmethod method_hostbased = {
 256         &methodcfg_hostbased,
 257         userauth_hostbased,
 258 };