crypto/openssh/auth2-hostbased.c

   1 /* $OpenBSD: auth2-hostbased.c,v 1.31 2017/06/24 06:34:38 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 <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 "buffer.h"
  38 #include "log.h"
  39 #include "misc.h"
  40 #include "servconf.h"
  41 #include "compat.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 extern u_char *session_id2;
  57 extern u_int session_id2_len;
  58
  59 static int
  60 userauth_hostbased(struct ssh *ssh)
  61 {
  62         Authctxt *authctxt = ssh->authctxt;
  63         struct sshbuf *b;
  64         struct sshkey *key = NULL;
  65         char *pkalg, *cuser, *chost, *service;
  66         u_char *pkblob, *sig;
  67         size_t alen, blen, slen;
  68         int r, pktype, authenticated = 0;
  69
  70         if (!authctxt->valid) {
  71                 debug2("%s: disabled because of invalid user", __func__);
  72                 return 0;
  73         }
  74         /* XXX use sshkey_froms() */
  75         if ((r = sshpkt_get_cstring(ssh, &pkalg, &alen)) != 0 ||
  76             (r = sshpkt_get_string(ssh, &pkblob, &blen)) != 0 ||
  77             (r = sshpkt_get_cstring(ssh, &chost, NULL)) != 0 ||
  78             (r = sshpkt_get_cstring(ssh, &cuser, NULL)) != 0 ||
  79             (r = sshpkt_get_string(ssh, &sig, &slen)) != 0)
  80                 fatal("%s: packet parsing: %s", __func__, ssh_err(r));
  81
  82         debug("%s: cuser %s chost %s pkalg %s slen %zu", __func__,
  83             cuser, chost, pkalg, slen);
  84 #ifdef DEBUG_PK
  85         debug("signature:");
  86         sshbuf_dump_data(sig, siglen, stderr);
  87 #endif
  88         pktype = sshkey_type_from_name(pkalg);
  89         if (pktype == KEY_UNSPEC) {
  90                 /* this is perfectly legal */
  91                 logit("%s: unsupported public key algorithm: %s",
  92                     __func__, pkalg);
  93                 goto done;
  94         }
  95         if ((r = sshkey_from_blob(pkblob, blen, &key)) != 0) {
  96                 error("%s: key_from_blob: %s", __func__, ssh_err(r));
  97                 goto done;
  98         }
  99         if (key == NULL) {
 100                 error("%s: cannot decode key: %s", __func__, pkalg);
 101                 goto done;
 102         }
 103         if (key->type != pktype) {
 104                 error("%s: type mismatch for decoded key "
 105                     "(received %d, expected %d)", __func__, key->type, pktype);
 106                 goto done;
 107         }
 108         if (sshkey_type_plain(key->type) == KEY_RSA &&
 109             (ssh->compat & SSH_BUG_RSASIGMD5) != 0) {
 110                 error("Refusing RSA key because peer uses unsafe "
 111                     "signature format");
 112                 goto done;
 113         }
 114         if (match_pattern_list(sshkey_ssh_name(key),
 115             options.hostbased_key_types, 0) != 1) {
 116                 logit("%s: key type %s not in HostbasedAcceptedKeyTypes",
 117                     __func__, sshkey_type(key));
 118                 goto done;
 119         }
 120
 121         service = ssh->compat & SSH_BUG_HBSERVICE ? "ssh-userauth" :
 122             authctxt->service;
 123         if ((b = sshbuf_new()) == NULL)
 124                 fatal("%s: sshbuf_new failed", __func__);
 125         /* reconstruct packet */
 126         if ((r = sshbuf_put_string(b, session_id2, session_id2_len)) != 0 ||
 127             (r = sshbuf_put_u8(b, SSH2_MSG_USERAUTH_REQUEST)) != 0 ||
 128             (r = sshbuf_put_cstring(b, authctxt->user)) != 0 ||
 129             (r = sshbuf_put_cstring(b, service)) != 0 ||
 130             (r = sshbuf_put_cstring(b, "hostbased")) != 0 ||
 131             (r = sshbuf_put_string(b, pkalg, alen)) != 0 ||
 132             (r = sshbuf_put_string(b, pkblob, blen)) != 0 ||
 133             (r = sshbuf_put_cstring(b, chost)) != 0 ||
 134             (r = sshbuf_put_cstring(b, cuser)) != 0)
 135                 fatal("%s: buffer error: %s", __func__, ssh_err(r));
 136 #ifdef DEBUG_PK
 137         sshbuf_dump(b, stderr);
 138 #endif
 139
 140         auth2_record_info(authctxt,
 141             "client user \"%.100s\", client host \"%.100s\"", cuser, chost);
 142
 143         /* test for allowed key and correct signature */
 144         authenticated = 0;
 145         if (PRIVSEP(hostbased_key_allowed(authctxt->pw, cuser, chost, key)) &&
 146             PRIVSEP(sshkey_verify(key, sig, slen,
 147             sshbuf_ptr(b), sshbuf_len(b), ssh->compat)) == 0)
 148                 authenticated = 1;
 149
 150         auth2_record_key(authctxt, authenticated, key);
 151         sshbuf_free(b);
 152 done:
 153         debug2("%s: authenticated %d", __func__, authenticated);
 154         sshkey_free(key);
 155         free(pkalg);
 156         free(pkblob);
 157         free(cuser);
 158         free(chost);
 159         free(sig);
 160         return authenticated;
 161 }
 162
 163 /* return 1 if given hostkey is allowed */
 164 int
 165 hostbased_key_allowed(struct passwd *pw, const char *cuser, char *chost,
 166     struct sshkey *key)
 167 {
 168         struct ssh *ssh = active_state; /* XXX */
 169         const char *resolvedname, *ipaddr, *lookup, *reason;
 170         HostStatus host_status;
 171         int len;
 172         char *fp;
 173
 174         if (auth_key_is_revoked(key))
 175                 return 0;
 176
 177         resolvedname = auth_get_canonical_hostname(ssh, options.use_dns);
 178         ipaddr = ssh_remote_ipaddr(ssh);
 179
 180         debug2("%s: chost %s resolvedname %s ipaddr %s", __func__,
 181             chost, resolvedname, ipaddr);
 182
 183         if (((len = strlen(chost)) > 0) && chost[len - 1] == '.') {
 184                 debug2("stripping trailing dot from chost %s", chost);
 185                 chost[len - 1] = '\0';
 186         }
 187
 188         if (options.hostbased_uses_name_from_packet_only) {
 189                 if (auth_rhosts2(pw, cuser, chost, chost) == 0) {
 190                         debug2("%s: auth_rhosts2 refused "
 191                             "user \"%.100s\" host \"%.100s\" (from packet)",
 192                             __func__, cuser, chost);
 193                         return 0;
 194                 }
 195                 lookup = chost;
 196         } else {
 197                 if (strcasecmp(resolvedname, chost) != 0)
 198                         logit("userauth_hostbased mismatch: "
 199                             "client sends %s, but we resolve %s to %s",
 200                             chost, ipaddr, resolvedname);
 201                 if (auth_rhosts2(pw, cuser, resolvedname, ipaddr) == 0) {
 202                         debug2("%s: auth_rhosts2 refused "
 203                             "user \"%.100s\" host \"%.100s\" addr \"%.100s\"",
 204                             __func__, cuser, resolvedname, ipaddr);
 205                         return 0;
 206                 }
 207                 lookup = resolvedname;
 208         }
 209         debug2("%s: access allowed by auth_rhosts2", __func__);
 210
 211         if (sshkey_is_cert(key) &&
 212             sshkey_cert_check_authority(key, 1, 0, lookup, &reason)) {
 213                 error("%s", reason);
 214                 auth_debug_add("%s", reason);
 215                 return 0;
 216         }
 217
 218         host_status = check_key_in_hostfiles(pw, key, lookup,
 219             _PATH_SSH_SYSTEM_HOSTFILE,
 220             options.ignore_user_known_hosts ? NULL : _PATH_SSH_USER_HOSTFILE);
 221
 222         /* backward compat if no key has been found. */
 223         if (host_status == HOST_NEW) {
 224                 host_status = check_key_in_hostfiles(pw, key, lookup,
 225                     _PATH_SSH_SYSTEM_HOSTFILE2,
 226                     options.ignore_user_known_hosts ? NULL :
 227                     _PATH_SSH_USER_HOSTFILE2);
 228         }
 229
 230         if (host_status == HOST_OK) {
 231                 if (sshkey_is_cert(key)) {
 232                         if ((fp = sshkey_fingerprint(key->cert->signature_key,
 233                             options.fingerprint_hash, SSH_FP_DEFAULT)) == NULL)
 234                                 fatal("%s: sshkey_fingerprint fail", __func__);
 235                         verbose("Accepted certificate ID \"%s\" signed by "
 236                             "%s CA %s from %s@%s", key->cert->key_id,
 237                             sshkey_type(key->cert->signature_key), fp,
 238                             cuser, lookup);
 239                 } else {
 240                         if ((fp = sshkey_fingerprint(key,
 241                             options.fingerprint_hash, SSH_FP_DEFAULT)) == NULL)
 242                                 fatal("%s: sshkey_fingerprint fail", __func__);
 243                         verbose("Accepted %s public key %s from %s@%s",
 244                             sshkey_type(key), fp, cuser, lookup);
 245                 }
 246                 free(fp);
 247         }
 248
 249         return (host_status == HOST_OK);
 250 }
 251
 252 Authmethod method_hostbased = {
 253         "hostbased",
 254         userauth_hostbased,
 255         &options.hostbased_authentication
 256 };