crypto/openssh/auth2-hostbased.c

   1 /* $OpenBSD: auth2-hostbased.c,v 1.26 2016/03/07 19:02:43 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 "key.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 "match.h"
  52
  53 /* import */
  54 extern ServerOptions options;
  55 extern u_char *session_id2;
  56 extern u_int session_id2_len;
  57
  58 static int
  59 userauth_hostbased(Authctxt *authctxt)
  60 {
  61         Buffer b;
  62         Key *key = NULL;
  63         char *pkalg, *cuser, *chost, *service;
  64         u_char *pkblob, *sig;
  65         u_int alen, blen, slen;
  66         int pktype;
  67         int authenticated = 0;
  68
  69         if (!authctxt->valid) {
  70                 debug2("userauth_hostbased: disabled because of invalid user");
  71                 return 0;
  72         }
  73         pkalg = packet_get_string(&alen);
  74         pkblob = packet_get_string(&blen);
  75         chost = packet_get_string(NULL);
  76         cuser = packet_get_string(NULL);
  77         sig = packet_get_string(&slen);
  78
  79         debug("userauth_hostbased: cuser %s chost %s pkalg %s slen %d",
  80             cuser, chost, pkalg, slen);
  81 #ifdef DEBUG_PK
  82         debug("signature:");
  83         buffer_init(&b);
  84         buffer_append(&b, sig, slen);
  85         buffer_dump(&b);
  86         buffer_free(&b);
  87 #endif
  88         pktype = key_type_from_name(pkalg);
  89         if (pktype == KEY_UNSPEC) {
  90                 /* this is perfectly legal */
  91                 logit("userauth_hostbased: unsupported "
  92                     "public key algorithm: %s", pkalg);
  93                 goto done;
  94         }
  95         key = key_from_blob(pkblob, blen);
  96         if (key == NULL) {
  97                 error("userauth_hostbased: cannot decode key: %s", pkalg);
  98                 goto done;
  99         }
 100         if (key->type != pktype) {
 101                 error("userauth_hostbased: type mismatch for decoded key "
 102                     "(received %d, expected %d)", key->type, pktype);
 103                 goto done;
 104         }
 105         if (key_type_plain(key->type) == KEY_RSA &&
 106             (datafellows & SSH_BUG_RSASIGMD5) != 0) {
 107                 error("Refusing RSA key because peer uses unsafe "
 108                     "signature format");
 109                 goto done;
 110         }
 111         if (match_pattern_list(sshkey_ssh_name(key),
 112             options.hostbased_key_types, 0) != 1) {
 113                 logit("%s: key type %s not in HostbasedAcceptedKeyTypes",
 114                     __func__, sshkey_type(key));
 115                 goto done;
 116         }
 117
 118         service = datafellows & SSH_BUG_HBSERVICE ? "ssh-userauth" :
 119             authctxt->service;
 120         buffer_init(&b);
 121         buffer_put_string(&b, session_id2, session_id2_len);
 122         /* reconstruct packet */
 123         buffer_put_char(&b, SSH2_MSG_USERAUTH_REQUEST);
 124         buffer_put_cstring(&b, authctxt->user);
 125         buffer_put_cstring(&b, service);
 126         buffer_put_cstring(&b, "hostbased");
 127         buffer_put_string(&b, pkalg, alen);
 128         buffer_put_string(&b, pkblob, blen);
 129         buffer_put_cstring(&b, chost);
 130         buffer_put_cstring(&b, cuser);
 131 #ifdef DEBUG_PK
 132         buffer_dump(&b);
 133 #endif
 134
 135         pubkey_auth_info(authctxt, key,
 136             "client user \"%.100s\", client host \"%.100s\"", cuser, chost);
 137
 138         /* test for allowed key and correct signature */
 139         authenticated = 0;
 140         if (PRIVSEP(hostbased_key_allowed(authctxt->pw, cuser, chost, key)) &&
 141             PRIVSEP(key_verify(key, sig, slen, buffer_ptr(&b),
 142                         buffer_len(&b))) == 1)
 143                 authenticated = 1;
 144
 145         buffer_free(&b);
 146 done:
 147         debug2("userauth_hostbased: authenticated %d", authenticated);
 148         if (key != NULL)
 149                 key_free(key);
 150         free(pkalg);
 151         free(pkblob);
 152         free(cuser);
 153         free(chost);
 154         free(sig);
 155         return authenticated;
 156 }
 157
 158 /* return 1 if given hostkey is allowed */
 159 int
 160 hostbased_key_allowed(struct passwd *pw, const char *cuser, char *chost,
 161     Key *key)
 162 {
 163         struct ssh *ssh = active_state; /* XXX */
 164         const char *resolvedname, *ipaddr, *lookup, *reason;
 165         HostStatus host_status;
 166         int len;
 167         char *fp;
 168
 169         if (auth_key_is_revoked(key))
 170                 return 0;
 171
 172         resolvedname = auth_get_canonical_hostname(ssh, options.use_dns);
 173         ipaddr = ssh_remote_ipaddr(ssh);
 174
 175         debug2("%s: chost %s resolvedname %s ipaddr %s", __func__,
 176             chost, resolvedname, ipaddr);
 177
 178         if (((len = strlen(chost)) > 0) && chost[len - 1] == '.') {
 179                 debug2("stripping trailing dot from chost %s", chost);
 180                 chost[len - 1] = '\0';
 181         }
 182
 183         if (options.hostbased_uses_name_from_packet_only) {
 184                 if (auth_rhosts2(pw, cuser, chost, chost) == 0) {
 185                         debug2("%s: auth_rhosts2 refused "
 186                             "user \"%.100s\" host \"%.100s\" (from packet)",
 187                             __func__, cuser, chost);
 188                         return 0;
 189                 }
 190                 lookup = chost;
 191         } else {
 192                 if (strcasecmp(resolvedname, chost) != 0)
 193                         logit("userauth_hostbased mismatch: "
 194                             "client sends %s, but we resolve %s to %s",
 195                             chost, ipaddr, resolvedname);
 196                 if (auth_rhosts2(pw, cuser, resolvedname, ipaddr) == 0) {
 197                         debug2("%s: auth_rhosts2 refused "
 198                             "user \"%.100s\" host \"%.100s\" addr \"%.100s\"",
 199                             __func__, cuser, resolvedname, ipaddr);
 200                         return 0;
 201                 }
 202                 lookup = resolvedname;
 203         }
 204         debug2("%s: access allowed by auth_rhosts2", __func__);
 205
 206         if (key_is_cert(key) &&
 207             key_cert_check_authority(key, 1, 0, lookup, &reason)) {
 208                 error("%s", reason);
 209                 auth_debug_add("%s", reason);
 210                 return 0;
 211         }
 212
 213         host_status = check_key_in_hostfiles(pw, key, lookup,
 214             _PATH_SSH_SYSTEM_HOSTFILE,
 215             options.ignore_user_known_hosts ? NULL : _PATH_SSH_USER_HOSTFILE);
 216
 217         /* backward compat if no key has been found. */
 218         if (host_status == HOST_NEW) {
 219                 host_status = check_key_in_hostfiles(pw, key, lookup,
 220                     _PATH_SSH_SYSTEM_HOSTFILE2,
 221                     options.ignore_user_known_hosts ? NULL :
 222                     _PATH_SSH_USER_HOSTFILE2);
 223         }
 224
 225         if (host_status == HOST_OK) {
 226                 if (key_is_cert(key)) {
 227                         if ((fp = sshkey_fingerprint(key->cert->signature_key,
 228                             options.fingerprint_hash, SSH_FP_DEFAULT)) == NULL)
 229                                 fatal("%s: sshkey_fingerprint fail", __func__);
 230                         verbose("Accepted certificate ID \"%s\" signed by "
 231                             "%s CA %s from %s@%s", key->cert->key_id,
 232                             key_type(key->cert->signature_key), fp,
 233                             cuser, lookup);
 234                 } else {
 235                         if ((fp = sshkey_fingerprint(key,
 236                             options.fingerprint_hash, SSH_FP_DEFAULT)) == NULL)
 237                                 fatal("%s: sshkey_fingerprint fail", __func__);
 238                         verbose("Accepted %s public key %s from %s@%s",
 239                             key_type(key), fp, cuser, lookup);
 240                 }
 241                 free(fp);
 242         }
 243
 244         return (host_status == HOST_OK);
 245 }
 246
 247 Authmethod method_hostbased = {
 248         "hostbased",
 249         userauth_hostbased,
 250         &options.hostbased_authentication
 251 };