auth2-hostbased.c

   1 /* $OpenBSD: auth2-hostbased.c,v 1.8 2006/03/25 13:17:01 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 "ssh2.h"
  29 #include "xmalloc.h"
  30 #include "packet.h"
  31 #include "buffer.h"
  32 #include "log.h"
  33 #include "servconf.h"
  34 #include "compat.h"
  35 #include "bufaux.h"
  36 #include "auth.h"
  37 #include "key.h"
  38 #include "canohost.h"
  39 #include "monitor_wrap.h"
  40 #include "pathnames.h"
  41
  42 /* import */
  43 extern ServerOptions options;
  44 extern u_char *session_id2;
  45 extern u_int session_id2_len;
  46
  47 static int
  48 userauth_hostbased(Authctxt *authctxt)
  49 {
  50         Buffer b;
  51         Key *key = NULL;
  52         char *pkalg, *cuser, *chost, *service;
  53         u_char *pkblob, *sig;
  54         u_int alen, blen, slen;
  55         int pktype;
  56         int authenticated = 0;
  57
  58         if (!authctxt->valid) {
  59                 debug2("userauth_hostbased: disabled because of invalid user");
  60                 return 0;
  61         }
  62         pkalg = packet_get_string(&alen);
  63         pkblob = packet_get_string(&blen);
  64         chost = packet_get_string(NULL);
  65         cuser = packet_get_string(NULL);
  66         sig = packet_get_string(&slen);
  67
  68         debug("userauth_hostbased: cuser %s chost %s pkalg %s slen %d",
  69             cuser, chost, pkalg, slen);
  70 #ifdef DEBUG_PK
  71         debug("signature:");
  72         buffer_init(&b);
  73         buffer_append(&b, sig, slen);
  74         buffer_dump(&b);
  75         buffer_free(&b);
  76 #endif
  77         pktype = key_type_from_name(pkalg);
  78         if (pktype == KEY_UNSPEC) {
  79                 /* this is perfectly legal */
  80                 logit("userauth_hostbased: unsupported "
  81                     "public key algorithm: %s", pkalg);
  82                 goto done;
  83         }
  84         key = key_from_blob(pkblob, blen);
  85         if (key == NULL) {
  86                 error("userauth_hostbased: cannot decode key: %s", pkalg);
  87                 goto done;
  88         }
  89         if (key->type != pktype) {
  90                 error("userauth_hostbased: type mismatch for decoded key "
  91                     "(received %d, expected %d)", key->type, pktype);
  92                 goto done;
  93         }
  94         service = datafellows & SSH_BUG_HBSERVICE ? "ssh-userauth" :
  95             authctxt->service;
  96         buffer_init(&b);
  97         buffer_put_string(&b, session_id2, session_id2_len);
  98         /* reconstruct packet */
  99         buffer_put_char(&b, SSH2_MSG_USERAUTH_REQUEST);
 100         buffer_put_cstring(&b, authctxt->user);
 101         buffer_put_cstring(&b, service);
 102         buffer_put_cstring(&b, "hostbased");
 103         buffer_put_string(&b, pkalg, alen);
 104         buffer_put_string(&b, pkblob, blen);
 105         buffer_put_cstring(&b, chost);
 106         buffer_put_cstring(&b, cuser);
 107 #ifdef DEBUG_PK
 108         buffer_dump(&b);
 109 #endif
 110         /* test for allowed key and correct signature */
 111         authenticated = 0;
 112         if (PRIVSEP(hostbased_key_allowed(authctxt->pw, cuser, chost, key)) &&
 113             PRIVSEP(key_verify(key, sig, slen, buffer_ptr(&b),
 114                         buffer_len(&b))) == 1)
 115                 authenticated = 1;
 116
 117         buffer_free(&b);
 118 done:
 119         debug2("userauth_hostbased: authenticated %d", authenticated);
 120         if (key != NULL)
 121                 key_free(key);
 122         xfree(pkalg);
 123         xfree(pkblob);
 124         xfree(cuser);
 125         xfree(chost);
 126         xfree(sig);
 127         return authenticated;
 128 }
 129
 130 /* return 1 if given hostkey is allowed */
 131 int
 132 hostbased_key_allowed(struct passwd *pw, const char *cuser, char *chost,
 133     Key *key)
 134 {
 135         const char *resolvedname, *ipaddr, *lookup;
 136         HostStatus host_status;
 137         int len;
 138
 139         resolvedname = get_canonical_hostname(options.use_dns);
 140         ipaddr = get_remote_ipaddr();
 141
 142         debug2("userauth_hostbased: chost %s resolvedname %s ipaddr %s",
 143             chost, resolvedname, ipaddr);
 144
 145         if (options.hostbased_uses_name_from_packet_only) {
 146                 if (auth_rhosts2(pw, cuser, chost, chost) == 0)
 147                         return 0;
 148                 lookup = chost;
 149         } else {
 150                 if (((len = strlen(chost)) > 0) && chost[len - 1] == '.') {
 151                         debug2("stripping trailing dot from chost %s", chost);
 152                         chost[len - 1] = '\0';
 153                 }
 154                 if (strcasecmp(resolvedname, chost) != 0)
 155                         logit("userauth_hostbased mismatch: "
 156                             "client sends %s, but we resolve %s to %s",
 157                             chost, ipaddr, resolvedname);
 158                 if (auth_rhosts2(pw, cuser, resolvedname, ipaddr) == 0)
 159                         return 0;
 160                 lookup = resolvedname;
 161         }
 162         debug2("userauth_hostbased: access allowed by auth_rhosts2");
 163
 164         host_status = check_key_in_hostfiles(pw, key, lookup,
 165             _PATH_SSH_SYSTEM_HOSTFILE,
 166             options.ignore_user_known_hosts ? NULL : _PATH_SSH_USER_HOSTFILE);
 167
 168         /* backward compat if no key has been found. */
 169         if (host_status == HOST_NEW)
 170                 host_status = check_key_in_hostfiles(pw, key, lookup,
 171                     _PATH_SSH_SYSTEM_HOSTFILE2,
 172                     options.ignore_user_known_hosts ? NULL :
 173                     _PATH_SSH_USER_HOSTFILE2);
 174
 175         return (host_status == HOST_OK);
 176 }
 177
 178 Authmethod method_hostbased = {
 179         "hostbased",
 180         userauth_hostbased,
 181         &options.hostbased_authentication
 182 };