auth2-hostbased.c

   1 /* $OpenBSD: auth2-hostbased.c,v 1.12 2008/07/17 08:51:07 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 "servconf.h"
  40 #include "compat.h"
  41 #include "key.h"
  42 #include "hostfile.h"
  43 #include "auth.h"
  44 #include "canohost.h"
  45 #ifdef GSSAPI
  46 #include "ssh-gss.h"
  47 #endif
  48 #include "monitor_wrap.h"
  49 #include "pathnames.h"
  50
  51 /* import */
  52 extern ServerOptions options;
  53 extern u_char *session_id2;
  54 extern u_int session_id2_len;
  55
  56 static int
  57 userauth_hostbased(Authctxt *authctxt)
  58 {
  59         Buffer b;
  60         Key *key = NULL;
  61         char *pkalg, *cuser, *chost, *service;
  62         u_char *pkblob, *sig;
  63         u_int alen, blen, slen;
  64         int pktype;
  65         int authenticated = 0;
  66
  67         if (!authctxt->valid) {
  68                 debug2("userauth_hostbased: disabled because of invalid user");
  69                 return 0;
  70         }
  71         pkalg = packet_get_string(&alen);
  72         pkblob = packet_get_string(&blen);
  73         chost = packet_get_string(NULL);
  74         cuser = packet_get_string(NULL);
  75         sig = packet_get_string(&slen);
  76
  77         debug("userauth_hostbased: cuser %s chost %s pkalg %s slen %d",
  78             cuser, chost, pkalg, slen);
  79 #ifdef DEBUG_PK
  80         debug("signature:");
  81         buffer_init(&b);
  82         buffer_append(&b, sig, slen);
  83         buffer_dump(&b);
  84         buffer_free(&b);
  85 #endif
  86         pktype = key_type_from_name(pkalg);
  87         if (pktype == KEY_UNSPEC) {
  88                 /* this is perfectly legal */
  89                 logit("userauth_hostbased: unsupported "
  90                     "public key algorithm: %s", pkalg);
  91                 goto done;
  92         }
  93         key = key_from_blob(pkblob, blen);
  94         if (key == NULL) {
  95                 error("userauth_hostbased: cannot decode key: %s", pkalg);
  96                 goto done;
  97         }
  98         if (key->type != pktype) {
  99                 error("userauth_hostbased: type mismatch for decoded key "
 100                     "(received %d, expected %d)", key->type, pktype);
 101                 goto done;
 102         }
 103         service = datafellows & SSH_BUG_HBSERVICE ? "ssh-userauth" :
 104             authctxt->service;
 105         buffer_init(&b);
 106         buffer_put_string(&b, session_id2, session_id2_len);
 107         /* reconstruct packet */
 108         buffer_put_char(&b, SSH2_MSG_USERAUTH_REQUEST);
 109         buffer_put_cstring(&b, authctxt->user);
 110         buffer_put_cstring(&b, service);
 111         buffer_put_cstring(&b, "hostbased");
 112         buffer_put_string(&b, pkalg, alen);
 113         buffer_put_string(&b, pkblob, blen);
 114         buffer_put_cstring(&b, chost);
 115         buffer_put_cstring(&b, cuser);
 116 #ifdef DEBUG_PK
 117         buffer_dump(&b);
 118 #endif
 119         /* test for allowed key and correct signature */
 120         authenticated = 0;
 121         if (PRIVSEP(hostbased_key_allowed(authctxt->pw, cuser, chost, key)) &&
 122             PRIVSEP(key_verify(key, sig, slen, buffer_ptr(&b),
 123                         buffer_len(&b))) == 1)
 124                 authenticated = 1;
 125
 126         buffer_free(&b);
 127 done:
 128         debug2("userauth_hostbased: authenticated %d", authenticated);
 129         if (key != NULL)
 130                 key_free(key);
 131         xfree(pkalg);
 132         xfree(pkblob);
 133         xfree(cuser);
 134         xfree(chost);
 135         xfree(sig);
 136         return authenticated;
 137 }
 138
 139 /* return 1 if given hostkey is allowed */
 140 int
 141 hostbased_key_allowed(struct passwd *pw, const char *cuser, char *chost,
 142     Key *key)
 143 {
 144         const char *resolvedname, *ipaddr, *lookup;
 145         HostStatus host_status;
 146         int len;
 147
 148         resolvedname = get_canonical_hostname(options.use_dns);
 149         ipaddr = get_remote_ipaddr();
 150
 151         debug2("userauth_hostbased: chost %s resolvedname %s ipaddr %s",
 152             chost, resolvedname, ipaddr);
 153
 154         if (((len = strlen(chost)) > 0) && chost[len - 1] == '.') {
 155                 debug2("stripping trailing dot from chost %s", chost);
 156                 chost[len - 1] = '\0';
 157         }
 158
 159         if (options.hostbased_uses_name_from_packet_only) {
 160                 if (auth_rhosts2(pw, cuser, chost, chost) == 0)
 161                         return 0;
 162                 lookup = chost;
 163         } else {
 164                 if (strcasecmp(resolvedname, chost) != 0)
 165                         logit("userauth_hostbased mismatch: "
 166                             "client sends %s, but we resolve %s to %s",
 167                             chost, ipaddr, resolvedname);
 168                 if (auth_rhosts2(pw, cuser, resolvedname, ipaddr) == 0)
 169                         return 0;
 170                 lookup = resolvedname;
 171         }
 172         debug2("userauth_hostbased: access allowed by auth_rhosts2");
 173
 174         host_status = check_key_in_hostfiles(pw, key, lookup,
 175             _PATH_SSH_SYSTEM_HOSTFILE,
 176             options.ignore_user_known_hosts ? NULL : _PATH_SSH_USER_HOSTFILE);
 177
 178         /* backward compat if no key has been found. */
 179         if (host_status == HOST_NEW)
 180                 host_status = check_key_in_hostfiles(pw, key, lookup,
 181                     _PATH_SSH_SYSTEM_HOSTFILE2,
 182                     options.ignore_user_known_hosts ? NULL :
 183                     _PATH_SSH_USER_HOSTFILE2);
 184
 185         return (host_status == HOST_OK);
 186 }
 187
 188 Authmethod method_hostbased = {
 189         "hostbased",
 190         userauth_hostbased,
 191         &options.hostbased_authentication
 192 };