auth2-hostbased.c

   1 /* $OpenBSD: auth2-hostbased.c,v 1.9 2006/07/06 16:03:53 stevesk 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
  32 #include "ssh2.h"
  33 #include "xmalloc.h"
  34 #include "packet.h"
  35 #include "buffer.h"
  36 #include "log.h"
  37 #include "servconf.h"
  38 #include "compat.h"
  39 #include "bufaux.h"
  40 #include "auth.h"
  41 #include "key.h"
  42 #include "canohost.h"
  43 #include "monitor_wrap.h"
  44 #include "pathnames.h"
  45
  46 /* import */
  47 extern ServerOptions options;
  48 extern u_char *session_id2;
  49 extern u_int session_id2_len;
  50
  51 static int
  52 userauth_hostbased(Authctxt *authctxt)
  53 {
  54         Buffer b;
  55         Key *key = NULL;
  56         char *pkalg, *cuser, *chost, *service;
  57         u_char *pkblob, *sig;
  58         u_int alen, blen, slen;
  59         int pktype;
  60         int authenticated = 0;
  61
  62         if (!authctxt->valid) {
  63                 debug2("userauth_hostbased: disabled because of invalid user");
  64                 return 0;
  65         }
  66         pkalg = packet_get_string(&alen);
  67         pkblob = packet_get_string(&blen);
  68         chost = packet_get_string(NULL);
  69         cuser = packet_get_string(NULL);
  70         sig = packet_get_string(&slen);
  71
  72         debug("userauth_hostbased: cuser %s chost %s pkalg %s slen %d",
  73             cuser, chost, pkalg, slen);
  74 #ifdef DEBUG_PK
  75         debug("signature:");
  76         buffer_init(&b);
  77         buffer_append(&b, sig, slen);
  78         buffer_dump(&b);
  79         buffer_free(&b);
  80 #endif
  81         pktype = key_type_from_name(pkalg);
  82         if (pktype == KEY_UNSPEC) {
  83                 /* this is perfectly legal */
  84                 logit("userauth_hostbased: unsupported "
  85                     "public key algorithm: %s", pkalg);
  86                 goto done;
  87         }
  88         key = key_from_blob(pkblob, blen);
  89         if (key == NULL) {
  90                 error("userauth_hostbased: cannot decode key: %s", pkalg);
  91                 goto done;
  92         }
  93         if (key->type != pktype) {
  94                 error("userauth_hostbased: type mismatch for decoded key "
  95                     "(received %d, expected %d)", key->type, pktype);
  96                 goto done;
  97         }
  98         service = datafellows & SSH_BUG_HBSERVICE ? "ssh-userauth" :
  99             authctxt->service;
 100         buffer_init(&b);
 101         buffer_put_string(&b, session_id2, session_id2_len);
 102         /* reconstruct packet */
 103         buffer_put_char(&b, SSH2_MSG_USERAUTH_REQUEST);
 104         buffer_put_cstring(&b, authctxt->user);
 105         buffer_put_cstring(&b, service);
 106         buffer_put_cstring(&b, "hostbased");
 107         buffer_put_string(&b, pkalg, alen);
 108         buffer_put_string(&b, pkblob, blen);
 109         buffer_put_cstring(&b, chost);
 110         buffer_put_cstring(&b, cuser);
 111 #ifdef DEBUG_PK
 112         buffer_dump(&b);
 113 #endif
 114         /* test for allowed key and correct signature */
 115         authenticated = 0;
 116         if (PRIVSEP(hostbased_key_allowed(authctxt->pw, cuser, chost, key)) &&
 117             PRIVSEP(key_verify(key, sig, slen, buffer_ptr(&b),
 118                         buffer_len(&b))) == 1)
 119                 authenticated = 1;
 120
 121         buffer_free(&b);
 122 done:
 123         debug2("userauth_hostbased: authenticated %d", authenticated);
 124         if (key != NULL)
 125                 key_free(key);
 126         xfree(pkalg);
 127         xfree(pkblob);
 128         xfree(cuser);
 129         xfree(chost);
 130         xfree(sig);
 131         return authenticated;
 132 }
 133
 134 /* return 1 if given hostkey is allowed */
 135 int
 136 hostbased_key_allowed(struct passwd *pw, const char *cuser, char *chost,
 137     Key *key)
 138 {
 139         const char *resolvedname, *ipaddr, *lookup;
 140         HostStatus host_status;
 141         int len;
 142
 143         resolvedname = get_canonical_hostname(options.use_dns);
 144         ipaddr = get_remote_ipaddr();
 145
 146         debug2("userauth_hostbased: chost %s resolvedname %s ipaddr %s",
 147             chost, resolvedname, ipaddr);
 148
 149         if (options.hostbased_uses_name_from_packet_only) {
 150                 if (auth_rhosts2(pw, cuser, chost, chost) == 0)
 151                         return 0;
 152                 lookup = chost;
 153         } else {
 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                 if (strcasecmp(resolvedname, chost) != 0)
 159                         logit("userauth_hostbased mismatch: "
 160                             "client sends %s, but we resolve %s to %s",
 161                             chost, ipaddr, resolvedname);
 162                 if (auth_rhosts2(pw, cuser, resolvedname, ipaddr) == 0)
 163                         return 0;
 164                 lookup = resolvedname;
 165         }
 166         debug2("userauth_hostbased: access allowed by auth_rhosts2");
 167
 168         host_status = check_key_in_hostfiles(pw, key, lookup,
 169             _PATH_SSH_SYSTEM_HOSTFILE,
 170             options.ignore_user_known_hosts ? NULL : _PATH_SSH_USER_HOSTFILE);
 171
 172         /* backward compat if no key has been found. */
 173         if (host_status == HOST_NEW)
 174                 host_status = check_key_in_hostfiles(pw, key, lookup,
 175                     _PATH_SSH_SYSTEM_HOSTFILE2,
 176                     options.ignore_user_known_hosts ? NULL :
 177                     _PATH_SSH_USER_HOSTFILE2);
 178
 179         return (host_status == HOST_OK);
 180 }
 181
 182 Authmethod method_hostbased = {
 183         "hostbased",
 184         userauth_hostbased,
 185         &options.hostbased_authentication
 186 };