auth2-hostbased.c

   1 /* $OpenBSD: auth2-hostbased.c,v 1.10 2006/07/22 20:48:22 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 #include <string.h>
  32
  33 #include "ssh2.h"
  34 #include "xmalloc.h"
  35 #include "packet.h"
  36 #include "buffer.h"
  37 #include "log.h"
  38 #include "servconf.h"
  39 #include "compat.h"
  40 #include "bufaux.h"
  41 #include "auth.h"
  42 #include "key.h"
  43 #include "canohost.h"
  44 #include "monitor_wrap.h"
  45 #include "pathnames.h"
  46
  47 /* import */
  48 extern ServerOptions options;
  49 extern u_char *session_id2;
  50 extern u_int session_id2_len;
  51
  52 static int
  53 userauth_hostbased(Authctxt *authctxt)
  54 {
  55         Buffer b;
  56         Key *key = NULL;
  57         char *pkalg, *cuser, *chost, *service;
  58         u_char *pkblob, *sig;
  59         u_int alen, blen, slen;
  60         int pktype;
  61         int authenticated = 0;
  62
  63         if (!authctxt->valid) {
  64                 debug2("userauth_hostbased: disabled because of invalid user");
  65                 return 0;
  66         }
  67         pkalg = packet_get_string(&alen);
  68         pkblob = packet_get_string(&blen);
  69         chost = packet_get_string(NULL);
  70         cuser = packet_get_string(NULL);
  71         sig = packet_get_string(&slen);
  72
  73         debug("userauth_hostbased: cuser %s chost %s pkalg %s slen %d",
  74             cuser, chost, pkalg, slen);
  75 #ifdef DEBUG_PK
  76         debug("signature:");
  77         buffer_init(&b);
  78         buffer_append(&b, sig, slen);
  79         buffer_dump(&b);
  80         buffer_free(&b);
  81 #endif
  82         pktype = key_type_from_name(pkalg);
  83         if (pktype == KEY_UNSPEC) {
  84                 /* this is perfectly legal */
  85                 logit("userauth_hostbased: unsupported "
  86                     "public key algorithm: %s", pkalg);
  87                 goto done;
  88         }
  89         key = key_from_blob(pkblob, blen);
  90         if (key == NULL) {
  91                 error("userauth_hostbased: cannot decode key: %s", pkalg);
  92                 goto done;
  93         }
  94         if (key->type != pktype) {
  95                 error("userauth_hostbased: type mismatch for decoded key "
  96                     "(received %d, expected %d)", key->type, pktype);
  97                 goto done;
  98         }
  99         service = datafellows & SSH_BUG_HBSERVICE ? "ssh-userauth" :
 100             authctxt->service;
 101         buffer_init(&b);
 102         buffer_put_string(&b, session_id2, session_id2_len);
 103         /* reconstruct packet */
 104         buffer_put_char(&b, SSH2_MSG_USERAUTH_REQUEST);
 105         buffer_put_cstring(&b, authctxt->user);
 106         buffer_put_cstring(&b, service);
 107         buffer_put_cstring(&b, "hostbased");
 108         buffer_put_string(&b, pkalg, alen);
 109         buffer_put_string(&b, pkblob, blen);
 110         buffer_put_cstring(&b, chost);
 111         buffer_put_cstring(&b, cuser);
 112 #ifdef DEBUG_PK
 113         buffer_dump(&b);
 114 #endif
 115         /* test for allowed key and correct signature */
 116         authenticated = 0;
 117         if (PRIVSEP(hostbased_key_allowed(authctxt->pw, cuser, chost, key)) &&
 118             PRIVSEP(key_verify(key, sig, slen, buffer_ptr(&b),
 119                         buffer_len(&b))) == 1)
 120                 authenticated = 1;
 121
 122         buffer_free(&b);
 123 done:
 124         debug2("userauth_hostbased: authenticated %d", authenticated);
 125         if (key != NULL)
 126                 key_free(key);
 127         xfree(pkalg);
 128         xfree(pkblob);
 129         xfree(cuser);
 130         xfree(chost);
 131         xfree(sig);
 132         return authenticated;
 133 }
 134
 135 /* return 1 if given hostkey is allowed */
 136 int
 137 hostbased_key_allowed(struct passwd *pw, const char *cuser, char *chost,
 138     Key *key)
 139 {
 140         const char *resolvedname, *ipaddr, *lookup;
 141         HostStatus host_status;
 142         int len;
 143
 144         resolvedname = get_canonical_hostname(options.use_dns);
 145         ipaddr = get_remote_ipaddr();
 146
 147         debug2("userauth_hostbased: chost %s resolvedname %s ipaddr %s",
 148             chost, resolvedname, ipaddr);
 149
 150         if (options.hostbased_uses_name_from_packet_only) {
 151                 if (auth_rhosts2(pw, cuser, chost, chost) == 0)
 152                         return 0;
 153                 lookup = chost;
 154         } else {
 155                 if (((len = strlen(chost)) > 0) && chost[len - 1] == '.') {
 156                         debug2("stripping trailing dot from chost %s", chost);
 157                         chost[len - 1] = '\0';
 158                 }
 159                 if (strcasecmp(resolvedname, chost) != 0)
 160                         logit("userauth_hostbased mismatch: "
 161                             "client sends %s, but we resolve %s to %s",
 162                             chost, ipaddr, resolvedname);
 163                 if (auth_rhosts2(pw, cuser, resolvedname, ipaddr) == 0)
 164                         return 0;
 165                 lookup = resolvedname;
 166         }
 167         debug2("userauth_hostbased: access allowed by auth_rhosts2");
 168
 169         host_status = check_key_in_hostfiles(pw, key, lookup,
 170             _PATH_SSH_SYSTEM_HOSTFILE,
 171             options.ignore_user_known_hosts ? NULL : _PATH_SSH_USER_HOSTFILE);
 172
 173         /* backward compat if no key has been found. */
 174         if (host_status == HOST_NEW)
 175                 host_status = check_key_in_hostfiles(pw, key, lookup,
 176                     _PATH_SSH_SYSTEM_HOSTFILE2,
 177                     options.ignore_user_known_hosts ? NULL :
 178                     _PATH_SSH_USER_HOSTFILE2);
 179
 180         return (host_status == HOST_OK);
 181 }
 182
 183 Authmethod method_hostbased = {
 184         "hostbased",
 185         userauth_hostbased,
 186         &options.hostbased_authentication
 187 };