auth2-pubkey.c

   1 /* $OpenBSD: auth2-pubkey.c,v 1.13 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 #include <sys/stat.h>
  30
  31 #include <pwd.h>
  32
  33 #include "ssh.h"
  34 #include "ssh2.h"
  35 #include "xmalloc.h"
  36 #include "packet.h"
  37 #include "buffer.h"
  38 #include "log.h"
  39 #include "servconf.h"
  40 #include "compat.h"
  41 #include "bufaux.h"
  42 #include "auth.h"
  43 #include "key.h"
  44 #include "pathnames.h"
  45 #include "uidswap.h"
  46 #include "auth-options.h"
  47 #include "canohost.h"
  48 #include "monitor_wrap.h"
  49 #include "misc.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_pubkey(Authctxt *authctxt)
  58 {
  59         Buffer b;
  60         Key *key = NULL;
  61         char *pkalg;
  62         u_char *pkblob, *sig;
  63         u_int alen, blen, slen;
  64         int have_sig, pktype;
  65         int authenticated = 0;
  66
  67         if (!authctxt->valid) {
  68                 debug2("userauth_pubkey: disabled because of invalid user");
  69                 return 0;
  70         }
  71         have_sig = packet_get_char();
  72         if (datafellows & SSH_BUG_PKAUTH) {
  73                 debug2("userauth_pubkey: SSH_BUG_PKAUTH");
  74                 /* no explicit pkalg given */
  75                 pkblob = packet_get_string(&blen);
  76                 buffer_init(&b);
  77                 buffer_append(&b, pkblob, blen);
  78                 /* so we have to extract the pkalg from the pkblob */
  79                 pkalg = buffer_get_string(&b, &alen);
  80                 buffer_free(&b);
  81         } else {
  82                 pkalg = packet_get_string(&alen);
  83                 pkblob = packet_get_string(&blen);
  84         }
  85         pktype = key_type_from_name(pkalg);
  86         if (pktype == KEY_UNSPEC) {
  87                 /* this is perfectly legal */
  88                 logit("userauth_pubkey: unsupported public key algorithm: %s",
  89                     pkalg);
  90                 goto done;
  91         }
  92         key = key_from_blob(pkblob, blen);
  93         if (key == NULL) {
  94                 error("userauth_pubkey: cannot decode key: %s", pkalg);
  95                 goto done;
  96         }
  97         if (key->type != pktype) {
  98                 error("userauth_pubkey: type mismatch for decoded key "
  99                     "(received %d, expected %d)", key->type, pktype);
 100                 goto done;
 101         }
 102         if (have_sig) {
 103                 sig = packet_get_string(&slen);
 104                 packet_check_eom();
 105                 buffer_init(&b);
 106                 if (datafellows & SSH_OLD_SESSIONID) {
 107                         buffer_append(&b, session_id2, session_id2_len);
 108                 } else {
 109                         buffer_put_string(&b, session_id2, session_id2_len);
 110                 }
 111                 /* reconstruct packet */
 112                 buffer_put_char(&b, SSH2_MSG_USERAUTH_REQUEST);
 113                 buffer_put_cstring(&b, authctxt->user);
 114                 buffer_put_cstring(&b,
 115                     datafellows & SSH_BUG_PKSERVICE ?
 116                     "ssh-userauth" :
 117                     authctxt->service);
 118                 if (datafellows & SSH_BUG_PKAUTH) {
 119                         buffer_put_char(&b, have_sig);
 120                 } else {
 121                         buffer_put_cstring(&b, "publickey");
 122                         buffer_put_char(&b, have_sig);
 123                         buffer_put_cstring(&b, pkalg);
 124                 }
 125                 buffer_put_string(&b, pkblob, blen);
 126 #ifdef DEBUG_PK
 127                 buffer_dump(&b);
 128 #endif
 129                 /* test for correct signature */
 130                 authenticated = 0;
 131                 if (PRIVSEP(user_key_allowed(authctxt->pw, key)) &&
 132                     PRIVSEP(key_verify(key, sig, slen, buffer_ptr(&b),
 133                     buffer_len(&b))) == 1)
 134                         authenticated = 1;
 135                 buffer_free(&b);
 136                 xfree(sig);
 137         } else {
 138                 debug("test whether pkalg/pkblob are acceptable");
 139                 packet_check_eom();
 140
 141                 /* XXX fake reply and always send PK_OK ? */
 142                 /*
 143                  * XXX this allows testing whether a user is allowed
 144                  * to login: if you happen to have a valid pubkey this
 145                  * message is sent. the message is NEVER sent at all
 146                  * if a user is not allowed to login. is this an
 147                  * issue? -markus
 148                  */
 149                 if (PRIVSEP(user_key_allowed(authctxt->pw, key))) {
 150                         packet_start(SSH2_MSG_USERAUTH_PK_OK);
 151                         packet_put_string(pkalg, alen);
 152                         packet_put_string(pkblob, blen);
 153                         packet_send();
 154                         packet_write_wait();
 155                         authctxt->postponed = 1;
 156                 }
 157         }
 158         if (authenticated != 1)
 159                 auth_clear_options();
 160 done:
 161         debug2("userauth_pubkey: authenticated %d pkalg %s", authenticated, pkalg);
 162         if (key != NULL)
 163                 key_free(key);
 164         xfree(pkalg);
 165         xfree(pkblob);
 166 #ifdef HAVE_CYGWIN
 167         if (check_nt_auth(0, authctxt->pw) == 0)
 168                 authenticated = 0;
 169 #endif
 170         return authenticated;
 171 }
 172
 173 /* return 1 if user allows given key */
 174 static int
 175 user_key_allowed2(struct passwd *pw, Key *key, char *file)
 176 {
 177         char line[SSH_MAX_PUBKEY_BYTES];
 178         int found_key = 0;
 179         FILE *f;
 180         u_long linenum = 0;
 181         struct stat st;
 182         Key *found;
 183         char *fp;
 184
 185         /* Temporarily use the user's uid. */
 186         temporarily_use_uid(pw);
 187
 188         debug("trying public key file %s", file);
 189
 190         /* Fail quietly if file does not exist */
 191         if (stat(file, &st) < 0) {
 192                 /* Restore the privileged uid. */
 193                 restore_uid();
 194                 return 0;
 195         }
 196         /* Open the file containing the authorized keys. */
 197         f = fopen(file, "r");
 198         if (!f) {
 199                 /* Restore the privileged uid. */
 200                 restore_uid();
 201                 return 0;
 202         }
 203         if (options.strict_modes &&
 204             secure_filename(f, file, pw, line, sizeof(line)) != 0) {
 205                 fclose(f);
 206                 logit("Authentication refused: %s", line);
 207                 restore_uid();
 208                 return 0;
 209         }
 210
 211         found_key = 0;
 212         found = key_new(key->type);
 213
 214         while (read_keyfile_line(f, file, line, sizeof(line), &linenum) != -1) {
 215                 char *cp, *key_options = NULL;
 216
 217                 /* Skip leading whitespace, empty and comment lines. */
 218                 for (cp = line; *cp == ' ' || *cp == '\t'; cp++)
 219                         ;
 220                 if (!*cp || *cp == '\n' || *cp == '#')
 221                         continue;
 222
 223                 if (key_read(found, &cp) != 1) {
 224                         /* no key?  check if there are options for this key */
 225                         int quoted = 0;
 226                         debug2("user_key_allowed: check options: '%s'", cp);
 227                         key_options = cp;
 228                         for (; *cp && (quoted || (*cp != ' ' && *cp != '\t')); cp++) {
 229                                 if (*cp == '\\' && cp[1] == '"')
 230                                         cp++;   /* Skip both */
 231                                 else if (*cp == '"')
 232                                         quoted = !quoted;
 233                         }
 234                         /* Skip remaining whitespace. */
 235                         for (; *cp == ' ' || *cp == '\t'; cp++)
 236                                 ;
 237                         if (key_read(found, &cp) != 1) {
 238                                 debug2("user_key_allowed: advance: '%s'", cp);
 239                                 /* still no key?  advance to next line*/
 240                                 continue;
 241                         }
 242                 }
 243                 if (key_equal(found, key) &&
 244                     auth_parse_options(pw, key_options, file, linenum) == 1) {
 245                         found_key = 1;
 246                         debug("matching key found: file %s, line %lu",
 247                             file, linenum);
 248                         fp = key_fingerprint(found, SSH_FP_MD5, SSH_FP_HEX);
 249                         verbose("Found matching %s key: %s",
 250                             key_type(found), fp);
 251                         xfree(fp);
 252                         break;
 253                 }
 254         }
 255         restore_uid();
 256         fclose(f);
 257         key_free(found);
 258         if (!found_key)
 259                 debug2("key not found");
 260         return found_key;
 261 }
 262
 263 /* check whether given key is in .ssh/authorized_keys* */
 264 int
 265 user_key_allowed(struct passwd *pw, Key *key)
 266 {
 267         int success;
 268         char *file;
 269
 270         file = authorized_keys_file(pw);
 271         success = user_key_allowed2(pw, key, file);
 272         xfree(file);
 273         if (success)
 274                 return success;
 275
 276         /* try suffix "2" for backward compat, too */
 277         file = authorized_keys_file2(pw);
 278         success = user_key_allowed2(pw, key, file);
 279         xfree(file);
 280         return success;
 281 }
 282
 283 Authmethod method_pubkey = {
 284         "publickey",
 285         userauth_pubkey,
 286         &options.pubkey_authentication
 287 };