auth2-pubkey.c

   1 /* $OpenBSD: auth2-pubkey.c,v 1.15 2006/08/03 03:34:41 deraadt 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 #include <stdio.h>
  33 #include <stdarg.h>
  34
  35 #include "xmalloc.h"
  36 #include "ssh.h"
  37 #include "ssh2.h"
  38 #include "packet.h"
  39 #include "buffer.h"
  40 #include "log.h"
  41 #include "servconf.h"
  42 #include "compat.h"
  43 #include "key.h"
  44 #include "hostfile.h"
  45 #include "auth.h"
  46 #include "pathnames.h"
  47 #include "uidswap.h"
  48 #include "auth-options.h"
  49 #include "canohost.h"
  50 #ifdef GSSAPI
  51 #include "ssh-gss.h"
  52 #endif
  53 #include "monitor_wrap.h"
  54 #include "misc.h"
  55
  56 /* import */
  57 extern ServerOptions options;
  58 extern u_char *session_id2;
  59 extern u_int session_id2_len;
  60
  61 static int
  62 userauth_pubkey(Authctxt *authctxt)
  63 {
  64         Buffer b;
  65         Key *key = NULL;
  66         char *pkalg;
  67         u_char *pkblob, *sig;
  68         u_int alen, blen, slen;
  69         int have_sig, pktype;
  70         int authenticated = 0;
  71
  72         if (!authctxt->valid) {
  73                 debug2("userauth_pubkey: disabled because of invalid user");
  74                 return 0;
  75         }
  76         have_sig = packet_get_char();
  77         if (datafellows & SSH_BUG_PKAUTH) {
  78                 debug2("userauth_pubkey: SSH_BUG_PKAUTH");
  79                 /* no explicit pkalg given */
  80                 pkblob = packet_get_string(&blen);
  81                 buffer_init(&b);
  82                 buffer_append(&b, pkblob, blen);
  83                 /* so we have to extract the pkalg from the pkblob */
  84                 pkalg = buffer_get_string(&b, &alen);
  85                 buffer_free(&b);
  86         } else {
  87                 pkalg = packet_get_string(&alen);
  88                 pkblob = packet_get_string(&blen);
  89         }
  90         pktype = key_type_from_name(pkalg);
  91         if (pktype == KEY_UNSPEC) {
  92                 /* this is perfectly legal */
  93                 logit("userauth_pubkey: unsupported public key algorithm: %s",
  94                     pkalg);
  95                 goto done;
  96         }
  97         key = key_from_blob(pkblob, blen);
  98         if (key == NULL) {
  99                 error("userauth_pubkey: cannot decode key: %s", pkalg);
 100                 goto done;
 101         }
 102         if (key->type != pktype) {
 103                 error("userauth_pubkey: type mismatch for decoded key "
 104                     "(received %d, expected %d)", key->type, pktype);
 105                 goto done;
 106         }
 107         if (have_sig) {
 108                 sig = packet_get_string(&slen);
 109                 packet_check_eom();
 110                 buffer_init(&b);
 111                 if (datafellows & SSH_OLD_SESSIONID) {
 112                         buffer_append(&b, session_id2, session_id2_len);
 113                 } else {
 114                         buffer_put_string(&b, session_id2, session_id2_len);
 115                 }
 116                 /* reconstruct packet */
 117                 buffer_put_char(&b, SSH2_MSG_USERAUTH_REQUEST);
 118                 buffer_put_cstring(&b, authctxt->user);
 119                 buffer_put_cstring(&b,
 120                     datafellows & SSH_BUG_PKSERVICE ?
 121                     "ssh-userauth" :
 122                     authctxt->service);
 123                 if (datafellows & SSH_BUG_PKAUTH) {
 124                         buffer_put_char(&b, have_sig);
 125                 } else {
 126                         buffer_put_cstring(&b, "publickey");
 127                         buffer_put_char(&b, have_sig);
 128                         buffer_put_cstring(&b, pkalg);
 129                 }
 130                 buffer_put_string(&b, pkblob, blen);
 131 #ifdef DEBUG_PK
 132                 buffer_dump(&b);
 133 #endif
 134                 /* test for correct signature */
 135                 authenticated = 0;
 136                 if (PRIVSEP(user_key_allowed(authctxt->pw, key)) &&
 137                     PRIVSEP(key_verify(key, sig, slen, buffer_ptr(&b),
 138                     buffer_len(&b))) == 1)
 139                         authenticated = 1;
 140                 buffer_free(&b);
 141                 xfree(sig);
 142         } else {
 143                 debug("test whether pkalg/pkblob are acceptable");
 144                 packet_check_eom();
 145
 146                 /* XXX fake reply and always send PK_OK ? */
 147                 /*
 148                  * XXX this allows testing whether a user is allowed
 149                  * to login: if you happen to have a valid pubkey this
 150                  * message is sent. the message is NEVER sent at all
 151                  * if a user is not allowed to login. is this an
 152                  * issue? -markus
 153                  */
 154                 if (PRIVSEP(user_key_allowed(authctxt->pw, key))) {
 155                         packet_start(SSH2_MSG_USERAUTH_PK_OK);
 156                         packet_put_string(pkalg, alen);
 157                         packet_put_string(pkblob, blen);
 158                         packet_send();
 159                         packet_write_wait();
 160                         authctxt->postponed = 1;
 161                 }
 162         }
 163         if (authenticated != 1)
 164                 auth_clear_options();
 165 done:
 166         debug2("userauth_pubkey: authenticated %d pkalg %s", authenticated, pkalg);
 167         if (key != NULL)
 168                 key_free(key);
 169         xfree(pkalg);
 170         xfree(pkblob);
 171 #ifdef HAVE_CYGWIN
 172         if (check_nt_auth(0, authctxt->pw) == 0)
 173                 authenticated = 0;
 174 #endif
 175         return authenticated;
 176 }
 177
 178 /* return 1 if user allows given key */
 179 static int
 180 user_key_allowed2(struct passwd *pw, Key *key, char *file)
 181 {
 182         char line[SSH_MAX_PUBKEY_BYTES];
 183         int found_key = 0;
 184         FILE *f;
 185         u_long linenum = 0;
 186         struct stat st;
 187         Key *found;
 188         char *fp;
 189
 190         /* Temporarily use the user's uid. */
 191         temporarily_use_uid(pw);
 192
 193         debug("trying public key file %s", file);
 194
 195         /* Fail quietly if file does not exist */
 196         if (stat(file, &st) < 0) {
 197                 /* Restore the privileged uid. */
 198                 restore_uid();
 199                 return 0;
 200         }
 201         /* Open the file containing the authorized keys. */
 202         f = fopen(file, "r");
 203         if (!f) {
 204                 /* Restore the privileged uid. */
 205                 restore_uid();
 206                 return 0;
 207         }
 208         if (options.strict_modes &&
 209             secure_filename(f, file, pw, line, sizeof(line)) != 0) {
 210                 fclose(f);
 211                 logit("Authentication refused: %s", line);
 212                 restore_uid();
 213                 return 0;
 214         }
 215
 216         found_key = 0;
 217         found = key_new(key->type);
 218
 219         while (read_keyfile_line(f, file, line, sizeof(line), &linenum) != -1) {
 220                 char *cp, *key_options = NULL;
 221
 222                 /* Skip leading whitespace, empty and comment lines. */
 223                 for (cp = line; *cp == ' ' || *cp == '\t'; cp++)
 224                         ;
 225                 if (!*cp || *cp == '\n' || *cp == '#')
 226                         continue;
 227
 228                 if (key_read(found, &cp) != 1) {
 229                         /* no key?  check if there are options for this key */
 230                         int quoted = 0;
 231                         debug2("user_key_allowed: check options: '%s'", cp);
 232                         key_options = cp;
 233                         for (; *cp && (quoted || (*cp != ' ' && *cp != '\t')); cp++) {
 234                                 if (*cp == '\\' && cp[1] == '"')
 235                                         cp++;   /* Skip both */
 236                                 else if (*cp == '"')
 237                                         quoted = !quoted;
 238                         }
 239                         /* Skip remaining whitespace. */
 240                         for (; *cp == ' ' || *cp == '\t'; cp++)
 241                                 ;
 242                         if (key_read(found, &cp) != 1) {
 243                                 debug2("user_key_allowed: advance: '%s'", cp);
 244                                 /* still no key?  advance to next line*/
 245                                 continue;
 246                         }
 247                 }
 248                 if (key_equal(found, key) &&
 249                     auth_parse_options(pw, key_options, file, linenum) == 1) {
 250                         found_key = 1;
 251                         debug("matching key found: file %s, line %lu",
 252                             file, linenum);
 253                         fp = key_fingerprint(found, SSH_FP_MD5, SSH_FP_HEX);
 254                         verbose("Found matching %s key: %s",
 255                             key_type(found), fp);
 256                         xfree(fp);
 257                         break;
 258                 }
 259         }
 260         restore_uid();
 261         fclose(f);
 262         key_free(found);
 263         if (!found_key)
 264                 debug2("key not found");
 265         return found_key;
 266 }
 267
 268 /* check whether given key is in .ssh/authorized_keys* */
 269 int
 270 user_key_allowed(struct passwd *pw, Key *key)
 271 {
 272         int success;
 273         char *file;
 274
 275         file = authorized_keys_file(pw);
 276         success = user_key_allowed2(pw, key, file);
 277         xfree(file);
 278         if (success)
 279                 return success;
 280
 281         /* try suffix "2" for backward compat, too */
 282         file = authorized_keys_file2(pw);
 283         success = user_key_allowed2(pw, key, file);
 284         xfree(file);
 285         return success;
 286 }
 287
 288 Authmethod method_pubkey = {
 289         "publickey",
 290         userauth_pubkey,
 291         &options.pubkey_authentication
 292 };