crypto/openssh/auth2-pubkey.c

   1 /* $OpenBSD: auth2-pubkey.c,v 1.19 2008/07/03 21:46:58 otto 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 <fcntl.h>
  32 #include <pwd.h>
  33 #include <stdio.h>
  34 #include <stdarg.h>
  35 #include <unistd.h>
  36
  37 #include "xmalloc.h"
  38 #include "ssh.h"
  39 #include "ssh2.h"
  40 #include "packet.h"
  41 #include "buffer.h"
  42 #include "log.h"
  43 #include "servconf.h"
  44 #include "compat.h"
  45 #include "key.h"
  46 #include "hostfile.h"
  47 #include "authfile.h"
  48 #include "auth.h"
  49 #include "pathnames.h"
  50 #include "uidswap.h"
  51 #include "auth-options.h"
  52 #include "canohost.h"
  53 #ifdef GSSAPI
  54 #include "ssh-gss.h"
  55 #endif
  56 #include "monitor_wrap.h"
  57 #include "misc.h"
  58
  59 /* import */
  60 extern ServerOptions options;
  61 extern u_char *session_id2;
  62 extern u_int session_id2_len;
  63
  64 static int
  65 userauth_pubkey(Authctxt *authctxt)
  66 {
  67         Buffer b;
  68         Key *key = NULL;
  69         char *pkalg;
  70         u_char *pkblob, *sig;
  71         u_int alen, blen, slen;
  72         int have_sig, pktype;
  73         int authenticated = 0;
  74
  75         if (!authctxt->valid) {
  76                 debug2("userauth_pubkey: disabled because of invalid user");
  77                 return 0;
  78         }
  79         have_sig = packet_get_char();
  80         if (datafellows & SSH_BUG_PKAUTH) {
  81                 debug2("userauth_pubkey: SSH_BUG_PKAUTH");
  82                 /* no explicit pkalg given */
  83                 pkblob = packet_get_string(&blen);
  84                 buffer_init(&b);
  85                 buffer_append(&b, pkblob, blen);
  86                 /* so we have to extract the pkalg from the pkblob */
  87                 pkalg = buffer_get_string(&b, &alen);
  88                 buffer_free(&b);
  89         } else {
  90                 pkalg = packet_get_string(&alen);
  91                 pkblob = packet_get_string(&blen);
  92         }
  93         pktype = key_type_from_name(pkalg);
  94         if (pktype == KEY_UNSPEC) {
  95                 /* this is perfectly legal */
  96                 logit("userauth_pubkey: unsupported public key algorithm: %s",
  97                     pkalg);
  98                 goto done;
  99         }
 100         key = key_from_blob(pkblob, blen);
 101         if (key == NULL) {
 102                 error("userauth_pubkey: cannot decode key: %s", pkalg);
 103                 goto done;
 104         }
 105         if (key->type != pktype) {
 106                 error("userauth_pubkey: type mismatch for decoded key "
 107                     "(received %d, expected %d)", key->type, pktype);
 108                 goto done;
 109         }
 110         if (have_sig) {
 111                 sig = packet_get_string(&slen);
 112                 packet_check_eom();
 113                 buffer_init(&b);
 114                 if (datafellows & SSH_OLD_SESSIONID) {
 115                         buffer_append(&b, session_id2, session_id2_len);
 116                 } else {
 117                         buffer_put_string(&b, session_id2, session_id2_len);
 118                 }
 119                 /* reconstruct packet */
 120                 buffer_put_char(&b, SSH2_MSG_USERAUTH_REQUEST);
 121                 buffer_put_cstring(&b, authctxt->user);
 122                 buffer_put_cstring(&b,
 123                     datafellows & SSH_BUG_PKSERVICE ?
 124                     "ssh-userauth" :
 125                     authctxt->service);
 126                 if (datafellows & SSH_BUG_PKAUTH) {
 127                         buffer_put_char(&b, have_sig);
 128                 } else {
 129                         buffer_put_cstring(&b, "publickey");
 130                         buffer_put_char(&b, have_sig);
 131                         buffer_put_cstring(&b, pkalg);
 132                 }
 133                 buffer_put_string(&b, pkblob, blen);
 134 #ifdef DEBUG_PK
 135                 buffer_dump(&b);
 136 #endif
 137                 /* test for correct signature */
 138                 authenticated = 0;
 139                 if (PRIVSEP(user_key_allowed(authctxt->pw, key)) &&
 140                     PRIVSEP(key_verify(key, sig, slen, buffer_ptr(&b),
 141                     buffer_len(&b))) == 1)
 142                         authenticated = 1;
 143                 buffer_free(&b);
 144                 xfree(sig);
 145         } else {
 146                 debug("test whether pkalg/pkblob are acceptable");
 147                 packet_check_eom();
 148
 149                 /* XXX fake reply and always send PK_OK ? */
 150                 /*
 151                  * XXX this allows testing whether a user is allowed
 152                  * to login: if you happen to have a valid pubkey this
 153                  * message is sent. the message is NEVER sent at all
 154                  * if a user is not allowed to login. is this an
 155                  * issue? -markus
 156                  */
 157                 if (PRIVSEP(user_key_allowed(authctxt->pw, key))) {
 158                         packet_start(SSH2_MSG_USERAUTH_PK_OK);
 159                         packet_put_string(pkalg, alen);
 160                         packet_put_string(pkblob, blen);
 161                         packet_send();
 162                         packet_write_wait();
 163                         authctxt->postponed = 1;
 164                 }
 165         }
 166         if (authenticated != 1)
 167                 auth_clear_options();
 168 done:
 169         debug2("userauth_pubkey: authenticated %d pkalg %s", authenticated, pkalg);
 170         if (key != NULL)
 171                 key_free(key);
 172         xfree(pkalg);
 173         xfree(pkblob);
 174 #ifdef HAVE_CYGWIN
 175         if (check_nt_auth(0, authctxt->pw) == 0)
 176                 authenticated = 0;
 177 #endif
 178         return authenticated;
 179 }
 180
 181 /* return 1 if user allows given key */
 182 static int
 183 user_key_allowed2(struct passwd *pw, Key *key, char *file)
 184 {
 185         char line[SSH_MAX_PUBKEY_BYTES];
 186         int found_key = 0;
 187         FILE *f;
 188         u_long linenum = 0;
 189         Key *found;
 190         char *fp;
 191
 192         /* Temporarily use the user's uid. */
 193         temporarily_use_uid(pw);
 194
 195         debug("trying public key file %s", file);
 196         f = auth_openkeyfile(file, pw, options.strict_modes);
 197
 198         if (!f) {
 199                 restore_uid();
 200                 return 0;
 201         }
 202
 203         found_key = 0;
 204         found = key_new(key->type);
 205
 206         while (read_keyfile_line(f, file, line, sizeof(line), &linenum) != -1) {
 207                 char *cp, *key_options = NULL;
 208
 209                 /* Skip leading whitespace, empty and comment lines. */
 210                 for (cp = line; *cp == ' ' || *cp == '\t'; cp++)
 211                         ;
 212                 if (!*cp || *cp == '\n' || *cp == '#')
 213                         continue;
 214
 215                 if (key_read(found, &cp) != 1) {
 216                         /* no key?  check if there are options for this key */
 217                         int quoted = 0;
 218                         debug2("user_key_allowed: check options: '%s'", cp);
 219                         key_options = cp;
 220                         for (; *cp && (quoted || (*cp != ' ' && *cp != '\t')); cp++) {
 221                                 if (*cp == '\\' && cp[1] == '"')
 222                                         cp++;   /* Skip both */
 223                                 else if (*cp == '"')
 224                                         quoted = !quoted;
 225                         }
 226                         /* Skip remaining whitespace. */
 227                         for (; *cp == ' ' || *cp == '\t'; cp++)
 228                                 ;
 229                         if (key_read(found, &cp) != 1) {
 230                                 debug2("user_key_allowed: advance: '%s'", cp);
 231                                 /* still no key?  advance to next line*/
 232                                 continue;
 233                         }
 234                 }
 235                 if (key_equal(found, key) &&
 236                     auth_parse_options(pw, key_options, file, linenum) == 1) {
 237                         found_key = 1;
 238                         debug("matching key found: file %s, line %lu",
 239                             file, linenum);
 240                         fp = key_fingerprint(found, SSH_FP_MD5, SSH_FP_HEX);
 241                         verbose("Found matching %s key: %s",
 242                             key_type(found), fp);
 243                         xfree(fp);
 244                         break;
 245                 }
 246         }
 247         restore_uid();
 248         fclose(f);
 249         key_free(found);
 250         if (!found_key)
 251                 debug2("key not found");
 252         return found_key;
 253 }
 254
 255 /* check whether given key is in .ssh/authorized_keys* */
 256 int
 257 user_key_allowed(struct passwd *pw, Key *key)
 258 {
 259         char *fp;
 260         int success;
 261         char *file;
 262
 263         if (blacklisted_key(key)) {
 264                 fp = key_fingerprint(key, SSH_FP_MD5, SSH_FP_HEX);
 265                 if (options.permit_blacklisted_keys)
 266                         logit("Public key %s blacklisted (see "
 267                             "ssh-vulnkey(1)); continuing anyway", fp);
 268                 else
 269                         logit("Public key %s blacklisted (see "
 270                             "ssh-vulnkey(1))", fp);
 271                 xfree(fp);
 272                 if (!options.permit_blacklisted_keys)
 273                         return 0;
 274         }
 275
 276         file = authorized_keys_file(pw);
 277         success = user_key_allowed2(pw, key, file);
 278         xfree(file);
 279         if (success)
 280                 return success;
 281
 282         /* try suffix "2" for backward compat, too */
 283         file = authorized_keys_file2(pw);
 284         success = user_key_allowed2(pw, key, file);
 285         xfree(file);
 286         return success;
 287 }
 288
 289 Authmethod method_pubkey = {
 290         "publickey",
 291         userauth_pubkey,
 292         &options.pubkey_authentication
 293 };