crypto/openssh-5/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 "authfile.h"
  46 #include "auth.h"
  47 #include "pathnames.h"
  48 #include "uidswap.h"
  49 #include "auth-options.h"
  50 #include "canohost.h"
  51 #ifdef GSSAPI
  52 #include "ssh-gss.h"
  53 #endif
  54 #include "monitor_wrap.h"
  55 #include "misc.h"
  56
  57 /* import */
  58 extern ServerOptions options;
  59 extern u_char *session_id2;
  60 extern u_int session_id2_len;
  61
  62 static int
  63 userauth_pubkey(Authctxt *authctxt)
  64 {
  65         Buffer b;
  66         Key *key = NULL;
  67         char *pkalg;
  68         u_char *pkblob, *sig;
  69         u_int alen, blen, slen;
  70         int have_sig, pktype;
  71         int authenticated = 0;
  72
  73         if (!authctxt->valid) {
  74                 debug2("userauth_pubkey: disabled because of invalid user");
  75                 return 0;
  76         }
  77         have_sig = packet_get_char();
  78         if (datafellows & SSH_BUG_PKAUTH) {
  79                 debug2("userauth_pubkey: SSH_BUG_PKAUTH");
  80                 /* no explicit pkalg given */
  81                 pkblob = packet_get_string(&blen);
  82                 buffer_init(&b);
  83                 buffer_append(&b, pkblob, blen);
  84                 /* so we have to extract the pkalg from the pkblob */
  85                 pkalg = buffer_get_string(&b, &alen);
  86                 buffer_free(&b);
  87         } else {
  88                 pkalg = packet_get_string(&alen);
  89                 pkblob = packet_get_string(&blen);
  90         }
  91         pktype = key_type_from_name(pkalg);
  92         if (pktype == KEY_UNSPEC) {
  93                 /* this is perfectly legal */
  94                 logit("userauth_pubkey: unsupported public key algorithm: %s",
  95                     pkalg);
  96                 goto done;
  97         }
  98         key = key_from_blob(pkblob, blen);
  99         if (key == NULL) {
 100                 error("userauth_pubkey: cannot decode key: %s", pkalg);
 101                 goto done;
 102         }
 103         if (key->type != pktype) {
 104                 error("userauth_pubkey: type mismatch for decoded key "
 105                     "(received %d, expected %d)", key->type, pktype);
 106                 goto done;
 107         }
 108         if (have_sig) {
 109                 sig = packet_get_string(&slen);
 110                 packet_check_eom();
 111                 buffer_init(&b);
 112                 if (datafellows & SSH_OLD_SESSIONID) {
 113                         buffer_append(&b, session_id2, session_id2_len);
 114                 } else {
 115                         buffer_put_string(&b, session_id2, session_id2_len);
 116                 }
 117                 /* reconstruct packet */
 118                 buffer_put_char(&b, SSH2_MSG_USERAUTH_REQUEST);
 119                 buffer_put_cstring(&b, authctxt->user);
 120                 buffer_put_cstring(&b,
 121                     datafellows & SSH_BUG_PKSERVICE ?
 122                     "ssh-userauth" :
 123                     authctxt->service);
 124                 if (datafellows & SSH_BUG_PKAUTH) {
 125                         buffer_put_char(&b, have_sig);
 126                 } else {
 127                         buffer_put_cstring(&b, "publickey");
 128                         buffer_put_char(&b, have_sig);
 129                         buffer_put_cstring(&b, pkalg);
 130                 }
 131                 buffer_put_string(&b, pkblob, blen);
 132 #ifdef DEBUG_PK
 133                 buffer_dump(&b);
 134 #endif
 135                 /* test for correct signature */
 136                 authenticated = 0;
 137                 if (PRIVSEP(user_key_allowed(authctxt->pw, key)) &&
 138                     PRIVSEP(key_verify(key, sig, slen, buffer_ptr(&b),
 139                     buffer_len(&b))) == 1)
 140                         authenticated = 1;
 141                 buffer_free(&b);
 142                 xfree(sig);
 143         } else {
 144                 debug("test whether pkalg/pkblob are acceptable");
 145                 packet_check_eom();
 146
 147                 /* XXX fake reply and always send PK_OK ? */
 148                 /*
 149                  * XXX this allows testing whether a user is allowed
 150                  * to login: if you happen to have a valid pubkey this
 151                  * message is sent. the message is NEVER sent at all
 152                  * if a user is not allowed to login. is this an
 153                  * issue? -markus
 154                  */
 155                 if (PRIVSEP(user_key_allowed(authctxt->pw, key))) {
 156                         packet_start(SSH2_MSG_USERAUTH_PK_OK);
 157                         packet_put_string(pkalg, alen);
 158                         packet_put_string(pkblob, blen);
 159                         packet_send();
 160                         packet_write_wait();
 161                         authctxt->postponed = 1;
 162                 }
 163         }
 164         if (authenticated != 1)
 165                 auth_clear_options();
 166 done:
 167         debug2("userauth_pubkey: authenticated %d pkalg %s", authenticated, pkalg);
 168         if (key != NULL)
 169                 key_free(key);
 170         xfree(pkalg);
 171         xfree(pkblob);
 172 #ifdef HAVE_CYGWIN
 173         if (check_nt_auth(0, authctxt->pw) == 0)
 174                 authenticated = 0;
 175 #endif
 176         return authenticated;
 177 }
 178
 179 /* return 1 if user allows given key */
 180 static int
 181 user_key_allowed2(struct passwd *pw, Key *key, char *file)
 182 {
 183         char line[SSH_MAX_PUBKEY_BYTES];
 184         int found_key = 0;
 185         FILE *f;
 186         u_long linenum = 0;
 187         struct stat st;
 188         Key *found;
 189         char *fp;
 190
 191         /* Temporarily use the user's uid. */
 192         temporarily_use_uid(pw);
 193
 194         debug("trying public key file %s", file);
 195
 196         /* Fail quietly if file does not exist */
 197         if (stat(file, &st) < 0) {
 198                 /* Restore the privileged uid. */
 199                 restore_uid();
 200                 return 0;
 201         }
 202         /* Open the file containing the authorized keys. */
 203         f = fopen(file, "r");
 204         if (!f) {
 205                 /* Restore the privileged uid. */
 206                 restore_uid();
 207                 return 0;
 208         }
 209         if (options.strict_modes &&
 210             secure_filename(f, file, pw, line, sizeof(line)) != 0) {
 211                 fclose(f);
 212                 logit("Authentication refused: %s", line);
 213                 restore_uid();
 214                 return 0;
 215         }
 216
 217         found_key = 0;
 218         found = key_new(key->type);
 219
 220         while (read_keyfile_line(f, file, line, sizeof(line), &linenum) != -1) {
 221                 char *cp, *key_options = NULL;
 222
 223                 /* Skip leading whitespace, empty and comment lines. */
 224                 for (cp = line; *cp == ' ' || *cp == '\t'; cp++)
 225                         ;
 226                 if (!*cp || *cp == '\n' || *cp == '#')
 227                         continue;
 228
 229                 if (key_read(found, &cp) != 1) {
 230                         /* no key?  check if there are options for this key */
 231                         int quoted = 0;
 232                         debug2("user_key_allowed: check options: '%s'", cp);
 233                         key_options = cp;
 234                         for (; *cp && (quoted || (*cp != ' ' && *cp != '\t')); cp++) {
 235                                 if (*cp == '\\' && cp[1] == '"')
 236                                         cp++;   /* Skip both */
 237                                 else if (*cp == '"')
 238                                         quoted = !quoted;
 239                         }
 240                         /* Skip remaining whitespace. */
 241                         for (; *cp == ' ' || *cp == '\t'; cp++)
 242                                 ;
 243                         if (key_read(found, &cp) != 1) {
 244                                 debug2("user_key_allowed: advance: '%s'", cp);
 245                                 /* still no key?  advance to next line*/
 246                                 continue;
 247                         }
 248                 }
 249                 if (key_equal(found, key) &&
 250                     auth_parse_options(pw, key_options, file, linenum) == 1) {
 251                         found_key = 1;
 252                         debug("matching key found: file %s, line %lu",
 253                             file, linenum);
 254                         fp = key_fingerprint(found, SSH_FP_MD5, SSH_FP_HEX);
 255                         verbose("Found matching %s key: %s",
 256                             key_type(found), fp);
 257                         xfree(fp);
 258                         break;
 259                 }
 260         }
 261         restore_uid();
 262         fclose(f);
 263         key_free(found);
 264         if (!found_key)
 265                 debug2("key not found");
 266         return found_key;
 267 }
 268
 269 /* check whether given key is in .ssh/authorized_keys* */
 270 int
 271 user_key_allowed(struct passwd *pw, Key *key)
 272 {
 273         char *fp;
 274         int success;
 275         char *file;
 276
 277         if (blacklisted_key(key)) {
 278                 fp = key_fingerprint(key, SSH_FP_MD5, SSH_FP_HEX);
 279                 if (options.permit_blacklisted_keys)
 280                         logit("Public key %s blacklisted (see "
 281                             "ssh-vulnkey(1)); continuing anyway", fp);
 282                 else
 283                         logit("Public key %s blacklisted (see "
 284                             "ssh-vulnkey(1))", fp);
 285                 xfree(fp);
 286                 if (!options.permit_blacklisted_keys)
 287                         return 0;
 288         }
 289
 290         file = authorized_keys_file(pw);
 291         success = user_key_allowed2(pw, key, file);
 292         xfree(file);
 293         if (success)
 294                 return success;
 295
 296         /* try suffix "2" for backward compat, too */
 297         file = authorized_keys_file2(pw);
 298         success = user_key_allowed2(pw, key, file);
 299         xfree(file);
 300         return success;
 301 }
 302
 303 Authmethod method_pubkey = {
 304         "publickey",
 305         userauth_pubkey,
 306         &options.pubkey_authentication
 307 };