auth2-pubkey.c

   1 /* $OpenBSD: auth2-pubkey.c,v 1.22 2010/03/10 23:27:17 djm 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 <string.h>
  36 #include <time.h>
  37 #include <unistd.h>
  38
  39 #include "xmalloc.h"
  40 #include "ssh.h"
  41 #include "ssh2.h"
  42 #include "packet.h"
  43 #include "buffer.h"
  44 #include "log.h"
  45 #include "servconf.h"
  46 #include "compat.h"
  47 #include "key.h"
  48 #include "hostfile.h"
  49 #include "auth.h"
  50 #include "pathnames.h"
  51 #include "uidswap.h"
  52 #include "auth-options.h"
  53 #include "canohost.h"
  54 #ifdef GSSAPI
  55 #include "ssh-gss.h"
  56 #endif
  57 #include "monitor_wrap.h"
  58 #include "misc.h"
  59 #include "authfile.h"
  60
  61 /* import */
  62 extern ServerOptions options;
  63 extern u_char *session_id2;
  64 extern u_int session_id2_len;
  65
  66 static int
  67 userauth_pubkey(Authctxt *authctxt)
  68 {
  69         Buffer b;
  70         Key *key = NULL;
  71         char *pkalg;
  72         u_char *pkblob, *sig;
  73         u_int alen, blen, slen;
  74         int have_sig, pktype;
  75         int authenticated = 0;
  76
  77         if (!authctxt->valid) {
  78                 debug2("userauth_pubkey: disabled because of invalid user");
  79                 return 0;
  80         }
  81         have_sig = packet_get_char();
  82         if (datafellows & SSH_BUG_PKAUTH) {
  83                 debug2("userauth_pubkey: SSH_BUG_PKAUTH");
  84                 /* no explicit pkalg given */
  85                 pkblob = packet_get_string(&blen);
  86                 buffer_init(&b);
  87                 buffer_append(&b, pkblob, blen);
  88                 /* so we have to extract the pkalg from the pkblob */
  89                 pkalg = buffer_get_string(&b, &alen);
  90                 buffer_free(&b);
  91         } else {
  92                 pkalg = packet_get_string(&alen);
  93                 pkblob = packet_get_string(&blen);
  94         }
  95         pktype = key_type_from_name(pkalg);
  96         if (pktype == KEY_UNSPEC) {
  97                 /* this is perfectly legal */
  98                 logit("userauth_pubkey: unsupported public key algorithm: %s",
  99                     pkalg);
 100                 goto done;
 101         }
 102         key = key_from_blob(pkblob, blen);
 103         if (key == NULL) {
 104                 error("userauth_pubkey: cannot decode key: %s", pkalg);
 105                 goto done;
 106         }
 107         if (key->type != pktype) {
 108                 error("userauth_pubkey: type mismatch for decoded key "
 109                     "(received %d, expected %d)", key->type, pktype);
 110                 goto done;
 111         }
 112         if (have_sig) {
 113                 sig = packet_get_string(&slen);
 114                 packet_check_eom();
 115                 buffer_init(&b);
 116                 if (datafellows & SSH_OLD_SESSIONID) {
 117                         buffer_append(&b, session_id2, session_id2_len);
 118                 } else {
 119                         buffer_put_string(&b, session_id2, session_id2_len);
 120                 }
 121                 /* reconstruct packet */
 122                 buffer_put_char(&b, SSH2_MSG_USERAUTH_REQUEST);
 123                 buffer_put_cstring(&b, authctxt->user);
 124                 buffer_put_cstring(&b,
 125                     datafellows & SSH_BUG_PKSERVICE ?
 126                     "ssh-userauth" :
 127                     authctxt->service);
 128                 if (datafellows & SSH_BUG_PKAUTH) {
 129                         buffer_put_char(&b, have_sig);
 130                 } else {
 131                         buffer_put_cstring(&b, "publickey");
 132                         buffer_put_char(&b, have_sig);
 133                         buffer_put_cstring(&b, pkalg);
 134                 }
 135                 buffer_put_string(&b, pkblob, blen);
 136 #ifdef DEBUG_PK
 137                 buffer_dump(&b);
 138 #endif
 139                 /* test for correct signature */
 140                 authenticated = 0;
 141                 if (PRIVSEP(user_key_allowed(authctxt->pw, key)) &&
 142                     PRIVSEP(key_verify(key, sig, slen, buffer_ptr(&b),
 143                     buffer_len(&b))) == 1)
 144                         authenticated = 1;
 145                 buffer_free(&b);
 146                 xfree(sig);
 147         } else {
 148                 debug("test whether pkalg/pkblob are acceptable");
 149                 packet_check_eom();
 150
 151                 /* XXX fake reply and always send PK_OK ? */
 152                 /*
 153                  * XXX this allows testing whether a user is allowed
 154                  * to login: if you happen to have a valid pubkey this
 155                  * message is sent. the message is NEVER sent at all
 156                  * if a user is not allowed to login. is this an
 157                  * issue? -markus
 158                  */
 159                 if (PRIVSEP(user_key_allowed(authctxt->pw, key))) {
 160                         packet_start(SSH2_MSG_USERAUTH_PK_OK);
 161                         packet_put_string(pkalg, alen);
 162                         packet_put_string(pkblob, blen);
 163                         packet_send();
 164                         packet_write_wait();
 165                         authctxt->postponed = 1;
 166                 }
 167         }
 168         if (authenticated != 1)
 169                 auth_clear_options();
 170 done:
 171         debug2("userauth_pubkey: authenticated %d pkalg %s", authenticated, pkalg);
 172         if (key != NULL)
 173                 key_free(key);
 174         xfree(pkalg);
 175         xfree(pkblob);
 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         const char *reason;
 185         int found_key = 0;
 186         FILE *f;
 187         u_long linenum = 0;
 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         f = auth_openkeyfile(file, pw, options.strict_modes);
 196
 197         if (!f) {
 198                 restore_uid();
 199                 return 0;
 200         }
 201
 202         found_key = 0;
 203         found = key_new(key_is_cert(key) ? KEY_UNSPEC : key->type);
 204
 205         while (read_keyfile_line(f, file, line, sizeof(line), &linenum) != -1) {
 206                 char *cp, *key_options = NULL;
 207
 208                 auth_clear_options();
 209
 210                 /* Skip leading whitespace, empty and comment lines. */
 211                 for (cp = line; *cp == ' ' || *cp == '\t'; cp++)
 212                         ;
 213                 if (!*cp || *cp == '\n' || *cp == '#')
 214                         continue;
 215
 216                 if (key_read(found, &cp) != 1) {
 217                         /* no key?  check if there are options for this key */
 218                         int quoted = 0;
 219                         debug2("user_key_allowed: check options: '%s'", cp);
 220                         key_options = cp;
 221                         for (; *cp && (quoted || (*cp != ' ' && *cp != '\t')); cp++) {
 222                                 if (*cp == '\\' && cp[1] == '"')
 223                                         cp++;   /* Skip both */
 224                                 else if (*cp == '"')
 225                                         quoted = !quoted;
 226                         }
 227                         /* Skip remaining whitespace. */
 228                         for (; *cp == ' ' || *cp == '\t'; cp++)
 229                                 ;
 230                         if (key_read(found, &cp) != 1) {
 231                                 debug2("user_key_allowed: advance: '%s'", cp);
 232                                 /* still no key?  advance to next line*/
 233                                 continue;
 234                         }
 235                 }
 236                 if (auth_parse_options(pw, key_options, file, linenum) != 1)
 237                         continue;
 238                 if (key->type == KEY_RSA_CERT || key->type == KEY_DSA_CERT) {
 239                         if (!key_is_cert_authority)
 240                                 continue;
 241                         if (!key_equal(found, key->cert->signature_key))
 242                                 continue;
 243                         fp = key_fingerprint(found, SSH_FP_MD5,
 244                             SSH_FP_HEX);
 245                         debug("matching CA found: file %s, line %lu, %s %s",
 246                             file, linenum, key_type(found), fp);
 247                         if (key_cert_check_authority(key, 0, 0, pw->pw_name,
 248                             &reason) != 0) {
 249                                 xfree(fp);
 250                                 error("%s", reason);
 251                                 auth_debug_add("%s", reason);
 252                                 continue;
 253                         }
 254                         if (auth_cert_constraints(&key->cert->constraints,
 255                             pw) != 0) {
 256                                 xfree(fp);
 257                                 continue;
 258                         }
 259                         verbose("Accepted certificate ID \"%s\" "
 260                             "signed by %s CA %s via %s", key->cert->key_id,
 261                             key_type(found), fp, file);
 262                         xfree(fp);
 263                         found_key = 1;
 264                         break;
 265                 } else if (!key_is_cert_authority && key_equal(found, key)) {
 266                         found_key = 1;
 267                         debug("matching key found: file %s, line %lu",
 268                             file, linenum);
 269                         fp = key_fingerprint(found, SSH_FP_MD5, SSH_FP_HEX);
 270                         verbose("Found matching %s key: %s",
 271                             key_type(found), fp);
 272                         xfree(fp);
 273                         break;
 274                 }
 275         }
 276         restore_uid();
 277         fclose(f);
 278         key_free(found);
 279         if (!found_key)
 280                 debug2("key not found");
 281         return found_key;
 282 }
 283
 284 /* Authenticate a certificate key against TrustedUserCAKeys */
 285 static int
 286 user_cert_trusted_ca(struct passwd *pw, Key *key)
 287 {
 288         char *ca_fp;
 289         const char *reason;
 290         int ret = 0;
 291
 292         if (!key_is_cert(key) || options.trusted_user_ca_keys == NULL)
 293                 return 0;
 294
 295         ca_fp = key_fingerprint(key->cert->signature_key,
 296             SSH_FP_MD5, SSH_FP_HEX);
 297
 298         if (key_in_file(key->cert->signature_key,
 299             options.trusted_user_ca_keys, 1) != 1) {
 300                 debug2("%s: CA %s %s is not listed in %s", __func__,
 301                     key_type(key->cert->signature_key), ca_fp,
 302                     options.trusted_user_ca_keys);
 303                 goto out;
 304         }
 305         if (key_cert_check_authority(key, 0, 1, pw->pw_name, &reason) != 0) {
 306                 error("%s", reason);
 307                 auth_debug_add("%s", reason);
 308                 goto out;
 309         }
 310         if (auth_cert_constraints(&key->cert->constraints, pw) != 0)
 311                 goto out;
 312
 313         verbose("Accepted certificate ID \"%s\" signed by %s CA %s via %s",
 314             key->cert->key_id, key_type(key->cert->signature_key), ca_fp,
 315             options.trusted_user_ca_keys);
 316         ret = 1;
 317
 318  out:
 319         if (ca_fp != NULL)
 320                 xfree(ca_fp);
 321         return ret;
 322 }
 323
 324 /* check whether given key is in .ssh/authorized_keys* */
 325 int
 326 user_key_allowed(struct passwd *pw, Key *key)
 327 {
 328         int success;
 329         char *file;
 330
 331         if (auth_key_is_revoked(key))
 332                 return 0;
 333         if (key_is_cert(key) && auth_key_is_revoked(key->cert->signature_key))
 334                 return 0;
 335
 336         success = user_cert_trusted_ca(pw, key);
 337         if (success)
 338                 return success;
 339
 340         file = authorized_keys_file(pw);
 341         success = user_key_allowed2(pw, key, file);
 342         xfree(file);
 343         if (success)
 344                 return success;
 345
 346         /* try suffix "2" for backward compat, too */
 347         file = authorized_keys_file2(pw);
 348         success = user_key_allowed2(pw, key, file);
 349         xfree(file);
 350         return success;
 351 }
 352
 353 Authmethod method_pubkey = {
 354         "publickey",
 355         userauth_pubkey,
 356         &options.pubkey_authentication
 357 };