auth2-pubkey.c

   1 /* $OpenBSD: auth2-pubkey.c,v 1.29 2011/05/23 03:30:07 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 #include "match.h"
  61
  62 /* import */
  63 extern ServerOptions options;
  64 extern u_char *session_id2;
  65 extern u_int session_id2_len;
  66
  67 static int
  68 userauth_pubkey(Authctxt *authctxt)
  69 {
  70         Buffer b;
  71         Key *key = NULL;
  72         char *pkalg;
  73         u_char *pkblob, *sig;
  74         u_int alen, blen, slen;
  75         int have_sig, pktype;
  76         int authenticated = 0;
  77
  78         if (!authctxt->valid) {
  79                 debug2("userauth_pubkey: disabled because of invalid user");
  80                 return 0;
  81         }
  82         have_sig = packet_get_char();
  83         if (datafellows & SSH_BUG_PKAUTH) {
  84                 debug2("userauth_pubkey: SSH_BUG_PKAUTH");
  85                 /* no explicit pkalg given */
  86                 pkblob = packet_get_string(&blen);
  87                 buffer_init(&b);
  88                 buffer_append(&b, pkblob, blen);
  89                 /* so we have to extract the pkalg from the pkblob */
  90                 pkalg = buffer_get_string(&b, &alen);
  91                 buffer_free(&b);
  92         } else {
  93                 pkalg = packet_get_string(&alen);
  94                 pkblob = packet_get_string(&blen);
  95         }
  96         pktype = key_type_from_name(pkalg);
  97         if (pktype == KEY_UNSPEC) {
  98                 /* this is perfectly legal */
  99                 logit("userauth_pubkey: unsupported public key algorithm: %s",
 100                     pkalg);
 101                 goto done;
 102         }
 103         key = key_from_blob(pkblob, blen);
 104         if (key == NULL) {
 105                 error("userauth_pubkey: cannot decode key: %s", pkalg);
 106                 goto done;
 107         }
 108         if (key->type != pktype) {
 109                 error("userauth_pubkey: type mismatch for decoded key "
 110                     "(received %d, expected %d)", key->type, pktype);
 111                 goto done;
 112         }
 113         if (have_sig) {
 114                 sig = packet_get_string(&slen);
 115                 packet_check_eom();
 116                 buffer_init(&b);
 117                 if (datafellows & SSH_OLD_SESSIONID) {
 118                         buffer_append(&b, session_id2, session_id2_len);
 119                 } else {
 120                         buffer_put_string(&b, session_id2, session_id2_len);
 121                 }
 122                 /* reconstruct packet */
 123                 buffer_put_char(&b, SSH2_MSG_USERAUTH_REQUEST);
 124                 buffer_put_cstring(&b, authctxt->user);
 125                 buffer_put_cstring(&b,
 126                     datafellows & SSH_BUG_PKSERVICE ?
 127                     "ssh-userauth" :
 128                     authctxt->service);
 129                 if (datafellows & SSH_BUG_PKAUTH) {
 130                         buffer_put_char(&b, have_sig);
 131                 } else {
 132                         buffer_put_cstring(&b, "publickey");
 133                         buffer_put_char(&b, have_sig);
 134                         buffer_put_cstring(&b, pkalg);
 135                 }
 136                 buffer_put_string(&b, pkblob, blen);
 137 #ifdef DEBUG_PK
 138                 buffer_dump(&b);
 139 #endif
 140                 /* test for correct signature */
 141                 authenticated = 0;
 142                 if (PRIVSEP(user_key_allowed(authctxt->pw, key)) &&
 143                     PRIVSEP(key_verify(key, sig, slen, buffer_ptr(&b),
 144                     buffer_len(&b))) == 1)
 145                         authenticated = 1;
 146                 buffer_free(&b);
 147                 xfree(sig);
 148         } else {
 149                 debug("test whether pkalg/pkblob are acceptable");
 150                 packet_check_eom();
 151
 152                 /* XXX fake reply and always send PK_OK ? */
 153                 /*
 154                  * XXX this allows testing whether a user is allowed
 155                  * to login: if you happen to have a valid pubkey this
 156                  * message is sent. the message is NEVER sent at all
 157                  * if a user is not allowed to login. is this an
 158                  * issue? -markus
 159                  */
 160                 if (PRIVSEP(user_key_allowed(authctxt->pw, key))) {
 161                         packet_start(SSH2_MSG_USERAUTH_PK_OK);
 162                         packet_put_string(pkalg, alen);
 163                         packet_put_string(pkblob, blen);
 164                         packet_send();
 165                         packet_write_wait();
 166                         authctxt->postponed = 1;
 167                 }
 168         }
 169         if (authenticated != 1)
 170                 auth_clear_options();
 171 done:
 172         debug2("userauth_pubkey: authenticated %d pkalg %s", authenticated, pkalg);
 173         if (key != NULL)
 174                 key_free(key);
 175         xfree(pkalg);
 176         xfree(pkblob);
 177         return authenticated;
 178 }
 179
 180 static int
 181 match_principals_option(const char *principal_list, struct KeyCert *cert)
 182 {
 183         char *result;
 184         u_int i;
 185
 186         /* XXX percent_expand() sequences for authorized_principals? */
 187
 188         for (i = 0; i < cert->nprincipals; i++) {
 189                 if ((result = match_list(cert->principals[i],
 190                     principal_list, NULL)) != NULL) {
 191                         debug3("matched principal from key options \"%.100s\"",
 192                             result);
 193                         xfree(result);
 194                         return 1;
 195                 }
 196         }
 197         return 0;
 198 }
 199
 200 static int
 201 match_principals_file(char *file, struct passwd *pw, struct KeyCert *cert)
 202 {
 203         FILE *f;
 204         char line[SSH_MAX_PUBKEY_BYTES], *cp, *ep, *line_opts;
 205         u_long linenum = 0;
 206         u_int i;
 207
 208         temporarily_use_uid(pw);
 209         debug("trying authorized principals file %s", file);
 210         if ((f = auth_openprincipals(file, pw, options.strict_modes)) == NULL) {
 211                 restore_uid();
 212                 return 0;
 213         }
 214         auth_start_parse_options();
 215         while (read_keyfile_line(f, file, line, sizeof(line), &linenum) != -1) {
 216                 /* Skip leading whitespace. */
 217                 for (cp = line; *cp == ' ' || *cp == '\t'; cp++)
 218                         ;
 219                 /* Skip blank and comment lines. */
 220                 if ((ep = strchr(cp, '#')) != NULL)
 221                         *ep = '\0';
 222                 if (!*cp || *cp == '\n')
 223                         continue;
 224                 /* Trim trailing whitespace. */
 225                 ep = cp + strlen(cp) - 1;
 226                 while (ep > cp && (*ep == '\n' || *ep == ' ' || *ep == '\t'))
 227                         *ep-- = '\0';
 228                 /*
 229                  * If the line has internal whitespace then assume it has
 230                  * key options.
 231                  */
 232                 line_opts = NULL;
 233                 if ((ep = strrchr(cp, ' ')) != NULL ||
 234                     (ep = strrchr(cp, '\t')) != NULL) {
 235                         for (; *ep == ' ' || *ep == '\t'; ep++)
 236                                 ;
 237                         line_opts = cp;
 238                         cp = ep;
 239                 }
 240                 for (i = 0; i < cert->nprincipals; i++) {
 241                         if (strcmp(cp, cert->principals[i]) == 0) {
 242                                 debug3("matched principal from file \"%.100s\"",
 243                                     cert->principals[i]);
 244                                 if (auth_parse_options(pw, line_opts,
 245                                     file, linenum) != 1)
 246                                         continue;
 247                                 fclose(f);
 248                                 restore_uid();
 249                                 return 1;
 250                         }
 251                 }
 252         }
 253         fclose(f);
 254         restore_uid();
 255         return 0;
 256 }
 257
 258 /* return 1 if user allows given key */
 259 static int
 260 user_key_allowed2(struct passwd *pw, Key *key, char *file)
 261 {
 262         char line[SSH_MAX_PUBKEY_BYTES];
 263         const char *reason;
 264         int found_key = 0;
 265         FILE *f;
 266         u_long linenum = 0;
 267         Key *found;
 268         char *fp;
 269
 270         /* Temporarily use the user's uid. */
 271         temporarily_use_uid(pw);
 272
 273         debug("trying public key file %s", file);
 274         f = auth_openkeyfile(file, pw, options.strict_modes);
 275
 276         if (!f) {
 277                 restore_uid();
 278                 return 0;
 279         }
 280
 281         found_key = 0;
 282         found = key_new(key_is_cert(key) ? KEY_UNSPEC : key->type);
 283
 284         auth_start_parse_options();
 285
 286         while (read_keyfile_line(f, file, line, sizeof(line), &linenum) != -1) {
 287                 char *cp, *key_options = NULL;
 288
 289                 auth_clear_options();
 290
 291                 /* Skip leading whitespace, empty and comment lines. */
 292                 for (cp = line; *cp == ' ' || *cp == '\t'; cp++)
 293                         ;
 294                 if (!*cp || *cp == '\n' || *cp == '#')
 295                         continue;
 296
 297                 if (key_read(found, &cp) != 1) {
 298                         /* no key?  check if there are options for this key */
 299                         int quoted = 0;
 300                         debug2("user_key_allowed: check options: '%s'", cp);
 301                         key_options = cp;
 302                         for (; *cp && (quoted || (*cp != ' ' && *cp != '\t')); cp++) {
 303                                 if (*cp == '\\' && cp[1] == '"')
 304                                         cp++;   /* Skip both */
 305                                 else if (*cp == '"')
 306                                         quoted = !quoted;
 307                         }
 308                         /* Skip remaining whitespace. */
 309                         for (; *cp == ' ' || *cp == '\t'; cp++)
 310                                 ;
 311                         if (key_read(found, &cp) != 1) {
 312                                 debug2("user_key_allowed: advance: '%s'", cp);
 313                                 /* still no key?  advance to next line*/
 314                                 continue;
 315                         }
 316                 }
 317                 if (key_is_cert(key)) {
 318                         if (!key_equal(found, key->cert->signature_key))
 319                                 continue;
 320                         if (auth_parse_options(pw, key_options, file,
 321                             linenum) != 1)
 322                                 continue;
 323                         if (!key_is_cert_authority)
 324                                 continue;
 325                         fp = key_fingerprint(found, SSH_FP_MD5,
 326                             SSH_FP_HEX);
 327                         debug("matching CA found: file %s, line %lu, %s %s",
 328                             file, linenum, key_type(found), fp);
 329                         /*
 330                          * If the user has specified a list of principals as
 331                          * a key option, then prefer that list to matching
 332                          * their username in the certificate principals list.
 333                          */
 334                         if (authorized_principals != NULL &&
 335                             !match_principals_option(authorized_principals,
 336                             key->cert)) {
 337                                 reason = "Certificate does not contain an "
 338                                     "authorized principal";
 339  fail_reason:
 340                                 xfree(fp);
 341                                 error("%s", reason);
 342                                 auth_debug_add("%s", reason);
 343                                 continue;
 344                         }
 345                         if (key_cert_check_authority(key, 0, 0,
 346                             authorized_principals == NULL ? pw->pw_name : NULL,
 347                             &reason) != 0)
 348                                 goto fail_reason;
 349                         if (auth_cert_options(key, pw) != 0) {
 350                                 xfree(fp);
 351                                 continue;
 352                         }
 353                         verbose("Accepted certificate ID \"%s\" "
 354                             "signed by %s CA %s via %s", key->cert->key_id,
 355                             key_type(found), fp, file);
 356                         xfree(fp);
 357                         found_key = 1;
 358                         break;
 359                 } else if (key_equal(found, key)) {
 360                         if (auth_parse_options(pw, key_options, file,
 361                             linenum) != 1)
 362                                 continue;
 363                         if (key_is_cert_authority)
 364                                 continue;
 365                         found_key = 1;
 366                         debug("matching key found: file %s, line %lu",
 367                             file, linenum);
 368                         fp = key_fingerprint(found, SSH_FP_MD5, SSH_FP_HEX);
 369                         verbose("Found matching %s key: %s",
 370                             key_type(found), fp);
 371                         xfree(fp);
 372                         break;
 373                 }
 374         }
 375         restore_uid();
 376         fclose(f);
 377         key_free(found);
 378         if (!found_key)
 379                 debug2("key not found");
 380         return found_key;
 381 }
 382
 383 /* Authenticate a certificate key against TrustedUserCAKeys */
 384 static int
 385 user_cert_trusted_ca(struct passwd *pw, Key *key)
 386 {
 387         char *ca_fp, *principals_file = NULL;
 388         const char *reason;
 389         int ret = 0;
 390
 391         if (!key_is_cert(key) || options.trusted_user_ca_keys == NULL)
 392                 return 0;
 393
 394         ca_fp = key_fingerprint(key->cert->signature_key,
 395             SSH_FP_MD5, SSH_FP_HEX);
 396
 397         if (key_in_file(key->cert->signature_key,
 398             options.trusted_user_ca_keys, 1) != 1) {
 399                 debug2("%s: CA %s %s is not listed in %s", __func__,
 400                     key_type(key->cert->signature_key), ca_fp,
 401                     options.trusted_user_ca_keys);
 402                 goto out;
 403         }
 404         /*
 405          * If AuthorizedPrincipals is in use, then compare the certificate
 406          * principals against the names in that file rather than matching
 407          * against the username.
 408          */
 409         if ((principals_file = authorized_principals_file(pw)) != NULL) {
 410                 if (!match_principals_file(principals_file, pw, key->cert)) {
 411                         reason = "Certificate does not contain an "
 412                             "authorized principal";
 413  fail_reason:
 414                         error("%s", reason);
 415                         auth_debug_add("%s", reason);
 416                         goto out;
 417                 }
 418         }
 419         if (key_cert_check_authority(key, 0, 1,
 420             principals_file == NULL ? pw->pw_name : NULL, &reason) != 0)
 421                 goto fail_reason;
 422         auth_start_parse_options();
 423         if (auth_cert_options(key, pw) != 0)
 424                 goto out;
 425
 426         verbose("Accepted certificate ID \"%s\" signed by %s CA %s via %s",
 427             key->cert->key_id, key_type(key->cert->signature_key), ca_fp,
 428             options.trusted_user_ca_keys);
 429         ret = 1;
 430
 431  out:
 432         if (principals_file != NULL)
 433                 xfree(principals_file);
 434         if (ca_fp != NULL)
 435                 xfree(ca_fp);
 436         return ret;
 437 }
 438
 439 /* check whether given key is in .ssh/authorized_keys* */
 440 int
 441 user_key_allowed(struct passwd *pw, Key *key)
 442 {
 443         u_int success, i;
 444         char *file;
 445
 446         if (auth_key_is_revoked(key, 0))
 447                 return 0;
 448         if (key_is_cert(key) &&
 449             auth_key_is_revoked(key->cert->signature_key, 0))
 450                 return 0;
 451
 452         success = user_cert_trusted_ca(pw, key);
 453         if (success)
 454                 return success;
 455
 456         for (i = 0; !success && i < options.num_authkeys_files; i++) {
 457                 file = expand_authorized_keys(
 458                     options.authorized_keys_files[i], pw);
 459                 success = user_key_allowed2(pw, key, file);
 460                 xfree(file);
 461         }
 462
 463         return success;
 464 }
 465
 466 Authmethod method_pubkey = {
 467         "publickey",
 468         userauth_pubkey,
 469         &options.pubkey_authentication
 470 };