crypto/openssh/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 "authfile.h"
  50 #include "auth.h"
  51 #include "pathnames.h"
  52 #include "uidswap.h"
  53 #include "auth-options.h"
  54 #include "canohost.h"
  55 #ifdef GSSAPI
  56 #include "ssh-gss.h"
  57 #endif
  58 #include "monitor_wrap.h"
  59 #include "misc.h"
  60 #include "authfile.h"
  61 #include "match.h"
  62
  63 /* import */
  64 extern ServerOptions options;
  65 extern u_char *session_id2;
  66 extern u_int session_id2_len;
  67
  68 static int
  69 userauth_pubkey(Authctxt *authctxt)
  70 {
  71         Buffer b;
  72         Key *key = NULL;
  73         char *pkalg;
  74         u_char *pkblob, *sig;
  75         u_int alen, blen, slen;
  76         int have_sig, pktype;
  77         int authenticated = 0;
  78
  79         if (!authctxt->valid) {
  80                 debug2("userauth_pubkey: disabled because of invalid user");
  81                 return 0;
  82         }
  83         have_sig = packet_get_char();
  84         if (datafellows & SSH_BUG_PKAUTH) {
  85                 debug2("userauth_pubkey: SSH_BUG_PKAUTH");
  86                 /* no explicit pkalg given */
  87                 pkblob = packet_get_string(&blen);
  88                 buffer_init(&b);
  89                 buffer_append(&b, pkblob, blen);
  90                 /* so we have to extract the pkalg from the pkblob */
  91                 pkalg = buffer_get_string(&b, &alen);
  92                 buffer_free(&b);
  93         } else {
  94                 pkalg = packet_get_string(&alen);
  95                 pkblob = packet_get_string(&blen);
  96         }
  97         pktype = key_type_from_name(pkalg);
  98         if (pktype == KEY_UNSPEC) {
  99                 /* this is perfectly legal */
 100                 logit("userauth_pubkey: unsupported public key algorithm: %s",
 101                     pkalg);
 102                 goto done;
 103         }
 104         key = key_from_blob(pkblob, blen);
 105         if (key == NULL) {
 106                 error("userauth_pubkey: cannot decode key: %s", pkalg);
 107                 goto done;
 108         }
 109         if (key->type != pktype) {
 110                 error("userauth_pubkey: type mismatch for decoded key "
 111                     "(received %d, expected %d)", key->type, pktype);
 112                 goto done;
 113         }
 114         if (have_sig) {
 115                 sig = packet_get_string(&slen);
 116                 packet_check_eom();
 117                 buffer_init(&b);
 118                 if (datafellows & SSH_OLD_SESSIONID) {
 119                         buffer_append(&b, session_id2, session_id2_len);
 120                 } else {
 121                         buffer_put_string(&b, session_id2, session_id2_len);
 122                 }
 123                 /* reconstruct packet */
 124                 buffer_put_char(&b, SSH2_MSG_USERAUTH_REQUEST);
 125                 buffer_put_cstring(&b, authctxt->user);
 126                 buffer_put_cstring(&b,
 127                     datafellows & SSH_BUG_PKSERVICE ?
 128                     "ssh-userauth" :
 129                     authctxt->service);
 130                 if (datafellows & SSH_BUG_PKAUTH) {
 131                         buffer_put_char(&b, have_sig);
 132                 } else {
 133                         buffer_put_cstring(&b, "publickey");
 134                         buffer_put_char(&b, have_sig);
 135                         buffer_put_cstring(&b, pkalg);
 136                 }
 137                 buffer_put_string(&b, pkblob, blen);
 138 #ifdef DEBUG_PK
 139                 buffer_dump(&b);
 140 #endif
 141                 /* test for correct signature */
 142                 authenticated = 0;
 143                 if (PRIVSEP(user_key_allowed(authctxt->pw, key)) &&
 144                     PRIVSEP(key_verify(key, sig, slen, buffer_ptr(&b),
 145                     buffer_len(&b))) == 1)
 146                         authenticated = 1;
 147                 buffer_free(&b);
 148                 xfree(sig);
 149         } else {
 150                 debug("test whether pkalg/pkblob are acceptable");
 151                 packet_check_eom();
 152
 153                 /* XXX fake reply and always send PK_OK ? */
 154                 /*
 155                  * XXX this allows testing whether a user is allowed
 156                  * to login: if you happen to have a valid pubkey this
 157                  * message is sent. the message is NEVER sent at all
 158                  * if a user is not allowed to login. is this an
 159                  * issue? -markus
 160                  */
 161                 if (PRIVSEP(user_key_allowed(authctxt->pw, key))) {
 162                         packet_start(SSH2_MSG_USERAUTH_PK_OK);
 163                         packet_put_string(pkalg, alen);
 164                         packet_put_string(pkblob, blen);
 165                         packet_send();
 166                         packet_write_wait();
 167                         authctxt->postponed = 1;
 168                 }
 169         }
 170         if (authenticated != 1)
 171                 auth_clear_options();
 172 done:
 173         debug2("userauth_pubkey: authenticated %d pkalg %s", authenticated, pkalg);
 174         if (key != NULL)
 175                 key_free(key);
 176         xfree(pkalg);
 177         xfree(pkblob);
 178         return authenticated;
 179 }
 180
 181 static int
 182 match_principals_option(const char *principal_list, struct KeyCert *cert)
 183 {
 184         char *result;
 185         u_int i;
 186
 187         /* XXX percent_expand() sequences for authorized_principals? */
 188
 189         for (i = 0; i < cert->nprincipals; i++) {
 190                 if ((result = match_list(cert->principals[i],
 191                     principal_list, NULL)) != NULL) {
 192                         debug3("matched principal from key options \"%.100s\"",
 193                             result);
 194                         xfree(result);
 195                         return 1;
 196                 }
 197         }
 198         return 0;
 199 }
 200
 201 static int
 202 match_principals_file(char *file, struct passwd *pw, struct KeyCert *cert)
 203 {
 204         FILE *f;
 205         char line[SSH_MAX_PUBKEY_BYTES], *cp, *ep, *line_opts;
 206         u_long linenum = 0;
 207         u_int i;
 208
 209         temporarily_use_uid(pw);
 210         debug("trying authorized principals file %s", file);
 211         if ((f = auth_openprincipals(file, pw, options.strict_modes)) == NULL) {
 212                 restore_uid();
 213                 return 0;
 214         }
 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         while (read_keyfile_line(f, file, line, sizeof(line), &linenum) != -1) {
 285                 char *cp, *key_options = NULL;
 286
 287                 auth_clear_options();
 288
 289                 /* Skip leading whitespace, empty and comment lines. */
 290                 for (cp = line; *cp == ' ' || *cp == '\t'; cp++)
 291                         ;
 292                 if (!*cp || *cp == '\n' || *cp == '#')
 293                         continue;
 294
 295                 if (key_read(found, &cp) != 1) {
 296                         /* no key?  check if there are options for this key */
 297                         int quoted = 0;
 298                         debug2("user_key_allowed: check options: '%s'", cp);
 299                         key_options = cp;
 300                         for (; *cp && (quoted || (*cp != ' ' && *cp != '\t')); cp++) {
 301                                 if (*cp == '\\' && cp[1] == '"')
 302                                         cp++;   /* Skip both */
 303                                 else if (*cp == '"')
 304                                         quoted = !quoted;
 305                         }
 306                         /* Skip remaining whitespace. */
 307                         for (; *cp == ' ' || *cp == '\t'; cp++)
 308                                 ;
 309                         if (key_read(found, &cp) != 1) {
 310                                 debug2("user_key_allowed: advance: '%s'", cp);
 311                                 /* still no key?  advance to next line*/
 312                                 continue;
 313                         }
 314                 }
 315                 if (key_is_cert(key)) {
 316                         if (!key_equal(found, key->cert->signature_key))
 317                                 continue;
 318                         if (auth_parse_options(pw, key_options, file,
 319                             linenum) != 1)
 320                                 continue;
 321                         if (!key_is_cert_authority)
 322                                 continue;
 323                         fp = key_fingerprint(found, SSH_FP_MD5,
 324                             SSH_FP_HEX);
 325                         debug("matching CA found: file %s, line %lu, %s %s",
 326                             file, linenum, key_type(found), fp);
 327                         /*
 328                          * If the user has specified a list of principals as
 329                          * a key option, then prefer that list to matching
 330                          * their username in the certificate principals list.
 331                          */
 332                         if (authorized_principals != NULL &&
 333                             !match_principals_option(authorized_principals,
 334                             key->cert)) {
 335                                 reason = "Certificate does not contain an "
 336                                     "authorized principal";
 337  fail_reason:
 338                                 xfree(fp);
 339                                 error("%s", reason);
 340                                 auth_debug_add("%s", reason);
 341                                 continue;
 342                         }
 343                         if (key_cert_check_authority(key, 0, 0,
 344                             authorized_principals == NULL ? pw->pw_name : NULL,
 345                             &reason) != 0)
 346                                 goto fail_reason;
 347                         if (auth_cert_options(key, pw) != 0) {
 348                                 xfree(fp);
 349                                 continue;
 350                         }
 351                         verbose("Accepted certificate ID \"%s\" "
 352                             "signed by %s CA %s via %s", key->cert->key_id,
 353                             key_type(found), fp, file);
 354                         xfree(fp);
 355                         found_key = 1;
 356                         break;
 357                 } else if (key_equal(found, key)) {
 358                         if (auth_parse_options(pw, key_options, file,
 359                             linenum) != 1)
 360                                 continue;
 361                         if (key_is_cert_authority)
 362                                 continue;
 363                         found_key = 1;
 364                         debug("matching key found: file %s, line %lu",
 365                             file, linenum);
 366                         fp = key_fingerprint(found, SSH_FP_MD5, SSH_FP_HEX);
 367                         verbose("Found matching %s key: %s",
 368                             key_type(found), fp);
 369                         xfree(fp);
 370                         break;
 371                 }
 372         }
 373         restore_uid();
 374         fclose(f);
 375         key_free(found);
 376         if (!found_key)
 377                 debug2("key not found");
 378         return found_key;
 379 }
 380
 381 /* Authenticate a certificate key against TrustedUserCAKeys */
 382 static int
 383 user_cert_trusted_ca(struct passwd *pw, Key *key)
 384 {
 385         char *ca_fp, *principals_file = NULL;
 386         const char *reason;
 387         int ret = 0;
 388
 389         if (!key_is_cert(key) || options.trusted_user_ca_keys == NULL)
 390                 return 0;
 391
 392         ca_fp = key_fingerprint(key->cert->signature_key,
 393             SSH_FP_MD5, SSH_FP_HEX);
 394
 395         if (key_in_file(key->cert->signature_key,
 396             options.trusted_user_ca_keys, 1) != 1) {
 397                 debug2("%s: CA %s %s is not listed in %s", __func__,
 398                     key_type(key->cert->signature_key), ca_fp,
 399                     options.trusted_user_ca_keys);
 400                 goto out;
 401         }
 402         /*
 403          * If AuthorizedPrincipals is in use, then compare the certificate
 404          * principals against the names in that file rather than matching
 405          * against the username.
 406          */
 407         if ((principals_file = authorized_principals_file(pw)) != NULL) {
 408                 if (!match_principals_file(principals_file, pw, key->cert)) {
 409                         reason = "Certificate does not contain an "
 410                             "authorized principal";
 411  fail_reason:
 412                         error("%s", reason);
 413                         auth_debug_add("%s", reason);
 414                         goto out;
 415                 }
 416         }
 417         if (key_cert_check_authority(key, 0, 1,
 418             principals_file == NULL ? pw->pw_name : NULL, &reason) != 0)
 419                 goto fail_reason;
 420         if (auth_cert_options(key, pw) != 0)
 421                 goto out;
 422
 423         verbose("Accepted certificate ID \"%s\" signed by %s CA %s via %s",
 424             key->cert->key_id, key_type(key->cert->signature_key), ca_fp,
 425             options.trusted_user_ca_keys);
 426         ret = 1;
 427
 428  out:
 429         if (principals_file != NULL)
 430                 xfree(principals_file);
 431         if (ca_fp != NULL)
 432                 xfree(ca_fp);
 433         return ret;
 434 }
 435
 436 /* check whether given key is in .ssh/authorized_keys* */
 437 int
 438 user_key_allowed(struct passwd *pw, Key *key)
 439 {
 440         char *fp;
 441         u_int success, i;
 442         char *file;
 443
 444         if (blacklisted_key(key)) {
 445                 fp = key_fingerprint(key, SSH_FP_MD5, SSH_FP_HEX);
 446                 if (options.permit_blacklisted_keys)
 447                         logit("Public key %s blacklisted (see "
 448                             "ssh-vulnkey(1)); continuing anyway", fp);
 449                 else
 450                         logit("Public key %s blacklisted (see "
 451                             "ssh-vulnkey(1))", fp);
 452                 xfree(fp);
 453                 if (!options.permit_blacklisted_keys)
 454                         return 0;
 455         }
 456
 457         if (auth_key_is_revoked(key))
 458                 return 0;
 459         if (key_is_cert(key) && auth_key_is_revoked(key->cert->signature_key))
 460                 return 0;
 461
 462         success = user_cert_trusted_ca(pw, key);
 463         if (success)
 464                 return success;
 465
 466         for (i = 0; !success && i < options.num_authkeys_files; i++) {
 467                 file = expand_authorized_keys(
 468                     options.authorized_keys_files[i], pw);
 469                 success = user_key_allowed2(pw, key, file);
 470                 xfree(file);
 471         }
 472
 473         return success;
 474 }
 475
 476 Authmethod method_pubkey = {
 477         "publickey",
 478         userauth_pubkey,
 479         &options.pubkey_authentication
 480 };