crypto/openssh/hostfile.c

   1 /* $OpenBSD: hostfile.c,v 1.57 2014/06/24 01:13:21 djm Exp $ */
   2 /*
   3  * Author: Tatu Ylonen <ylo@cs.hut.fi>
   4  * Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
   5  *                    All rights reserved
   6  * Functions for manipulating the known hosts files.
   7  *
   8  * As far as I am concerned, the code I have written for this software
   9  * can be used freely for any purpose.  Any derived versions of this
  10  * software must be clearly marked as such, and if the derived work is
  11  * incompatible with the protocol description in the RFC file, it must be
  12  * called by a name other than "ssh" or "Secure Shell".
  13  *
  14  *
  15  * Copyright (c) 1999, 2000 Markus Friedl.  All rights reserved.
  16  * Copyright (c) 1999 Niels Provos.  All rights reserved.
  17  *
  18  * Redistribution and use in source and binary forms, with or without
  19  * modification, are permitted provided that the following conditions
  20  * are met:
  21  * 1. Redistributions of source code must retain the above copyright
  22  *    notice, this list of conditions and the following disclaimer.
  23  * 2. Redistributions in binary form must reproduce the above copyright
  24  *    notice, this list of conditions and the following disclaimer in the
  25  *    documentation and/or other materials provided with the distribution.
  26  *
  27  * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
  28  * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
  29  * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
  30  * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
  31  * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
  32  * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
  33  * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
  34  * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
  35  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
  36  * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  37  */
  38
  39 #include "includes.h"
  40
  41 #include <sys/types.h>
  42
  43 #include <netinet/in.h>
  44
  45 #include <resolv.h>
  46 #include <stdarg.h>
  47 #include <stdio.h>
  48 #include <stdlib.h>
  49 #include <string.h>
  50 #include <stdarg.h>
  51
  52 #include "xmalloc.h"
  53 #include "match.h"
  54 #include "key.h"
  55 #include "hostfile.h"
  56 #include "log.h"
  57 #include "misc.h"
  58 #include "digest.h"
  59 #include "hmac.h"
  60
  61 struct hostkeys {
  62         struct hostkey_entry *entries;
  63         u_int num_entries;
  64 };
  65
  66 static int
  67 extract_salt(const char *s, u_int l, u_char *salt, size_t salt_len)
  68 {
  69         char *p, *b64salt;
  70         u_int b64len;
  71         int ret;
  72
  73         if (l < sizeof(HASH_MAGIC) - 1) {
  74                 debug2("extract_salt: string too short");
  75                 return (-1);
  76         }
  77         if (strncmp(s, HASH_MAGIC, sizeof(HASH_MAGIC) - 1) != 0) {
  78                 debug2("extract_salt: invalid magic identifier");
  79                 return (-1);
  80         }
  81         s += sizeof(HASH_MAGIC) - 1;
  82         l -= sizeof(HASH_MAGIC) - 1;
  83         if ((p = memchr(s, HASH_DELIM, l)) == NULL) {
  84                 debug2("extract_salt: missing salt termination character");
  85                 return (-1);
  86         }
  87
  88         b64len = p - s;
  89         /* Sanity check */
  90         if (b64len == 0 || b64len > 1024) {
  91                 debug2("extract_salt: bad encoded salt length %u", b64len);
  92                 return (-1);
  93         }
  94         b64salt = xmalloc(1 + b64len);
  95         memcpy(b64salt, s, b64len);
  96         b64salt[b64len] = '\0';
  97
  98         ret = __b64_pton(b64salt, salt, salt_len);
  99         free(b64salt);
 100         if (ret == -1) {
 101                 debug2("extract_salt: salt decode error");
 102                 return (-1);
 103         }
 104         if (ret != (int)ssh_hmac_bytes(SSH_DIGEST_SHA1)) {
 105                 debug2("extract_salt: expected salt len %zd, got %d",
 106                     ssh_hmac_bytes(SSH_DIGEST_SHA1), ret);
 107                 return (-1);
 108         }
 109
 110         return (0);
 111 }
 112
 113 char *
 114 host_hash(const char *host, const char *name_from_hostfile, u_int src_len)
 115 {
 116         struct ssh_hmac_ctx *ctx;
 117         u_char salt[256], result[256];
 118         char uu_salt[512], uu_result[512];
 119         static char encoded[1024];
 120         u_int i, len;
 121
 122         len = ssh_digest_bytes(SSH_DIGEST_SHA1);
 123
 124         if (name_from_hostfile == NULL) {
 125                 /* Create new salt */
 126                 for (i = 0; i < len; i++)
 127                         salt[i] = arc4random();
 128         } else {
 129                 /* Extract salt from known host entry */
 130                 if (extract_salt(name_from_hostfile, src_len, salt,
 131                     sizeof(salt)) == -1)
 132                         return (NULL);
 133         }
 134
 135         if ((ctx = ssh_hmac_start(SSH_DIGEST_SHA1)) == NULL ||
 136             ssh_hmac_init(ctx, salt, len) < 0 ||
 137             ssh_hmac_update(ctx, host, strlen(host)) < 0 ||
 138             ssh_hmac_final(ctx, result, sizeof(result)))
 139                 fatal("%s: ssh_hmac failed", __func__);
 140         ssh_hmac_free(ctx);
 141
 142         if (__b64_ntop(salt, len, uu_salt, sizeof(uu_salt)) == -1 ||
 143             __b64_ntop(result, len, uu_result, sizeof(uu_result)) == -1)
 144                 fatal("%s: __b64_ntop failed", __func__);
 145
 146         snprintf(encoded, sizeof(encoded), "%s%s%c%s", HASH_MAGIC, uu_salt,
 147             HASH_DELIM, uu_result);
 148
 149         return (encoded);
 150 }
 151
 152 /*
 153  * Parses an RSA (number of bits, e, n) or DSA key from a string.  Moves the
 154  * pointer over the key.  Skips any whitespace at the beginning and at end.
 155  */
 156
 157 int
 158 hostfile_read_key(char **cpp, int *bitsp, Key *ret)
 159 {
 160         char *cp;
 161
 162         /* Skip leading whitespace. */
 163         for (cp = *cpp; *cp == ' ' || *cp == '\t'; cp++)
 164                 ;
 165
 166         if (key_read(ret, &cp) != 1)
 167                 return 0;
 168
 169         /* Skip trailing whitespace. */
 170         for (; *cp == ' ' || *cp == '\t'; cp++)
 171                 ;
 172
 173         /* Return results. */
 174         *cpp = cp;
 175         if (bitsp != NULL) {
 176                 if ((*bitsp = key_size(ret)) <= 0)
 177                         return 0;
 178         }
 179         return 1;
 180 }
 181
 182 static int
 183 hostfile_check_key(int bits, const Key *key, const char *host,
 184     const char *filename, u_long linenum)
 185 {
 186 #ifdef WITH_SSH1
 187         if (key == NULL || key->type != KEY_RSA1 || key->rsa == NULL)
 188                 return 1;
 189         if (bits != BN_num_bits(key->rsa->n)) {
 190                 logit("Warning: %s, line %lu: keysize mismatch for host %s: "
 191                     "actual %d vs. announced %d.",
 192                     filename, linenum, host, BN_num_bits(key->rsa->n), bits);
 193                 logit("Warning: replace %d with %d in %s, line %lu.",
 194                     bits, BN_num_bits(key->rsa->n), filename, linenum);
 195         }
 196 #endif
 197         return 1;
 198 }
 199
 200 static HostkeyMarker
 201 check_markers(char **cpp)
 202 {
 203         char marker[32], *sp, *cp = *cpp;
 204         int ret = MRK_NONE;
 205
 206         while (*cp == '@') {
 207                 /* Only one marker is allowed */
 208                 if (ret != MRK_NONE)
 209                         return MRK_ERROR;
 210                 /* Markers are terminated by whitespace */
 211                 if ((sp = strchr(cp, ' ')) == NULL &&
 212                     (sp = strchr(cp, '\t')) == NULL)
 213                         return MRK_ERROR;
 214                 /* Extract marker for comparison */
 215                 if (sp <= cp + 1 || sp >= cp + sizeof(marker))
 216                         return MRK_ERROR;
 217                 memcpy(marker, cp, sp - cp);
 218                 marker[sp - cp] = '\0';
 219                 if (strcmp(marker, CA_MARKER) == 0)
 220                         ret = MRK_CA;
 221                 else if (strcmp(marker, REVOKE_MARKER) == 0)
 222                         ret = MRK_REVOKE;
 223                 else
 224                         return MRK_ERROR;
 225
 226                 /* Skip past marker and any whitespace that follows it */
 227                 cp = sp;
 228                 for (; *cp == ' ' || *cp == '\t'; cp++)
 229                         ;
 230         }
 231         *cpp = cp;
 232         return ret;
 233 }
 234
 235 struct hostkeys *
 236 init_hostkeys(void)
 237 {
 238         struct hostkeys *ret = xcalloc(1, sizeof(*ret));
 239
 240         ret->entries = NULL;
 241         return ret;
 242 }
 243
 244 void
 245 load_hostkeys(struct hostkeys *hostkeys, const char *host, const char *path)
 246 {
 247         FILE *f;
 248         char line[8192];
 249         u_long linenum = 0, num_loaded = 0;
 250         char *cp, *cp2, *hashed_host;
 251         HostkeyMarker marker;
 252         Key *key;
 253         int kbits;
 254
 255         if ((f = fopen(path, "r")) == NULL)
 256                 return;
 257         debug3("%s: loading entries for host \"%.100s\" from file \"%s\"",
 258             __func__, host, path);
 259         while (read_keyfile_line(f, path, line, sizeof(line), &linenum) == 0) {
 260                 cp = line;
 261
 262                 /* Skip any leading whitespace, comments and empty lines. */
 263                 for (; *cp == ' ' || *cp == '\t'; cp++)
 264                         ;
 265                 if (!*cp || *cp == '#' || *cp == '\n')
 266                         continue;
 267
 268                 if ((marker = check_markers(&cp)) == MRK_ERROR) {
 269                         verbose("%s: invalid marker at %s:%lu",
 270                             __func__, path, linenum);
 271                         continue;
 272                 }
 273
 274                 /* Find the end of the host name portion. */
 275                 for (cp2 = cp; *cp2 && *cp2 != ' ' && *cp2 != '\t'; cp2++)
 276                         ;
 277
 278                 /* Check if the host name matches. */
 279                 if (match_hostname(host, cp, (u_int) (cp2 - cp)) != 1) {
 280                         if (*cp != HASH_DELIM)
 281                                 continue;
 282                         hashed_host = host_hash(host, cp, (u_int) (cp2 - cp));
 283                         if (hashed_host == NULL) {
 284                                 debug("Invalid hashed host line %lu of %s",
 285                                     linenum, path);
 286                                 continue;
 287                         }
 288                         if (strncmp(hashed_host, cp, (u_int) (cp2 - cp)) != 0)
 289                                 continue;
 290                 }
 291
 292                 /* Got a match.  Skip host name. */
 293                 cp = cp2;
 294
 295                 /*
 296                  * Extract the key from the line.  This will skip any leading
 297                  * whitespace.  Ignore badly formatted lines.
 298                  */
 299                 key = key_new(KEY_UNSPEC);
 300                 if (!hostfile_read_key(&cp, &kbits, key)) {
 301                         key_free(key);
 302 #ifdef WITH_SSH1
 303                         key = key_new(KEY_RSA1);
 304                         if (!hostfile_read_key(&cp, &kbits, key)) {
 305                                 key_free(key);
 306                                 continue;
 307                         }
 308 #else
 309                         continue;
 310 #endif
 311                 }
 312                 if (!hostfile_check_key(kbits, key, host, path, linenum))
 313                         continue;
 314
 315                 debug3("%s: found %skey type %s in file %s:%lu", __func__,
 316                     marker == MRK_NONE ? "" :
 317                     (marker == MRK_CA ? "ca " : "revoked "),
 318                     key_type(key), path, linenum);
 319                 hostkeys->entries = xrealloc(hostkeys->entries,
 320                     hostkeys->num_entries + 1, sizeof(*hostkeys->entries));
 321                 hostkeys->entries[hostkeys->num_entries].host = xstrdup(host);
 322                 hostkeys->entries[hostkeys->num_entries].file = xstrdup(path);
 323                 hostkeys->entries[hostkeys->num_entries].line = linenum;
 324                 hostkeys->entries[hostkeys->num_entries].key = key;
 325                 hostkeys->entries[hostkeys->num_entries].marker = marker;
 326                 hostkeys->num_entries++;
 327                 num_loaded++;
 328         }
 329         debug3("%s: loaded %lu keys", __func__, num_loaded);
 330         fclose(f);
 331         return;
 332 }
 333
 334 void
 335 free_hostkeys(struct hostkeys *hostkeys)
 336 {
 337         u_int i;
 338
 339         for (i = 0; i < hostkeys->num_entries; i++) {
 340                 free(hostkeys->entries[i].host);
 341                 free(hostkeys->entries[i].file);
 342                 key_free(hostkeys->entries[i].key);
 343                 explicit_bzero(hostkeys->entries + i, sizeof(*hostkeys->entries));
 344         }
 345         free(hostkeys->entries);
 346         explicit_bzero(hostkeys, sizeof(*hostkeys));
 347         free(hostkeys);
 348 }
 349
 350 static int
 351 check_key_not_revoked(struct hostkeys *hostkeys, Key *k)
 352 {
 353         int is_cert = key_is_cert(k);
 354         u_int i;
 355
 356         for (i = 0; i < hostkeys->num_entries; i++) {
 357                 if (hostkeys->entries[i].marker != MRK_REVOKE)
 358                         continue;
 359                 if (key_equal_public(k, hostkeys->entries[i].key))
 360                         return -1;
 361                 if (is_cert &&
 362                     key_equal_public(k->cert->signature_key,
 363                     hostkeys->entries[i].key))
 364                         return -1;
 365         }
 366         return 0;
 367 }
 368
 369 /*
 370  * Match keys against a specified key, or look one up by key type.
 371  *
 372  * If looking for a keytype (key == NULL) and one is found then return
 373  * HOST_FOUND, otherwise HOST_NEW.
 374  *
 375  * If looking for a key (key != NULL):
 376  *  1. If the key is a cert and a matching CA is found, return HOST_OK
 377  *  2. If the key is not a cert and a matching key is found, return HOST_OK
 378  *  3. If no key matches but a key with a different type is found, then
 379  *     return HOST_CHANGED
 380  *  4. If no matching keys are found, then return HOST_NEW.
 381  *
 382  * Finally, check any found key is not revoked.
 383  */
 384 static HostStatus
 385 check_hostkeys_by_key_or_type(struct hostkeys *hostkeys,
 386     Key *k, int keytype, const struct hostkey_entry **found)
 387 {
 388         u_int i;
 389         HostStatus end_return = HOST_NEW;
 390         int want_cert = key_is_cert(k);
 391         HostkeyMarker want_marker = want_cert ? MRK_CA : MRK_NONE;
 392         int proto = (k ? k->type : keytype) == KEY_RSA1 ? 1 : 2;
 393
 394         if (found != NULL)
 395                 *found = NULL;
 396
 397         for (i = 0; i < hostkeys->num_entries; i++) {
 398                 if (proto == 1 && hostkeys->entries[i].key->type != KEY_RSA1)
 399                         continue;
 400                 if (proto == 2 && hostkeys->entries[i].key->type == KEY_RSA1)
 401                         continue;
 402                 if (hostkeys->entries[i].marker != want_marker)
 403                         continue;
 404                 if (k == NULL) {
 405                         if (hostkeys->entries[i].key->type != keytype)
 406                                 continue;
 407                         end_return = HOST_FOUND;
 408                         if (found != NULL)
 409                                 *found = hostkeys->entries + i;
 410                         k = hostkeys->entries[i].key;
 411                         break;
 412                 }
 413                 if (want_cert) {
 414                         if (key_equal_public(k->cert->signature_key,
 415                             hostkeys->entries[i].key)) {
 416                                 /* A matching CA exists */
 417                                 end_return = HOST_OK;
 418                                 if (found != NULL)
 419                                         *found = hostkeys->entries + i;
 420                                 break;
 421                         }
 422                 } else {
 423                         if (key_equal(k, hostkeys->entries[i].key)) {
 424                                 end_return = HOST_OK;
 425                                 if (found != NULL)
 426                                         *found = hostkeys->entries + i;
 427                                 break;
 428                         }
 429                         /* A non-maching key exists */
 430                         end_return = HOST_CHANGED;
 431                         if (found != NULL)
 432                                 *found = hostkeys->entries + i;
 433                 }
 434         }
 435         if (check_key_not_revoked(hostkeys, k) != 0) {
 436                 end_return = HOST_REVOKED;
 437                 if (found != NULL)
 438                         *found = NULL;
 439         }
 440         return end_return;
 441 }
 442
 443 HostStatus
 444 check_key_in_hostkeys(struct hostkeys *hostkeys, Key *key,
 445     const struct hostkey_entry **found)
 446 {
 447         if (key == NULL)
 448                 fatal("no key to look up");
 449         return check_hostkeys_by_key_or_type(hostkeys, key, 0, found);
 450 }
 451
 452 int
 453 lookup_key_in_hostkeys_by_type(struct hostkeys *hostkeys, int keytype,
 454     const struct hostkey_entry **found)
 455 {
 456         return (check_hostkeys_by_key_or_type(hostkeys, NULL, keytype,
 457             found) == HOST_FOUND);
 458 }
 459
 460 /*
 461  * Appends an entry to the host file.  Returns false if the entry could not
 462  * be appended.
 463  */
 464
 465 int
 466 add_host_to_hostfile(const char *filename, const char *host, const Key *key,
 467     int store_hash)
 468 {
 469         FILE *f;
 470         int success = 0;
 471         char *hashed_host = NULL;
 472
 473         if (key == NULL)
 474                 return 1;       /* XXX ? */
 475         f = fopen(filename, "a");
 476         if (!f)
 477                 return 0;
 478
 479         if (store_hash) {
 480                 if ((hashed_host = host_hash(host, NULL, 0)) == NULL) {
 481                         error("add_host_to_hostfile: host_hash failed");
 482                         fclose(f);
 483                         return 0;
 484                 }
 485         }
 486         fprintf(f, "%s ", store_hash ? hashed_host : host);
 487
 488         if (key_write(key, f)) {
 489                 success = 1;
 490         } else {
 491                 error("add_host_to_hostfile: saving key in %s failed", filename);
 492         }
 493         fprintf(f, "\n");
 494         fclose(f);
 495         return success;
 496 }