hostfile.c

   1 /* $OpenBSD: hostfile.c,v 1.49 2010/11/29 23:45:51 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 <openssl/hmac.h>
  46 #include <openssl/sha.h>
  47
  48 #include <resolv.h>
  49 #include <stdarg.h>
  50 #include <stdio.h>
  51 #include <stdlib.h>
  52 #include <string.h>
  53
  54 #include "xmalloc.h"
  55 #include "match.h"
  56 #include "key.h"
  57 #include "hostfile.h"
  58 #include "log.h"
  59 #include "misc.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, 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         xfree(b64salt);
 100         if (ret == -1) {
 101                 debug2("extract_salt: salt decode error");
 102                 return (-1);
 103         }
 104         if (ret != SHA_DIGEST_LENGTH) {
 105                 debug2("extract_salt: expected salt len %d, got %d",
 106                     SHA_DIGEST_LENGTH, 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         const EVP_MD *md = EVP_sha1();
 117         HMAC_CTX mac_ctx;
 118         char salt[256], result[256], uu_salt[512], uu_result[512];
 119         static char encoded[1024];
 120         u_int i, len;
 121
 122         len = EVP_MD_size(md);
 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         HMAC_Init(&mac_ctx, salt, len, md);
 136         HMAC_Update(&mac_ctx, host, strlen(host));
 137         HMAC_Final(&mac_ctx, result, NULL);
 138         HMAC_cleanup(&mac_ctx);
 139
 140         if (__b64_ntop(salt, len, uu_salt, sizeof(uu_salt)) == -1 ||
 141             __b64_ntop(result, len, uu_result, sizeof(uu_result)) == -1)
 142                 fatal("host_hash: __b64_ntop failed");
 143
 144         snprintf(encoded, sizeof(encoded), "%s%s%c%s", HASH_MAGIC, uu_salt,
 145             HASH_DELIM, uu_result);
 146
 147         return (encoded);
 148 }
 149
 150 /*
 151  * Parses an RSA (number of bits, e, n) or DSA key from a string.  Moves the
 152  * pointer over the key.  Skips any whitespace at the beginning and at end.
 153  */
 154
 155 int
 156 hostfile_read_key(char **cpp, u_int *bitsp, Key *ret)
 157 {
 158         char *cp;
 159
 160         /* Skip leading whitespace. */
 161         for (cp = *cpp; *cp == ' ' || *cp == '\t'; cp++)
 162                 ;
 163
 164         if (key_read(ret, &cp) != 1)
 165                 return 0;
 166
 167         /* Skip trailing whitespace. */
 168         for (; *cp == ' ' || *cp == '\t'; cp++)
 169                 ;
 170
 171         /* Return results. */
 172         *cpp = cp;
 173         if (bitsp != NULL)
 174                 *bitsp = key_size(ret);
 175         return 1;
 176 }
 177
 178 static int
 179 hostfile_check_key(int bits, const Key *key, const char *host,
 180     const char *filename, u_long linenum)
 181 {
 182         if (key == NULL || key->type != KEY_RSA1 || key->rsa == NULL)
 183                 return 1;
 184         if (bits != BN_num_bits(key->rsa->n)) {
 185                 logit("Warning: %s, line %lu: keysize mismatch for host %s: "
 186                     "actual %d vs. announced %d.",
 187                     filename, linenum, host, BN_num_bits(key->rsa->n), bits);
 188                 logit("Warning: replace %d with %d in %s, line %lu.",
 189                     bits, BN_num_bits(key->rsa->n), filename, linenum);
 190         }
 191         return 1;
 192 }
 193
 194 static HostkeyMarker
 195 check_markers(char **cpp)
 196 {
 197         char marker[32], *sp, *cp = *cpp;
 198         int ret = MRK_NONE;
 199
 200         while (*cp == '@') {
 201                 /* Only one marker is allowed */
 202                 if (ret != MRK_NONE)
 203                         return MRK_ERROR;
 204                 /* Markers are terminated by whitespace */
 205                 if ((sp = strchr(cp, ' ')) == NULL &&
 206                     (sp = strchr(cp, '\t')) == NULL)
 207                         return MRK_ERROR;
 208                 /* Extract marker for comparison */
 209                 if (sp <= cp + 1 || sp >= cp + sizeof(marker))
 210                         return MRK_ERROR;
 211                 memcpy(marker, cp, sp - cp);
 212                 marker[sp - cp] = '\0';
 213                 if (strcmp(marker, CA_MARKER) == 0)
 214                         ret = MRK_CA;
 215                 else if (strcmp(marker, REVOKE_MARKER) == 0)
 216                         ret = MRK_REVOKE;
 217                 else
 218                         return MRK_ERROR;
 219
 220                 /* Skip past marker and any whitespace that follows it */
 221                 cp = sp;
 222                 for (; *cp == ' ' || *cp == '\t'; cp++)
 223                         ;
 224         }
 225         *cpp = cp;
 226         return ret;
 227 }
 228
 229 struct hostkeys *
 230 init_hostkeys(void)
 231 {
 232         struct hostkeys *ret = xcalloc(1, sizeof(*ret));
 233
 234         ret->entries = NULL;
 235         return ret;
 236 }
 237
 238 void
 239 load_hostkeys(struct hostkeys *hostkeys, const char *host, const char *path)
 240 {
 241         FILE *f;
 242         char line[8192];
 243         u_long linenum = 0, num_loaded = 0;
 244         char *cp, *cp2, *hashed_host;
 245         HostkeyMarker marker;
 246         Key *key;
 247         int kbits;
 248
 249         if ((f = fopen(path, "r")) == NULL)
 250                 return;
 251         debug3("%s: loading entries for host \"%.100s\" from file \"%s\"",
 252             __func__, host, path);
 253         while (read_keyfile_line(f, path, line, sizeof(line), &linenum) == 0) {
 254                 cp = line;
 255
 256                 /* Skip any leading whitespace, comments and empty lines. */
 257                 for (; *cp == ' ' || *cp == '\t'; cp++)
 258                         ;
 259                 if (!*cp || *cp == '#' || *cp == '\n')
 260                         continue;
 261
 262                 if ((marker = check_markers(&cp)) == MRK_ERROR) {
 263                         verbose("%s: invalid marker at %s:%lu",
 264                             __func__, path, linenum);
 265                         continue;
 266                 }
 267
 268                 /* Find the end of the host name portion. */
 269                 for (cp2 = cp; *cp2 && *cp2 != ' ' && *cp2 != '\t'; cp2++)
 270                         ;
 271
 272                 /* Check if the host name matches. */
 273                 if (match_hostname(host, cp, (u_int) (cp2 - cp)) != 1) {
 274                         if (*cp != HASH_DELIM)
 275                                 continue;
 276                         hashed_host = host_hash(host, cp, (u_int) (cp2 - cp));
 277                         if (hashed_host == NULL) {
 278                                 debug("Invalid hashed host line %lu of %s",
 279                                     linenum, path);
 280                                 continue;
 281                         }
 282                         if (strncmp(hashed_host, cp, (u_int) (cp2 - cp)) != 0)
 283                                 continue;
 284                 }
 285
 286                 /* Got a match.  Skip host name. */
 287                 cp = cp2;
 288
 289                 /*
 290                  * Extract the key from the line.  This will skip any leading
 291                  * whitespace.  Ignore badly formatted lines.
 292                  */
 293                 key = key_new(KEY_UNSPEC);
 294                 if (!hostfile_read_key(&cp, &kbits, key)) {
 295                         key_free(key);
 296                         key = key_new(KEY_RSA1);
 297                         if (!hostfile_read_key(&cp, &kbits, key)) {
 298                                 key_free(key);
 299                                 continue;
 300                         }
 301                 }
 302                 if (!hostfile_check_key(kbits, key, host, path, linenum))
 303                         continue;
 304
 305                 debug3("%s: found %skey type %s in file %s:%lu", __func__,
 306                     marker == MRK_NONE ? "" :
 307                     (marker == MRK_CA ? "ca " : "revoked "),
 308                     key_type(key), path, linenum);
 309                 hostkeys->entries = xrealloc(hostkeys->entries,
 310                     hostkeys->num_entries + 1, sizeof(*hostkeys->entries));
 311                 hostkeys->entries[hostkeys->num_entries].host = xstrdup(host);
 312                 hostkeys->entries[hostkeys->num_entries].file = xstrdup(path);
 313                 hostkeys->entries[hostkeys->num_entries].line = linenum;
 314                 hostkeys->entries[hostkeys->num_entries].key = key;
 315                 hostkeys->entries[hostkeys->num_entries].marker = marker;
 316                 hostkeys->num_entries++;
 317                 num_loaded++;
 318         }
 319         debug3("%s: loaded %lu keys", __func__, num_loaded);
 320         return;
 321 }
 322
 323 void
 324 free_hostkeys(struct hostkeys *hostkeys)
 325 {
 326         u_int i;
 327
 328         for (i = 0; i < hostkeys->num_entries; i++) {
 329                 xfree(hostkeys->entries[i].host);
 330                 xfree(hostkeys->entries[i].file);
 331                 key_free(hostkeys->entries[i].key);
 332                 bzero(hostkeys->entries + i, sizeof(*hostkeys->entries));
 333         }
 334         if (hostkeys->entries != NULL)
 335                 xfree(hostkeys->entries);
 336         hostkeys->entries = NULL;
 337         hostkeys->num_entries = 0;
 338         xfree(hostkeys);
 339 }
 340
 341 static int
 342 check_key_not_revoked(struct hostkeys *hostkeys, Key *k)
 343 {
 344         int is_cert = key_is_cert(k);
 345         u_int i;
 346
 347         for (i = 0; i < hostkeys->num_entries; i++) {
 348                 if (hostkeys->entries[i].marker != MRK_REVOKE)
 349                         continue;
 350                 if (key_equal_public(k, hostkeys->entries[i].key))
 351                         return -1;
 352                 if (is_cert &&
 353                     key_equal_public(k->cert->signature_key,
 354                     hostkeys->entries[i].key))
 355                         return -1;
 356         }
 357         return 0;
 358 }
 359
 360 /*
 361  * Match keys against a specified key, or look one up by key type.
 362  *
 363  * If looking for a keytype (key == NULL) and one is found then return
 364  * HOST_FOUND, otherwise HOST_NEW.
 365  *
 366  * If looking for a key (key != NULL):
 367  *  1. If the key is a cert and a matching CA is found, return HOST_OK
 368  *  2. If the key is not a cert and a matching key is found, return HOST_OK
 369  *  3. If no key matches but a key with a different type is found, then
 370  *     return HOST_CHANGED
 371  *  4. If no matching keys are found, then return HOST_NEW.
 372  *
 373  * Finally, check any found key is not revoked.
 374  */
 375 static HostStatus
 376 check_hostkeys_by_key_or_type(struct hostkeys *hostkeys,
 377     Key *k, int keytype, const struct hostkey_entry **found)
 378 {
 379         u_int i;
 380         HostStatus end_return = HOST_NEW;
 381         int want_cert = key_is_cert(k);
 382         HostkeyMarker want_marker = want_cert ? MRK_CA : MRK_NONE;
 383         int proto = (k ? k->type : keytype) == KEY_RSA1 ? 1 : 2;
 384
 385         if (found != NULL)
 386                 *found = NULL;
 387
 388         for (i = 0; i < hostkeys->num_entries; i++) {
 389                 if (proto == 1 && hostkeys->entries[i].key->type != KEY_RSA1)
 390                         continue;
 391                 if (proto == 2 && hostkeys->entries[i].key->type == KEY_RSA1)
 392                         continue;
 393                 if (hostkeys->entries[i].marker != want_marker)
 394                         continue;
 395                 if (k == NULL) {
 396                         if (hostkeys->entries[i].key->type != keytype)
 397                                 continue;
 398                         end_return = HOST_FOUND;
 399                         if (found != NULL)
 400                                 *found = hostkeys->entries + i;
 401                         k = hostkeys->entries[i].key;
 402                         break;
 403                 }
 404                 if (want_cert) {
 405                         if (key_equal_public(k->cert->signature_key,
 406                             hostkeys->entries[i].key)) {
 407                                 /* A matching CA exists */
 408                                 end_return = HOST_OK;
 409                                 if (found != NULL)
 410                                         *found = hostkeys->entries + i;
 411                                 break;
 412                         }
 413                 } else {
 414                         if (key_equal(k, hostkeys->entries[i].key)) {
 415                                 end_return = HOST_OK;
 416                                 if (found != NULL)
 417                                         *found = hostkeys->entries + i;
 418                                 break;
 419                         }
 420                         /* A non-maching key exists */
 421                         end_return = HOST_CHANGED;
 422                         if (found != NULL)
 423                                 *found = hostkeys->entries + i;
 424                 }
 425         }
 426         if (check_key_not_revoked(hostkeys, k) != 0) {
 427                 end_return = HOST_REVOKED;
 428                 if (found != NULL)
 429                         *found = NULL;
 430         }
 431         return end_return;
 432 }
 433
 434 HostStatus
 435 check_key_in_hostkeys(struct hostkeys *hostkeys, Key *key,
 436     const struct hostkey_entry **found)
 437 {
 438         if (key == NULL)
 439                 fatal("no key to look up");
 440         return check_hostkeys_by_key_or_type(hostkeys, key, 0, found);
 441 }
 442
 443 int
 444 lookup_key_in_hostkeys_by_type(struct hostkeys *hostkeys, int keytype,
 445     const struct hostkey_entry **found)
 446 {
 447         return (check_hostkeys_by_key_or_type(hostkeys, NULL, keytype,
 448             found) == HOST_FOUND);
 449 }
 450
 451 /*
 452  * Appends an entry to the host file.  Returns false if the entry could not
 453  * be appended.
 454  */
 455
 456 int
 457 add_host_to_hostfile(const char *filename, const char *host, const Key *key,
 458     int store_hash)
 459 {
 460         FILE *f;
 461         int success = 0;
 462         char *hashed_host = NULL;
 463
 464         if (key == NULL)
 465                 return 1;       /* XXX ? */
 466         f = fopen(filename, "a");
 467         if (!f)
 468                 return 0;
 469
 470         if (store_hash) {
 471                 if ((hashed_host = host_hash(host, NULL, 0)) == NULL) {
 472                         error("add_host_to_hostfile: host_hash failed");
 473                         fclose(f);
 474                         return 0;
 475                 }
 476         }
 477         fprintf(f, "%s ", store_hash ? hashed_host : host);
 478
 479         if (key_write(key, f)) {
 480                 success = 1;
 481         } else {
 482                 error("add_host_to_hostfile: saving key in %s failed", filename);
 483         }
 484         fprintf(f, "\n");
 485         fclose(f);
 486         return success;
 487 }