hostfile.c

   1 /* $OpenBSD: hostfile.c,v 1.48 2010/03/04 10:36:03 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
  60 static int
  61 extract_salt(const char *s, u_int l, char *salt, size_t salt_len)
  62 {
  63         char *p, *b64salt;
  64         u_int b64len;
  65         int ret;
  66
  67         if (l < sizeof(HASH_MAGIC) - 1) {
  68                 debug2("extract_salt: string too short");
  69                 return (-1);
  70         }
  71         if (strncmp(s, HASH_MAGIC, sizeof(HASH_MAGIC) - 1) != 0) {
  72                 debug2("extract_salt: invalid magic identifier");
  73                 return (-1);
  74         }
  75         s += sizeof(HASH_MAGIC) - 1;
  76         l -= sizeof(HASH_MAGIC) - 1;
  77         if ((p = memchr(s, HASH_DELIM, l)) == NULL) {
  78                 debug2("extract_salt: missing salt termination character");
  79                 return (-1);
  80         }
  81
  82         b64len = p - s;
  83         /* Sanity check */
  84         if (b64len == 0 || b64len > 1024) {
  85                 debug2("extract_salt: bad encoded salt length %u", b64len);
  86                 return (-1);
  87         }
  88         b64salt = xmalloc(1 + b64len);
  89         memcpy(b64salt, s, b64len);
  90         b64salt[b64len] = '\0';
  91
  92         ret = __b64_pton(b64salt, salt, salt_len);
  93         xfree(b64salt);
  94         if (ret == -1) {
  95                 debug2("extract_salt: salt decode error");
  96                 return (-1);
  97         }
  98         if (ret != SHA_DIGEST_LENGTH) {
  99                 debug2("extract_salt: expected salt len %d, got %d",
 100                     SHA_DIGEST_LENGTH, ret);
 101                 return (-1);
 102         }
 103
 104         return (0);
 105 }
 106
 107 char *
 108 host_hash(const char *host, const char *name_from_hostfile, u_int src_len)
 109 {
 110         const EVP_MD *md = EVP_sha1();
 111         HMAC_CTX mac_ctx;
 112         char salt[256], result[256], uu_salt[512], uu_result[512];
 113         static char encoded[1024];
 114         u_int i, len;
 115
 116         len = EVP_MD_size(md);
 117
 118         if (name_from_hostfile == NULL) {
 119                 /* Create new salt */
 120                 for (i = 0; i < len; i++)
 121                         salt[i] = arc4random();
 122         } else {
 123                 /* Extract salt from known host entry */
 124                 if (extract_salt(name_from_hostfile, src_len, salt,
 125                     sizeof(salt)) == -1)
 126                         return (NULL);
 127         }
 128
 129         HMAC_Init(&mac_ctx, salt, len, md);
 130         HMAC_Update(&mac_ctx, host, strlen(host));
 131         HMAC_Final(&mac_ctx, result, NULL);
 132         HMAC_cleanup(&mac_ctx);
 133
 134         if (__b64_ntop(salt, len, uu_salt, sizeof(uu_salt)) == -1 ||
 135             __b64_ntop(result, len, uu_result, sizeof(uu_result)) == -1)
 136                 fatal("host_hash: __b64_ntop failed");
 137
 138         snprintf(encoded, sizeof(encoded), "%s%s%c%s", HASH_MAGIC, uu_salt,
 139             HASH_DELIM, uu_result);
 140
 141         return (encoded);
 142 }
 143
 144 /*
 145  * Parses an RSA (number of bits, e, n) or DSA key from a string.  Moves the
 146  * pointer over the key.  Skips any whitespace at the beginning and at end.
 147  */
 148
 149 int
 150 hostfile_read_key(char **cpp, u_int *bitsp, Key *ret)
 151 {
 152         char *cp;
 153
 154         /* Skip leading whitespace. */
 155         for (cp = *cpp; *cp == ' ' || *cp == '\t'; cp++)
 156                 ;
 157
 158         if (key_read(ret, &cp) != 1)
 159                 return 0;
 160
 161         /* Skip trailing whitespace. */
 162         for (; *cp == ' ' || *cp == '\t'; cp++)
 163                 ;
 164
 165         /* Return results. */
 166         *cpp = cp;
 167         *bitsp = key_size(ret);
 168         return 1;
 169 }
 170
 171 static int
 172 hostfile_check_key(int bits, const Key *key, const char *host, const char *filename, int linenum)
 173 {
 174         if (key == NULL || key->type != KEY_RSA1 || key->rsa == NULL)
 175                 return 1;
 176         if (bits != BN_num_bits(key->rsa->n)) {
 177                 logit("Warning: %s, line %d: keysize mismatch for host %s: "
 178                     "actual %d vs. announced %d.",
 179                     filename, linenum, host, BN_num_bits(key->rsa->n), bits);
 180                 logit("Warning: replace %d with %d in %s, line %d.",
 181                     bits, BN_num_bits(key->rsa->n), filename, linenum);
 182         }
 183         return 1;
 184 }
 185
 186 static enum { MRK_ERROR, MRK_NONE, MRK_REVOKE, MRK_CA }
 187 check_markers(char **cpp)
 188 {
 189         char marker[32], *sp, *cp = *cpp;
 190         int ret = MRK_NONE;
 191
 192         while (*cp == '@') {
 193                 /* Only one marker is allowed */
 194                 if (ret != MRK_NONE)
 195                         return MRK_ERROR;
 196                 /* Markers are terminated by whitespace */
 197                 if ((sp = strchr(cp, ' ')) == NULL &&
 198                     (sp = strchr(cp, '\t')) == NULL)
 199                         return MRK_ERROR;
 200                 /* Extract marker for comparison */
 201                 if (sp <= cp + 1 || sp >= cp + sizeof(marker))
 202                         return MRK_ERROR;
 203                 memcpy(marker, cp, sp - cp);
 204                 marker[sp - cp] = '\0';
 205                 if (strcmp(marker, CA_MARKER) == 0)
 206                         ret = MRK_CA;
 207                 else if (strcmp(marker, REVOKE_MARKER) == 0)
 208                         ret = MRK_REVOKE;
 209                 else
 210                         return MRK_ERROR;
 211
 212                 /* Skip past marker and any whitespace that follows it */
 213                 cp = sp;
 214                 for (; *cp == ' ' || *cp == '\t'; cp++)
 215                         ;
 216         }
 217         *cpp = cp;
 218         return ret;
 219 }
 220
 221 /*
 222  * Checks whether the given host (which must be in all lowercase) is already
 223  * in the list of our known hosts. Returns HOST_OK if the host is known and
 224  * has the specified key, HOST_NEW if the host is not known, and HOST_CHANGED
 225  * if the host is known but used to have a different host key.
 226  *
 227  * If no 'key' has been specified and a key of type 'keytype' is known
 228  * for the specified host, then HOST_FOUND is returned.
 229  */
 230
 231 static HostStatus
 232 check_host_in_hostfile_by_key_or_type(const char *filename,
 233     const char *host, const Key *key, int keytype, Key *found,
 234     int want_revocation, int *numret)
 235 {
 236         FILE *f;
 237         char line[8192];
 238         int want, have, linenum = 0, want_cert = key_is_cert(key);
 239         u_int kbits;
 240         char *cp, *cp2, *hashed_host;
 241         HostStatus end_return;
 242
 243         debug3("check_host_in_hostfile: host %s filename %s", host, filename);
 244
 245         if (want_revocation && (key == NULL || keytype != 0 || found != NULL))
 246                 fatal("%s: invalid arguments", __func__);
 247
 248         /* Open the file containing the list of known hosts. */
 249         f = fopen(filename, "r");
 250         if (!f)
 251                 return HOST_NEW;
 252
 253         /*
 254          * Return value when the loop terminates.  This is set to
 255          * HOST_CHANGED if we have seen a different key for the host and have
 256          * not found the proper one.
 257          */
 258         end_return = HOST_NEW;
 259
 260         /* Go through the file. */
 261         while (fgets(line, sizeof(line), f)) {
 262                 cp = line;
 263                 linenum++;
 264
 265                 /* Skip any leading whitespace, comments and empty lines. */
 266                 for (; *cp == ' ' || *cp == '\t'; cp++)
 267                         ;
 268                 if (!*cp || *cp == '#' || *cp == '\n')
 269                         continue;
 270
 271                 if (want_revocation)
 272                         want = MRK_REVOKE;
 273                 else if (want_cert)
 274                         want = MRK_CA;
 275                 else
 276                         want = MRK_NONE;
 277
 278                 if ((have = check_markers(&cp)) == MRK_ERROR) {
 279                         verbose("%s: invalid marker at %s:%d",
 280                             __func__, filename, linenum);
 281                         continue;
 282                 } else if (want != have)
 283                         continue;
 284
 285                 /* Find the end of the host name portion. */
 286                 for (cp2 = cp; *cp2 && *cp2 != ' ' && *cp2 != '\t'; cp2++)
 287                         ;
 288
 289                 /* Check if the host name matches. */
 290                 if (match_hostname(host, cp, (u_int) (cp2 - cp)) != 1) {
 291                         if (*cp != HASH_DELIM)
 292                                 continue;
 293                         hashed_host = host_hash(host, cp, (u_int) (cp2 - cp));
 294                         if (hashed_host == NULL) {
 295                                 debug("Invalid hashed host line %d of %s",
 296                                     linenum, filename);
 297                                 continue;
 298                         }
 299                         if (strncmp(hashed_host, cp, (u_int) (cp2 - cp)) != 0)
 300                                 continue;
 301                 }
 302
 303                 /* Got a match.  Skip host name. */
 304                 cp = cp2;
 305
 306                 if (want_revocation)
 307                         found = key_new(KEY_UNSPEC);
 308
 309                 /*
 310                  * Extract the key from the line.  This will skip any leading
 311                  * whitespace.  Ignore badly formatted lines.
 312                  */
 313                 if (!hostfile_read_key(&cp, &kbits, found))
 314                         continue;
 315
 316                 if (numret != NULL)
 317                         *numret = linenum;
 318
 319                 if (key == NULL) {
 320                         /* we found a key of the requested type */
 321                         if (found->type == keytype) {
 322                                 fclose(f);
 323                                 return HOST_FOUND;
 324                         }
 325                         continue;
 326                 }
 327
 328                 if (!hostfile_check_key(kbits, found, host, filename, linenum))
 329                         continue;
 330
 331                 if (want_revocation) {
 332                         if (key_is_cert(key) &&
 333                             key_equal_public(key->cert->signature_key, found)) {
 334                                 verbose("check_host_in_hostfile: revoked CA "
 335                                     "line %d", linenum);
 336                                 key_free(found);
 337                                 return HOST_REVOKED;
 338                         }
 339                         if (key_equal_public(key, found)) {
 340                                 verbose("check_host_in_hostfile: revoked key "
 341                                     "line %d", linenum);
 342                                 key_free(found);
 343                                 return HOST_REVOKED;
 344                         }
 345                         key_free(found);
 346                         continue;
 347                 }
 348
 349                 /* Check if the current key is the same as the given key. */
 350                 if (want_cert && key_equal(key->cert->signature_key, found)) {
 351                         /* Found CA cert for key */
 352                         debug3("check_host_in_hostfile: CA match line %d",
 353                             linenum);
 354                         fclose(f);
 355                         return HOST_OK;
 356                 } else if (!want_cert && key_equal(key, found)) {
 357                         /* Found identical key */
 358                         debug3("check_host_in_hostfile: match line %d", linenum);
 359                         fclose(f);
 360                         return HOST_OK;
 361                 }
 362                 /*
 363                  * They do not match.  We will continue to go through the
 364                  * file; however, we note that we will not return that it is
 365                  * new.
 366                  */
 367                 end_return = HOST_CHANGED;
 368         }
 369         /* Clear variables and close the file. */
 370         fclose(f);
 371
 372         /*
 373          * Return either HOST_NEW or HOST_CHANGED, depending on whether we
 374          * saw a different key for the host.
 375          */
 376         return end_return;
 377 }
 378
 379 HostStatus
 380 check_host_in_hostfile(const char *filename, const char *host, const Key *key,
 381     Key *found, int *numret)
 382 {
 383         if (key == NULL)
 384                 fatal("no key to look up");
 385         if (check_host_in_hostfile_by_key_or_type(filename, host,
 386             key, 0, NULL, 1, NULL) == HOST_REVOKED)
 387                 return HOST_REVOKED;
 388         return check_host_in_hostfile_by_key_or_type(filename, host, key, 0,
 389             found, 0, numret);
 390 }
 391
 392 int
 393 lookup_key_in_hostfile_by_type(const char *filename, const char *host,
 394     int keytype, Key *found, int *numret)
 395 {
 396         return (check_host_in_hostfile_by_key_or_type(filename, host, NULL,
 397             keytype, found, 0, numret) == HOST_FOUND);
 398 }
 399
 400 /*
 401  * Appends an entry to the host file.  Returns false if the entry could not
 402  * be appended.
 403  */
 404
 405 int
 406 add_host_to_hostfile(const char *filename, const char *host, const Key *key,
 407     int store_hash)
 408 {
 409         FILE *f;
 410         int success = 0;
 411         char *hashed_host = NULL;
 412
 413         if (key == NULL)
 414                 return 1;       /* XXX ? */
 415         f = fopen(filename, "a");
 416         if (!f)
 417                 return 0;
 418
 419         if (store_hash) {
 420                 if ((hashed_host = host_hash(host, NULL, 0)) == NULL) {
 421                         error("add_host_to_hostfile: host_hash failed");
 422                         fclose(f);
 423                         return 0;
 424                 }
 425         }
 426         fprintf(f, "%s ", store_hash ? hashed_host : host);
 427
 428         if (key_write(key, f)) {
 429                 success = 1;
 430         } else {
 431                 error("add_host_to_hostfile: saving key in %s failed", filename);
 432         }
 433         fprintf(f, "\n");
 434         fclose(f);
 435         return success;
 436 }