hostfile.c

   1 /* $OpenBSD: hostfile.c,v 1.46 2009/10/11 23:03:15 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 /*
 187  * Checks whether the given host (which must be in all lowercase) is already
 188  * in the list of our known hosts. Returns HOST_OK if the host is known and
 189  * has the specified key, HOST_NEW if the host is not known, and HOST_CHANGED
 190  * if the host is known but used to have a different host key.
 191  *
 192  * If no 'key' has been specified and a key of type 'keytype' is known
 193  * for the specified host, then HOST_FOUND is returned.
 194  */
 195
 196 static HostStatus
 197 check_host_in_hostfile_by_key_or_type(const char *filename,
 198     const char *host, const Key *key, int keytype, Key *found, int *numret)
 199 {
 200         FILE *f;
 201         char line[8192];
 202         int linenum = 0;
 203         u_int kbits;
 204         char *cp, *cp2, *hashed_host;
 205         HostStatus end_return;
 206
 207         debug3("check_host_in_hostfile: host %s filename %s", host, filename);
 208
 209         /* Open the file containing the list of known hosts. */
 210         f = fopen(filename, "r");
 211         if (!f)
 212                 return HOST_NEW;
 213
 214         /*
 215          * Return value when the loop terminates.  This is set to
 216          * HOST_CHANGED if we have seen a different key for the host and have
 217          * not found the proper one.
 218          */
 219         end_return = HOST_NEW;
 220
 221         /* Go through the file. */
 222         while (fgets(line, sizeof(line), f)) {
 223                 cp = line;
 224                 linenum++;
 225
 226                 /* Skip any leading whitespace, comments and empty lines. */
 227                 for (; *cp == ' ' || *cp == '\t'; cp++)
 228                         ;
 229                 if (!*cp || *cp == '#' || *cp == '\n')
 230                         continue;
 231
 232                 /* Find the end of the host name portion. */
 233                 for (cp2 = cp; *cp2 && *cp2 != ' ' && *cp2 != '\t'; cp2++)
 234                         ;
 235
 236                 /* Check if the host name matches. */
 237                 if (match_hostname(host, cp, (u_int) (cp2 - cp)) != 1) {
 238                         if (*cp != HASH_DELIM)
 239                                 continue;
 240                         hashed_host = host_hash(host, cp, (u_int) (cp2 - cp));
 241                         if (hashed_host == NULL) {
 242                                 debug("Invalid hashed host line %d of %s",
 243                                     linenum, filename);
 244                                 continue;
 245                         }
 246                         if (strncmp(hashed_host, cp, (u_int) (cp2 - cp)) != 0)
 247                                 continue;
 248                 }
 249
 250                 /* Got a match.  Skip host name. */
 251                 cp = cp2;
 252
 253                 /*
 254                  * Extract the key from the line.  This will skip any leading
 255                  * whitespace.  Ignore badly formatted lines.
 256                  */
 257                 if (!hostfile_read_key(&cp, &kbits, found))
 258                         continue;
 259
 260                 if (numret != NULL)
 261                         *numret = linenum;
 262
 263                 if (key == NULL) {
 264                         /* we found a key of the requested type */
 265                         if (found->type == keytype) {
 266                                 fclose(f);
 267                                 return HOST_FOUND;
 268                         }
 269                         continue;
 270                 }
 271
 272                 if (!hostfile_check_key(kbits, found, host, filename, linenum))
 273                         continue;
 274
 275                 /* Check if the current key is the same as the given key. */
 276                 if (key_equal(key, found)) {
 277                         /* Ok, they match. */
 278                         debug3("check_host_in_hostfile: match line %d", linenum);
 279                         fclose(f);
 280                         return HOST_OK;
 281                 }
 282                 /*
 283                  * They do not match.  We will continue to go through the
 284                  * file; however, we note that we will not return that it is
 285                  * new.
 286                  */
 287                 end_return = HOST_CHANGED;
 288         }
 289         /* Clear variables and close the file. */
 290         fclose(f);
 291
 292         /*
 293          * Return either HOST_NEW or HOST_CHANGED, depending on whether we
 294          * saw a different key for the host.
 295          */
 296         return end_return;
 297 }
 298
 299 HostStatus
 300 check_host_in_hostfile(const char *filename, const char *host, const Key *key,
 301     Key *found, int *numret)
 302 {
 303         if (key == NULL)
 304                 fatal("no key to look up");
 305         return (check_host_in_hostfile_by_key_or_type(filename, host, key, 0,
 306             found, numret));
 307 }
 308
 309 int
 310 lookup_key_in_hostfile_by_type(const char *filename, const char *host,
 311     int keytype, Key *found, int *numret)
 312 {
 313         return (check_host_in_hostfile_by_key_or_type(filename, host, NULL,
 314             keytype, found, numret) == HOST_FOUND);
 315 }
 316
 317 /*
 318  * Appends an entry to the host file.  Returns false if the entry could not
 319  * be appended.
 320  */
 321
 322 int
 323 add_host_to_hostfile(const char *filename, const char *host, const Key *key,
 324     int store_hash)
 325 {
 326         FILE *f;
 327         int success = 0;
 328         char *hashed_host = NULL;
 329
 330         if (key == NULL)
 331                 return 1;       /* XXX ? */
 332         f = fopen(filename, "a");
 333         if (!f)
 334                 return 0;
 335
 336         if (store_hash) {
 337                 if ((hashed_host = host_hash(host, NULL, 0)) == NULL) {
 338                         error("add_host_to_hostfile: host_hash failed");
 339                         fclose(f);
 340                         return 0;
 341                 }
 342         }
 343         fprintf(f, "%s ", store_hash ? hashed_host : host);
 344
 345         if (key_write(key, f)) {
 346                 success = 1;
 347         } else {
 348                 error("add_host_to_hostfile: saving key in %s failed", filename);
 349         }
 350         fprintf(f, "\n");
 351         fclose(f);
 352         return success;
 353 }