hostfile.c

   1 /* $OpenBSD: hostfile.c,v 1.42 2006/07/22 20:48:23 stevesk 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 <string.h>
  47
  48 #include <openssl/hmac.h>
  49 #include <openssl/sha.h>
  50
  51 #include "match.h"
  52 #include "key.h"
  53 #include "hostfile.h"
  54 #include "log.h"
  55 #include "xmalloc.h"
  56
  57 static int
  58 extract_salt(const char *s, u_int l, char *salt, size_t salt_len)
  59 {
  60         char *p, *b64salt;
  61         u_int b64len;
  62         int ret;
  63
  64         if (l < sizeof(HASH_MAGIC) - 1) {
  65                 debug2("extract_salt: string too short");
  66                 return (-1);
  67         }
  68         if (strncmp(s, HASH_MAGIC, sizeof(HASH_MAGIC) - 1) != 0) {
  69                 debug2("extract_salt: invalid magic identifier");
  70                 return (-1);
  71         }
  72         s += sizeof(HASH_MAGIC) - 1;
  73         l -= sizeof(HASH_MAGIC) - 1;
  74         if ((p = memchr(s, HASH_DELIM, l)) == NULL) {
  75                 debug2("extract_salt: missing salt termination character");
  76                 return (-1);
  77         }
  78
  79         b64len = p - s;
  80         /* Sanity check */
  81         if (b64len == 0 || b64len > 1024) {
  82                 debug2("extract_salt: bad encoded salt length %u", b64len);
  83                 return (-1);
  84         }
  85         b64salt = xmalloc(1 + b64len);
  86         memcpy(b64salt, s, b64len);
  87         b64salt[b64len] = '\0';
  88
  89         ret = __b64_pton(b64salt, salt, salt_len);
  90         xfree(b64salt);
  91         if (ret == -1) {
  92                 debug2("extract_salt: salt decode error");
  93                 return (-1);
  94         }
  95         if (ret != SHA_DIGEST_LENGTH) {
  96                 debug2("extract_salt: expected salt len %d, got %d",
  97                     SHA_DIGEST_LENGTH, ret);
  98                 return (-1);
  99         }
 100
 101         return (0);
 102 }
 103
 104 char *
 105 host_hash(const char *host, const char *name_from_hostfile, u_int src_len)
 106 {
 107         const EVP_MD *md = EVP_sha1();
 108         HMAC_CTX mac_ctx;
 109         char salt[256], result[256], uu_salt[512], uu_result[512];
 110         static char encoded[1024];
 111         u_int i, len;
 112
 113         len = EVP_MD_size(md);
 114
 115         if (name_from_hostfile == NULL) {
 116                 /* Create new salt */
 117                 for (i = 0; i < len; i++)
 118                         salt[i] = arc4random();
 119         } else {
 120                 /* Extract salt from known host entry */
 121                 if (extract_salt(name_from_hostfile, src_len, salt,
 122                     sizeof(salt)) == -1)
 123                         return (NULL);
 124         }
 125
 126         HMAC_Init(&mac_ctx, salt, len, md);
 127         HMAC_Update(&mac_ctx, host, strlen(host));
 128         HMAC_Final(&mac_ctx, result, NULL);
 129         HMAC_cleanup(&mac_ctx);
 130
 131         if (__b64_ntop(salt, len, uu_salt, sizeof(uu_salt)) == -1 ||
 132             __b64_ntop(result, len, uu_result, sizeof(uu_result)) == -1)
 133                 fatal("host_hash: __b64_ntop failed");
 134
 135         snprintf(encoded, sizeof(encoded), "%s%s%c%s", HASH_MAGIC, uu_salt,
 136             HASH_DELIM, uu_result);
 137
 138         return (encoded);
 139 }
 140
 141 /*
 142  * Parses an RSA (number of bits, e, n) or DSA key from a string.  Moves the
 143  * pointer over the key.  Skips any whitespace at the beginning and at end.
 144  */
 145
 146 int
 147 hostfile_read_key(char **cpp, u_int *bitsp, Key *ret)
 148 {
 149         char *cp;
 150
 151         /* Skip leading whitespace. */
 152         for (cp = *cpp; *cp == ' ' || *cp == '\t'; cp++)
 153                 ;
 154
 155         if (key_read(ret, &cp) != 1)
 156                 return 0;
 157
 158         /* Skip trailing whitespace. */
 159         for (; *cp == ' ' || *cp == '\t'; cp++)
 160                 ;
 161
 162         /* Return results. */
 163         *cpp = cp;
 164         *bitsp = key_size(ret);
 165         return 1;
 166 }
 167
 168 static int
 169 hostfile_check_key(int bits, const Key *key, const char *host, const char *filename, int linenum)
 170 {
 171         if (key == NULL || key->type != KEY_RSA1 || key->rsa == NULL)
 172                 return 1;
 173         if (bits != BN_num_bits(key->rsa->n)) {
 174                 logit("Warning: %s, line %d: keysize mismatch for host %s: "
 175                     "actual %d vs. announced %d.",
 176                     filename, linenum, host, BN_num_bits(key->rsa->n), bits);
 177                 logit("Warning: replace %d with %d in %s, line %d.",
 178                     bits, BN_num_bits(key->rsa->n), filename, linenum);
 179         }
 180         return 1;
 181 }
 182
 183 /*
 184  * Checks whether the given host (which must be in all lowercase) is already
 185  * in the list of our known hosts. Returns HOST_OK if the host is known and
 186  * has the specified key, HOST_NEW if the host is not known, and HOST_CHANGED
 187  * if the host is known but used to have a different host key.
 188  *
 189  * If no 'key' has been specified and a key of type 'keytype' is known
 190  * for the specified host, then HOST_FOUND is returned.
 191  */
 192
 193 static HostStatus
 194 check_host_in_hostfile_by_key_or_type(const char *filename,
 195     const char *host, const Key *key, int keytype, Key *found, int *numret)
 196 {
 197         FILE *f;
 198         char line[8192];
 199         int linenum = 0;
 200         u_int kbits;
 201         char *cp, *cp2, *hashed_host;
 202         HostStatus end_return;
 203
 204         debug3("check_host_in_hostfile: filename %s", filename);
 205
 206         /* Open the file containing the list of known hosts. */
 207         f = fopen(filename, "r");
 208         if (!f)
 209                 return HOST_NEW;
 210
 211         /*
 212          * Return value when the loop terminates.  This is set to
 213          * HOST_CHANGED if we have seen a different key for the host and have
 214          * not found the proper one.
 215          */
 216         end_return = HOST_NEW;
 217
 218         /* Go through the file. */
 219         while (fgets(line, sizeof(line), f)) {
 220                 cp = line;
 221                 linenum++;
 222
 223                 /* Skip any leading whitespace, comments and empty lines. */
 224                 for (; *cp == ' ' || *cp == '\t'; cp++)
 225                         ;
 226                 if (!*cp || *cp == '#' || *cp == '\n')
 227                         continue;
 228
 229                 /* Find the end of the host name portion. */
 230                 for (cp2 = cp; *cp2 && *cp2 != ' ' && *cp2 != '\t'; cp2++)
 231                         ;
 232
 233                 /* Check if the host name matches. */
 234                 if (match_hostname(host, cp, (u_int) (cp2 - cp)) != 1) {
 235                         if (*cp != HASH_DELIM)
 236                                 continue;
 237                         hashed_host = host_hash(host, cp, (u_int) (cp2 - cp));
 238                         if (hashed_host == NULL) {
 239                                 debug("Invalid hashed host line %d of %s",
 240                                     linenum, filename);
 241                                 continue;
 242                         }
 243                         if (strncmp(hashed_host, cp, (u_int) (cp2 - cp)) != 0)
 244                                 continue;
 245                 }
 246
 247                 /* Got a match.  Skip host name. */
 248                 cp = cp2;
 249
 250                 /*
 251                  * Extract the key from the line.  This will skip any leading
 252                  * whitespace.  Ignore badly formatted lines.
 253                  */
 254                 if (!hostfile_read_key(&cp, &kbits, found))
 255                         continue;
 256
 257                 if (numret != NULL)
 258                         *numret = linenum;
 259
 260                 if (key == NULL) {
 261                         /* we found a key of the requested type */
 262                         if (found->type == keytype) {
 263                                 fclose(f);
 264                                 return HOST_FOUND;
 265                         }
 266                         continue;
 267                 }
 268
 269                 if (!hostfile_check_key(kbits, found, host, filename, linenum))
 270                         continue;
 271
 272                 /* Check if the current key is the same as the given key. */
 273                 if (key_equal(key, found)) {
 274                         /* Ok, they match. */
 275                         debug3("check_host_in_hostfile: match line %d", linenum);
 276                         fclose(f);
 277                         return HOST_OK;
 278                 }
 279                 /*
 280                  * They do not match.  We will continue to go through the
 281                  * file; however, we note that we will not return that it is
 282                  * new.
 283                  */
 284                 end_return = HOST_CHANGED;
 285         }
 286         /* Clear variables and close the file. */
 287         fclose(f);
 288
 289         /*
 290          * Return either HOST_NEW or HOST_CHANGED, depending on whether we
 291          * saw a different key for the host.
 292          */
 293         return end_return;
 294 }
 295
 296 HostStatus
 297 check_host_in_hostfile(const char *filename, const char *host, const Key *key,
 298     Key *found, int *numret)
 299 {
 300         if (key == NULL)
 301                 fatal("no key to look up");
 302         return (check_host_in_hostfile_by_key_or_type(filename, host, key, 0,
 303             found, numret));
 304 }
 305
 306 int
 307 lookup_key_in_hostfile_by_type(const char *filename, const char *host,
 308     int keytype, Key *found, int *numret)
 309 {
 310         return (check_host_in_hostfile_by_key_or_type(filename, host, NULL,
 311             keytype, found, numret) == HOST_FOUND);
 312 }
 313
 314 /*
 315  * Appends an entry to the host file.  Returns false if the entry could not
 316  * be appended.
 317  */
 318
 319 int
 320 add_host_to_hostfile(const char *filename, const char *host, const Key *key,
 321     int store_hash)
 322 {
 323         FILE *f;
 324         int success = 0;
 325         char *hashed_host = NULL;
 326
 327         if (key == NULL)
 328                 return 1;       /* XXX ? */
 329         f = fopen(filename, "a");
 330         if (!f)
 331                 return 0;
 332
 333         if (store_hash) {
 334                 if ((hashed_host = host_hash(host, NULL, 0)) == NULL) {
 335                         error("add_host_to_hostfile: host_hash failed");
 336                         fclose(f);
 337                         return 0;
 338                 }
 339         }
 340         fprintf(f, "%s ", store_hash ? hashed_host : host);
 341
 342         if (key_write(key, f)) {
 343                 success = 1;
 344         } else {
 345                 error("add_host_to_hostfile: saving key in %s failed", filename);
 346         }
 347         fprintf(f, "\n");
 348         fclose(f);
 349         return success;
 350 }