hostfile.c

   1 /*
   2  * Author: Tatu Ylonen <ylo@cs.hut.fi>
   3  * Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
   4  *                    All rights reserved
   5  * Functions for manipulating the known hosts files.
   6  *
   7  * As far as I am concerned, the code I have written for this software
   8  * can be used freely for any purpose.  Any derived versions of this
   9  * software must be clearly marked as such, and if the derived work is
  10  * incompatible with the protocol description in the RFC file, it must be
  11  * called by a name other than "ssh" or "Secure Shell".
  12  *
  13  *
  14  * Copyright (c) 1999, 2000 Markus Friedl.  All rights reserved.
  15  * Copyright (c) 1999 Niels Provos.  All rights reserved.
  16  *
  17  * Redistribution and use in source and binary forms, with or without
  18  * modification, are permitted provided that the following conditions
  19  * are met:
  20  * 1. Redistributions of source code must retain the above copyright
  21  *    notice, this list of conditions and the following disclaimer.
  22  * 2. Redistributions in binary form must reproduce the above copyright
  23  *    notice, this list of conditions and the following disclaimer in the
  24  *    documentation and/or other materials provided with the distribution.
  25  *
  26  * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
  27  * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
  28  * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
  29  * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
  30  * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
  31  * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
  32  * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
  33  * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
  34  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
  35  * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  36  */
  37
  38 #include "includes.h"
  39 RCSID("$OpenBSD: hostfile.c,v 1.34 2005/03/10 22:01:05 deraadt Exp $");
  40
  41 #include <resolv.h>
  42 #include <openssl/hmac.h>
  43 #include <openssl/sha.h>
  44
  45 #include "packet.h"
  46 #include "match.h"
  47 #include "key.h"
  48 #include "hostfile.h"
  49 #include "log.h"
  50 #include "xmalloc.h"
  51
  52 static int
  53 extract_salt(const char *s, u_int l, char *salt, size_t salt_len)
  54 {
  55         char *p, *b64salt;
  56         u_int b64len;
  57         int ret;
  58
  59         if (l < sizeof(HASH_MAGIC) - 1) {
  60                 debug2("extract_salt: string too short");
  61                 return (-1);
  62         }
  63         if (strncmp(s, HASH_MAGIC, sizeof(HASH_MAGIC) - 1) != 0) {
  64                 debug2("extract_salt: invalid magic identifier");
  65                 return (-1);
  66         }
  67         s += sizeof(HASH_MAGIC) - 1;
  68         l -= sizeof(HASH_MAGIC) - 1;
  69         if ((p = memchr(s, HASH_DELIM, l)) == NULL) {
  70                 debug2("extract_salt: missing salt termination character");
  71                 return (-1);
  72         }
  73
  74         b64len = p - s;
  75         /* Sanity check */
  76         if (b64len == 0 || b64len > 1024) {
  77                 debug2("extract_salt: bad encoded salt length %u", b64len);
  78                 return (-1);
  79         }
  80         b64salt = xmalloc(1 + b64len);
  81         memcpy(b64salt, s, b64len);
  82         b64salt[b64len] = '\0';
  83
  84         ret = __b64_pton(b64salt, salt, salt_len);
  85         xfree(b64salt);
  86         if (ret == -1) {
  87                 debug2("extract_salt: salt decode error");
  88                 return (-1);
  89         }
  90         if (ret != SHA_DIGEST_LENGTH) {
  91                 debug2("extract_salt: expected salt len %u, got %u",
  92                     salt_len, ret);
  93                 return (-1);
  94         }
  95
  96         return (0);
  97 }
  98
  99 char *
 100 host_hash(const char *host, const char *name_from_hostfile, u_int src_len)
 101 {
 102         const EVP_MD *md = EVP_sha1();
 103         HMAC_CTX mac_ctx;
 104         char salt[256], result[256], uu_salt[512], uu_result[512];
 105         static char encoded[1024];
 106         u_int i, len;
 107
 108         len = EVP_MD_size(md);
 109
 110         if (name_from_hostfile == NULL) {
 111                 /* Create new salt */
 112                 for (i = 0; i < len; i++)
 113                         salt[i] = arc4random();
 114         } else {
 115                 /* Extract salt from known host entry */
 116                 if (extract_salt(name_from_hostfile, src_len, salt,
 117                     sizeof(salt)) == -1)
 118                         return (NULL);
 119         }
 120
 121         HMAC_Init(&mac_ctx, salt, len, md);
 122         HMAC_Update(&mac_ctx, host, strlen(host));
 123         HMAC_Final(&mac_ctx, result, NULL);
 124         HMAC_cleanup(&mac_ctx);
 125
 126         if (__b64_ntop(salt, len, uu_salt, sizeof(uu_salt)) == -1 ||
 127             __b64_ntop(result, len, uu_result, sizeof(uu_result)) == -1)
 128                 fatal("host_hash: __b64_ntop failed");
 129
 130         snprintf(encoded, sizeof(encoded), "%s%s%c%s", HASH_MAGIC, uu_salt,
 131             HASH_DELIM, uu_result);
 132
 133         return (encoded);
 134 }
 135
 136 /*
 137  * Parses an RSA (number of bits, e, n) or DSA key from a string.  Moves the
 138  * pointer over the key.  Skips any whitespace at the beginning and at end.
 139  */
 140
 141 int
 142 hostfile_read_key(char **cpp, u_int *bitsp, Key *ret)
 143 {
 144         char *cp;
 145
 146         /* Skip leading whitespace. */
 147         for (cp = *cpp; *cp == ' ' || *cp == '\t'; cp++)
 148                 ;
 149
 150         if (key_read(ret, &cp) != 1)
 151                 return 0;
 152
 153         /* Skip trailing whitespace. */
 154         for (; *cp == ' ' || *cp == '\t'; cp++)
 155                 ;
 156
 157         /* Return results. */
 158         *cpp = cp;
 159         *bitsp = key_size(ret);
 160         return 1;
 161 }
 162
 163 static int
 164 hostfile_check_key(int bits, const Key *key, const char *host, const char *filename, int linenum)
 165 {
 166         if (key == NULL || key->type != KEY_RSA1 || key->rsa == NULL)
 167                 return 1;
 168         if (bits != BN_num_bits(key->rsa->n)) {
 169                 logit("Warning: %s, line %d: keysize mismatch for host %s: "
 170                     "actual %d vs. announced %d.",
 171                     filename, linenum, host, BN_num_bits(key->rsa->n), bits);
 172                 logit("Warning: replace %d with %d in %s, line %d.",
 173                     bits, BN_num_bits(key->rsa->n), filename, linenum);
 174         }
 175         return 1;
 176 }
 177
 178 /*
 179  * Checks whether the given host (which must be in all lowercase) is already
 180  * in the list of our known hosts. Returns HOST_OK if the host is known and
 181  * has the specified key, HOST_NEW if the host is not known, and HOST_CHANGED
 182  * if the host is known but used to have a different host key.
 183  *
 184  * If no 'key' has been specified and a key of type 'keytype' is known
 185  * for the specified host, then HOST_FOUND is returned.
 186  */
 187
 188 static HostStatus
 189 check_host_in_hostfile_by_key_or_type(const char *filename,
 190     const char *host, const Key *key, int keytype, Key *found, int *numret)
 191 {
 192         FILE *f;
 193         char line[8192];
 194         int linenum = 0;
 195         u_int kbits;
 196         char *cp, *cp2, *hashed_host;
 197         HostStatus end_return;
 198
 199         debug3("check_host_in_hostfile: filename %s", filename);
 200
 201         /* Open the file containing the list of known hosts. */
 202         f = fopen(filename, "r");
 203         if (!f)
 204                 return HOST_NEW;
 205
 206         /*
 207          * Return value when the loop terminates.  This is set to
 208          * HOST_CHANGED if we have seen a different key for the host and have
 209          * not found the proper one.
 210          */
 211         end_return = HOST_NEW;
 212
 213         /* Go through the file. */
 214         while (fgets(line, sizeof(line), f)) {
 215                 cp = line;
 216                 linenum++;
 217
 218                 /* Skip any leading whitespace, comments and empty lines. */
 219                 for (; *cp == ' ' || *cp == '\t'; cp++)
 220                         ;
 221                 if (!*cp || *cp == '#' || *cp == '\n')
 222                         continue;
 223
 224                 /* Find the end of the host name portion. */
 225                 for (cp2 = cp; *cp2 && *cp2 != ' ' && *cp2 != '\t'; cp2++)
 226                         ;
 227
 228                 /* Check if the host name matches. */
 229                 if (match_hostname(host, cp, (u_int) (cp2 - cp)) != 1) {
 230                         if (*cp != HASH_DELIM)
 231                                 continue;
 232                         hashed_host = host_hash(host, cp, (u_int) (cp2 - cp));
 233                         if (hashed_host == NULL) {
 234                                 debug("Invalid hashed host line %d of %s",
 235                                     linenum, filename);
 236                                 continue;
 237                         }
 238                         if (strncmp(hashed_host, cp, (u_int) (cp2 - cp)) != 0)
 239                                 continue;
 240                 }
 241
 242                 /* Got a match.  Skip host name. */
 243                 cp = cp2;
 244
 245                 /*
 246                  * Extract the key from the line.  This will skip any leading
 247                  * whitespace.  Ignore badly formatted lines.
 248                  */
 249                 if (!hostfile_read_key(&cp, &kbits, found))
 250                         continue;
 251
 252                 if (numret != NULL)
 253                         *numret = linenum;
 254
 255                 if (key == NULL) {
 256                         /* we found a key of the requested type */
 257                         if (found->type == keytype)
 258                                 return HOST_FOUND;
 259                         continue;
 260                 }
 261
 262                 if (!hostfile_check_key(kbits, found, host, filename, linenum))
 263                         continue;
 264
 265                 /* Check if the current key is the same as the given key. */
 266                 if (key_equal(key, found)) {
 267                         /* Ok, they match. */
 268                         debug3("check_host_in_hostfile: match line %d", linenum);
 269                         fclose(f);
 270                         return HOST_OK;
 271                 }
 272                 /*
 273                  * They do not match.  We will continue to go through the
 274                  * file; however, we note that we will not return that it is
 275                  * new.
 276                  */
 277                 end_return = HOST_CHANGED;
 278         }
 279         /* Clear variables and close the file. */
 280         fclose(f);
 281
 282         /*
 283          * Return either HOST_NEW or HOST_CHANGED, depending on whether we
 284          * saw a different key for the host.
 285          */
 286         return end_return;
 287 }
 288
 289 HostStatus
 290 check_host_in_hostfile(const char *filename, const char *host, const Key *key,
 291     Key *found, int *numret)
 292 {
 293         if (key == NULL)
 294                 fatal("no key to look up");
 295         return (check_host_in_hostfile_by_key_or_type(filename, host, key, 0,
 296             found, numret));
 297 }
 298
 299 int
 300 lookup_key_in_hostfile_by_type(const char *filename, const char *host,
 301     int keytype, Key *found, int *numret)
 302 {
 303         return (check_host_in_hostfile_by_key_or_type(filename, host, NULL,
 304             keytype, found, numret) == HOST_FOUND);
 305 }
 306
 307 /*
 308  * Appends an entry to the host file.  Returns false if the entry could not
 309  * be appended.
 310  */
 311
 312 int
 313 add_host_to_hostfile(const char *filename, const char *host, const Key *key,
 314     int store_hash)
 315 {
 316         FILE *f;
 317         int success = 0;
 318         char *hashed_host;
 319
 320         if (key == NULL)
 321                 return 1;       /* XXX ? */
 322         f = fopen(filename, "a");
 323         if (!f)
 324                 return 0;
 325
 326         if (store_hash) {
 327                 if ((hashed_host = host_hash(host, NULL, 0)) == NULL) {
 328                         error("add_host_to_hostfile: host_hash failed");
 329                         fclose(f);
 330                         return 0;
 331                 }
 332         }
 333         fprintf(f, "%s ", store_hash ? hashed_host : host);
 334
 335         if (key_write(key, f)) {
 336                 success = 1;
 337         } else {
 338                 error("add_host_to_hostfile: saving key in %s failed", filename);
 339         }
 340         fprintf(f, "\n");
 341         fclose(f);
 342         return success;
 343 }