hostfile.c

   1 /* $OpenBSD: hostfile.c,v 1.41 2006/07/05 02:42:09 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
  47 #include <openssl/hmac.h>
  48 #include <openssl/sha.h>
  49
  50 #include "match.h"
  51 #include "key.h"
  52 #include "hostfile.h"
  53 #include "log.h"
  54 #include "xmalloc.h"
  55
  56 static int
  57 extract_salt(const char *s, u_int l, char *salt, size_t salt_len)
  58 {
  59         char *p, *b64salt;
  60         u_int b64len;
  61         int ret;
  62
  63         if (l < sizeof(HASH_MAGIC) - 1) {
  64                 debug2("extract_salt: string too short");
  65                 return (-1);
  66         }
  67         if (strncmp(s, HASH_MAGIC, sizeof(HASH_MAGIC) - 1) != 0) {
  68                 debug2("extract_salt: invalid magic identifier");
  69                 return (-1);
  70         }
  71         s += sizeof(HASH_MAGIC) - 1;
  72         l -= sizeof(HASH_MAGIC) - 1;
  73         if ((p = memchr(s, HASH_DELIM, l)) == NULL) {
  74                 debug2("extract_salt: missing salt termination character");
  75                 return (-1);
  76         }
  77
  78         b64len = p - s;
  79         /* Sanity check */
  80         if (b64len == 0 || b64len > 1024) {
  81                 debug2("extract_salt: bad encoded salt length %u", b64len);
  82                 return (-1);
  83         }
  84         b64salt = xmalloc(1 + b64len);
  85         memcpy(b64salt, s, b64len);
  86         b64salt[b64len] = '\0';
  87
  88         ret = __b64_pton(b64salt, salt, salt_len);
  89         xfree(b64salt);
  90         if (ret == -1) {
  91                 debug2("extract_salt: salt decode error");
  92                 return (-1);
  93         }
  94         if (ret != SHA_DIGEST_LENGTH) {
  95                 debug2("extract_salt: expected salt len %d, got %d",
  96                     SHA_DIGEST_LENGTH, ret);
  97                 return (-1);
  98         }
  99
 100         return (0);
 101 }
 102
 103 char *
 104 host_hash(const char *host, const char *name_from_hostfile, u_int src_len)
 105 {
 106         const EVP_MD *md = EVP_sha1();
 107         HMAC_CTX mac_ctx;
 108         char salt[256], result[256], uu_salt[512], uu_result[512];
 109         static char encoded[1024];
 110         u_int i, len;
 111
 112         len = EVP_MD_size(md);
 113
 114         if (name_from_hostfile == NULL) {
 115                 /* Create new salt */
 116                 for (i = 0; i < len; i++)
 117                         salt[i] = arc4random();
 118         } else {
 119                 /* Extract salt from known host entry */
 120                 if (extract_salt(name_from_hostfile, src_len, salt,
 121                     sizeof(salt)) == -1)
 122                         return (NULL);
 123         }
 124
 125         HMAC_Init(&mac_ctx, salt, len, md);
 126         HMAC_Update(&mac_ctx, host, strlen(host));
 127         HMAC_Final(&mac_ctx, result, NULL);
 128         HMAC_cleanup(&mac_ctx);
 129
 130         if (__b64_ntop(salt, len, uu_salt, sizeof(uu_salt)) == -1 ||
 131             __b64_ntop(result, len, uu_result, sizeof(uu_result)) == -1)
 132                 fatal("host_hash: __b64_ntop failed");
 133
 134         snprintf(encoded, sizeof(encoded), "%s%s%c%s", HASH_MAGIC, uu_salt,
 135             HASH_DELIM, uu_result);
 136
 137         return (encoded);
 138 }
 139
 140 /*
 141  * Parses an RSA (number of bits, e, n) or DSA key from a string.  Moves the
 142  * pointer over the key.  Skips any whitespace at the beginning and at end.
 143  */
 144
 145 int
 146 hostfile_read_key(char **cpp, u_int *bitsp, Key *ret)
 147 {
 148         char *cp;
 149
 150         /* Skip leading whitespace. */
 151         for (cp = *cpp; *cp == ' ' || *cp == '\t'; cp++)
 152                 ;
 153
 154         if (key_read(ret, &cp) != 1)
 155                 return 0;
 156
 157         /* Skip trailing whitespace. */
 158         for (; *cp == ' ' || *cp == '\t'; cp++)
 159                 ;
 160
 161         /* Return results. */
 162         *cpp = cp;
 163         *bitsp = key_size(ret);
 164         return 1;
 165 }
 166
 167 static int
 168 hostfile_check_key(int bits, const Key *key, const char *host, const char *filename, int linenum)
 169 {
 170         if (key == NULL || key->type != KEY_RSA1 || key->rsa == NULL)
 171                 return 1;
 172         if (bits != BN_num_bits(key->rsa->n)) {
 173                 logit("Warning: %s, line %d: keysize mismatch for host %s: "
 174                     "actual %d vs. announced %d.",
 175                     filename, linenum, host, BN_num_bits(key->rsa->n), bits);
 176                 logit("Warning: replace %d with %d in %s, line %d.",
 177                     bits, BN_num_bits(key->rsa->n), filename, linenum);
 178         }
 179         return 1;
 180 }
 181
 182 /*
 183  * Checks whether the given host (which must be in all lowercase) is already
 184  * in the list of our known hosts. Returns HOST_OK if the host is known and
 185  * has the specified key, HOST_NEW if the host is not known, and HOST_CHANGED
 186  * if the host is known but used to have a different host key.
 187  *
 188  * If no 'key' has been specified and a key of type 'keytype' is known
 189  * for the specified host, then HOST_FOUND is returned.
 190  */
 191
 192 static HostStatus
 193 check_host_in_hostfile_by_key_or_type(const char *filename,
 194     const char *host, const Key *key, int keytype, Key *found, int *numret)
 195 {
 196         FILE *f;
 197         char line[8192];
 198         int linenum = 0;
 199         u_int kbits;
 200         char *cp, *cp2, *hashed_host;
 201         HostStatus end_return;
 202
 203         debug3("check_host_in_hostfile: filename %s", filename);
 204
 205         /* Open the file containing the list of known hosts. */
 206         f = fopen(filename, "r");
 207         if (!f)
 208                 return HOST_NEW;
 209
 210         /*
 211          * Return value when the loop terminates.  This is set to
 212          * HOST_CHANGED if we have seen a different key for the host and have
 213          * not found the proper one.
 214          */
 215         end_return = HOST_NEW;
 216
 217         /* Go through the file. */
 218         while (fgets(line, sizeof(line), f)) {
 219                 cp = line;
 220                 linenum++;
 221
 222                 /* Skip any leading whitespace, comments and empty lines. */
 223                 for (; *cp == ' ' || *cp == '\t'; cp++)
 224                         ;
 225                 if (!*cp || *cp == '#' || *cp == '\n')
 226                         continue;
 227
 228                 /* Find the end of the host name portion. */
 229                 for (cp2 = cp; *cp2 && *cp2 != ' ' && *cp2 != '\t'; cp2++)
 230                         ;
 231
 232                 /* Check if the host name matches. */
 233                 if (match_hostname(host, cp, (u_int) (cp2 - cp)) != 1) {
 234                         if (*cp != HASH_DELIM)
 235                                 continue;
 236                         hashed_host = host_hash(host, cp, (u_int) (cp2 - cp));
 237                         if (hashed_host == NULL) {
 238                                 debug("Invalid hashed host line %d of %s",
 239                                     linenum, filename);
 240                                 continue;
 241                         }
 242                         if (strncmp(hashed_host, cp, (u_int) (cp2 - cp)) != 0)
 243                                 continue;
 244                 }
 245
 246                 /* Got a match.  Skip host name. */
 247                 cp = cp2;
 248
 249                 /*
 250                  * Extract the key from the line.  This will skip any leading
 251                  * whitespace.  Ignore badly formatted lines.
 252                  */
 253                 if (!hostfile_read_key(&cp, &kbits, found))
 254                         continue;
 255
 256                 if (numret != NULL)
 257                         *numret = linenum;
 258
 259                 if (key == NULL) {
 260                         /* we found a key of the requested type */
 261                         if (found->type == keytype) {
 262                                 fclose(f);
 263                                 return HOST_FOUND;
 264                         }
 265                         continue;
 266                 }
 267
 268                 if (!hostfile_check_key(kbits, found, host, filename, linenum))
 269                         continue;
 270
 271                 /* Check if the current key is the same as the given key. */
 272                 if (key_equal(key, found)) {
 273                         /* Ok, they match. */
 274                         debug3("check_host_in_hostfile: match line %d", linenum);
 275                         fclose(f);
 276                         return HOST_OK;
 277                 }
 278                 /*
 279                  * They do not match.  We will continue to go through the
 280                  * file; however, we note that we will not return that it is
 281                  * new.
 282                  */
 283                 end_return = HOST_CHANGED;
 284         }
 285         /* Clear variables and close the file. */
 286         fclose(f);
 287
 288         /*
 289          * Return either HOST_NEW or HOST_CHANGED, depending on whether we
 290          * saw a different key for the host.
 291          */
 292         return end_return;
 293 }
 294
 295 HostStatus
 296 check_host_in_hostfile(const char *filename, const char *host, const Key *key,
 297     Key *found, int *numret)
 298 {
 299         if (key == NULL)
 300                 fatal("no key to look up");
 301         return (check_host_in_hostfile_by_key_or_type(filename, host, key, 0,
 302             found, numret));
 303 }
 304
 305 int
 306 lookup_key_in_hostfile_by_type(const char *filename, const char *host,
 307     int keytype, Key *found, int *numret)
 308 {
 309         return (check_host_in_hostfile_by_key_or_type(filename, host, NULL,
 310             keytype, found, numret) == HOST_FOUND);
 311 }
 312
 313 /*
 314  * Appends an entry to the host file.  Returns false if the entry could not
 315  * be appended.
 316  */
 317
 318 int
 319 add_host_to_hostfile(const char *filename, const char *host, const Key *key,
 320     int store_hash)
 321 {
 322         FILE *f;
 323         int success = 0;
 324         char *hashed_host = NULL;
 325
 326         if (key == NULL)
 327                 return 1;       /* XXX ? */
 328         f = fopen(filename, "a");
 329         if (!f)
 330                 return 0;
 331
 332         if (store_hash) {
 333                 if ((hashed_host = host_hash(host, NULL, 0)) == NULL) {
 334                         error("add_host_to_hostfile: host_hash failed");
 335                         fclose(f);
 336                         return 0;
 337                 }
 338         }
 339         fprintf(f, "%s ", store_hash ? hashed_host : host);
 340
 341         if (key_write(key, f)) {
 342                 success = 1;
 343         } else {
 344                 error("add_host_to_hostfile: saving key in %s failed", filename);
 345         }
 346         fprintf(f, "\n");
 347         fclose(f);
 348         return success;
 349 }