hostfile.c

   1 /* $OpenBSD: hostfile.c,v 1.45 2006/08/03 03:34:42 deraadt 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 <stdio.h>
  50 #include <stdlib.h>
  51 #include <string.h>
  52
  53 #include "xmalloc.h"
  54 #include "match.h"
  55 #include "key.h"
  56 #include "hostfile.h"
  57 #include "log.h"
  58
  59 static int
  60 extract_salt(const char *s, u_int l, char *salt, size_t salt_len)
  61 {
  62         char *p, *b64salt;
  63         u_int b64len;
  64         int ret;
  65
  66         if (l < sizeof(HASH_MAGIC) - 1) {
  67                 debug2("extract_salt: string too short");
  68                 return (-1);
  69         }
  70         if (strncmp(s, HASH_MAGIC, sizeof(HASH_MAGIC) - 1) != 0) {
  71                 debug2("extract_salt: invalid magic identifier");
  72                 return (-1);
  73         }
  74         s += sizeof(HASH_MAGIC) - 1;
  75         l -= sizeof(HASH_MAGIC) - 1;
  76         if ((p = memchr(s, HASH_DELIM, l)) == NULL) {
  77                 debug2("extract_salt: missing salt termination character");
  78                 return (-1);
  79         }
  80
  81         b64len = p - s;
  82         /* Sanity check */
  83         if (b64len == 0 || b64len > 1024) {
  84                 debug2("extract_salt: bad encoded salt length %u", b64len);
  85                 return (-1);
  86         }
  87         b64salt = xmalloc(1 + b64len);
  88         memcpy(b64salt, s, b64len);
  89         b64salt[b64len] = '\0';
  90
  91         ret = __b64_pton(b64salt, salt, salt_len);
  92         xfree(b64salt);
  93         if (ret == -1) {
  94                 debug2("extract_salt: salt decode error");
  95                 return (-1);
  96         }
  97         if (ret != SHA_DIGEST_LENGTH) {
  98                 debug2("extract_salt: expected salt len %d, got %d",
  99                     SHA_DIGEST_LENGTH, ret);
 100                 return (-1);
 101         }
 102
 103         return (0);
 104 }
 105
 106 char *
 107 host_hash(const char *host, const char *name_from_hostfile, u_int src_len)
 108 {
 109         const EVP_MD *md = EVP_sha1();
 110         HMAC_CTX mac_ctx;
 111         char salt[256], result[256], uu_salt[512], uu_result[512];
 112         static char encoded[1024];
 113         u_int i, len;
 114
 115         len = EVP_MD_size(md);
 116
 117         if (name_from_hostfile == NULL) {
 118                 /* Create new salt */
 119                 for (i = 0; i < len; i++)
 120                         salt[i] = arc4random();
 121         } else {
 122                 /* Extract salt from known host entry */
 123                 if (extract_salt(name_from_hostfile, src_len, salt,
 124                     sizeof(salt)) == -1)
 125                         return (NULL);
 126         }
 127
 128         HMAC_Init(&mac_ctx, salt, len, md);
 129         HMAC_Update(&mac_ctx, host, strlen(host));
 130         HMAC_Final(&mac_ctx, result, NULL);
 131         HMAC_cleanup(&mac_ctx);
 132
 133         if (__b64_ntop(salt, len, uu_salt, sizeof(uu_salt)) == -1 ||
 134             __b64_ntop(result, len, uu_result, sizeof(uu_result)) == -1)
 135                 fatal("host_hash: __b64_ntop failed");
 136
 137         snprintf(encoded, sizeof(encoded), "%s%s%c%s", HASH_MAGIC, uu_salt,
 138             HASH_DELIM, uu_result);
 139
 140         return (encoded);
 141 }
 142
 143 /*
 144  * Parses an RSA (number of bits, e, n) or DSA key from a string.  Moves the
 145  * pointer over the key.  Skips any whitespace at the beginning and at end.
 146  */
 147
 148 int
 149 hostfile_read_key(char **cpp, u_int *bitsp, Key *ret)
 150 {
 151         char *cp;
 152
 153         /* Skip leading whitespace. */
 154         for (cp = *cpp; *cp == ' ' || *cp == '\t'; cp++)
 155                 ;
 156
 157         if (key_read(ret, &cp) != 1)
 158                 return 0;
 159
 160         /* Skip trailing whitespace. */
 161         for (; *cp == ' ' || *cp == '\t'; cp++)
 162                 ;
 163
 164         /* Return results. */
 165         *cpp = cp;
 166         *bitsp = key_size(ret);
 167         return 1;
 168 }
 169
 170 static int
 171 hostfile_check_key(int bits, const Key *key, const char *host, const char *filename, int linenum)
 172 {
 173         if (key == NULL || key->type != KEY_RSA1 || key->rsa == NULL)
 174                 return 1;
 175         if (bits != BN_num_bits(key->rsa->n)) {
 176                 logit("Warning: %s, line %d: keysize mismatch for host %s: "
 177                     "actual %d vs. announced %d.",
 178                     filename, linenum, host, BN_num_bits(key->rsa->n), bits);
 179                 logit("Warning: replace %d with %d in %s, line %d.",
 180                     bits, BN_num_bits(key->rsa->n), filename, linenum);
 181         }
 182         return 1;
 183 }
 184
 185 /*
 186  * Checks whether the given host (which must be in all lowercase) is already
 187  * in the list of our known hosts. Returns HOST_OK if the host is known and
 188  * has the specified key, HOST_NEW if the host is not known, and HOST_CHANGED
 189  * if the host is known but used to have a different host key.
 190  *
 191  * If no 'key' has been specified and a key of type 'keytype' is known
 192  * for the specified host, then HOST_FOUND is returned.
 193  */
 194
 195 static HostStatus
 196 check_host_in_hostfile_by_key_or_type(const char *filename,
 197     const char *host, const Key *key, int keytype, Key *found, int *numret)
 198 {
 199         FILE *f;
 200         char line[8192];
 201         int linenum = 0;
 202         u_int kbits;
 203         char *cp, *cp2, *hashed_host;
 204         HostStatus end_return;
 205
 206         debug3("check_host_in_hostfile: filename %s", filename);
 207
 208         /* Open the file containing the list of known hosts. */
 209         f = fopen(filename, "r");
 210         if (!f)
 211                 return HOST_NEW;
 212
 213         /*
 214          * Return value when the loop terminates.  This is set to
 215          * HOST_CHANGED if we have seen a different key for the host and have
 216          * not found the proper one.
 217          */
 218         end_return = HOST_NEW;
 219
 220         /* Go through the file. */
 221         while (fgets(line, sizeof(line), f)) {
 222                 cp = line;
 223                 linenum++;
 224
 225                 /* Skip any leading whitespace, comments and empty lines. */
 226                 for (; *cp == ' ' || *cp == '\t'; cp++)
 227                         ;
 228                 if (!*cp || *cp == '#' || *cp == '\n')
 229                         continue;
 230
 231                 /* Find the end of the host name portion. */
 232                 for (cp2 = cp; *cp2 && *cp2 != ' ' && *cp2 != '\t'; cp2++)
 233                         ;
 234
 235                 /* Check if the host name matches. */
 236                 if (match_hostname(host, cp, (u_int) (cp2 - cp)) != 1) {
 237                         if (*cp != HASH_DELIM)
 238                                 continue;
 239                         hashed_host = host_hash(host, cp, (u_int) (cp2 - cp));
 240                         if (hashed_host == NULL) {
 241                                 debug("Invalid hashed host line %d of %s",
 242                                     linenum, filename);
 243                                 continue;
 244                         }
 245                         if (strncmp(hashed_host, cp, (u_int) (cp2 - cp)) != 0)
 246                                 continue;
 247                 }
 248
 249                 /* Got a match.  Skip host name. */
 250                 cp = cp2;
 251
 252                 /*
 253                  * Extract the key from the line.  This will skip any leading
 254                  * whitespace.  Ignore badly formatted lines.
 255                  */
 256                 if (!hostfile_read_key(&cp, &kbits, found))
 257                         continue;
 258
 259                 if (numret != NULL)
 260                         *numret = linenum;
 261
 262                 if (key == NULL) {
 263                         /* we found a key of the requested type */
 264                         if (found->type == keytype) {
 265                                 fclose(f);
 266                                 return HOST_FOUND;
 267                         }
 268                         continue;
 269                 }
 270
 271                 if (!hostfile_check_key(kbits, found, host, filename, linenum))
 272                         continue;
 273
 274                 /* Check if the current key is the same as the given key. */
 275                 if (key_equal(key, found)) {
 276                         /* Ok, they match. */
 277                         debug3("check_host_in_hostfile: match line %d", linenum);
 278                         fclose(f);
 279                         return HOST_OK;
 280                 }
 281                 /*
 282                  * They do not match.  We will continue to go through the
 283                  * file; however, we note that we will not return that it is
 284                  * new.
 285                  */
 286                 end_return = HOST_CHANGED;
 287         }
 288         /* Clear variables and close the file. */
 289         fclose(f);
 290
 291         /*
 292          * Return either HOST_NEW or HOST_CHANGED, depending on whether we
 293          * saw a different key for the host.
 294          */
 295         return end_return;
 296 }
 297
 298 HostStatus
 299 check_host_in_hostfile(const char *filename, const char *host, const Key *key,
 300     Key *found, int *numret)
 301 {
 302         if (key == NULL)
 303                 fatal("no key to look up");
 304         return (check_host_in_hostfile_by_key_or_type(filename, host, key, 0,
 305             found, numret));
 306 }
 307
 308 int
 309 lookup_key_in_hostfile_by_type(const char *filename, const char *host,
 310     int keytype, Key *found, int *numret)
 311 {
 312         return (check_host_in_hostfile_by_key_or_type(filename, host, NULL,
 313             keytype, found, numret) == HOST_FOUND);
 314 }
 315
 316 /*
 317  * Appends an entry to the host file.  Returns false if the entry could not
 318  * be appended.
 319  */
 320
 321 int
 322 add_host_to_hostfile(const char *filename, const char *host, const Key *key,
 323     int store_hash)
 324 {
 325         FILE *f;
 326         int success = 0;
 327         char *hashed_host = NULL;
 328
 329         if (key == NULL)
 330                 return 1;       /* XXX ? */
 331         f = fopen(filename, "a");
 332         if (!f)
 333                 return 0;
 334
 335         if (store_hash) {
 336                 if ((hashed_host = host_hash(host, NULL, 0)) == NULL) {
 337                         error("add_host_to_hostfile: host_hash failed");
 338                         fclose(f);
 339                         return 0;
 340                 }
 341         }
 342         fprintf(f, "%s ", store_hash ? hashed_host : host);
 343
 344         if (key_write(key, f)) {
 345                 success = 1;
 346         } else {
 347                 error("add_host_to_hostfile: saving key in %s failed", filename);
 348         }
 349         fprintf(f, "\n");
 350         fclose(f);
 351         return success;
 352 }