The Design and Implementation of the FreeBSD Operating System, Second Edition
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sys/geom/bde/g_bde_lock.c

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    1 /*-
    2  * Copyright (c) 2002 Poul-Henning Kamp
    3  * Copyright (c) 2002 Networks Associates Technology, Inc.
    4  * All rights reserved.
    5  *
    6  * This software was developed for the FreeBSD Project by Poul-Henning Kamp
    7  * and NAI Labs, the Security Research Division of Network Associates, Inc.
    8  * under DARPA/SPAWAR contract N66001-01-C-8035 ("CBOSS"), as part of the
    9  * DARPA CHATS research program.
   10  *
   11  * Redistribution and use in source and binary forms, with or without
   12  * modification, are permitted provided that the following conditions
   13  * are met:
   14  * 1. Redistributions of source code must retain the above copyright
   15  *    notice, this list of conditions and the following disclaimer.
   16  * 2. Redistributions in binary form must reproduce the above copyright
   17  *    notice, this list of conditions and the following disclaimer in the
   18  *    documentation and/or other materials provided with the distribution.
   19  *
   20  * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
   21  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
   22  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
   23  * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
   24  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
   25  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
   26  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
   27  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
   28  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
   29  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
   30  * SUCH DAMAGE.
   31  *
   32  * $FreeBSD: releng/10.0/sys/geom/bde/g_bde_lock.c 152966 2005-11-30 19:07:28Z sobomax $
   33  */
   34 /* This souce file contains routines which operates on the lock sectors, both
   35  * for the kernel and the userland program gbde(1).
   36  *
   37  */
   38 
   39 #include <sys/param.h>
   40 #include <sys/queue.h>
   41 #include <sys/lock.h>
   42 #include <sys/mutex.h>
   43 #include <sys/endian.h>
   44 #include <sys/md5.h>
   45 
   46 #ifdef _KERNEL
   47 #include <sys/malloc.h>
   48 #include <sys/systm.h>
   49 #else
   50 #include <err.h>
   51 #define CTASSERT(foo)
   52 #define KASSERT(foo, bar) do { if(!(foo)) { warn bar ; exit (1); } } while (0)
   53 #include <errno.h>
   54 #include <string.h>
   55 #include <stdlib.h>
   56 #include <stdio.h>
   57 #define g_free(foo)     free(foo)
   58 #endif
   59 
   60 #include <crypto/rijndael/rijndael-api-fst.h>
   61 #include <crypto/sha2/sha2.h>
   62 
   63 #include <geom/geom.h>
   64 #include <geom/bde/g_bde.h>
   65 
   66 /*
   67  * Hash the raw pass-phrase.
   68  *
   69  * Security objectives: produce from the pass-phrase a fixed length
   70  * bytesequence with PRN like properties in a reproducible way retaining
   71  * as much entropy from the pass-phrase as possible.
   72  *
   73  * SHA2-512 makes this easy.
   74  */
   75 
   76 void
   77 g_bde_hash_pass(struct g_bde_softc *sc, const void *input, u_int len)
   78 {
   79         SHA512_CTX cx;
   80 
   81         SHA512_Init(&cx);
   82         SHA512_Update(&cx, input, len);
   83         SHA512_Final(sc->sha2, &cx);
   84 }
   85 
   86 /*
   87  * Encode/Decode the lock structure in byte-sequence format.
   88  *
   89  * Security objectives: Store in pass-phrase dependent variant format.
   90  *
   91  * C-structure packing and byte-endianess depends on architecture, compiler
   92  * and compiler options.  Writing raw structures to disk is therefore a bad
   93  * idea in these enlightend days.
   94  *
   95  * We spend a fraction of the key-material on shuffling the fields around
   96  * so they will be stored in an unpredictable sequence.
   97  *
   98  * For each byte of the key-material we derive two field indexes, and swap
   99  * the position of those two fields.
  100  *
  101  * I have not worked out the statistical properties of this shuffle, but
  102  * given that the key-material has PRN properties, the primary objective
  103  * of making it hard to figure out which bits are where in the lock sector
  104  * is sufficiently fulfilled.
  105  *
  106  * We include (and shuffle) an extra hash field in the stored version for
  107  * identification and versioning purposes.  This field contains the MD5 hash
  108  * of a version identifier (currently "0000") followed by the stored lock
  109  * sector byte-sequence substituting zero bytes for the hash field.
  110  *
  111  * The stored keysequence is protected by AES/256/CBC elsewhere in the code
  112  * so the fact that the generated byte sequence has a much higher than
  113  * average density of zero bits (from the numeric fields) is not currently
  114  * a concern.
  115  *
  116  * Should this later become a concern, a simple software update and 
  117  * pass-phrase change can remedy the situation.  One possible solution 
  118  * could be to XOR the numeric fields with a key-material derived PRN.
  119  *
  120  * The chosen shuffle algorithm only works as long as we have no more than 16 
  121  * fields in the stored part of the lock structure (hence the CTASSERT below).
  122  */
  123 
  124 CTASSERT(NLOCK_FIELDS <= 16);
  125 
  126 static void
  127 g_bde_shuffle_lock(u_char *sha2, int *buf)
  128 {
  129         int j, k, l;
  130         u_int u;
  131 
  132         /* Assign the fields sequential positions */
  133         for(u = 0; u < NLOCK_FIELDS; u++)
  134                 buf[u] = u;
  135 
  136         /* Then mix it all up */
  137         for(u = 48; u < SHA512_DIGEST_LENGTH; u++) {
  138                 j = sha2[u] % NLOCK_FIELDS;
  139                 k = (sha2[u] / NLOCK_FIELDS) % NLOCK_FIELDS;
  140                 l = buf[j];
  141                 buf[j] = buf[k];
  142                 buf[k] = l;
  143         }
  144 }
  145 
  146 int
  147 g_bde_encode_lock(u_char *sha2, struct g_bde_key *gl, u_char *ptr)
  148 {
  149         int shuffle[NLOCK_FIELDS];
  150         u_char *hash, *p;
  151         int i;
  152         MD5_CTX c;
  153 
  154         p = ptr;
  155         hash = NULL;
  156         g_bde_shuffle_lock(sha2, shuffle);
  157         for (i = 0; i < NLOCK_FIELDS; i++) {
  158                 switch(shuffle[i]) {
  159                 case 0:
  160                         le64enc(p, gl->sector0);
  161                         p += 8;
  162                         break;
  163                 case 1:
  164                         le64enc(p, gl->sectorN);
  165                         p += 8;
  166                         break;
  167                 case 2:
  168                         le64enc(p, gl->keyoffset);
  169                         p += 8;
  170                         break;
  171                 case 3:
  172                         le32enc(p, gl->sectorsize);
  173                         p += 4;
  174                         break;
  175                 case 4:
  176                         le32enc(p, gl->flags);
  177                         p += 4;
  178                         break;
  179                 case 5:
  180                 case 6:
  181                 case 7:
  182                 case 8:
  183                         le64enc(p, gl->lsector[shuffle[i] - 5]);
  184                         p += 8;
  185                         break;
  186                 case 9:
  187                         bcopy(gl->spare, p, sizeof gl->spare);
  188                         p += sizeof gl->spare;
  189                         break;
  190                 case 10:
  191                         bcopy(gl->salt, p, sizeof gl->salt);
  192                         p += sizeof gl->salt;
  193                         break;
  194                 case 11:
  195                         bcopy(gl->mkey, p, sizeof gl->mkey);
  196                         p += sizeof gl->mkey;
  197                         break;
  198                 case 12:
  199                         bzero(p, 16);
  200                         hash = p;
  201                         p += 16;
  202                         break;
  203                 }
  204         }
  205         if(ptr + G_BDE_LOCKSIZE != p)
  206                 return(-1);
  207         if (hash == NULL)
  208                 return(-1);
  209         MD5Init(&c);
  210         MD5Update(&c, "0000", 4);       /* Versioning */
  211         MD5Update(&c, ptr, G_BDE_LOCKSIZE);
  212         MD5Final(hash, &c);
  213         return(0);
  214 }
  215 
  216 int
  217 g_bde_decode_lock(struct g_bde_softc *sc, struct g_bde_key *gl, u_char *ptr)
  218 {
  219         int shuffle[NLOCK_FIELDS];
  220         u_char *p;
  221         u_char hash[16], hash2[16];
  222         MD5_CTX c;
  223         int i;
  224 
  225         p = ptr;
  226         g_bde_shuffle_lock(sc->sha2, shuffle);
  227         for (i = 0; i < NLOCK_FIELDS; i++) {
  228                 switch(shuffle[i]) {
  229                 case 0:
  230                         gl->sector0 = le64dec(p);
  231                         p += 8;
  232                         break;
  233                 case 1:
  234                         gl->sectorN = le64dec(p);
  235                         p += 8;
  236                         break;
  237                 case 2:
  238                         gl->keyoffset = le64dec(p);
  239                         p += 8;
  240                         break;
  241                 case 3:
  242                         gl->sectorsize = le32dec(p);
  243                         p += 4;
  244                         break;
  245                 case 4:
  246                         gl->flags = le32dec(p);
  247                         p += 4;
  248                         break;
  249                 case 5:
  250                 case 6:
  251                 case 7:
  252                 case 8:
  253                         gl->lsector[shuffle[i] - 5] = le64dec(p);
  254                         p += 8;
  255                         break;
  256                 case 9:
  257                         bcopy(p, gl->spare, sizeof gl->spare);
  258                         p += sizeof gl->spare;
  259                         break;
  260                 case 10:
  261                         bcopy(p, gl->salt, sizeof gl->salt);
  262                         p += sizeof gl->salt;
  263                         break;
  264                 case 11:
  265                         bcopy(p, gl->mkey, sizeof gl->mkey);
  266                         p += sizeof gl->mkey;
  267                         break;
  268                 case 12:
  269                         bcopy(p, hash2, sizeof hash2);
  270                         bzero(p, sizeof hash2);
  271                         p += sizeof hash2;
  272                         break;
  273                 }
  274         }
  275         if(ptr + G_BDE_LOCKSIZE != p)
  276                 return(-1);
  277         MD5Init(&c);
  278         MD5Update(&c, "0000", 4);       /* Versioning */
  279         MD5Update(&c, ptr, G_BDE_LOCKSIZE);
  280         MD5Final(hash, &c);
  281         if (bcmp(hash, hash2, sizeof hash2))
  282                 return (1);
  283         return (0);
  284 }
  285 
  286 /*
  287  * Encode/Decode the locksector address ("metadata") with key-material.
  288  *
  289  * Security objectives: Encode/Decode the metadata encrypted by key-material.
  290  *
  291  * A simple AES/128/CBC will do.  We take care to always store the metadata
  292  * in the same endianess to make it MI.
  293  *
  294  * In the typical case the metadata is stored in encrypted format in sector
  295  * zero on the media, but at the users discretion or if the piece of the
  296  * device used (sector0...sectorN) does not contain sector zero, it can
  297  * be stored in a filesystem or on a PostIt.
  298  *
  299  * The inability to easily locate the lock sectors makes an attack on a
  300  * cold disk much less attractive, without unduly inconveniencing the
  301  * legitimate user who can feasibly do a brute-force scan if the metadata
  302  * was lost.
  303  */
  304 
  305 int
  306 g_bde_keyloc_encrypt(u_char *sha2, uint64_t v0, uint64_t v1, void *output)
  307 {
  308         u_char buf[16];
  309         keyInstance ki;
  310         cipherInstance ci;
  311 
  312         le64enc(buf, v0);
  313         le64enc(buf + 8, v1);
  314         AES_init(&ci);
  315         AES_makekey(&ki, DIR_ENCRYPT, G_BDE_KKEYBITS, sha2 + 0);
  316         AES_encrypt(&ci, &ki, buf, output, sizeof buf);
  317         bzero(buf, sizeof buf);
  318         bzero(&ci, sizeof ci);
  319         bzero(&ki, sizeof ki);
  320         return (0);
  321 }
  322 
  323 int
  324 g_bde_keyloc_decrypt(u_char *sha2, void *input, uint64_t *output)
  325 {
  326         keyInstance ki;
  327         cipherInstance ci;
  328         u_char buf[16];
  329 
  330         AES_init(&ci);
  331         AES_makekey(&ki, DIR_DECRYPT, G_BDE_KKEYBITS, sha2 + 0);
  332         AES_decrypt(&ci, &ki, input, buf, sizeof buf);
  333         *output = le64dec(buf);
  334         bzero(buf, sizeof buf);
  335         bzero(&ci, sizeof ci);
  336         bzero(&ki, sizeof ki);
  337         return(0);
  338 }
  339 
  340 /*
  341  * Find and Encode/Decode lock sectors.
  342  *
  343  * Security objective: given the pass-phrase, find, decrypt, decode and
  344  * validate the lock sector contents.
  345  *
  346  * For ondisk metadata we cannot know beforehand which of the lock sectors
  347  * a given pass-phrase opens so we must try each of the metadata copies in
  348  * sector zero in turn.  If metadata was passed as an argument, we don't
  349  * have this problem.
  350  *
  351  */
  352 
  353 static int
  354 g_bde_decrypt_lockx(struct g_bde_softc *sc, u_char *meta, off_t mediasize, u_int sectorsize, u_int *nkey)
  355 {
  356         u_char *buf, *q;
  357         struct g_bde_key *gl;
  358         uint64_t off, q1;
  359         int error, m, i;
  360         keyInstance ki;
  361         cipherInstance ci;
  362 
  363         gl = &sc->key;
  364 
  365         /* Try to decrypt the metadata */
  366         error = g_bde_keyloc_decrypt(sc->sha2, meta, &off);
  367         if (error)
  368                 return (error);
  369 
  370         /* If it points into thin blue air, forget it */
  371         if (off + G_BDE_LOCKSIZE > (uint64_t)mediasize) {
  372                 off = 0;
  373                 return (EINVAL);
  374         }
  375 
  376         /* The lock data may span two physical sectors. */
  377 
  378         m = 1;
  379         if (off % sectorsize > sectorsize - G_BDE_LOCKSIZE)
  380                 m++;
  381 
  382         /* Read the suspected sector(s) */
  383         buf = g_read_data(sc->consumer,
  384                 off - (off % sectorsize),
  385                 m * sectorsize, &error);
  386         if (buf == NULL) {
  387                 off = 0;
  388                 return(error);
  389         }
  390 
  391         /* Find the byte-offset of the stored byte sequence */
  392         q = buf + off % sectorsize;
  393 
  394         /* If it is all zero, somebody nuked our lock sector */
  395         q1 = 0;
  396         for (i = 0; i < G_BDE_LOCKSIZE; i++)
  397                 q1 += q[i];
  398         if (q1 == 0) {
  399                 off = 0;
  400                 g_free(buf);
  401                 return (ESRCH);
  402         }
  403 
  404         /* Decrypt the byte-sequence in place */
  405         AES_init(&ci);
  406         AES_makekey(&ki, DIR_DECRYPT, 256, sc->sha2 + 16);
  407         AES_decrypt(&ci, &ki, q, q, G_BDE_LOCKSIZE);
  408 
  409         /* Decode the byte-sequence */
  410         i = g_bde_decode_lock(sc, gl, q);
  411         q = NULL;
  412         if (i < 0) {
  413                 off = 0;
  414                 return (EDOOFUS);       /* Programming error */
  415         } else if (i > 0) {
  416                 off = 0;
  417                 return (ENOTDIR);       /* Hash didn't match */
  418         }
  419 
  420         bzero(buf, sectorsize * m);
  421         g_free(buf);
  422 
  423         /* If the masterkey is all zeros, user destroyed it */
  424         q1 = 0;
  425         for (i = 0; i < (int)sizeof(gl->mkey); i++)
  426                 q1 += gl->mkey[i];
  427         if (q1 == 0)
  428                 return (ENOENT);
  429 
  430         /* If we have an unsorted lock-sequence, refuse */
  431         for (i = 0; i < G_BDE_MAXKEYS - 1; i++)
  432                 if (gl->lsector[i] >= gl->lsector[i + 1])
  433                         return (EINVAL);
  434 
  435         /* Finally, find out which key was used by matching the byte offset */
  436         for (i = 0; i < G_BDE_MAXKEYS; i++)
  437                 if (nkey != NULL && off == gl->lsector[i])
  438                         *nkey = i;
  439         off = 0;
  440         return (0);
  441 }
  442 
  443 int
  444 g_bde_decrypt_lock(struct g_bde_softc *sc, u_char *keymat, u_char *meta, off_t mediasize, u_int sectorsize, u_int *nkey)
  445 {
  446         u_char *buf, buf1[16];
  447         int error, e, i;
  448 
  449         /* set up the key-material */
  450         bcopy(keymat, sc->sha2, SHA512_DIGEST_LENGTH);
  451 
  452         /* If passed-in metadata is non-zero, use it */
  453         bzero(buf1, sizeof buf1);
  454         if (meta != NULL && bcmp(buf1, meta, sizeof buf1))
  455                 return (g_bde_decrypt_lockx(sc, meta, mediasize,
  456                     sectorsize, nkey));
  457 
  458         /* Read sector zero */
  459         buf = g_read_data(sc->consumer, 0, sectorsize, &error);
  460         if (buf == NULL)
  461                 return(error);
  462 
  463         /* Try each index in turn, save indicative errors for final result */
  464         error = EINVAL;
  465         for (i = 0; i < G_BDE_MAXKEYS; i++) {
  466                 e = g_bde_decrypt_lockx(sc, buf + i * 16, mediasize,
  467                     sectorsize, nkey);
  468                 /* Success or destroyed master key terminates */
  469                 if (e == 0 || e == ENOENT) {
  470                         error = e;
  471                         break;
  472                 }
  473                 if (e != 0 && error == EINVAL)
  474                         error = e;
  475         }
  476         g_free(buf);
  477         return (error);
  478 }

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