sbin/fsck_msdosfs/boot.c

   1 /*-
   2  * SPDX-License-Identifier: BSD-2-Clause-FreeBSD
   3  *
   4  * Copyright (C) 1995, 1997 Wolfgang Solfrank
   5  * Copyright (c) 1995 Martin Husemann
   6  *
   7  * Redistribution and use in source and binary forms, with or without
   8  * modification, are permitted provided that the following conditions
   9  * are met:
  10  * 1. Redistributions of source code must retain the above copyright
  11  *    notice, this list of conditions and the following disclaimer.
  12  * 2. Redistributions in binary form must reproduce the above copyright
  13  *    notice, this list of conditions and the following disclaimer in the
  14  *    documentation and/or other materials provided with the distribution.
  15  *
  16  * THIS SOFTWARE IS PROVIDED BY THE AUTHORS ``AS IS'' AND ANY EXPRESS OR
  17  * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
  18  * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
  19  * IN NO EVENT SHALL THE AUTHORS BE LIABLE FOR ANY DIRECT, INDIRECT,
  20  * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
  21  * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
  22  * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
  23  * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
  24  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
  25  * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  26  */
  27
  28
  29 #include <sys/cdefs.h>
  30 #ifndef lint
  31 __RCSID("$NetBSD: boot.c,v 1.11 2006/06/05 16:51:18 christos Exp ");
  32 static const char rcsid[] =
  33   "$FreeBSD$";
  34 #endif /* not lint */
  35
  36 #include <stdlib.h>
  37 #include <string.h>
  38 #include <stdio.h>
  39 #include <unistd.h>
  40
  41 #include "ext.h"
  42 #include "fsutil.h"
  43
  44 int
  45 readboot(int dosfs, struct bootblock *boot)
  46 {
  47         u_char block[DOSBOOTBLOCKSIZE];
  48         u_char fsinfo[2 * DOSBOOTBLOCKSIZE];
  49         u_char backup[DOSBOOTBLOCKSIZE];
  50         int ret = FSOK;
  51         int i;
  52
  53         if ((size_t)read(dosfs, block, sizeof block) != sizeof block) {
  54                 perr("could not read boot block");
  55                 return FSFATAL;
  56         }
  57
  58         if (block[510] != 0x55 || block[511] != 0xaa) {
  59                 pfatal("Invalid signature in boot block: %02x%02x",
  60                     block[511], block[510]);
  61                 return FSFATAL;
  62         }
  63
  64         memset(boot, 0, sizeof *boot);
  65         boot->ValidFat = -1;
  66
  67         /* decode bios parameter block */
  68         boot->bpbBytesPerSec = block[11] + (block[12] << 8);
  69         boot->bpbSecPerClust = block[13];
  70         boot->bpbResSectors = block[14] + (block[15] << 8);
  71         boot->bpbFATs = block[16];
  72         boot->bpbRootDirEnts = block[17] + (block[18] << 8);
  73         boot->bpbSectors = block[19] + (block[20] << 8);
  74         boot->bpbMedia = block[21];
  75         boot->bpbFATsmall = block[22] + (block[23] << 8);
  76         boot->SecPerTrack = block[24] + (block[25] << 8);
  77         boot->bpbHeads = block[26] + (block[27] << 8);
  78         boot->bpbHiddenSecs = block[28] + (block[29] << 8) +
  79             (block[30] << 16) + (block[31] << 24);
  80         boot->bpbHugeSectors = block[32] + (block[33] << 8) +
  81             (block[34] << 16) + (block[35] << 24);
  82
  83         boot->FATsecs = boot->bpbFATsmall;
  84
  85         if (boot->bpbBytesPerSec % DOSBOOTBLOCKSIZE_REAL != 0 ||
  86             boot->bpbBytesPerSec / DOSBOOTBLOCKSIZE_REAL == 0) {
  87                 pfatal("Invalid sector size: %u", boot->bpbBytesPerSec);
  88                 return FSFATAL;
  89         }
  90         if (boot->bpbFATs == 0) {
  91                 pfatal("Invalid number of FATs: %u", boot->bpbFATs);
  92                 return FSFATAL;
  93         }
  94         if (!boot->bpbRootDirEnts)
  95                 boot->flags |= FAT32;
  96         if (boot->flags & FAT32) {
  97                 boot->FATsecs = block[36] + (block[37] << 8)
  98                                 + (block[38] << 16) + (block[39] << 24);
  99                 if (block[40] & 0x80)
 100                         boot->ValidFat = block[40] & 0x0f;
 101
 102                 /* check version number: */
 103                 if (block[42] || block[43]) {
 104                         /* Correct?                             XXX */
 105                         pfatal("Unknown file system version: %x.%x",
 106                                block[43], block[42]);
 107                         return FSFATAL;
 108                 }
 109                 boot->bpbRootClust = block[44] + (block[45] << 8)
 110                                + (block[46] << 16) + (block[47] << 24);
 111                 boot->bpbFSInfo = block[48] + (block[49] << 8);
 112                 boot->bpbBackup = block[50] + (block[51] << 8);
 113
 114                 /* If the OEM Name field is EXFAT, it's not FAT32, so bail */
 115                 if (!memcmp(&block[3], "EXFAT   ", 8)) {
 116                         pfatal("exFAT filesystem is not supported.");
 117                         return FSFATAL;
 118                 }
 119
 120                 /* check basic parameters */
 121                 if ((boot->bpbFSInfo == 0) || (boot->bpbSecPerClust == 0)) {
 122                         /*
 123                          * Either the BIOS Parameter Block has been corrupted,
 124                          * or this is not a FAT32 filesystem, most likely an
 125                          * exFAT filesystem.
 126                          */
 127                         pfatal("Invalid FAT32 Extended BIOS Parameter Block");
 128                         return FSFATAL;
 129                 }
 130                 if (lseek(dosfs, boot->bpbFSInfo * boot->bpbBytesPerSec,
 131                     SEEK_SET) != boot->bpbFSInfo * boot->bpbBytesPerSec
 132                     || read(dosfs, fsinfo, sizeof fsinfo) != sizeof fsinfo) {
 133                         perr("could not read fsinfo block");
 134                         return FSFATAL;
 135                 }
 136                 if (memcmp(fsinfo, "RRaA", 4)
 137                     || memcmp(fsinfo + 0x1e4, "rrAa", 4)
 138                     || fsinfo[0x1fc]
 139                     || fsinfo[0x1fd]
 140                     || fsinfo[0x1fe] != 0x55
 141                     || fsinfo[0x1ff] != 0xaa
 142                     || fsinfo[0x3fc]
 143                     || fsinfo[0x3fd]
 144                     || fsinfo[0x3fe] != 0x55
 145                     || fsinfo[0x3ff] != 0xaa) {
 146                         pwarn("Invalid signature in fsinfo block\n");
 147                         if (ask(0, "Fix")) {
 148                                 memcpy(fsinfo, "RRaA", 4);
 149                                 memcpy(fsinfo + 0x1e4, "rrAa", 4);
 150                                 fsinfo[0x1fc] = fsinfo[0x1fd] = 0;
 151                                 fsinfo[0x1fe] = 0x55;
 152                                 fsinfo[0x1ff] = 0xaa;
 153                                 fsinfo[0x3fc] = fsinfo[0x3fd] = 0;
 154                                 fsinfo[0x3fe] = 0x55;
 155                                 fsinfo[0x3ff] = 0xaa;
 156                                 if (lseek(dosfs, boot->bpbFSInfo *
 157                                     boot->bpbBytesPerSec, SEEK_SET)
 158                                     != boot->bpbFSInfo * boot->bpbBytesPerSec
 159                                     || write(dosfs, fsinfo, sizeof fsinfo)
 160                                     != sizeof fsinfo) {
 161                                         perr("Unable to write bpbFSInfo");
 162                                         return FSFATAL;
 163                                 }
 164                                 ret = FSBOOTMOD;
 165                         } else
 166                                 boot->bpbFSInfo = 0;
 167                 }
 168                 if (boot->bpbFSInfo) {
 169                         boot->FSFree = fsinfo[0x1e8] + (fsinfo[0x1e9] << 8)
 170                                        + (fsinfo[0x1ea] << 16)
 171                                        + (fsinfo[0x1eb] << 24);
 172                         boot->FSNext = fsinfo[0x1ec] + (fsinfo[0x1ed] << 8)
 173                                        + (fsinfo[0x1ee] << 16)
 174                                        + (fsinfo[0x1ef] << 24);
 175                 }
 176
 177                 if (lseek(dosfs, boot->bpbBackup * boot->bpbBytesPerSec,
 178                     SEEK_SET)
 179                     != boot->bpbBackup * boot->bpbBytesPerSec
 180                     || read(dosfs, backup, sizeof backup) != sizeof  backup) {
 181                         perr("could not read backup bootblock");
 182                         return FSFATAL;
 183                 }
 184                 backup[65] = block[65];                         /* XXX */
 185                 if (memcmp(block + 11, backup + 11, 79)) {
 186                         /*
 187                          * XXX We require a reference that explains
 188                          * that these bytes need to match, or should
 189                          * drop the check.  gdt@NetBSD has observed
 190                          * filesystems that work fine under Windows XP
 191                          * and NetBSD that do not match, so the
 192                          * requirement is suspect.  For now, just
 193                          * print out useful information and continue.
 194                          */
 195                         pwarn("backup (block %d) mismatch with primary bootblock:\n",
 196                                 boot->bpbBackup);
 197                         for (i = 11; i < 11 + 90; i++) {
 198                                 if (block[i] != backup[i])
 199                                         pwarn("\ti=%d\tprimary 0x%02x\tbackup 0x%02x\n",
 200                                                i, block[i], backup[i]);
 201                         }
 202                 }
 203                 /* Check backup bpbFSInfo?                                      XXX */
 204         }
 205
 206         if (boot->bpbSecPerClust == 0) {
 207                 pfatal("Invalid cluster size: %u", boot->bpbSecPerClust);
 208                 return FSFATAL;
 209         }
 210         if (boot->bpbSectors) {
 211                 boot->bpbHugeSectors = 0;
 212                 boot->NumSectors = boot->bpbSectors;
 213         } else
 214                 boot->NumSectors = boot->bpbHugeSectors;
 215         boot->ClusterOffset = (boot->bpbRootDirEnts * 32 +
 216             boot->bpbBytesPerSec - 1) / boot->bpbBytesPerSec +
 217             boot->bpbResSectors + boot->bpbFATs * boot->FATsecs -
 218             CLUST_FIRST * boot->bpbSecPerClust;
 219         boot->NumClusters = (boot->NumSectors - boot->ClusterOffset) /
 220             boot->bpbSecPerClust;
 221
 222         if (boot->flags & FAT32)
 223                 boot->ClustMask = CLUST32_MASK;
 224         else if (boot->NumClusters < (CLUST_RSRVD&CLUST12_MASK))
 225                 boot->ClustMask = CLUST12_MASK;
 226         else if (boot->NumClusters < (CLUST_RSRVD&CLUST16_MASK))
 227                 boot->ClustMask = CLUST16_MASK;
 228         else {
 229                 pfatal("Filesystem too big (%u clusters) for non-FAT32 partition",
 230                        boot->NumClusters);
 231                 return FSFATAL;
 232         }
 233
 234         switch (boot->ClustMask) {
 235         case CLUST32_MASK:
 236                 boot->NumFatEntries = (boot->FATsecs * boot->bpbBytesPerSec) / 4;
 237                 break;
 238         case CLUST16_MASK:
 239                 boot->NumFatEntries = (boot->FATsecs * boot->bpbBytesPerSec) / 2;
 240                 break;
 241         default:
 242                 boot->NumFatEntries = (boot->FATsecs * boot->bpbBytesPerSec * 2) / 3;
 243                 break;
 244         }
 245
 246         if (boot->NumFatEntries < boot->NumClusters - CLUST_FIRST) {
 247                 pfatal("FAT size too small, %u entries won't fit into %u sectors\n",
 248                        boot->NumClusters, boot->FATsecs);
 249                 return FSFATAL;
 250         }
 251         boot->ClusterSize = boot->bpbBytesPerSec * boot->bpbSecPerClust;
 252
 253         boot->NumFiles = 1;
 254         boot->NumFree = 0;
 255
 256         return ret;
 257 }
 258
 259 int
 260 writefsinfo(int dosfs, struct bootblock *boot)
 261 {
 262         u_char fsinfo[2 * DOSBOOTBLOCKSIZE];
 263
 264         if (lseek(dosfs, boot->bpbFSInfo * boot->bpbBytesPerSec, SEEK_SET)
 265             != boot->bpbFSInfo * boot->bpbBytesPerSec
 266             || read(dosfs, fsinfo, sizeof fsinfo) != sizeof fsinfo) {
 267                 perr("could not read fsinfo block");
 268                 return FSFATAL;
 269         }
 270         fsinfo[0x1e8] = (u_char)boot->FSFree;
 271         fsinfo[0x1e9] = (u_char)(boot->FSFree >> 8);
 272         fsinfo[0x1ea] = (u_char)(boot->FSFree >> 16);
 273         fsinfo[0x1eb] = (u_char)(boot->FSFree >> 24);
 274         fsinfo[0x1ec] = (u_char)boot->FSNext;
 275         fsinfo[0x1ed] = (u_char)(boot->FSNext >> 8);
 276         fsinfo[0x1ee] = (u_char)(boot->FSNext >> 16);
 277         fsinfo[0x1ef] = (u_char)(boot->FSNext >> 24);
 278         if (lseek(dosfs, boot->bpbFSInfo * boot->bpbBytesPerSec, SEEK_SET)
 279             != boot->bpbFSInfo * boot->bpbBytesPerSec
 280             || write(dosfs, fsinfo, sizeof fsinfo)
 281             != sizeof fsinfo) {
 282                 perr("Unable to write bpbFSInfo");
 283                 return FSFATAL;
 284         }
 285         /*
 286          * Technically, we should return FSBOOTMOD here.
 287          *
 288          * However, since Win95 OSR2 (the first M$ OS that has
 289          * support for FAT32) doesn't maintain the FSINFO block
 290          * correctly, it has to be fixed pretty often.
 291          *
 292          * Therefor, we handle the FSINFO block only informally,
 293          * fixing it if necessary, but otherwise ignoring the
 294          * fact that it was incorrect.
 295          */
 296         return 0;
 297 }