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->bpbRootDirEnts)
  86                 boot->flags |= FAT32;
  87         if (boot->flags & FAT32) {
  88                 boot->FATsecs = block[36] + (block[37] << 8)
  89                                 + (block[38] << 16) + (block[39] << 24);
  90                 if (block[40] & 0x80)
  91                         boot->ValidFat = block[40] & 0x0f;
  92
  93                 /* check version number: */
  94                 if (block[42] || block[43]) {
  95                         /* Correct?                             XXX */
  96                         pfatal("Unknown file system version: %x.%x",
  97                                block[43], block[42]);
  98                         return FSFATAL;
  99                 }
 100                 boot->bpbRootClust = block[44] + (block[45] << 8)
 101                                + (block[46] << 16) + (block[47] << 24);
 102                 boot->bpbFSInfo = block[48] + (block[49] << 8);
 103                 boot->bpbBackup = block[50] + (block[51] << 8);
 104
 105                 if (lseek(dosfs, boot->bpbFSInfo * boot->bpbBytesPerSec,
 106                     SEEK_SET) != boot->bpbFSInfo * boot->bpbBytesPerSec
 107                     || read(dosfs, fsinfo, sizeof fsinfo) != sizeof fsinfo) {
 108                         perr("could not read fsinfo block");
 109                         return FSFATAL;
 110                 }
 111                 if (memcmp(fsinfo, "RRaA", 4)
 112                     || memcmp(fsinfo + 0x1e4, "rrAa", 4)
 113                     || fsinfo[0x1fc]
 114                     || fsinfo[0x1fd]
 115                     || fsinfo[0x1fe] != 0x55
 116                     || fsinfo[0x1ff] != 0xaa
 117                     || fsinfo[0x3fc]
 118                     || fsinfo[0x3fd]
 119                     || fsinfo[0x3fe] != 0x55
 120                     || fsinfo[0x3ff] != 0xaa) {
 121                         pwarn("Invalid signature in fsinfo block\n");
 122                         if (ask(0, "Fix")) {
 123                                 memcpy(fsinfo, "RRaA", 4);
 124                                 memcpy(fsinfo + 0x1e4, "rrAa", 4);
 125                                 fsinfo[0x1fc] = fsinfo[0x1fd] = 0;
 126                                 fsinfo[0x1fe] = 0x55;
 127                                 fsinfo[0x1ff] = 0xaa;
 128                                 fsinfo[0x3fc] = fsinfo[0x3fd] = 0;
 129                                 fsinfo[0x3fe] = 0x55;
 130                                 fsinfo[0x3ff] = 0xaa;
 131                                 if (lseek(dosfs, boot->bpbFSInfo *
 132                                     boot->bpbBytesPerSec, SEEK_SET)
 133                                     != boot->bpbFSInfo * boot->bpbBytesPerSec
 134                                     || write(dosfs, fsinfo, sizeof fsinfo)
 135                                     != sizeof fsinfo) {
 136                                         perr("Unable to write bpbFSInfo");
 137                                         return FSFATAL;
 138                                 }
 139                                 ret = FSBOOTMOD;
 140                         } else
 141                                 boot->bpbFSInfo = 0;
 142                 }
 143                 if (boot->bpbFSInfo) {
 144                         boot->FSFree = fsinfo[0x1e8] + (fsinfo[0x1e9] << 8)
 145                                        + (fsinfo[0x1ea] << 16)
 146                                        + (fsinfo[0x1eb] << 24);
 147                         boot->FSNext = fsinfo[0x1ec] + (fsinfo[0x1ed] << 8)
 148                                        + (fsinfo[0x1ee] << 16)
 149                                        + (fsinfo[0x1ef] << 24);
 150                 }
 151
 152                 if (lseek(dosfs, boot->bpbBackup * boot->bpbBytesPerSec,
 153                     SEEK_SET)
 154                     != boot->bpbBackup * boot->bpbBytesPerSec
 155                     || read(dosfs, backup, sizeof backup) != sizeof  backup) {
 156                         perr("could not read backup bootblock");
 157                         return FSFATAL;
 158                 }
 159                 backup[65] = block[65];                         /* XXX */
 160                 if (memcmp(block + 11, backup + 11, 79)) {
 161                         /*
 162                          * XXX We require a reference that explains
 163                          * that these bytes need to match, or should
 164                          * drop the check.  gdt@NetBSD has observed
 165                          * filesystems that work fine under Windows XP
 166                          * and NetBSD that do not match, so the
 167                          * requirement is suspect.  For now, just
 168                          * print out useful information and continue.
 169                          */
 170                         pfatal("backup (block %d) mismatch with primary bootblock:\n",
 171                                 boot->bpbBackup);
 172                         for (i = 11; i < 11 + 90; i++) {
 173                                 if (block[i] != backup[i])
 174                                         pfatal("\ti=%d\tprimary 0x%02x\tbackup 0x%02x\n",
 175                                                i, block[i], backup[i]);
 176                         }
 177                 }
 178                 /* Check backup bpbFSInfo?                                      XXX */
 179         }
 180
 181         boot->ClusterOffset = (boot->bpbRootDirEnts * 32 +
 182             boot->bpbBytesPerSec - 1) / boot->bpbBytesPerSec +
 183             boot->bpbResSectors + boot->bpbFATs * boot->FATsecs -
 184             CLUST_FIRST * boot->bpbSecPerClust;
 185
 186         if (boot->bpbBytesPerSec % DOSBOOTBLOCKSIZE_REAL != 0) {
 187                 pfatal("Invalid sector size: %u", boot->bpbBytesPerSec);
 188                 return FSFATAL;
 189         }
 190         if (boot->bpbSecPerClust == 0) {
 191                 pfatal("Invalid cluster size: %u", boot->bpbSecPerClust);
 192                 return FSFATAL;
 193         }
 194         if (boot->bpbSectors) {
 195                 boot->bpbHugeSectors = 0;
 196                 boot->NumSectors = boot->bpbSectors;
 197         } else
 198                 boot->NumSectors = boot->bpbHugeSectors;
 199         boot->NumClusters = (boot->NumSectors - boot->ClusterOffset) /
 200             boot->bpbSecPerClust;
 201
 202         if (boot->flags&FAT32)
 203                 boot->ClustMask = CLUST32_MASK;
 204         else if (boot->NumClusters < (CLUST_RSRVD&CLUST12_MASK))
 205                 boot->ClustMask = CLUST12_MASK;
 206         else if (boot->NumClusters < (CLUST_RSRVD&CLUST16_MASK))
 207                 boot->ClustMask = CLUST16_MASK;
 208         else {
 209                 pfatal("Filesystem too big (%u clusters) for non-FAT32 partition",
 210                        boot->NumClusters);
 211                 return FSFATAL;
 212         }
 213
 214         switch (boot->ClustMask) {
 215         case CLUST32_MASK:
 216                 boot->NumFatEntries = (boot->FATsecs * boot->bpbBytesPerSec) / 4;
 217                 break;
 218         case CLUST16_MASK:
 219                 boot->NumFatEntries = (boot->FATsecs * boot->bpbBytesPerSec) / 2;
 220                 break;
 221         default:
 222                 boot->NumFatEntries = (boot->FATsecs * boot->bpbBytesPerSec * 2) / 3;
 223                 break;
 224         }
 225
 226         if (boot->NumFatEntries < boot->NumClusters - CLUST_FIRST) {
 227                 pfatal("FAT size too small, %u entries won't fit into %u sectors\n",
 228                        boot->NumClusters, boot->FATsecs);
 229                 return FSFATAL;
 230         }
 231         boot->ClusterSize = boot->bpbBytesPerSec * boot->bpbSecPerClust;
 232
 233         boot->NumFiles = 1;
 234         boot->NumFree = 0;
 235
 236         return ret;
 237 }
 238
 239 int
 240 writefsinfo(int dosfs, struct bootblock *boot)
 241 {
 242         u_char fsinfo[2 * DOSBOOTBLOCKSIZE];
 243
 244         if (lseek(dosfs, boot->bpbFSInfo * boot->bpbBytesPerSec, SEEK_SET)
 245             != boot->bpbFSInfo * boot->bpbBytesPerSec
 246             || read(dosfs, fsinfo, sizeof fsinfo) != sizeof fsinfo) {
 247                 perr("could not read fsinfo block");
 248                 return FSFATAL;
 249         }
 250         fsinfo[0x1e8] = (u_char)boot->FSFree;
 251         fsinfo[0x1e9] = (u_char)(boot->FSFree >> 8);
 252         fsinfo[0x1ea] = (u_char)(boot->FSFree >> 16);
 253         fsinfo[0x1eb] = (u_char)(boot->FSFree >> 24);
 254         fsinfo[0x1ec] = (u_char)boot->FSNext;
 255         fsinfo[0x1ed] = (u_char)(boot->FSNext >> 8);
 256         fsinfo[0x1ee] = (u_char)(boot->FSNext >> 16);
 257         fsinfo[0x1ef] = (u_char)(boot->FSNext >> 24);
 258         if (lseek(dosfs, boot->bpbFSInfo * boot->bpbBytesPerSec, SEEK_SET)
 259             != boot->bpbFSInfo * boot->bpbBytesPerSec
 260             || write(dosfs, fsinfo, sizeof fsinfo)
 261             != sizeof fsinfo) {
 262                 perr("Unable to write bpbFSInfo");
 263                 return FSFATAL;
 264         }
 265         /*
 266          * Technically, we should return FSBOOTMOD here.
 267          *
 268          * However, since Win95 OSR2 (the first M$ OS that has
 269          * support for FAT32) doesn't maintain the FSINFO block
 270          * correctly, it has to be fixed pretty often.
 271          *
 272          * Therefor, we handle the FSINFO block only informally,
 273          * fixing it if necessary, but otherwise ignoring the
 274          * fact that it was incorrect.
 275          */
 276         return 0;
 277 }