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 #include <sys/param.h>
  29
  30 #include <stdint.h>
  31 #include <stdlib.h>
  32 #include <string.h>
  33 #include <stdio.h>
  34 #include <unistd.h>
  35
  36 #include "ext.h"
  37 #include "fsutil.h"
  38
  39 int
  40 readboot(int dosfs, struct bootblock *boot)
  41 {
  42         u_char block[DOSBOOTBLOCKSIZE];
  43         u_char fsinfo[2 * DOSBOOTBLOCKSIZE];
  44         int ret = FSOK;
  45
  46         if ((size_t)read(dosfs, block, sizeof block) != sizeof block) {
  47                 perr("could not read boot block");
  48                 return FSFATAL;
  49         }
  50
  51         if (block[510] != 0x55 || block[511] != 0xaa) {
  52                 pfatal("Invalid signature in boot block: %02x%02x",
  53                     block[511], block[510]);
  54                 return FSFATAL;
  55         }
  56
  57         memset(boot, 0, sizeof *boot);
  58         boot->ValidFat = -1;
  59
  60         /* Decode BIOS Parameter Block */
  61
  62         /* Bytes per sector: can only be  512, 1024, 2048 and 4096. */
  63         boot->bpbBytesPerSec = block[11] + (block[12] << 8);
  64         if (boot->bpbBytesPerSec < DOSBOOTBLOCKSIZE_REAL ||
  65             boot->bpbBytesPerSec > DOSBOOTBLOCKSIZE ||
  66             !powerof2(boot->bpbBytesPerSec)) {
  67                 pfatal("Invalid sector size: %u", boot->bpbBytesPerSec);
  68                 return FSFATAL;
  69         }
  70
  71         /* Sectors per cluster: can only be: 1, 2, 4, 8, 16, 32, 64, 128. */
  72         boot->bpbSecPerClust = block[13];
  73         if (boot->bpbSecPerClust == 0 || !powerof2(boot->bpbSecPerClust)) {
  74                 pfatal("Invalid cluster size: %u", boot->bpbSecPerClust);
  75                 return FSFATAL;
  76         }
  77
  78         /* Reserved sectors: must be non-zero */
  79         boot->bpbResSectors = block[14] + (block[15] << 8);
  80         if (boot->bpbResSectors < 1) {
  81                 pfatal("Invalid reserved sectors: %u",
  82                     boot->bpbResSectors);
  83                 return FSFATAL;
  84         }
  85
  86         /* Number of FATs */
  87         boot->bpbFATs = block[16];
  88         if (boot->bpbFATs == 0) {
  89                 pfatal("Invalid number of FATs: %u", boot->bpbFATs);
  90                 return FSFATAL;
  91         }
  92
  93         /* Root directory entries for FAT12 and FAT16 */
  94         boot->bpbRootDirEnts = block[17] + (block[18] << 8);
  95         if (!boot->bpbRootDirEnts) {
  96                 /* bpbRootDirEnts = 0 suggests that we are FAT32 */
  97                 boot->flags |= FAT32;
  98         }
  99
 100         /* Total sectors (16 bits) */
 101         boot->bpbSectors = block[19] + (block[20] << 8);
 102         if (boot->bpbSectors != 0 && (boot->flags & FAT32)) {
 103                 pfatal("Invalid 16-bit total sector count on FAT32: %u",
 104                     boot->bpbSectors);
 105                 return FSFATAL;
 106         }
 107
 108         /* Media type: ignored */
 109         boot->bpbMedia = block[21];
 110
 111         /* FAT12/FAT16: 16-bit count of sectors per FAT */
 112         boot->bpbFATsmall = block[22] + (block[23] << 8);
 113         if (boot->bpbFATsmall != 0 && (boot->flags & FAT32)) {
 114                 pfatal("Invalid 16-bit FAT sector count on FAT32: %u",
 115                     boot->bpbFATsmall);
 116                 return FSFATAL;
 117         }
 118
 119         /* Legacy CHS geometry numbers: ignored */
 120         boot->SecPerTrack = block[24] + (block[25] << 8);
 121         boot->bpbHeads = block[26] + (block[27] << 8);
 122
 123         /* Hidden sectors: ignored */
 124         boot->bpbHiddenSecs = block[28] + (block[29] << 8) +
 125             (block[30] << 16) + (block[31] << 24);
 126
 127         /* Total sectors (32 bits) */
 128         boot->bpbHugeSectors = block[32] + (block[33] << 8) +
 129             (block[34] << 16) + (block[35] << 24);
 130         if (boot->bpbHugeSectors == 0) {
 131                 if (boot->flags & FAT32) {
 132                         pfatal("FAT32 with sector count of zero");
 133                         return FSFATAL;
 134                 } else if (boot->bpbSectors == 0) {
 135                         pfatal("FAT with sector count of zero");
 136                         return FSFATAL;
 137                 }
 138                 boot->NumSectors = boot->bpbSectors;
 139         } else {
 140                 if (boot->bpbSectors != 0) {
 141                         pfatal("Invalid FAT sector count");
 142                         return FSFATAL;
 143                 }
 144                 boot->NumSectors = boot->bpbHugeSectors;
 145         }
 146
 147         if (boot->flags & FAT32) {
 148                 /* If the OEM Name field is EXFAT, it's not FAT32, so bail */
 149                 if (!memcmp(&block[3], "EXFAT   ", 8)) {
 150                         pfatal("exFAT filesystem is not supported.");
 151                         return FSFATAL;
 152                 }
 153
 154                 /* 32-bit count of sectors per FAT */
 155                 boot->FATsecs = block[36] + (block[37] << 8)
 156                                 + (block[38] << 16) + (block[39] << 24);
 157
 158                 if (block[40] & 0x80)
 159                         boot->ValidFat = block[40] & 0x0f;
 160
 161                 /* FAT32 version, bail out if not 0.0 */
 162                 if (block[42] || block[43]) {
 163                         pfatal("Unknown file system version: %x.%x",
 164                                block[43], block[42]);
 165                         return FSFATAL;
 166                 }
 167
 168                 /*
 169                  * Cluster number of the first cluster of root directory.
 170                  *
 171                  * Should be 2 but do not require it.
 172                  */
 173                 boot->bpbRootClust = block[44] + (block[45] << 8)
 174                                + (block[46] << 16) + (block[47] << 24);
 175
 176                 /* Sector number of the FSInfo structure, usually 1 */
 177                 boot->bpbFSInfo = block[48] + (block[49] << 8);
 178
 179                 /* Sector number of the backup boot block, ignored */
 180                 boot->bpbBackup = block[50] + (block[51] << 8);
 181
 182                 /* Check basic parameters */
 183                 if (boot->bpbFSInfo == 0) {
 184                         /*
 185                          * Either the BIOS Parameter Block has been corrupted,
 186                          * or this is not a FAT32 filesystem, most likely an
 187                          * exFAT filesystem.
 188                          */
 189                         pfatal("Invalid FAT32 Extended BIOS Parameter Block");
 190                         return FSFATAL;
 191                 }
 192
 193                 /* Read in and verify the FSInfo block */
 194                 if (lseek(dosfs, boot->bpbFSInfo * boot->bpbBytesPerSec,
 195                     SEEK_SET) != boot->bpbFSInfo * boot->bpbBytesPerSec
 196                     || read(dosfs, fsinfo, sizeof fsinfo) != sizeof fsinfo) {
 197                         perr("could not read fsinfo block");
 198                         return FSFATAL;
 199                 }
 200                 if (memcmp(fsinfo, "RRaA", 4)
 201                     || memcmp(fsinfo + 0x1e4, "rrAa", 4)
 202                     || fsinfo[0x1fc]
 203                     || fsinfo[0x1fd]
 204                     || fsinfo[0x1fe] != 0x55
 205                     || fsinfo[0x1ff] != 0xaa
 206                     || fsinfo[0x3fc]
 207                     || fsinfo[0x3fd]
 208                     || fsinfo[0x3fe] != 0x55
 209                     || fsinfo[0x3ff] != 0xaa) {
 210                         pwarn("Invalid signature in fsinfo block\n");
 211                         if (ask(0, "Fix")) {
 212                                 memcpy(fsinfo, "RRaA", 4);
 213                                 memcpy(fsinfo + 0x1e4, "rrAa", 4);
 214                                 fsinfo[0x1fc] = fsinfo[0x1fd] = 0;
 215                                 fsinfo[0x1fe] = 0x55;
 216                                 fsinfo[0x1ff] = 0xaa;
 217                                 fsinfo[0x3fc] = fsinfo[0x3fd] = 0;
 218                                 fsinfo[0x3fe] = 0x55;
 219                                 fsinfo[0x3ff] = 0xaa;
 220                                 if (lseek(dosfs, boot->bpbFSInfo *
 221                                     boot->bpbBytesPerSec, SEEK_SET)
 222                                     != boot->bpbFSInfo * boot->bpbBytesPerSec
 223                                     || write(dosfs, fsinfo, sizeof fsinfo)
 224                                     != sizeof fsinfo) {
 225                                         perr("Unable to write bpbFSInfo");
 226                                         return FSFATAL;
 227                                 }
 228                                 ret = FSBOOTMOD;
 229                         } else
 230                                 boot->bpbFSInfo = 0;
 231                 } else {
 232                         /* We appear to have a valid FSInfo block, decode */
 233                         boot->FSFree = fsinfo[0x1e8] + (fsinfo[0x1e9] << 8)
 234                                        + (fsinfo[0x1ea] << 16)
 235                                        + (fsinfo[0x1eb] << 24);
 236                         boot->FSNext = fsinfo[0x1ec] + (fsinfo[0x1ed] << 8)
 237                                        + (fsinfo[0x1ee] << 16)
 238                                        + (fsinfo[0x1ef] << 24);
 239                 }
 240         } else {
 241                 /* !FAT32: FAT12/FAT16 */
 242                 boot->FATsecs = boot->bpbFATsmall;
 243         }
 244
 245         if (boot->FATsecs > UINT32_MAX / boot->bpbFATs) {
 246                 pfatal("Invalid FATs(%u) with FATsecs(%zu)",
 247                         boot->bpbFATs, (size_t)boot->FATsecs);
 248                 return FSFATAL;
 249         }
 250
 251         boot->ClusterOffset = (boot->bpbRootDirEnts * 32 +
 252             boot->bpbBytesPerSec - 1) / boot->bpbBytesPerSec +
 253             boot->bpbResSectors + boot->bpbFATs * boot->FATsecs -
 254             CLUST_FIRST * boot->bpbSecPerClust;
 255         boot->NumClusters = (boot->NumSectors - boot->ClusterOffset) /
 256             boot->bpbSecPerClust;
 257
 258         if (boot->flags & FAT32)
 259                 boot->ClustMask = CLUST32_MASK;
 260         else if (boot->NumClusters < (CLUST_RSRVD&CLUST12_MASK))
 261                 boot->ClustMask = CLUST12_MASK;
 262         else if (boot->NumClusters < (CLUST_RSRVD&CLUST16_MASK))
 263                 boot->ClustMask = CLUST16_MASK;
 264         else {
 265                 pfatal("Filesystem too big (%u clusters) for non-FAT32 partition",
 266                        boot->NumClusters);
 267                 return FSFATAL;
 268         }
 269
 270         switch (boot->ClustMask) {
 271         case CLUST32_MASK:
 272                 boot->NumFatEntries = (boot->FATsecs * boot->bpbBytesPerSec) / 4;
 273                 break;
 274         case CLUST16_MASK:
 275                 boot->NumFatEntries = (boot->FATsecs * boot->bpbBytesPerSec) / 2;
 276                 break;
 277         default:
 278                 boot->NumFatEntries = (boot->FATsecs * boot->bpbBytesPerSec * 2) / 3;
 279                 break;
 280         }
 281
 282         if (boot->NumFatEntries < boot->NumClusters - CLUST_FIRST) {
 283                 pfatal("FAT size too small, %u entries won't fit into %u sectors\n",
 284                        boot->NumClusters, boot->FATsecs);
 285                 return FSFATAL;
 286         }
 287         boot->ClusterSize = boot->bpbBytesPerSec * boot->bpbSecPerClust;
 288
 289         boot->NumFiles = 1;
 290         boot->NumFree = 0;
 291
 292         return ret;
 293 }
 294
 295 int
 296 writefsinfo(int dosfs, struct bootblock *boot)
 297 {
 298         u_char fsinfo[2 * DOSBOOTBLOCKSIZE];
 299
 300         if (lseek(dosfs, boot->bpbFSInfo * boot->bpbBytesPerSec, SEEK_SET)
 301             != boot->bpbFSInfo * boot->bpbBytesPerSec
 302             || read(dosfs, fsinfo, sizeof fsinfo) != sizeof fsinfo) {
 303                 perr("could not read fsinfo block");
 304                 return FSFATAL;
 305         }
 306         fsinfo[0x1e8] = (u_char)boot->FSFree;
 307         fsinfo[0x1e9] = (u_char)(boot->FSFree >> 8);
 308         fsinfo[0x1ea] = (u_char)(boot->FSFree >> 16);
 309         fsinfo[0x1eb] = (u_char)(boot->FSFree >> 24);
 310         fsinfo[0x1ec] = (u_char)boot->FSNext;
 311         fsinfo[0x1ed] = (u_char)(boot->FSNext >> 8);
 312         fsinfo[0x1ee] = (u_char)(boot->FSNext >> 16);
 313         fsinfo[0x1ef] = (u_char)(boot->FSNext >> 24);
 314         if (lseek(dosfs, boot->bpbFSInfo * boot->bpbBytesPerSec, SEEK_SET)
 315             != boot->bpbFSInfo * boot->bpbBytesPerSec
 316             || write(dosfs, fsinfo, sizeof fsinfo)
 317             != sizeof fsinfo) {
 318                 perr("Unable to write bpbFSInfo");
 319                 return FSFATAL;
 320         }
 321         /*
 322          * Technically, we should return FSBOOTMOD here.
 323          *
 324          * However, since Win95 OSR2 (the first M$ OS that has
 325          * support for FAT32) doesn't maintain the FSINFO block
 326          * correctly, it has to be fixed pretty often.
 327          *
 328          * Therefor, we handle the FSINFO block only informally,
 329          * fixing it if necessary, but otherwise ignoring the
 330          * fact that it was incorrect.
 331          */
 332         return 0;
 333 }