Comment boot block checks and perform additional sanity checks:
The following checks are now being enforced: - bpbBytesPerSec: only accept 512, 1024, 2048 and 4096. - bpbSecPerClust: only accept 1, 2, 4, 8, 16, 32, 64 and 128. - bpbResSectors: require non-zero. - bpbFATs: require non-zero. - bpbSectors: require zero for FAT32. - bpbFATsmall: require zero for FAT32. - bpbHugeSectors: require non-zero for FAT32. Bail out if the BPB contained values that do not meet these requirements. We also require FATsecs * FATsecs to not overflow 32-bit unsigned integer. Check for backup boot block was removed because the checker does not take corrective action, and msdosfs driver ignores it too.
This commit is contained in:
Xin LI
parent
110f229794
commit
b770b08061
@ -33,6 +33,9 @@ static const char rcsid[] =
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"$FreeBSD$";
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#endif /* not lint */
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#include <sys/param.h>
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#include <stdint.h>
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#include <stdlib.h>
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#include <string.h>
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#include <stdio.h>
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@ -46,9 +49,7 @@ readboot(int dosfs, struct bootblock *boot)
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{
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u_char block[DOSBOOTBLOCKSIZE];
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u_char fsinfo[2 * DOSBOOTBLOCKSIZE];
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u_char backup[DOSBOOTBLOCKSIZE];
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int ret = FSOK;
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int i;
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if ((size_t)read(dosfs, block, sizeof block) != sizeof block) {
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perr("could not read boot block");
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@ -64,61 +65,133 @@ readboot(int dosfs, struct bootblock *boot)
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memset(boot, 0, sizeof *boot);
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boot->ValidFat = -1;
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/* decode bios parameter block */
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/* Decode BIOS Parameter Block */
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/* Bytes per sector: can only be 512, 1024, 2048 and 4096. */
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boot->bpbBytesPerSec = block[11] + (block[12] << 8);
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boot->bpbSecPerClust = block[13];
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boot->bpbResSectors = block[14] + (block[15] << 8);
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boot->bpbFATs = block[16];
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boot->bpbRootDirEnts = block[17] + (block[18] << 8);
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boot->bpbSectors = block[19] + (block[20] << 8);
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boot->bpbMedia = block[21];
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boot->bpbFATsmall = block[22] + (block[23] << 8);
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boot->SecPerTrack = block[24] + (block[25] << 8);
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boot->bpbHeads = block[26] + (block[27] << 8);
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boot->bpbHiddenSecs = block[28] + (block[29] << 8) +
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(block[30] << 16) + (block[31] << 24);
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boot->bpbHugeSectors = block[32] + (block[33] << 8) +
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(block[34] << 16) + (block[35] << 24);
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boot->FATsecs = boot->bpbFATsmall;
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if (boot->bpbBytesPerSec % DOSBOOTBLOCKSIZE_REAL != 0 ||
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boot->bpbBytesPerSec / DOSBOOTBLOCKSIZE_REAL == 0) {
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if (boot->bpbBytesPerSec < DOSBOOTBLOCKSIZE_REAL ||
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boot->bpbBytesPerSec > DOSBOOTBLOCKSIZE ||
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!powerof2(boot->bpbBytesPerSec)) {
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pfatal("Invalid sector size: %u", boot->bpbBytesPerSec);
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return FSFATAL;
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}
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/* Sectors per cluster: can only be: 1, 2, 4, 8, 16, 32, 64, 128. */
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boot->bpbSecPerClust = block[13];
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if (boot->bpbSecPerClust == 0 || !powerof2(boot->bpbSecPerClust)) {
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pfatal("Invalid cluster size: %u", boot->bpbSecPerClust);
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return FSFATAL;
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}
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/* Reserved sectors: must be non-zero */
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boot->bpbResSectors = block[14] + (block[15] << 8);
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if (boot->bpbResSectors < 1) {
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pfatal("Invalid reserved sectors: %u",
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boot->bpbResSectors);
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return FSFATAL;
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}
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/* Number of FATs */
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boot->bpbFATs = block[16];
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if (boot->bpbFATs == 0) {
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pfatal("Invalid number of FATs: %u", boot->bpbFATs);
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return FSFATAL;
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}
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if (!boot->bpbRootDirEnts)
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boot->flags |= FAT32;
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if (boot->flags & FAT32) {
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boot->FATsecs = block[36] + (block[37] << 8)
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+ (block[38] << 16) + (block[39] << 24);
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if (block[40] & 0x80)
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boot->ValidFat = block[40] & 0x0f;
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/* check version number: */
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if (block[42] || block[43]) {
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/* Correct? XXX */
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pfatal("Unknown file system version: %x.%x",
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block[43], block[42]);
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/* Root directory entries for FAT12 and FAT16 */
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boot->bpbRootDirEnts = block[17] + (block[18] << 8);
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if (!boot->bpbRootDirEnts) {
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/* bpbRootDirEnts = 0 suggests that we are FAT32 */
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boot->flags |= FAT32;
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}
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/* Total sectors (16 bits) */
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boot->bpbSectors = block[19] + (block[20] << 8);
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if (boot->bpbSectors != 0 && (boot->flags & FAT32)) {
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pfatal("Invalid 16-bit total sector count on FAT32: %u",
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boot->bpbSectors);
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return FSFATAL;
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}
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/* Media type: ignored */
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boot->bpbMedia = block[21];
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/* FAT12/FAT16: 16-bit count of sectors per FAT */
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boot->bpbFATsmall = block[22] + (block[23] << 8);
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if (boot->bpbFATsmall != 0 && (boot->flags & FAT32)) {
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pfatal("Invalid 16-bit FAT sector count on FAT32: %u",
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boot->bpbFATsmall);
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return FSFATAL;
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}
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/* Legacy CHS geometry numbers: ignored */
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boot->SecPerTrack = block[24] + (block[25] << 8);
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boot->bpbHeads = block[26] + (block[27] << 8);
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/* Hidden sectors: ignored */
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boot->bpbHiddenSecs = block[28] + (block[29] << 8) +
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(block[30] << 16) + (block[31] << 24);
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/* Total sectors (32 bits) */
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boot->bpbHugeSectors = block[32] + (block[33] << 8) +
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(block[34] << 16) + (block[35] << 24);
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if (boot->bpbHugeSectors == 0) {
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if (boot->flags & FAT32) {
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pfatal("FAT32 with sector count of zero");
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return FSFATAL;
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} else if (boot->bpbSectors == 0) {
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pfatal("FAT with sector count of zero");
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return FSFATAL;
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}
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boot->bpbRootClust = block[44] + (block[45] << 8)
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+ (block[46] << 16) + (block[47] << 24);
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boot->bpbFSInfo = block[48] + (block[49] << 8);
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boot->bpbBackup = block[50] + (block[51] << 8);
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boot->NumSectors = boot->bpbSectors;
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} else {
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if (boot->bpbSectors != 0) {
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pfatal("Invalid FAT sector count");
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return FSFATAL;
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}
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boot->NumSectors = boot->bpbHugeSectors;
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}
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if (boot->flags & FAT32) {
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/* If the OEM Name field is EXFAT, it's not FAT32, so bail */
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if (!memcmp(&block[3], "EXFAT ", 8)) {
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pfatal("exFAT filesystem is not supported.");
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return FSFATAL;
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}
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/* check basic parameters */
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if ((boot->bpbFSInfo == 0) || (boot->bpbSecPerClust == 0)) {
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/* 32-bit count of sectors per FAT */
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boot->FATsecs = block[36] + (block[37] << 8)
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+ (block[38] << 16) + (block[39] << 24);
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if (block[40] & 0x80)
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boot->ValidFat = block[40] & 0x0f;
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/* FAT32 version, bail out if not 0.0 */
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if (block[42] || block[43]) {
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pfatal("Unknown file system version: %x.%x",
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block[43], block[42]);
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return FSFATAL;
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}
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/*
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* Cluster number of the first cluster of root directory.
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*
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* Should be 2 but do not require it.
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*/
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boot->bpbRootClust = block[44] + (block[45] << 8)
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+ (block[46] << 16) + (block[47] << 24);
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/* Sector number of the FSInfo structure, usually 1 */
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boot->bpbFSInfo = block[48] + (block[49] << 8);
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/* Sector number of the backup boot block, ignored */
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boot->bpbBackup = block[50] + (block[51] << 8);
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/* Check basic parameters */
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if (boot->bpbFSInfo == 0) {
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/*
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* Either the BIOS Parameter Block has been corrupted,
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* or this is not a FAT32 filesystem, most likely an
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@ -127,6 +200,8 @@ readboot(int dosfs, struct bootblock *boot)
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pfatal("Invalid FAT32 Extended BIOS Parameter Block");
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return FSFATAL;
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}
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/* Read in and verify the FSInfo block */
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if (lseek(dosfs, boot->bpbFSInfo * boot->bpbBytesPerSec,
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SEEK_SET) != boot->bpbFSInfo * boot->bpbBytesPerSec
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|| read(dosfs, fsinfo, sizeof fsinfo) != sizeof fsinfo) {
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@ -164,8 +239,8 @@ readboot(int dosfs, struct bootblock *boot)
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ret = FSBOOTMOD;
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} else
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boot->bpbFSInfo = 0;
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}
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if (boot->bpbFSInfo) {
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} else {
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/* We appear to have a valid FSInfo block, decode */
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boot->FSFree = fsinfo[0x1e8] + (fsinfo[0x1e9] << 8)
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+ (fsinfo[0x1ea] << 16)
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+ (fsinfo[0x1eb] << 24);
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@ -173,45 +248,17 @@ readboot(int dosfs, struct bootblock *boot)
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+ (fsinfo[0x1ee] << 16)
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+ (fsinfo[0x1ef] << 24);
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}
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if (lseek(dosfs, boot->bpbBackup * boot->bpbBytesPerSec,
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SEEK_SET)
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!= boot->bpbBackup * boot->bpbBytesPerSec
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|| read(dosfs, backup, sizeof backup) != sizeof backup) {
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perr("could not read backup bootblock");
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return FSFATAL;
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}
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backup[65] = block[65]; /* XXX */
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if (memcmp(block + 11, backup + 11, 79)) {
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/*
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* XXX We require a reference that explains
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* that these bytes need to match, or should
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* drop the check. gdt@NetBSD has observed
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* filesystems that work fine under Windows XP
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* and NetBSD that do not match, so the
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* requirement is suspect. For now, just
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* print out useful information and continue.
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*/
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pwarn("backup (block %d) mismatch with primary bootblock:\n",
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boot->bpbBackup);
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for (i = 11; i < 11 + 90; i++) {
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if (block[i] != backup[i])
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pwarn("\ti=%d\tprimary 0x%02x\tbackup 0x%02x\n",
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i, block[i], backup[i]);
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}
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}
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/* Check backup bpbFSInfo? XXX */
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} else {
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/* !FAT32: FAT12/FAT16 */
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boot->FATsecs = boot->bpbFATsmall;
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}
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if (boot->bpbSecPerClust == 0) {
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pfatal("Invalid cluster size: %u", boot->bpbSecPerClust);
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if (boot->FATsecs > UINT32_MAX / boot->bpbFATs) {
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pfatal("Invalid FATs(%u) with FATsecs(%zu)",
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boot->bpbFATs, (size_t)boot->FATsecs);
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return FSFATAL;
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}
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if (boot->bpbSectors) {
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boot->bpbHugeSectors = 0;
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boot->NumSectors = boot->bpbSectors;
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} else
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boot->NumSectors = boot->bpbHugeSectors;
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boot->ClusterOffset = (boot->bpbRootDirEnts * 32 +
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boot->bpbBytesPerSec - 1) / boot->bpbBytesPerSec +
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boot->bpbResSectors + boot->bpbFATs * boot->FATsecs -
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