Author: delphij
Date: Mon Aug 26 06:41:17 2019
New Revision: 351502
URL: https://svnweb.freebsd.org/changeset/base/351502
Log:
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.
Modified:
head/sbin/fsck_msdosfs/boot.c
Modified: head/sbin/fsck_msdosfs/boot.c
==============================================================================
--- head/sbin/fsck_msdosfs/boot.c Mon Aug 26 00:46:39 2019
(r351501)
+++ head/sbin/fsck_msdosfs/boot.c Mon Aug 26 06:41:17 2019
(r351502)
@@ -33,6 +33,9 @@ static const char rcsid[] =
"$FreeBSD$";
#endif /* not lint */
+#include <sys/param.h>
+
+#include <stdint.h>
#include <stdlib.h>
#include <string.h>
#include <stdio.h>
@@ -46,9 +49,7 @@ readboot(int dosfs, struct bootblock *boot)
{
u_char block[DOSBOOTBLOCKSIZE];
u_char fsinfo[2 * DOSBOOTBLOCKSIZE];
- u_char backup[DOSBOOTBLOCKSIZE];
int ret = FSOK;
- int i;
if ((size_t)read(dosfs, block, sizeof block) != sizeof block) {
perr("could not read boot block");
@@ -64,61 +65,133 @@ readboot(int dosfs, struct bootblock *boot)
memset(boot, 0, sizeof *boot);
boot->ValidFat = -1;
- /* decode bios parameter block */
+ /* Decode BIOS Parameter Block */
+
+ /* Bytes per sector: can only be 512, 1024, 2048 and 4096. */
boot->bpbBytesPerSec = block[11] + (block[12] << 8);
+ if (boot->bpbBytesPerSec < DOSBOOTBLOCKSIZE_REAL ||
+ boot->bpbBytesPerSec > DOSBOOTBLOCKSIZE ||
+ !powerof2(boot->bpbBytesPerSec)) {
+ pfatal("Invalid sector size: %u", boot->bpbBytesPerSec);
+ return FSFATAL;
+ }
+
+ /* Sectors per cluster: can only be: 1, 2, 4, 8, 16, 32, 64, 128. */
boot->bpbSecPerClust = block[13];
+ if (boot->bpbSecPerClust == 0 || !powerof2(boot->bpbSecPerClust)) {
+ pfatal("Invalid cluster size: %u", boot->bpbSecPerClust);
+ return FSFATAL;
+ }
+
+ /* Reserved sectors: must be non-zero */
boot->bpbResSectors = block[14] + (block[15] << 8);
+ if (boot->bpbResSectors < 1) {
+ pfatal("Invalid reserved sectors: %u",
+ boot->bpbResSectors);
+ return FSFATAL;
+ }
+
+ /* Number of FATs */
boot->bpbFATs = block[16];
+ if (boot->bpbFATs == 0) {
+ pfatal("Invalid number of FATs: %u", boot->bpbFATs);
+ return FSFATAL;
+ }
+
+ /* Root directory entries for FAT12 and FAT16 */
boot->bpbRootDirEnts = block[17] + (block[18] << 8);
+ if (!boot->bpbRootDirEnts) {
+ /* bpbRootDirEnts = 0 suggests that we are FAT32 */
+ boot->flags |= FAT32;
+ }
+
+ /* Total sectors (16 bits) */
boot->bpbSectors = block[19] + (block[20] << 8);
+ if (boot->bpbSectors != 0 && (boot->flags & FAT32)) {
+ pfatal("Invalid 16-bit total sector count on FAT32: %u",
+ boot->bpbSectors);
+ return FSFATAL;
+ }
+
+ /* Media type: ignored */
boot->bpbMedia = block[21];
+
+ /* FAT12/FAT16: 16-bit count of sectors per FAT */
boot->bpbFATsmall = block[22] + (block[23] << 8);
+ if (boot->bpbFATsmall != 0 && (boot->flags & FAT32)) {
+ pfatal("Invalid 16-bit FAT sector count on FAT32: %u",
+ boot->bpbFATsmall);
+ return FSFATAL;
+ }
+
+ /* Legacy CHS geometry numbers: ignored */
boot->SecPerTrack = block[24] + (block[25] << 8);
boot->bpbHeads = block[26] + (block[27] << 8);
+
+ /* Hidden sectors: ignored */
boot->bpbHiddenSecs = block[28] + (block[29] << 8) +
(block[30] << 16) + (block[31] << 24);
+
+ /* Total sectors (32 bits) */
boot->bpbHugeSectors = block[32] + (block[33] << 8) +
(block[34] << 16) + (block[35] << 24);
+ if (boot->bpbHugeSectors == 0) {
+ if (boot->flags & FAT32) {
+ pfatal("FAT32 with sector count of zero");
+ return FSFATAL;
+ } else if (boot->bpbSectors == 0) {
+ pfatal("FAT with sector count of zero");
+ return FSFATAL;
+ }
+ boot->NumSectors = boot->bpbSectors;
+ } else {
+ if (boot->bpbSectors != 0) {
+ pfatal("Invalid FAT sector count");
+ return FSFATAL;
+ }
+ boot->NumSectors = boot->bpbHugeSectors;
+ }
- boot->FATsecs = boot->bpbFATsmall;
- if (boot->bpbBytesPerSec % DOSBOOTBLOCKSIZE_REAL != 0 ||
- boot->bpbBytesPerSec / DOSBOOTBLOCKSIZE_REAL == 0) {
- pfatal("Invalid sector size: %u", boot->bpbBytesPerSec);
- return FSFATAL;
- }
- if (boot->bpbFATs == 0) {
- pfatal("Invalid number of FATs: %u", boot->bpbFATs);
- return FSFATAL;
- }
- if (!boot->bpbRootDirEnts)
- boot->flags |= FAT32;
+
+
if (boot->flags & FAT32) {
+ /* If the OEM Name field is EXFAT, it's not FAT32, so bail */
+ if (!memcmp(&block[3], "EXFAT ", 8)) {
+ pfatal("exFAT filesystem is not supported.");
+ return FSFATAL;
+ }
+
+ /* 32-bit count of sectors per FAT */
boot->FATsecs = block[36] + (block[37] << 8)
+ (block[38] << 16) + (block[39] << 24);
+
if (block[40] & 0x80)
boot->ValidFat = block[40] & 0x0f;
- /* check version number: */
+ /* FAT32 version, bail out if not 0.0 */
if (block[42] || block[43]) {
- /* Correct? XXX */
pfatal("Unknown file system version: %x.%x",
block[43], block[42]);
return FSFATAL;
}
+
+ /*
+ * Cluster number of the first cluster of root directory.
+ *
+ * Should be 2 but do not require it.
+ */
boot->bpbRootClust = block[44] + (block[45] << 8)
+ (block[46] << 16) + (block[47] << 24);
+
+ /* Sector number of the FSInfo structure, usually 1 */
boot->bpbFSInfo = block[48] + (block[49] << 8);
+
+ /* Sector number of the backup boot block, ignored */
boot->bpbBackup = block[50] + (block[51] << 8);
- /* If the OEM Name field is EXFAT, it's not FAT32, so bail */
- if (!memcmp(&block[3], "EXFAT ", 8)) {
- pfatal("exFAT filesystem is not supported.");
- return FSFATAL;
- }
-
- /* check basic parameters */
- if ((boot->bpbFSInfo == 0) || (boot->bpbSecPerClust == 0)) {
+ /* Check basic parameters */
+ if (boot->bpbFSInfo == 0) {
/*
* Either the BIOS Parameter Block has been corrupted,
* or this is not a FAT32 filesystem, most likely an
@@ -127,6 +200,8 @@ readboot(int dosfs, struct bootblock *boot)
pfatal("Invalid FAT32 Extended BIOS Parameter Block");
return FSFATAL;
}
+
+ /* Read in and verify the FSInfo block */
if (lseek(dosfs, boot->bpbFSInfo * boot->bpbBytesPerSec,
SEEK_SET) != boot->bpbFSInfo * boot->bpbBytesPerSec
|| read(dosfs, fsinfo, sizeof fsinfo) != sizeof fsinfo) {
@@ -164,8 +239,8 @@ readboot(int dosfs, struct bootblock *boot)
ret = FSBOOTMOD;
} else
boot->bpbFSInfo = 0;
- }
- if (boot->bpbFSInfo) {
+ } else {
+ /* We appear to have a valid FSInfo block, decode */
boot->FSFree = fsinfo[0x1e8] + (fsinfo[0x1e9] << 8)
+ (fsinfo[0x1ea] << 16)
+ (fsinfo[0x1eb] << 24);
@@ -173,45 +248,17 @@ readboot(int dosfs, struct bootblock *boot)
+ (fsinfo[0x1ee] << 16)
+ (fsinfo[0x1ef] << 24);
}
-
- if (lseek(dosfs, boot->bpbBackup * boot->bpbBytesPerSec,
- SEEK_SET)
- != boot->bpbBackup * boot->bpbBytesPerSec
- || read(dosfs, backup, sizeof backup) != sizeof backup) {
- perr("could not read backup bootblock");
- return FSFATAL;
- }
- backup[65] = block[65]; /* XXX */
- if (memcmp(block + 11, backup + 11, 79)) {
- /*
- * XXX We require a reference that explains
- * that these bytes need to match, or should
- * drop the check. gdt@NetBSD has observed
- * filesystems that work fine under Windows XP
- * and NetBSD that do not match, so the
- * requirement is suspect. For now, just
- * print out useful information and continue.
- */
- pwarn("backup (block %d) mismatch with primary
bootblock:\n",
- boot->bpbBackup);
- for (i = 11; i < 11 + 90; i++) {
- if (block[i] != backup[i])
- pwarn("\ti=%d\tprimary 0x%02x\tbackup
0x%02x\n",
- i, block[i], backup[i]);
- }
- }
- /* Check backup bpbFSInfo?
XXX */
+ } else {
+ /* !FAT32: FAT12/FAT16 */
+ boot->FATsecs = boot->bpbFATsmall;
}
- if (boot->bpbSecPerClust == 0) {
- pfatal("Invalid cluster size: %u", boot->bpbSecPerClust);
+ if (boot->FATsecs > UINT32_MAX / boot->bpbFATs) {
+ pfatal("Invalid FATs(%u) with FATsecs(%zu)",
+ boot->bpbFATs, (size_t)boot->FATsecs);
return FSFATAL;
}
- if (boot->bpbSectors) {
- boot->bpbHugeSectors = 0;
- boot->NumSectors = boot->bpbSectors;
- } else
- boot->NumSectors = boot->bpbHugeSectors;
+
boot->ClusterOffset = (boot->bpbRootDirEnts * 32 +
boot->bpbBytesPerSec - 1) / boot->bpbBytesPerSec +
boot->bpbResSectors + boot->bpbFATs * boot->FATsecs -
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