From 4438d71949e8a59f2ac2349a450f6965fee6c6e4 Mon Sep 17 00:00:00 2001 From: delphij Date: Mon, 26 Aug 2019 06:41:17 +0000 Subject: [PATCH] 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. --- sbin/fsck_msdosfs/boot.c | 171 +++++++++++++++++++++++++-------------- 1 file changed, 109 insertions(+), 62 deletions(-) diff --git a/sbin/fsck_msdosfs/boot.c b/sbin/fsck_msdosfs/boot.c index 56bd57d7be1..5816b986f69 100644 --- a/sbin/fsck_msdosfs/boot.c +++ b/sbin/fsck_msdosfs/boot.c @@ -33,6 +33,9 @@ static const char rcsid[] = "$FreeBSD$"; #endif /* not lint */ +#include + +#include #include #include #include @@ -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); - 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; - } + /* Sector number of the backup boot block, ignored */ + boot->bpbBackup = block[50] + (block[51] << 8); - /* 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 - -- 2.45.0