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util-linux/libblkid/src/superblocks/vfat.c

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/*
* Copyright (C) 1999 by Andries Brouwer
* Copyright (C) 1999, 2000, 2003 by Theodore Ts'o
* Copyright (C) 2001 by Andreas Dilger
* Copyright (C) 2004 Kay Sievers <kay.sievers@vrfy.org>
* Copyright (C) 2008 Karel Zak <kzak@redhat.com>
*
* This file may be redistributed under the terms of the
* GNU Lesser General Public License.
*/
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>
#include <errno.h>
#include <ctype.h>
#include <stdint.h>
#include <inttypes.h>
#include "pt-mbr.h"
#include "superblocks.h"
/* Yucky misaligned values */
struct vfat_super_block {
/* 00*/ unsigned char vs_ignored[3];
/* 03*/ unsigned char vs_sysid[8];
/* 0b*/ unsigned char vs_sector_size[2];
/* 0d*/ uint8_t vs_cluster_size;
/* 0e*/ uint16_t vs_reserved;
/* 10*/ uint8_t vs_fats;
/* 11*/ unsigned char vs_dir_entries[2];
/* 13*/ unsigned char vs_sectors[2];
/* 15*/ unsigned char vs_media;
/* 16*/ uint16_t vs_fat_length;
/* 18*/ uint16_t vs_secs_track;
/* 1a*/ uint16_t vs_heads;
/* 1c*/ uint32_t vs_hidden;
/* 20*/ uint32_t vs_total_sect;
/* 24*/ uint32_t vs_fat32_length;
/* 28*/ uint16_t vs_flags;
/* 2a*/ uint8_t vs_version[2];
/* 2c*/ uint32_t vs_root_cluster;
/* 30*/ uint16_t vs_fsinfo_sector;
/* 32*/ uint16_t vs_backup_boot;
/* 34*/ uint16_t vs_reserved2[6];
/* 40*/ unsigned char vs_unknown[3];
/* 43*/ unsigned char vs_serno[4];
/* 47*/ unsigned char vs_label[11];
/* 52*/ unsigned char vs_magic[8];
/* 5a*/ unsigned char vs_dummy2[0x1fe - 0x5a];
/*1fe*/ unsigned char vs_pmagic[2];
} __attribute__((packed));
/* Yucky misaligned values */
struct msdos_super_block {
/* 00*/ unsigned char ms_ignored[3];
/* 03*/ unsigned char ms_sysid[8];
/* 0b*/ unsigned char ms_sector_size[2];
/* 0d*/ uint8_t ms_cluster_size;
/* 0e*/ uint16_t ms_reserved;
/* 10*/ uint8_t ms_fats;
/* 11*/ unsigned char ms_dir_entries[2];
/* 13*/ unsigned char ms_sectors[2]; /* =0 iff V3 or later */
/* 15*/ unsigned char ms_media;
/* 16*/ uint16_t ms_fat_length; /* Sectors per FAT */
/* 18*/ uint16_t ms_secs_track;
/* 1a*/ uint16_t ms_heads;
/* 1c*/ uint32_t ms_hidden;
/* V3 BPB */
/* 20*/ uint32_t ms_total_sect; /* iff ms_sectors == 0 */
/* V4 BPB */
/* 24*/ unsigned char ms_unknown[3]; /* Phys drive no., resvd, V4 sig (0x29) */
/* 27*/ unsigned char ms_serno[4];
/* 2b*/ unsigned char ms_label[11];
/* 36*/ unsigned char ms_magic[8];
/* 3e*/ unsigned char ms_dummy2[0x1fe - 0x3e];
/*1fe*/ unsigned char ms_pmagic[2];
} __attribute__((packed));
struct vfat_dir_entry {
uint8_t name[11];
uint8_t attr;
uint16_t time_creat;
uint16_t date_creat;
uint16_t time_acc;
uint16_t date_acc;
uint16_t cluster_high;
uint16_t time_write;
uint16_t date_write;
uint16_t cluster_low;
uint32_t size;
} __attribute__((packed));
struct fat32_fsinfo {
uint8_t signature1[4];
uint32_t reserved1[120];
uint8_t signature2[4];
uint32_t free_clusters;
uint32_t next_cluster;
uint32_t reserved2[4];
} __attribute__((packed));
/* maximum number of clusters */
#define FAT12_MAX 0xFF4
#define FAT16_MAX 0xFFF4
#define FAT32_MAX 0x0FFFFFF6
#define FAT_ATTR_VOLUME_ID 0x08
#define FAT_ATTR_DIR 0x10
#define FAT_ATTR_LONG_NAME 0x0f
#define FAT_ATTR_MASK 0x3f
#define FAT_ENTRY_FREE 0xe5
static const char *no_name = "NO NAME ";
#define unaligned_le16(x) \
(((unsigned char *) x)[0] + (((unsigned char *) x)[1] << 8))
/*
* Look for LABEL (name) in the FAT root directory.
*/
static unsigned char *search_fat_label(blkid_probe pr,
uint64_t offset, uint32_t entries)
{
struct vfat_dir_entry *ent, *dir = NULL;
uint32_t i;
DBG(LOWPROBE, ul_debug("\tlook for label in root-dir "
"(entries: %"PRIu32", offset: %"PRIu64")", entries, offset));
if (!blkid_probe_is_tiny(pr)) {
/* large disk, read whole root directory */
dir = (struct vfat_dir_entry *)
blkid_probe_get_buffer(pr,
offset,
(uint64_t) entries *
sizeof(struct vfat_dir_entry));
if (!dir)
return NULL;
}
for (i = 0; i < entries; i++) {
/*
* The root directory could be relatively large (4-16kB).
* Fortunately, the LABEL is usually the first entry in the
* directory. On tiny disks we call read() per entry.
*/
if (!dir)
ent = (struct vfat_dir_entry *)
blkid_probe_get_buffer(pr,
(uint64_t) offset + (i *
sizeof(struct vfat_dir_entry)),
sizeof(struct vfat_dir_entry));
else
ent = &dir[i];
if (!ent || ent->name[0] == 0x00)
break;
if ((ent->name[0] == FAT_ENTRY_FREE) ||
(ent->cluster_high != 0 || ent->cluster_low != 0) ||
((ent->attr & FAT_ATTR_MASK) == FAT_ATTR_LONG_NAME))
continue;
if ((ent->attr & (FAT_ATTR_VOLUME_ID | FAT_ATTR_DIR)) ==
FAT_ATTR_VOLUME_ID) {
DBG(LOWPROBE, ul_debug("\tfound fs LABEL at entry %d", i));
if (ent->name[0] == 0x05)
ent->name[0] = 0xE5;
return ent->name;
}
}
return NULL;
}
static int fat_valid_superblock(blkid_probe pr,
const struct blkid_idmag *mag,
struct msdos_super_block *ms,
struct vfat_super_block *vs,
uint32_t *cluster_count, uint32_t *fat_size)
{
uint16_t sector_size, dir_entries, reserved;
uint32_t sect_count, __fat_size, dir_size, __cluster_count, fat_length;
uint32_t max_count;
/* extra check for FATs without magic strings */
if (mag->len <= 2) {
/* Old floppies have a valid MBR signature */
if (ms->ms_pmagic[0] != 0x55 || ms->ms_pmagic[1] != 0xAA)
return 0;
/*
* OS/2 and apparently DFSee will place a FAT12/16-like
* pseudo-superblock in the first 512 bytes of non-FAT
* filesystems --- at least JFS and HPFS, and possibly others.
* So we explicitly check for those filesystems at the
* FAT12/16 filesystem magic field identifier, and if they are
* present, we rule this out as a FAT filesystem, despite the
* FAT-like pseudo-header.
*/
if ((memcmp(ms->ms_magic, "JFS ", 8) == 0) ||
(memcmp(ms->ms_magic, "HPFS ", 8) == 0)) {
DBG(LOWPROBE, ul_debug("\tJFS/HPFS detected"));
return 0;
}
}
/* fat counts(Linux kernel expects at least 1 FAT table) */
if (!ms->ms_fats)
return 0;
if (!ms->ms_reserved)
return 0;
if (!(0xf8 <= ms->ms_media || ms->ms_media == 0xf0))
return 0;
if (!is_power_of_2(ms->ms_cluster_size))
return 0;
sector_size = unaligned_le16(&ms->ms_sector_size);
if (!is_power_of_2(sector_size) ||
sector_size < 512 || sector_size > 4096)
return 0;
dir_entries = unaligned_le16(&ms->ms_dir_entries);
reserved = le16_to_cpu(ms->ms_reserved);
sect_count = unaligned_le16(&ms->ms_sectors);
if (sect_count == 0)
sect_count = le32_to_cpu(ms->ms_total_sect);
fat_length = le16_to_cpu(ms->ms_fat_length);
if (fat_length == 0)
fat_length = le32_to_cpu(vs->vs_fat32_length);
__fat_size = fat_length * ms->ms_fats;
dir_size = ((dir_entries * sizeof(struct vfat_dir_entry)) +
(sector_size-1)) / sector_size;
__cluster_count = (sect_count - (reserved + __fat_size + dir_size)) /
ms->ms_cluster_size;
if (!ms->ms_fat_length && vs->vs_fat32_length)
max_count = FAT32_MAX;
else
max_count = __cluster_count > FAT12_MAX ? FAT16_MAX : FAT12_MAX;
if (__cluster_count > max_count)
return 0;
if (fat_size)
*fat_size = __fat_size;
if (cluster_count)
*cluster_count = __cluster_count;
if (blkid_probe_is_wholedisk(pr)) {
/* OK, seems like FAT, but it's possible that we found boot
* sector with crazy FAT-like stuff (magic strings, media,
* etc..) before MBR. Let's make sure that there is no MBR with
* usable partition. */
unsigned char *buf = (unsigned char *) ms;
if (mbr_is_valid_magic(buf)) {
struct dos_partition *p0 = mbr_get_partition(buf, 0);
if (dos_partition_get_size(p0) != 0 &&
(p0->boot_ind == 0 || p0->boot_ind == 0x80)) {
DBG(LOWPROBE, ul_debug("\tMBR detected"));
return 0;
}
}
}
if (blkid_probe_is_bitlocker(pr))
return 0;
return 1; /* valid */
}
/* function prototype to avoid warnings (duplicate in partitions/dos.c) */
extern int blkid_probe_is_vfat(blkid_probe pr);
/*
* This function is used by MBR partition table parser to avoid
* misinterpretation of FAT filesystem.
*/
int blkid_probe_is_vfat(blkid_probe pr)
{
struct vfat_super_block *vs;
struct msdos_super_block *ms;
const struct blkid_idmag *mag = NULL;
int rc;
rc = blkid_probe_get_idmag(pr, &vfat_idinfo, NULL, &mag);
if (rc < 0)
return rc; /* error */
if (rc != BLKID_PROBE_OK || !mag)
return 0;
ms = blkid_probe_get_sb(pr, mag, struct msdos_super_block);
if (!ms)
return errno ? -errno : 0;
vs = blkid_probe_get_sb(pr, mag, struct vfat_super_block);
if (!vs)
return errno ? -errno : 0;
return fat_valid_superblock(pr, mag, ms, vs, NULL, NULL);
}
/* FAT label extraction from the root directory taken from Kay
* Sievers's volume_id library */
static int probe_vfat(blkid_probe pr, const struct blkid_idmag *mag)
{
struct vfat_super_block *vs;
struct msdos_super_block *ms;
const unsigned char *vol_label = NULL;
const unsigned char *boot_label = NULL;
unsigned char *vol_serno = NULL, vol_label_buf[11];
uint16_t sector_size = 0, reserved;
uint32_t cluster_count, fat_size;
const char *version = NULL;
ms = blkid_probe_get_sb(pr, mag, struct msdos_super_block);
if (!ms)
return errno ? -errno : 1;
vs = blkid_probe_get_sb(pr, mag, struct vfat_super_block);
if (!vs)
return errno ? -errno : 1;
if (!fat_valid_superblock(pr, mag, ms, vs, &cluster_count, &fat_size))
return 1;
sector_size = unaligned_le16(&ms->ms_sector_size);
reserved = le16_to_cpu(ms->ms_reserved);
if (ms->ms_fat_length) {
/* the label may be an attribute in the root directory */
uint32_t root_start = (reserved + fat_size) * sector_size;
uint32_t root_dir_entries = unaligned_le16(&vs->vs_dir_entries);
vol_label = search_fat_label(pr, root_start, root_dir_entries);
if (vol_label) {
memcpy(vol_label_buf, vol_label, 11);
vol_label = vol_label_buf;
}
boot_label = ms->ms_label;
vol_serno = ms->ms_serno;
blkid_probe_set_value(pr, "SEC_TYPE", (unsigned char *) "msdos",
sizeof("msdos"));
if (cluster_count < FAT12_MAX)
version = "FAT12";
else if (cluster_count < FAT16_MAX)
version = "FAT16";
} else if (vs->vs_fat32_length) {
unsigned char *buf;
uint16_t fsinfo_sect;
int maxloop = 100;
/* Search the FAT32 root dir for the label attribute */
uint32_t buf_size = vs->vs_cluster_size * sector_size;
uint32_t start_data_sect = reserved + fat_size;
uint32_t entries = le32_to_cpu(vs->vs_fat32_length) *
sector_size / sizeof(uint32_t);
uint32_t next = le32_to_cpu(vs->vs_root_cluster);
while (next && next < entries && --maxloop) {
uint32_t next_sect_off;
uint64_t next_off, fat_entry_off;
int count;
next_sect_off = (next - 2) * vs->vs_cluster_size;
next_off = (uint64_t)(start_data_sect + next_sect_off) *
sector_size;
count = buf_size / sizeof(struct vfat_dir_entry);
vol_label = search_fat_label(pr, next_off, count);
if (vol_label) {
memcpy(vol_label_buf, vol_label, 11);
vol_label = vol_label_buf;
break;
}
/* get FAT entry */
fat_entry_off = ((uint64_t) reserved * sector_size) +
(next * sizeof(uint32_t));
buf = blkid_probe_get_buffer(pr, fat_entry_off, buf_size);
if (buf == NULL)
break;
/* set next cluster */
next = le32_to_cpu(*((uint32_t *) buf)) & 0x0fffffff;
}
version = "FAT32";
boot_label = vs->vs_label;
vol_serno = vs->vs_serno;
/*
* FAT32 should have a valid signature in the fsinfo block,
* but also allow all bytes set to '\0', because some volumes
* do not set the signature at all.
*/
fsinfo_sect = le16_to_cpu(vs->vs_fsinfo_sector);
if (fsinfo_sect) {
struct fat32_fsinfo *fsinfo;
buf = blkid_probe_get_buffer(pr,
(uint64_t) fsinfo_sect * sector_size,
sizeof(struct fat32_fsinfo));
if (buf == NULL)
return errno ? -errno : 1;
fsinfo = (struct fat32_fsinfo *) buf;
if (memcmp(fsinfo->signature1, "\x52\x52\x61\x41", 4) != 0 &&
memcmp(fsinfo->signature1, "\x52\x52\x64\x41", 4) != 0 &&
memcmp(fsinfo->signature1, "\x00\x00\x00\x00", 4) != 0)
return 1;
if (memcmp(fsinfo->signature2, "\x72\x72\x41\x61", 4) != 0 &&
memcmp(fsinfo->signature2, "\x00\x00\x00\x00", 4) != 0)
return 1;
}
}
if (boot_label && memcmp(boot_label, no_name, 11))
blkid_probe_set_id_label(pr, "LABEL_FATBOOT", boot_label, 11);
if (vol_label)
blkid_probe_set_label(pr, vol_label, 11);
/* We can't just print them as %04X, because they are unaligned */
if (vol_serno)
blkid_probe_sprintf_uuid(pr, vol_serno, 4, "%02X%02X-%02X%02X",
vol_serno[3], vol_serno[2], vol_serno[1], vol_serno[0]);
if (version)
blkid_probe_set_version(pr, version);
return 0;
}
const struct blkid_idinfo vfat_idinfo =
{
.name = "vfat",
.usage = BLKID_USAGE_FILESYSTEM,
.probefunc = probe_vfat,
.magics =
{
{ .magic = "MSWIN", .len = 5, .sboff = 0x52 },
{ .magic = "FAT32 ", .len = 8, .sboff = 0x52 },
{ .magic = "MSDOS", .len = 5, .sboff = 0x36 },
{ .magic = "FAT16 ", .len = 8, .sboff = 0x36 },
{ .magic = "FAT12 ", .len = 8, .sboff = 0x36 },
{ .magic = "FAT ", .len = 8, .sboff = 0x36 },
{ .magic = "\353", .len = 1, },
{ .magic = "\351", .len = 1, },
{ .magic = "\125\252", .len = 2, .sboff = 0x1fe },
{ NULL }
}
};
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