fat.c revision 2603474ff9be2418900581da1af5cccc9f13cae1
/*
* volume_id - reads filesystem label and uuid
*
* Copyright (C) 2004-2007 Kay Sievers <kay.sievers@vrfy.org>
* Copyright (C) 2007 Ryan Lortie <desrt@desrt.ca>
*
* This program is free software; you can redistribute it and/or modify it
* under the terms of the GNU General Public License as published by the
* Free Software Foundation version 2 of the License.
*/
#ifndef _GNU_SOURCE
#define _GNU_SOURCE 1
#endif
#ifdef HAVE_CONFIG_H
# include <config.h>
#endif
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>
#include <errno.h>
#include <ctype.h>
#include "libvolume_id.h"
#include "libvolume_id-private.h"
#include "util.h"
#define FAT12_MAX 0xff5
#define FAT16_MAX 0xfff5
#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
#define VFAT_LFN_SEQ_MASK 0x3f
#define VFAT_LFN_SEQ_LAST 0x40
#define VFAT_LFN_SEQ_MAX 20
#define VFAT_LFN_CHARS_PER_ENTRY (5 + 6 + 2)
#define VFAT_LOWERCASE_NAME 0x10
#define VFAT_LOWERCASE_EXT 0x08
struct vfat_super_block {
uint8_t boot_jump[3];
uint8_t sysid[8];
uint16_t sector_size;
uint8_t sectors_per_cluster;
uint16_t reserved;
uint8_t fats;
uint16_t dir_entries;
uint16_t sectors;
uint8_t media;
uint16_t fat_length;
uint16_t secs_track;
uint16_t heads;
uint32_t hidden;
uint32_t total_sect;
union {
struct fat_super_block {
uint8_t unknown[3];
uint8_t serno[4];
uint8_t label[11];
uint8_t magic[8];
uint8_t dummy2[192];
uint8_t pmagic[2];
} PACKED fat;
struct fat32_super_block {
uint32_t fat32_length;
uint16_t flags;
uint8_t version[2];
uint32_t root_cluster;
uint16_t fsinfo_sector;
uint16_t backup_boot;
uint16_t reserved2[6];
uint8_t unknown[3];
uint8_t serno[4];
uint8_t label[11];
uint8_t magic[8];
uint8_t dummy2[164];
uint8_t pmagic[2];
} PACKED fat32;
} PACKED type;
} 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];
} PACKED;
struct vfat_dir_entry {
uint8_t name[11];
uint8_t attr;
uint8_t lowercase;
uint8_t fine_time_creat;
uint16_t time_creat;
uint16_t date_creat;
uint16_t date_acc;
uint16_t cluster_high;
uint16_t time_write;
uint16_t date_write;
uint16_t cluster_low;
uint32_t size;
} PACKED;
struct vfat_lfn_entry {
uint8_t seq;
uint16_t name0[5];
uint8_t attr;
uint8_t reserved;
uint8_t cksum;
uint16_t name1[6];
uint16_t cluster;
uint16_t name2[2];
} PACKED;
static uint8_t fat_lfn_checksum(const uint8_t name[11])
{
uint8_t cksum = 0;
int i;
/* http://en.wikipedia.org/wiki/File_Allocation_Table */
for (i = 0; i < 11; i++)
cksum = ((cksum & 1) ? 0x80 : 0) + (cksum >> 1) + name[i];
return cksum;
}
static size_t fat_read_lfn(uint8_t *filename, size_t fnsize,
struct vfat_dir_entry *dir,
struct vfat_dir_entry *entry)
{
uint8_t buffer[VFAT_LFN_SEQ_MAX * VFAT_LFN_CHARS_PER_ENTRY * 2];
uint8_t expected_seq = 1;
uint8_t cksum;
size_t len = 0;
size_t fnlen = 0;
cksum = fat_lfn_checksum(entry->name);
while (--entry >= dir) {
struct vfat_lfn_entry *lfn = (struct vfat_lfn_entry *) entry;
if (expected_seq > VFAT_LFN_SEQ_MAX)
break;
if ((lfn->attr & FAT_ATTR_MASK) != FAT_ATTR_LONG_NAME)
break;
if (lfn->cksum != cksum)
break;
if ((lfn->seq & VFAT_LFN_SEQ_MASK) != expected_seq++)
break;
if (lfn->cluster != 0)
break;
/* extra paranoia -- should never happen */
if (len + sizeof(lfn->name0) + sizeof(lfn->name1) +
sizeof(lfn->name2) > sizeof(buffer))
break;
memcpy (&buffer[len], lfn->name0, sizeof(lfn->name0));
len += sizeof(lfn->name0);
memcpy (&buffer[len], lfn->name1, sizeof(lfn->name1));
len += sizeof(lfn->name1);
memcpy (&buffer[len], lfn->name2, sizeof(lfn->name2));
len += sizeof(lfn->name2);
if (lfn->seq & VFAT_LFN_SEQ_LAST) {
fnlen = volume_id_set_unicode16(filename, fnsize, buffer, LE, len);
break;
}
}
return fnlen;
}
static size_t fat_read_filename(uint8_t *filename, size_t fnsize,
struct vfat_dir_entry *dir, struct vfat_dir_entry *entry)
{
size_t len;
int i;
/* check if maybe we have LFN entries */
len = fat_read_lfn(filename, fnsize, dir, entry);
if (len > 0)
goto out;
/* else, read the normal 8.3 name */
for (i = 0; i < 11; i++) {
if (entry->lowercase & ((i < 8) ? VFAT_LOWERCASE_NAME : VFAT_LOWERCASE_EXT))
filename[i] = tolower(entry->name[i]);
else
filename[i] = entry->name[i];
}
len = 11;
out:
filename[len] = '\0';
return len;
}
/* fills filename, returns string length */
static size_t get_fat_attr_volume_id(uint8_t *filename, size_t fnsize,
struct vfat_dir_entry *dir, unsigned int count)
{
unsigned int i;
for (i = 0; i < count; i++) {
/* end marker */
if (dir[i].name[0] == 0x00) {
dbg("end of dir\n");
break;
}
/* empty entry */
if (dir[i].name[0] == FAT_ENTRY_FREE)
continue;
/* long name */
if ((dir[i].attr & FAT_ATTR_MASK) == FAT_ATTR_LONG_NAME)
continue;
if ((dir[i].attr & (FAT_ATTR_VOLUME_ID | FAT_ATTR_DIR)) == FAT_ATTR_VOLUME_ID) {
/* labels do not have file data */
if (dir[i].cluster_high != 0 || dir[i].cluster_low != 0)
continue;
dbg("found ATTR_VOLUME_ID id in root dir\n");
return fat_read_filename(filename, fnsize, dir, &dir[i]);
}
dbg("skip dir entry\n");
}
return 0;
}
int volume_id_probe_vfat(struct volume_id *id, uint64_t off, uint64_t size)
{
uint8_t filename[255 * 3];
struct vfat_super_block *vs;
struct vfat_dir_entry *dir;
struct fat32_fsinfo *fsinfo;
uint16_t sector_size;
uint16_t dir_entries;
uint32_t sect_count;
uint16_t reserved;
uint32_t fat_size;
uint32_t root_cluster;
uint32_t dir_size;
uint32_t cluster_count;
uint16_t fat_length;
uint32_t fat32_length;
uint64_t root_start;
uint32_t start_data_sect;
uint16_t root_dir_entries;
uint16_t fsinfo_sect;
uint8_t *buf;
uint32_t buf_size;
uint32_t next;
int maxloop;
size_t fnlen;
info("probing at offset 0x%llx\n", (unsigned long long) off);
buf = volume_id_get_buffer(id, off, 0x400);
if (buf == NULL)
return -1;
/* check signature */
if (buf[510] != 0x55 || buf[511] != 0xaa)
return -1;
vs = (struct vfat_super_block *) buf;
if (memcmp(vs->sysid, "NTFS", 4) == 0)
return -1;
/* believe only that's fat, don't trust the version */
if (memcmp(vs->type.fat32.magic, "MSWIN", 5) == 0)
goto magic;
if (memcmp(vs->type.fat32.magic, "FAT32 ", 8) == 0)
goto magic;
if (memcmp(vs->type.fat.magic, "FAT16 ", 8) == 0)
goto magic;
if (memcmp(vs->type.fat.magic, "MSDOS", 5) == 0)
goto magic;
if (memcmp(vs->type.fat.magic, "FAT12 ", 8) == 0)
goto magic;
/* some old floppies don't have a magic, expect the boot jump address to match */
if ((vs->boot_jump[0] != 0xeb || vs->boot_jump[2] != 0x90) &&
vs->boot_jump[0] != 0xe9)
return -1;
magic:
/* reserverd sector count */
if (!vs->reserved)
return -1;
/* fat count */
if (!vs->fats)
return -1;
/* media check */
if (vs->media < 0xf8 && vs->media != 0xf0)
return -1;
/* cluster size check */
if (vs->sectors_per_cluster == 0 ||
(vs->sectors_per_cluster & (vs->sectors_per_cluster-1)))
return -1;
/* sector size check */
sector_size = le16_to_cpu(vs->sector_size);
if (sector_size == 0 || ((sector_size & (sector_size-1)) != 0))
return -1;
dbg("sector_size 0x%x\n", sector_size);
dbg("sectors_per_cluster 0x%x\n", vs->sectors_per_cluster);
dir_entries = le16_to_cpu(vs->dir_entries);
reserved = le16_to_cpu(vs->reserved);
dbg("reserved 0x%x\n", reserved);
sect_count = le16_to_cpu(vs->sectors);
if (sect_count == 0)
sect_count = le32_to_cpu(vs->total_sect);
dbg("sect_count 0x%x\n", sect_count);
fat_length = le16_to_cpu(vs->fat_length);
dbg("fat_length 0x%x\n", fat_length);
fat32_length = le32_to_cpu(vs->type.fat32.fat32_length);
dbg("fat32_length 0x%x\n", fat32_length);
if (fat_length)
fat_size = fat_length * vs->fats;
else if (fat32_length)
fat_size = fat32_length * vs->fats;
else
return -1;
dbg("fat_size 0x%x\n", fat_size);
dir_size = ((dir_entries * sizeof(struct vfat_dir_entry)) +
(sector_size-1)) / sector_size;
dbg("dir_size 0x%x\n", dir_size);
cluster_count = sect_count - (reserved + fat_size + dir_size);
cluster_count /= vs->sectors_per_cluster;
dbg("cluster_count 0x%x\n", cluster_count);
/* must be FAT32 */
if (!fat_length && fat32_length)
goto fat32;
/* cluster_count tells us the format */
if (cluster_count < FAT12_MAX)
strcpy(id->type_version, "FAT12");
else if (cluster_count < FAT16_MAX)
strcpy(id->type_version, "FAT16");
else
goto fat32;
/* the label may be an attribute in the root directory */
root_start = (reserved + fat_size) * sector_size;
dbg("root dir start 0x%llx\n", (unsigned long long) root_start);
root_dir_entries = le16_to_cpu(vs->dir_entries);
dbg("expected entries 0x%x\n", root_dir_entries);
buf_size = root_dir_entries * sizeof(struct vfat_dir_entry);
buf = volume_id_get_buffer(id, off + root_start, buf_size);
if (buf == NULL)
goto found;
dir = (struct vfat_dir_entry*) buf;
fnlen = get_fat_attr_volume_id(filename, sizeof(filename), dir, root_dir_entries);
vs = (struct vfat_super_block *) volume_id_get_buffer(id, off, 0x200);
if (vs == NULL)
return -1;
if (fnlen > 0 && memcmp(filename, "NO NAME ", 11) != 0) {
volume_id_set_label_raw(id, filename, fnlen);
volume_id_set_label_string(id, filename, fnlen);
} else if (memcmp(vs->type.fat.label, "NO NAME ", 11) != 0) {
volume_id_set_label_raw(id, vs->type.fat.label, 11);
volume_id_set_label_string(id, vs->type.fat.label, 11);
}
volume_id_set_uuid(id, vs->type.fat.serno, 0, UUID_DOS);
goto found;
fat32:
/* FAT32 should have a valid signature in the fsinfo block */
fsinfo_sect = le16_to_cpu(vs->type.fat32.fsinfo_sector);
buf = volume_id_get_buffer(id, off + (fsinfo_sect * sector_size), 0x200);
if (buf == NULL)
return -1;
fsinfo = (struct fat32_fsinfo *) buf;
if (memcmp(fsinfo->signature1, "\x52\x52\x61\x41", 4) != 0)
return -1;
if (memcmp(fsinfo->signature2, "\x72\x72\x41\x61", 4) != 0)
return -1 ;
vs = (struct vfat_super_block *) volume_id_get_buffer(id, off, 0x200);
if (vs == NULL)
return -1;
strcpy(id->type_version, "FAT32");
/* FAT32 root dir is a cluster chain like any other directory */
buf_size = vs->sectors_per_cluster * sector_size;
root_cluster = le32_to_cpu(vs->type.fat32.root_cluster);
dbg("root dir cluster %u\n", root_cluster);
start_data_sect = reserved + fat_size;
next = root_cluster;
maxloop = 100;
while (--maxloop) {
uint32_t next_sect_off;
uint64_t next_off;
uint64_t fat_entry_off;
int count;
dbg("next cluster %u\n", next);
next_sect_off = (next - 2) * vs->sectors_per_cluster;
next_off = (start_data_sect + next_sect_off) * sector_size;
dbg("cluster offset 0x%llx\n", (unsigned long long) next_off);
/* get cluster */
buf = volume_id_get_buffer(id, off + next_off, buf_size);
if (buf == NULL)
goto found;
dir = (struct vfat_dir_entry*) buf;
count = buf_size / sizeof(struct vfat_dir_entry);
dbg("expected entries 0x%x\n", count);
fnlen = get_fat_attr_volume_id(filename, sizeof(filename), dir, count);
if (fnlen > 0)
break;
/* get FAT entry */
fat_entry_off = (reserved * sector_size) + (next * sizeof(uint32_t));
buf = volume_id_get_buffer(id, off + fat_entry_off, buf_size);
if (buf == NULL)
goto found;
/* set next cluster */
next = le32_to_cpu(*((uint32_t *) buf)) & 0x0fffffff;
if (next < 2 || next >= 0x0ffffff0)
break;
}
if (maxloop == 0)
dbg("reached maximum follow count of root cluster chain, give up\n");
vs = (struct vfat_super_block *) volume_id_get_buffer(id, off, 0x200);
if (vs == NULL)
return -1;
if (fnlen > 0 && memcmp(filename, "NO NAME ", 11) != 0) {
volume_id_set_label_raw(id, filename, fnlen);
volume_id_set_label_string(id, filename, fnlen);
} else if (memcmp(vs->type.fat32.label, "NO NAME ", 11) != 0) {
volume_id_set_label_raw(id, vs->type.fat32.label, 11);
volume_id_set_label_string(id, vs->type.fat32.label, 11);
}
volume_id_set_uuid(id, vs->type.fat32.serno, 0, UUID_DOS);
found:
volume_id_set_usage(id, VOLUME_ID_FILESYSTEM);
id->type = "vfat";
return 0;
}