libblkid/src/superblocks/vfat.c

/*
 * 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 "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: %d, offset: %jd)", 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,
					(blkid_loff_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,
					(blkid_loff_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));
			return ent->name;
		}
	}
	return NULL;
}

static int fat_valid_superblock(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))
			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;

	return 1;	/* valid */
}

/*
 * 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(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 = 0;
	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(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;
		}

		if (!vol_label || !memcmp(vol_label, no_name, 11))
			vol_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";

		if (!vol_label || !memcmp(vol_label, no_name, 11))
			vol_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,
					(blkid_loff_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 (vol_label && memcmp(vol_label, no_name, 11))
		blkid_probe_set_label(pr, (unsigned char *) 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 }
	}
};