Commit 190a8843 authored by Conrad Meyer's avatar Conrad Meyer Committed by Linus Torvalds
Browse files

fs/fat/: add support for DOS 1.x formatted volumes 

Add structure for parsed BPB information, struct fat_bios_param_block,
and move all of the deserialization and validation logic from
fat_fill_super() into fat_read_bpb().

Add a 'dos1xfloppy' mount option to infer DOS 2.x BIOS Parameter Block
defaults from block device geometry for ancient floppies and floppy
images, as a fall-back from the default BPB parsing logic.

When fat_read_bpb() finds an invalid FAT filesystem and dos1xfloppy is
set, fall back to fat_read_static_bpb().  fat_read_static_bpb()
validates that the entire BPB is zero, and that the floppy has a
DOS-style 8086 code bootstrapping header.  Then it fills in default BPB
values from media size and a table.[0]

Media size is assumed to be static for archaic FAT volumes.  See also:
[1].

Fixes kernel.org bug #42617.

[0]: https://en.wikipedia.org/wiki/File_Allocation_Table#Exceptions
[1]: http://www.win.tue.nl/~aeb/linux/fs/fat/fat-1.html



[hirofumi@mail.parknet.co.jp: fix missed error code]
Signed-off-by: default avatarConrad Meyer <cse.cem@gmail.com>
Acked-by: default avatarOGAWA Hirofumi <hirofumi@mail.parknet.co.jp>
Signed-off-by: default avatarOGAWA Hirofumi <hirofumi@mail.parknet.co.jp>
Tested-by: default avatarAlan Cox <alan@linux.intel.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent a19189e5

Documentation/filesystems/vfat.txt

+5 −0
Original line number Diff line number Diff line
@@ -172,6 +172,11 @@ nfs=stale_rw|nostale_ro 
		To maintain backward compatibility, '-o nfs' is also accepted,

		defaulting to stale_rw



dos1xfloppy  -- If set, use a fallback default BIOS Parameter Block

		configuration, determined by backing device size. These static

		parameters match defaults assumed by DOS 1.x for 160 kiB,

		180 kiB, 320 kiB, and 360 kiB floppies and floppy images.





<bool>: 0,1,yes,no,true,false

fs/fat/fat.h

+2 −1
Original line number Diff line number Diff line
@@ -52,7 +52,8 @@ struct fat_mount_options { 
		 usefree:1,	   /* Use free_clusters for FAT32 */

		 tz_set:1,	   /* Filesystem timestamps' offset set */

		 rodir:1,	   /* allow ATTR_RO for directory */

		 discard:1;	   /* Issue discard requests on deletions */

		 discard:1,	   /* Issue discard requests on deletions */

		 dos1xfloppy:1;	   /* Assume default BPB for DOS 1.x floppies */

};



#define FAT_HASH_BITS	8

fs/fat/inode.c

+267 −76
Original line number Diff line number Diff line
@@ -35,9 +35,71 @@ 
#define CONFIG_FAT_DEFAULT_IOCHARSET	""

#endif



#define KB_IN_SECTORS 2



/*

 * A deserialized copy of the on-disk structure laid out in struct

 * fat_boot_sector.

 */

struct fat_bios_param_block {

	u16	fat_sector_size;

	u8	fat_sec_per_clus;

	u16	fat_reserved;

	u8	fat_fats;

	u16	fat_dir_entries;

	u16	fat_sectors;

	u16	fat_fat_length;

	u32	fat_total_sect;



	u8	fat16_state;

	u32	fat16_vol_id;



	u32	fat32_length;

	u32	fat32_root_cluster;

	u16	fat32_info_sector;

	u8	fat32_state;

	u32	fat32_vol_id;

};



static int fat_default_codepage = CONFIG_FAT_DEFAULT_CODEPAGE;

static char fat_default_iocharset[] = CONFIG_FAT_DEFAULT_IOCHARSET;



static struct fat_floppy_defaults {

	unsigned nr_sectors;

	unsigned sec_per_clus;

	unsigned dir_entries;

	unsigned media;

	unsigned fat_length;

} floppy_defaults[] = {

{

	.nr_sectors = 160 * KB_IN_SECTORS,

	.sec_per_clus = 1,

	.dir_entries = 64,

	.media = 0xFE,

	.fat_length = 1,

},

{

	.nr_sectors = 180 * KB_IN_SECTORS,

	.sec_per_clus = 1,

	.dir_entries = 64,

	.media = 0xFC,

	.fat_length = 2,

},

{

	.nr_sectors = 320 * KB_IN_SECTORS,

	.sec_per_clus = 2,

	.dir_entries = 112,

	.media = 0xFF,

	.fat_length = 1,

},

{

	.nr_sectors = 360 * KB_IN_SECTORS,

	.sec_per_clus = 2,

	.dir_entries = 112,

	.media = 0xFD,

	.fat_length = 2,

},

};



static int fat_add_cluster(struct inode *inode)

{
@@ -853,6 +915,8 @@ static int fat_show_options(struct seq_file *m, struct dentry *root) 
		seq_puts(m, ",nfs=stale_rw");

	if (opts->discard)

		seq_puts(m, ",discard");

	if (opts->dos1xfloppy)

		seq_puts(m, ",dos1xfloppy");



	return 0;

}
@@ -867,7 +931,7 @@ enum { 
	Opt_uni_xl_no, Opt_uni_xl_yes, Opt_nonumtail_no, Opt_nonumtail_yes,

	Opt_obsolete, Opt_flush, Opt_tz_utc, Opt_rodir, Opt_err_cont,

	Opt_err_panic, Opt_err_ro, Opt_discard, Opt_nfs, Opt_time_offset,

	Opt_nfs_stale_rw, Opt_nfs_nostale_ro, Opt_err,

	Opt_nfs_stale_rw, Opt_nfs_nostale_ro, Opt_err, Opt_dos1xfloppy,

};



static const match_table_t fat_tokens = {
@@ -900,6 +964,7 @@ static const match_table_t fat_tokens = { 
	{Opt_nfs_stale_rw, "nfs"},

	{Opt_nfs_stale_rw, "nfs=stale_rw"},

	{Opt_nfs_nostale_ro, "nfs=nostale_ro"},

	{Opt_dos1xfloppy, "dos1xfloppy"},

	{Opt_obsolete, "conv=binary"},

	{Opt_obsolete, "conv=text"},

	{Opt_obsolete, "conv=auto"},
@@ -1102,6 +1167,9 @@ static int parse_options(struct super_block *sb, char *options, int is_vfat, 
		case Opt_nfs_nostale_ro:

			opts->nfs = FAT_NFS_NOSTALE_RO;

			break;

		case Opt_dos1xfloppy:

			opts->dos1xfloppy = 1;

			break;



		/* msdos specific */

		case Opt_dots:
@@ -1247,6 +1315,169 @@ static unsigned long calc_fat_clusters(struct super_block *sb) 
	return sbi->fat_length * sb->s_blocksize * 8 / sbi->fat_bits;

}



static bool fat_bpb_is_zero(struct fat_boot_sector *b)

{

	if (get_unaligned_le16(&b->sector_size))

		return false;

	if (b->sec_per_clus)

		return false;

	if (b->reserved)

		return false;

	if (b->fats)

		return false;

	if (get_unaligned_le16(&b->dir_entries))

		return false;

	if (get_unaligned_le16(&b->sectors))

		return false;

	if (b->media)

		return false;

	if (b->fat_length)

		return false;

	if (b->secs_track)

		return false;

	if (b->heads)

		return false;

	return true;

}



static int fat_read_bpb(struct super_block *sb, struct fat_boot_sector *b,

	int silent, struct fat_bios_param_block *bpb)

{

	int error = -EINVAL;



	/* Read in BPB ... */

	memset(bpb, 0, sizeof(*bpb));

	bpb->fat_sector_size = get_unaligned_le16(&b->sector_size);

	bpb->fat_sec_per_clus = b->sec_per_clus;

	bpb->fat_reserved = le16_to_cpu(b->reserved);

	bpb->fat_fats = b->fats;

	bpb->fat_dir_entries = get_unaligned_le16(&b->dir_entries);

	bpb->fat_sectors = get_unaligned_le16(&b->sectors);

	bpb->fat_fat_length = le16_to_cpu(b->fat_length);

	bpb->fat_total_sect = le32_to_cpu(b->total_sect);



	bpb->fat16_state = b->fat16.state;

	bpb->fat16_vol_id = get_unaligned_le32(b->fat16.vol_id);



	bpb->fat32_length = le32_to_cpu(b->fat32.length);

	bpb->fat32_root_cluster = le32_to_cpu(b->fat32.root_cluster);

	bpb->fat32_info_sector = le16_to_cpu(b->fat32.info_sector);

	bpb->fat32_state = b->fat32.state;

	bpb->fat32_vol_id = get_unaligned_le32(b->fat32.vol_id);



	/* Validate this looks like a FAT filesystem BPB */

	if (!bpb->fat_reserved) {

		if (!silent)

			fat_msg(sb, KERN_ERR,

				"bogus number of reserved sectors");

		goto out;

	}

	if (!bpb->fat_fats) {

		if (!silent)

			fat_msg(sb, KERN_ERR, "bogus number of FAT structure");

		goto out;

	}



	/*

	 * Earlier we checked here that b->secs_track and b->head are nonzero,

	 * but it turns out valid FAT filesystems can have zero there.

	 */



	if (!fat_valid_media(b->media)) {

		if (!silent)

			fat_msg(sb, KERN_ERR, "invalid media value (0x%02x)",

				(unsigned)b->media);

		goto out;

	}



	if (!is_power_of_2(bpb->fat_sector_size)

	    || (bpb->fat_sector_size < 512)

	    || (bpb->fat_sector_size > 4096)) {

		if (!silent)

			fat_msg(sb, KERN_ERR, "bogus logical sector size %u",

			       (unsigned)bpb->fat_sector_size);

		goto out;

	}



	if (!is_power_of_2(bpb->fat_sec_per_clus)) {

		if (!silent)

			fat_msg(sb, KERN_ERR, "bogus sectors per cluster %u",

				(unsigned)bpb->fat_sec_per_clus);

		goto out;

	}



	error = 0;



out:

	return error;

}



static int fat_read_static_bpb(struct super_block *sb,

	struct fat_boot_sector *b, int silent,

	struct fat_bios_param_block *bpb)

{

	static const char *notdos1x = "This doesn't look like a DOS 1.x volume";



	struct fat_floppy_defaults *fdefaults = NULL;

	int error = -EINVAL;

	sector_t bd_sects;

	unsigned i;



	bd_sects = i_size_read(sb->s_bdev->bd_inode) / SECTOR_SIZE;



	/* 16-bit DOS 1.x reliably wrote bootstrap short-jmp code */

	if (b->ignored[0] != 0xeb || b->ignored[2] != 0x90) {

		if (!silent)

			fat_msg(sb, KERN_ERR,

				"%s; no bootstrapping code", notdos1x);

		goto out;

	}



	/*

	 * If any value in this region is non-zero, it isn't archaic

	 * DOS.

	 */

	if (!fat_bpb_is_zero(b)) {

		if (!silent)

			fat_msg(sb, KERN_ERR,

				"%s; DOS 2.x BPB is non-zero", notdos1x);

		goto out;

	}



	for (i = 0; i < ARRAY_SIZE(floppy_defaults); i++) {

		if (floppy_defaults[i].nr_sectors == bd_sects) {

			fdefaults = &floppy_defaults[i];

			break;

		}

	}



	if (fdefaults == NULL) {

		if (!silent)

			fat_msg(sb, KERN_WARNING,

				"This looks like a DOS 1.x volume, but isn't a recognized floppy size (%llu sectors)",

				(u64)bd_sects);

		goto out;

	}



	if (!silent)

		fat_msg(sb, KERN_INFO,

			"This looks like a DOS 1.x volume; assuming default BPB values");



	memset(bpb, 0, sizeof(*bpb));

	bpb->fat_sector_size = SECTOR_SIZE;

	bpb->fat_sec_per_clus = fdefaults->sec_per_clus;

	bpb->fat_reserved = 1;

	bpb->fat_fats = 2;

	bpb->fat_dir_entries = fdefaults->dir_entries;

	bpb->fat_sectors = fdefaults->nr_sectors;

	bpb->fat_fat_length = fdefaults->fat_length;



	error = 0;



out:

	return error;

}



/*

 * Read the super block of an MS-DOS FS.

 */
@@ -1256,12 +1487,11 @@ int fat_fill_super(struct super_block *sb, void *data, int silent, int isvfat, 
	struct inode *root_inode = NULL, *fat_inode = NULL;

	struct inode *fsinfo_inode = NULL;

	struct buffer_head *bh;

	struct fat_boot_sector *b;

	struct fat_bios_param_block bpb;

	struct msdos_sb_info *sbi;

	u16 logical_sector_size;

	u32 total_sectors, total_clusters, fat_clusters, rootdir_sectors;

	int debug;

	unsigned int media;

	long error;

	char buf[50];
@@ -1298,100 +1528,72 @@ int fat_fill_super(struct super_block *sb, void *data, int silent, int isvfat, 
		goto out_fail;

	}



	b = (struct fat_boot_sector *) bh->b_data;

	if (!b->reserved) {

		if (!silent)

			fat_msg(sb, KERN_ERR, "bogus number of reserved sectors");

	error = fat_read_bpb(sb, (struct fat_boot_sector *)bh->b_data, silent,

		&bpb);

	if (error == -EINVAL && sbi->options.dos1xfloppy)

		error = fat_read_static_bpb(sb,

			(struct fat_boot_sector *)bh->b_data, silent, &bpb);

	brelse(bh);

		goto out_invalid;

	}

	if (!b->fats) {

		if (!silent)

			fat_msg(sb, KERN_ERR, "bogus number of FAT structure");

		brelse(bh);

		goto out_invalid;

	}



	/*

	 * Earlier we checked here that b->secs_track and b->head are nonzero,

	 * but it turns out valid FAT filesystems can have zero there.

	 */



	media = b->media;

	if (!fat_valid_media(media)) {

		if (!silent)

			fat_msg(sb, KERN_ERR, "invalid media value (0x%02x)",

			       media);

		brelse(bh);

		goto out_invalid;

	}

	logical_sector_size = get_unaligned_le16(&b->sector_size);

	if (!is_power_of_2(logical_sector_size)

	    || (logical_sector_size < 512)

	    || (logical_sector_size > 4096)) {

		if (!silent)

			fat_msg(sb, KERN_ERR, "bogus logical sector size %u",

			       logical_sector_size);

		brelse(bh);

		goto out_invalid;

	}

	sbi->sec_per_clus = b->sec_per_clus;

	if (!is_power_of_2(sbi->sec_per_clus)) {

		if (!silent)

			fat_msg(sb, KERN_ERR, "bogus sectors per cluster %u",

			       sbi->sec_per_clus);

		brelse(bh);

	if (error == -EINVAL)

		goto out_invalid;

	}

	else if (error)

		goto out_fail;



	logical_sector_size = bpb.fat_sector_size;

	sbi->sec_per_clus = bpb.fat_sec_per_clus;



	error = -EIO;

	if (logical_sector_size < sb->s_blocksize) {

		fat_msg(sb, KERN_ERR, "logical sector size too small for device"

		       " (logical sector size = %u)", logical_sector_size);

		brelse(bh);

		goto out_fail;

	}



	if (logical_sector_size > sb->s_blocksize) {

		brelse(bh);

		struct buffer_head *bh_resize;



		if (!sb_set_blocksize(sb, logical_sector_size)) {

			fat_msg(sb, KERN_ERR, "unable to set blocksize %u",

			       logical_sector_size);

			goto out_fail;

		}

		bh = sb_bread(sb, 0);

		if (bh == NULL) {



		/* Verify that the larger boot sector is fully readable */

		bh_resize = sb_bread(sb, 0);

		if (bh_resize == NULL) {

			fat_msg(sb, KERN_ERR, "unable to read boot sector"

			       " (logical sector size = %lu)",

			       sb->s_blocksize);

			goto out_fail;

		}

		b = (struct fat_boot_sector *) bh->b_data;

		brelse(bh_resize);

	}



	mutex_init(&sbi->s_lock);

	sbi->cluster_size = sb->s_blocksize * sbi->sec_per_clus;

	sbi->cluster_bits = ffs(sbi->cluster_size) - 1;

	sbi->fats = b->fats;

	sbi->fats = bpb.fat_fats;

	sbi->fat_bits = 0;		/* Don't know yet */

	sbi->fat_start = le16_to_cpu(b->reserved);

	sbi->fat_length = le16_to_cpu(b->fat_length);

	sbi->fat_start = bpb.fat_reserved;

	sbi->fat_length = bpb.fat_fat_length;

	sbi->root_cluster = 0;

	sbi->free_clusters = -1;	/* Don't know yet */

	sbi->free_clus_valid = 0;

	sbi->prev_free = FAT_START_ENT;

	sb->s_maxbytes = 0xffffffff;



	if (!sbi->fat_length && b->fat32.length) {

	if (!sbi->fat_length && bpb.fat32_length) {

		struct fat_boot_fsinfo *fsinfo;

		struct buffer_head *fsinfo_bh;



		/* Must be FAT32 */

		sbi->fat_bits = 32;

		sbi->fat_length = le32_to_cpu(b->fat32.length);

		sbi->root_cluster = le32_to_cpu(b->fat32.root_cluster);

		sbi->fat_length = bpb.fat32_length;

		sbi->root_cluster = bpb.fat32_root_cluster;



		/* MC - if info_sector is 0, don't multiply by 0 */

		sbi->fsinfo_sector = le16_to_cpu(b->fat32.info_sector);

		sbi->fsinfo_sector = bpb.fat32_info_sector;

		if (sbi->fsinfo_sector == 0)

			sbi->fsinfo_sector = 1;
@@ -1399,7 +1601,6 @@ int fat_fill_super(struct super_block *sb, void *data, int silent, int isvfat, 
		if (fsinfo_bh == NULL) {

			fat_msg(sb, KERN_ERR, "bread failed, FSINFO block"

			       " (sector = %lu)", sbi->fsinfo_sector);

			brelse(bh);

			goto out_fail;

		}
@@ -1422,35 +1623,28 @@ int fat_fill_super(struct super_block *sb, void *data, int silent, int isvfat, 


	/* interpret volume ID as a little endian 32 bit integer */

	if (sbi->fat_bits == 32)

		sbi->vol_id = (((u32)b->fat32.vol_id[0]) |

					((u32)b->fat32.vol_id[1] << 8) |

					((u32)b->fat32.vol_id[2] << 16) |

					((u32)b->fat32.vol_id[3] << 24));

		sbi->vol_id = bpb.fat32_vol_id;

	else /* fat 16 or 12 */

		sbi->vol_id = (((u32)b->fat16.vol_id[0]) |

					((u32)b->fat16.vol_id[1] << 8) |

					((u32)b->fat16.vol_id[2] << 16) |

					((u32)b->fat16.vol_id[3] << 24));

		sbi->vol_id = bpb.fat16_vol_id;



	sbi->dir_per_block = sb->s_blocksize / sizeof(struct msdos_dir_entry);

	sbi->dir_per_block_bits = ffs(sbi->dir_per_block) - 1;



	sbi->dir_start = sbi->fat_start + sbi->fats * sbi->fat_length;

	sbi->dir_entries = get_unaligned_le16(&b->dir_entries);

	sbi->dir_entries = bpb.fat_dir_entries;

	if (sbi->dir_entries & (sbi->dir_per_block - 1)) {

		if (!silent)

			fat_msg(sb, KERN_ERR, "bogus directory-entries per block"

			       " (%u)", sbi->dir_entries);

		brelse(bh);

		goto out_invalid;

	}



	rootdir_sectors = sbi->dir_entries

		* sizeof(struct msdos_dir_entry) / sb->s_blocksize;

	sbi->data_start = sbi->dir_start + rootdir_sectors;

	total_sectors = get_unaligned_le16(&b->sectors);

	total_sectors = bpb.fat_sectors;

	if (total_sectors == 0)

		total_sectors = le32_to_cpu(b->total_sect);

		total_sectors = bpb.fat_total_sect;



	total_clusters = (total_sectors - sbi->data_start) / sbi->sec_per_clus;
@@ -1459,9 +1653,9 @@ int fat_fill_super(struct super_block *sb, void *data, int silent, int isvfat, 


	/* some OSes set FAT_STATE_DIRTY and clean it on unmount. */

	if (sbi->fat_bits == 32)

		sbi->dirty = b->fat32.state & FAT_STATE_DIRTY;

		sbi->dirty = bpb.fat32_state & FAT_STATE_DIRTY;

	else /* fat 16 or 12 */

		sbi->dirty = b->fat16.state & FAT_STATE_DIRTY;

		sbi->dirty = bpb.fat16_state & FAT_STATE_DIRTY;



	/* check that FAT table does not overflow */

	fat_clusters = calc_fat_clusters(sb);
@@ -1470,7 +1664,6 @@ int fat_fill_super(struct super_block *sb, void *data, int silent, int isvfat, 
		if (!silent)

			fat_msg(sb, KERN_ERR, "count of clusters too big (%u)",

			       total_clusters);

		brelse(bh);

		goto out_invalid;

	}
@@ -1483,8 +1676,6 @@ int fat_fill_super(struct super_block *sb, void *data, int silent, int isvfat, 
	if (sbi->prev_free < FAT_START_ENT)

		sbi->prev_free = FAT_START_ENT;



	brelse(bh);



	/* set up enough so that it can read an inode */

	fat_hash_init(sb);

	dir_hash_init(sb);

CRA Git | Maintained and supported by SUSTech CRA and CCSE