Re: [PATCH v8] fs: FAT: Add support for DOS 1.x formatted volumes
From: OGAWA Hirofumi
Date: Mon Apr 21 2014 - 14:52:22 EST
Conrad Meyer <cse.cem@xxxxxxxxx> writes:
> 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
>
> Signed-off-by: Conrad Meyer <cse.cem@xxxxxxxxx>
Looks good.
Acked-by: OGAWA Hirofumi <hirofumi@xxxxxxxxxxxxxxxxxx>
Thanks.
> ---
> Changes from v7:
> * Move struct fat_bios_param_block from fat.h to fat/inode.c
> ---
> Documentation/filesystems/vfat.txt | 5 +
> fs/fat/fat.h | 3 +-
> fs/fat/inode.c | 342 ++++++++++++++++++++++++++++---------
> 3 files changed, 273 insertions(+), 77 deletions(-)
>
> diff --git a/Documentation/filesystems/vfat.txt b/Documentation/filesystems/vfat.txt
> index 5cf57b3..223c321 100644
> --- a/Documentation/filesystems/vfat.txt
> +++ b/Documentation/filesystems/vfat.txt
> @@ -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
>
> diff --git a/fs/fat/fat.h b/fs/fat/fat.h
> index 7270bdb..13b7202 100644
> --- a/fs/fat/fat.h
> +++ b/fs/fat/fat.h
> @@ -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
> diff --git a/fs/fat/inode.c b/fs/fat/inode.c
> index 992e8cb..d44c510 100644
> --- a/fs/fat/inode.c
> +++ b/fs/fat/inode.c
> @@ -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)
> {
> @@ -931,6 +993,8 @@ 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;
> }
> @@ -945,7 +1009,7 @@ 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 = {
> @@ -978,6 +1042,7 @@ 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"},
> @@ -1180,6 +1245,9 @@ 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:
> @@ -1326,6 +1394,169 @@ 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.
> */
> @@ -1335,12 +1566,11 @@ 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];
>
> @@ -1377,100 +1607,71 @@ 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");
> - 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.
> - */
> + 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);
>
> - 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;
>
> 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;
>
> @@ -1478,7 +1679,6 @@ 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;
> }
>
> @@ -1501,35 +1701,28 @@ 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;
>
> @@ -1538,9 +1731,9 @@ 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);
> @@ -1549,7 +1742,6 @@ 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;
> }
>
> @@ -1562,8 +1754,6 @@ 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);
--
OGAWA Hirofumi <hirofumi@xxxxxxxxxxxxxxxxxx>
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