> Separate the boot sector analysis to read_boot_sector().
> And add a check for the fs_name field.
> Furthermore, add a strict consistency check, because overlapping areas can
> cause serious corruption.
>
> Signed-off-by: Tetsuhiro Kohada <kohada.t2@xxxxxxxxx>
Reviewed-by: Sungjong Seo <sj1557.seo@xxxxxxxxxxx>
> ---
> Changes in v2:
> - rebase with patch 'optimize dir-cache' applied Changes in v3:
> - add a check for the fs_name field
>
> fs/exfat/exfat_raw.h | 2 +
> fs/exfat/super.c | 97 ++++++++++++++++++++++++--------------------
> 2 files changed, 56 insertions(+), 43 deletions(-)
>
> diff --git a/fs/exfat/exfat_raw.h b/fs/exfat/exfat_raw.h index
> 07f74190df44..350ce59cc324 100644
> --- a/fs/exfat/exfat_raw.h
> +++ b/fs/exfat/exfat_raw.h
> @@ -10,11 +10,13 @@
>
> #define BOOT_SIGNATURE 0xAA55
> #define EXBOOT_SIGNATURE 0xAA550000
> +#define STR_EXFAT "EXFAT " /* size should be 8 */
>
> #define EXFAT_MAX_FILE_LEN 255
>
> #define VOL_CLEAN 0x0000
> #define VOL_DIRTY 0x0002
> +#define ERR_MEDIUM 0x0004
>
> #define EXFAT_EOF_CLUSTER 0xFFFFFFFFu
> #define EXFAT_BAD_CLUSTER 0xFFFFFFF7u
> diff --git a/fs/exfat/super.c b/fs/exfat/super.c index
> e60d28e73ff0..6a1330be5a9a 100644
> --- a/fs/exfat/super.c
> +++ b/fs/exfat/super.c
> @@ -366,25 +366,20 @@ static int exfat_read_root(struct inode *inode)
> return 0;
> }
>
> -static struct boot_sector *exfat_read_boot_with_logical_sector(
> - struct super_block *sb)
> +static int exfat_calibrate_blocksize(struct super_block *sb, int
> +logical_sect)
> {
> struct exfat_sb_info *sbi = EXFAT_SB(sb);
> - struct boot_sector *p_boot = (struct boot_sector *)sbi->boot_bh-
> >b_data;
> - unsigned short logical_sect = 0;
> -
> - logical_sect = 1 << p_boot->sect_size_bits;
>
> if (!is_power_of_2(logical_sect) ||
> logical_sect < 512 || logical_sect > 4096) {
> exfat_err(sb, "bogus logical sector size %u", logical_sect);
> - return NULL;
> + return -EIO;
> }
>
> if (logical_sect < sb->s_blocksize) {
> exfat_err(sb, "logical sector size too small for device
> (logical sector size = %u)",
> logical_sect);
> - return NULL;
> + return -EIO;
> }
>
> if (logical_sect > sb->s_blocksize) {
> @@ -394,24 +389,20 @@ static struct boot_sector
> *exfat_read_boot_with_logical_sector(
> if (!sb_set_blocksize(sb, logical_sect)) {
> exfat_err(sb, "unable to set blocksize %u",
> logical_sect);
> - return NULL;
> + return -EIO;
> }
> sbi->boot_bh = sb_bread(sb, 0);
> if (!sbi->boot_bh) {
> exfat_err(sb, "unable to read boot sector (logical
> sector size = %lu)",
> sb->s_blocksize);
> - return NULL;
> + return -EIO;
> }
> -
> - p_boot = (struct boot_sector *)sbi->boot_bh->b_data;
> }
> - return p_boot;
> + return 0;
> }
>
> -/* mount the file system volume */
> -static int __exfat_fill_super(struct super_block *sb)
> +static int exfat_read_boot_sector(struct super_block *sb)
> {
> - int ret;
> struct boot_sector *p_boot;
> struct exfat_sb_info *sbi = EXFAT_SB(sb);
>
> @@ -424,51 +415,41 @@ static int __exfat_fill_super(struct super_block
*sb)
> exfat_err(sb, "unable to read boot sector");
> return -EIO;
> }
> -
> - /* PRB is read */
> p_boot = (struct boot_sector *)sbi->boot_bh->b_data;
>
> /* check the validity of BOOT */
> if (le16_to_cpu((p_boot->signature)) != BOOT_SIGNATURE) {
> exfat_err(sb, "invalid boot record signature");
> - ret = -EINVAL;
> - goto free_bh;
> + return -EINVAL;
> }
>
> -
> - /* check logical sector size */
> - p_boot = exfat_read_boot_with_logical_sector(sb);
> - if (!p_boot) {
> - ret = -EIO;
> - goto free_bh;
> + if (memcmp(p_boot->fs_name, STR_EXFAT, BOOTSEC_FS_NAME_LEN)) {
> + exfat_err(sb, "invalid fs_name"); /* fs_name may unprintable
> */
> + return -EINVAL;
> }
>
> /*
> - * res_zero field must be filled with zero to prevent mounting
> + * must_be_zero field must be filled with zero to prevent mounting
> * from FAT volume.
> */
> - if (memchr_inv(p_boot->must_be_zero, 0,
> - sizeof(p_boot->must_be_zero))) {
> - ret = -EINVAL;
> - goto free_bh;
> - }
> + if (memchr_inv(p_boot->must_be_zero, 0, sizeof(p_boot-
> >must_be_zero)))
> + return -EINVAL;
>
> - p_boot = (struct boot_sector *)p_boot;
> - if (!p_boot->num_fats) {
> + if (p_boot->num_fats != 1 && p_boot->num_fats != 2) {
> exfat_err(sb, "bogus number of FAT structure");
> - ret = -EINVAL;
> - goto free_bh;
> + return -EINVAL;
> }
>
> sbi->sect_per_clus = 1 << p_boot->sect_per_clus_bits;
> sbi->sect_per_clus_bits = p_boot->sect_per_clus_bits;
> - sbi->cluster_size_bits = sbi->sect_per_clus_bits + sb-
> >s_blocksize_bits;
> + sbi->cluster_size_bits = p_boot->sect_per_clus_bits +
> + p_boot->sect_size_bits;
> sbi->cluster_size = 1 << sbi->cluster_size_bits;
> sbi->num_FAT_sectors = le32_to_cpu(p_boot->fat_length);
> sbi->FAT1_start_sector = le32_to_cpu(p_boot->fat_offset);
> - sbi->FAT2_start_sector = p_boot->num_fats == 1 ?
> - sbi->FAT1_start_sector :
> - sbi->FAT1_start_sector + sbi->num_FAT_sectors;
> + sbi->FAT2_start_sector = le32_to_cpu(p_boot->fat_offset);
> + if (p_boot->num_fats == 2)
> + sbi->FAT2_start_sector += sbi->num_FAT_sectors;
> sbi->data_start_sector = le32_to_cpu(p_boot->clu_offset);
> sbi->num_sectors = le64_to_cpu(p_boot->vol_length);
> /* because the cluster index starts with 2 */ @@ -483,15 +464,45 @@
> static int __exfat_fill_super(struct super_block *sb)
> sbi->clu_srch_ptr = EXFAT_FIRST_CLUSTER;
> sbi->used_clusters = EXFAT_CLUSTERS_UNTRACKED;
>
> - if (le16_to_cpu(p_boot->vol_flags) & VOL_DIRTY) {
> - sbi->vol_flag |= VOL_DIRTY;
> - exfat_warn(sb, "Volume was not properly unmounted. Some data
> may be corrupt. Please run fsck.");
> + /* check consistencies */
> + if (sbi->num_FAT_sectors << p_boot->sect_size_bits <
> + sbi->num_clusters * 4) {
> + exfat_err(sb, "bogus fat length");
> + return -EINVAL;
> + }
> + if (sbi->data_start_sector <
> + sbi->FAT1_start_sector + sbi->num_FAT_sectors *
p_boot->num_fats)
> {
> + exfat_err(sb, "bogus data start sector");
> + return -EINVAL;
> }
> + if (sbi->vol_flag & VOL_DIRTY)
> + exfat_warn(sb, "Volume was not properly unmounted. Some data
> may be corrupt. Please run fsck.");
> + if (sbi->vol_flag & ERR_MEDIUM)
> + exfat_warn(sb, "Medium has reported failures. Some data may
> be
> +lost.");
>
> /* exFAT file size is limited by a disk volume size */
> sb->s_maxbytes = (u64)(sbi->num_clusters - EXFAT_RESERVED_CLUSTERS)
> <<
> sbi->cluster_size_bits;
>
> + /* check logical sector size */
> + if (exfat_calibrate_blocksize(sb, 1 << p_boot->sect_size_bits))
> + return -EIO;
> +
> + return 0;
> +}
> +
> +/* mount the file system volume */
> +static int __exfat_fill_super(struct super_block *sb) {
> + int ret;
> + struct exfat_sb_info *sbi = EXFAT_SB(sb);
> +
> + ret = exfat_read_boot_sector(sb);
> + if (ret) {
> + exfat_err(sb, "failed to read boot sector");
> + goto free_bh;
> + }
> +
> ret = exfat_create_upcase_table(sb);
> if (ret) {
> exfat_err(sb, "failed to load upcase table");
> --
> 2.25.1
