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fs: fat: add bootsector validity check

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The performed checks are similar to the checks performed by the Linux
kernel in the function fat_read_bpb() in the file fs/fat/inode.c.

Signed-off-by: Christian Taedcke <christian.taedcke@weidmueller.com>
This commit is contained in:
Christian Taedcke 2023-11-15 13:44:20 +01:00 • committed by Tom Rini
parent 33daef49b0
commit c489937a6f
1 changed files with 53 additions and 0 deletions
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53
fs/fat/fat.c
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@ -25,6 +25,7 @@
#include <asm/cache.h>
#include <linux/compiler.h>
#include <linux/ctype.h>
#include <linux/log2.h>
/* maximum number of clusters for FAT12 */
#define MAX_FAT12 0xFF4
@ -508,6 +509,52 @@ static int determine_legacy_fat_bits(const boot_sector *bs)
return (total_clusters > MAX_FAT12) ? 16 : 12;
}
/*
* Determines if the boot sector's media field is valid
*
* Based on fat_valid_media() from Linux kernel's include/linux/msdos_fs.h
*/
static int fat_valid_media(u8 media)
{
return media >= 0xf8 || media == 0xf0;
}
/*
* Determines if the given boot sector is valid
*
* Based on fat_read_bpb() from the Linux kernel's fs/fat/inode.c
*/
static int is_bootsector_valid(const boot_sector *bs)
{
u16 sector_size = get_unaligned_le16(bs->sector_size);
u16 dir_per_block = sector_size / sizeof(dir_entry);
if (!bs->reserved)
return 0;
if (!bs->fats)
return 0;
if (!fat_valid_media(bs->media))
return 0;
if (!is_power_of_2(sector_size) ||
sector_size < 512 ||
sector_size > 4096)
return 0;
if (!is_power_of_2(bs->cluster_size))
return 0;
if (!bs->fat_length && !bs->fat32_length)
return 0;
if (get_unaligned_le16(bs->dir_entries) & (dir_per_block - 1))
return 0;
return 1;
}
/*
* Read boot sector and volume info from a FAT filesystem
*/
@ -542,6 +589,12 @@ read_bootsectandvi(boot_sector *bs, volume_info *volinfo, int *fatsize)
bs->heads = FAT2CPU16(bs->heads);
bs->total_sect = FAT2CPU32(bs->total_sect);
if (!is_bootsector_valid(bs)) {
debug("Error: bootsector is invalid\n");
ret = -1;
goto out_free;
}
/* FAT32 entries */
if (!bs->fat_length && bs->fat32_length) {
/* Assume FAT32 */