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Subject[PATCH 3/4 v4] exfat: add boot region verification
Date
Add Boot-Regions verification specified in exFAT specification.
Note that the checksum type is strongly related to the raw structure,
so the'u32 'type is used to clarify the number of bits.

Signed-off-by: Tetsuhiro Kohada <kohada.t2@gmail.com>
---
Changes in v2:
- rebase with patch 'optimize dir-cache' applied
- just print a warning when invalid exboot-signature detected
- print additional information when invalid boot-checksum detected
Changes in v3:
- based on '[PATCH 2/4 v3] exfat: separate the boot sector analysis'
Changes in v4:
- fix type of p_sig/p_chksum to __le32

fs/exfat/exfat_fs.h | 1 +
fs/exfat/misc.c | 14 +++++++++++++
fs/exfat/super.c | 50 +++++++++++++++++++++++++++++++++++++++++++++
3 files changed, 65 insertions(+)

diff --git a/fs/exfat/exfat_fs.h b/fs/exfat/exfat_fs.h
index 9673e2d31045..eebbe5a84b2b 100644
--- a/fs/exfat/exfat_fs.h
+++ b/fs/exfat/exfat_fs.h
@@ -514,6 +514,7 @@ void exfat_set_entry_time(struct exfat_sb_info *sbi, struct timespec64 *ts,
u8 *tz, __le16 *time, __le16 *date, u8 *time_cs);
unsigned short exfat_calc_chksum_2byte(void *data, int len,
unsigned short chksum, int type);
+u32 exfat_calc_chksum32(void *data, int len, u32 chksum, int type);
void exfat_update_bh(struct super_block *sb, struct buffer_head *bh, int sync);
void exfat_chain_set(struct exfat_chain *ec, unsigned int dir,
unsigned int size, unsigned char flags);
diff --git a/fs/exfat/misc.c b/fs/exfat/misc.c
index ab7f88b1f6d3..b82d2dd5bd7c 100644
--- a/fs/exfat/misc.c
+++ b/fs/exfat/misc.c
@@ -151,6 +151,20 @@ unsigned short exfat_calc_chksum_2byte(void *data, int len,
return chksum;
}

+u32 exfat_calc_chksum32(void *data, int len, u32 chksum, int type)
+{
+ int i;
+ u8 *c = (u8 *)data;
+
+ for (i = 0; i < len; i++, c++) {
+ if (unlikely(type == CS_BOOT_SECTOR &&
+ (i == 106 || i == 107 || i == 112)))
+ continue;
+ chksum = ((chksum << 31) | (chksum >> 1)) + *c;
+ }
+ return chksum;
+}
+
void exfat_update_bh(struct super_block *sb, struct buffer_head *bh, int sync)
{
set_bit(EXFAT_SB_DIRTY, &EXFAT_SB(sb)->s_state);
diff --git a/fs/exfat/super.c b/fs/exfat/super.c
index 6a1330be5a9a..405717e4e3ea 100644
--- a/fs/exfat/super.c
+++ b/fs/exfat/super.c
@@ -491,6 +491,50 @@ static int exfat_read_boot_sector(struct super_block *sb)
return 0;
}

+static int exfat_verify_boot_region(struct super_block *sb)
+{
+ struct buffer_head *bh = NULL;
+ u32 chksum = 0;
+ __le32 *p_sig, *p_chksum;
+ int sn, i;
+
+ /* read boot sector sub-regions */
+ for (sn = 0; sn < 11; sn++) {
+ bh = sb_bread(sb, sn);
+ if (!bh)
+ return -EIO;
+
+ if (sn != 0 && sn <= 8) {
+ /* extended boot sector sub-regions */
+ p_sig = (__le32 *)&bh->b_data[sb->s_blocksize - 4];
+ if (le32_to_cpu(*p_sig) != EXBOOT_SIGNATURE)
+ exfat_warn(sb, "Invalid exboot-signature(sector = %d): 0x%08x",
+ sn, le32_to_cpu(*p_sig));
+ }
+
+ chksum = exfat_calc_chksum32(bh->b_data, sb->s_blocksize,
+ chksum, sn ? CS_DEFAULT : CS_BOOT_SECTOR);
+ brelse(bh);
+ }
+
+ /* boot checksum sub-regions */
+ bh = sb_bread(sb, sn);
+ if (!bh)
+ return -EIO;
+
+ for (i = 0; i < sb->s_blocksize; i += sizeof(u32)) {
+ p_chksum = (__le32 *)&bh->b_data[i];
+ if (le32_to_cpu(*p_chksum) != chksum) {
+ exfat_err(sb, "Invalid boot checksum (boot checksum : 0x%08x, checksum : 0x%08x)",
+ le32_to_cpu(*p_chksum), chksum);
+ brelse(bh);
+ return -EINVAL;
+ }
+ }
+ brelse(bh);
+ return 0;
+}
+
/* mount the file system volume */
static int __exfat_fill_super(struct super_block *sb)
{
@@ -503,6 +547,12 @@ static int __exfat_fill_super(struct super_block *sb)
goto free_bh;
}

+ ret = exfat_verify_boot_region(sb);
+ if (ret) {
+ exfat_err(sb, "invalid boot region");
+ goto free_bh;
+ }
+
ret = exfat_create_upcase_table(sb);
if (ret) {
exfat_err(sb, "failed to load upcase table");
--
2.25.1
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