linux-kernel - RE: [PATCH 3/4 v4] exfat: add boot region verification

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Date:   Mon, 1 Jun 2020 21:21:16 +0900
From:   "Sungjong Seo" <sj1557.seo@...sung.com>
To:     "'Tetsuhiro Kohada'" <kohada.t2@...il.com>
Cc:     <kohada.tetsuhiro@...mitsubishielectric.co.jp>,
        <mori.takahiro@...mitsubishielectric.co.jp>,
        <motai.hirotaka@...mitsubishielectric.co.jp>,
        "'Namjae Jeon'" <namjae.jeon@...sung.com>,
        <linux-fsdevel@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH 3/4 v4] exfat: add boot region verification

> 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@...il.com>

Reviewed-by: Sungjong Seo <sj1557.seo@...sung.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