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

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Date:   Tue, 26 May 2020 16:23:03 +0900
From:   "Namjae Jeon" <namjae.jeon@...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>,
        "'Sungjong Seo'" <sj1557.seo@...sung.com>,
        <linux-fsdevel@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH 3/4] exfat: add boot region verification

[snip]
> +static int exfat_verify_boot_region(struct super_block *sb) {
> +	struct buffer_head *bh = NULL;
> +	u32 chksum = 0, *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 = (u32 *)&bh->b_data[sb->s_blocksize - 4];
> +			if (le32_to_cpu(*p_sig) != EXBOOT_SIGNATURE) {
> +				exfat_err(sb, "no exboot-signature");
                                exfat_warn(sb, "Invalid exboot-signature(sector = %d): 0x%08x", sn, *p_sig);
> +				brelse(bh);
> +				return -EINVAL;
Don't make mount error, Just print warning message.
> +			}
> +		}
> +
> +		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 = (u32 *)&bh->b_data[i];
> +		if (le32_to_cpu(*p_chksum) != chksum) {
> +			exfat_err(sb, "mismatch checksum");
Print invalid checksum value also.
> +			brelse(bh);
> +			return -EINVAL;
> +		}
> +	}
> +	brelse(bh);
> +	return 0;
> +}
> +
>  /* mount the file system volume */
>  static int __exfat_fill_super(struct super_block *sb)  { @@ -498,6 +542,12 @@ 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