linux-ext4 - Re: [PATCH 2/4] ext4: validate external journal superblock checksum

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Message-ID: <20140911132554.GC30901@quack.suse.cz>
Date:	Thu, 11 Sep 2014 15:25:54 +0200
From:	Jan Kara <jack@...e.cz>
To:	"Darrick J. Wong" <darrick.wong@...cle.com>
Cc:	tytso@....edu, linux-ext4@...r.kernel.org
Subject: Re: [PATCH 2/4] ext4: validate external journal superblock checksum

On Wed 10-09-14 17:28:32, Darrick J. Wong wrote:
> If the external journal device has metadata_csum enabled, verify
> that the superblock checksum matches the block before we try to
> mount.
  Looks good. You can add:
Reviewed-by: Jan Kara <jack@...e.cz>

								Honza

PS: On a general note the way we are checking checksums in ext4 seems to be
a bit arbitrary. It would seem more robust to just have ext4_bread() take
data type of the buffer and if the buffer doesn't have buffer_verified set,
it would run appropriate checksum check on the buffer. That way we are sure
that the buffer is checked whenever it's loaded from disk. ocfs2 and xfs
are doing it this way...

> 
> Signed-off-by: Darrick J. Wong <darrick.wong@...cle.com>
> ---
>  fs/ext4/super.c |    9 +++++++++
>  1 file changed, 9 insertions(+)
> 
> 
> diff --git a/fs/ext4/super.c b/fs/ext4/super.c
> index 7045f1d..222ed5d 100644
> --- a/fs/ext4/super.c
> +++ b/fs/ext4/super.c
> @@ -4372,6 +4372,15 @@ static journal_t *ext4_get_dev_journal(struct super_block *sb,
>  		goto out_bdev;
>  	}
>  
> +	if ((le32_to_cpu(es->s_feature_ro_compat) &
> +	     EXT4_FEATURE_RO_COMPAT_METADATA_CSUM) &&
> +	    es->s_checksum != ext4_superblock_csum(sb, es)) {
> +		ext4_msg(sb, KERN_ERR, "external journal has "
> +				       "corrupt superblock");
> +		brelse(bh);
> +		goto out_bdev;
> +	}
> +
>  	if (memcmp(EXT4_SB(sb)->s_es->s_journal_uuid, es->s_uuid, 16)) {
>  		ext4_msg(sb, KERN_ERR, "journal UUID does not match");
>  		brelse(bh);
> 
> --
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-- 
Jan Kara <jack@...e.cz>
SUSE Labs, CR
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