linux-ext4 - Re: [PATCH RFC] jbd2: detect old record when do journal scan

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Message-ID: <20220819095445.yq4d2qhrhb73p3zk@quack3>
Date:   Fri, 19 Aug 2022 11:54:45 +0200
From:   Jan Kara <jack@...e.cz>
To:     Ye Bin <yebin10@...wei.com>
Cc:     tytso@....edu, adilger.kernel@...ger.ca,
        linux-ext4@...r.kernel.org, linux-kernel@...r.kernel.org,
        jack@...e.cz
Subject: Re: [PATCH RFC] jbd2: detect old record when do journal scan

On Wed 10-08-22 09:34:42, Ye Bin wrote:
> As https://github.com/tytso/e2fsprogs/issues/120 describe tune2fs do not update
> j_tail_sequence when do journal recovery. This maybe recover old journal record,
> then will lead to file system corruption.
> To avoid file system corruption in this case, if detect current transaction's
> commit time earlier than previous transaction's commit time when do journal
> scan, just return error.
> 
> Signed-off-by: Ye Bin <yebin10@...wei.com>

Thanks for the patch! Let me see if I understand your concern right. You
are concerned about the following scenario:

1) Kernel uses the filesystem, there's a crash.
2) E2fsprogs replays the journal but fails to update sb->s_sequence in the
journal superblock.
3) Kernel mounts the fs again - however note that even if kernel skips
recovery, it does scan the journal jbd2_journal_skip_recovery() and
journal->j_transaction_sequence is set based on the last transaction found
in the journal.

So I don't think there is really possibility we will quickly reuse some
transaction IDs and thus possibility of corruption on replay? Am I missing
something?

								Honza


> ---
>  fs/jbd2/recovery.c | 11 ++++++++++-
>  1 file changed, 10 insertions(+), 1 deletion(-)
> 
> diff --git a/fs/jbd2/recovery.c b/fs/jbd2/recovery.c
> index f548479615c6..f3def21a96a5 100644
> --- a/fs/jbd2/recovery.c
> +++ b/fs/jbd2/recovery.c
> @@ -812,8 +812,17 @@ static int do_one_pass(journal_t *journal,
>  					break;
>  				}
>  			}
> -			if (pass == PASS_SCAN)
> +			if (pass == PASS_SCAN) {
> +				if (commit_time < last_trans_commit_time) {
> +					pr_err("JBD2: old journal record found "
> +					       "in transaction %u\n",
> +					       next_commit_ID);
> +					err = -EFSBADCRC;
> +					brelse(bh);
> +					goto failed;
> +				}
>  				last_trans_commit_time = commit_time;
> +			}
>  			brelse(bh);
>  			next_commit_ID++;
>  			continue;
> -- 
> 2.31.1
> 
-- 
Jan Kara <jack@...e.com>
SUSE Labs, CR