linux-kernel - Re: [PATCH 2/2] ext4: update s_journal_inum if it changes after journal replay

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Message-ID: <20230106143612.nzif3jndh7p32nej@quack3>
Date:   Fri, 6 Jan 2023 15:36:12 +0100
From:   Jan Kara <jack@...e.cz>
To:     Baokun Li <libaokun1@...wei.com>
Cc:     linux-ext4@...r.kernel.org, tytso@....edu,
        adilger.kernel@...ger.ca, jack@...e.cz, ritesh.list@...il.com,
        linux-kernel@...r.kernel.org, yi.zhang@...wei.com,
        yukuai3@...wei.com,
        Luís Henriques <lhenriques@...e.de>
Subject: Re: [PATCH 2/2] ext4: update s_journal_inum if it changes after
 journal replay

On Fri 06-01-23 18:47:06, Baokun Li wrote:
> When mounting a crafted ext4 image, s_journal_inum may change after journal
> replay, which is obviously unreasonable because we have successfully loaded
> and replayed the journal through the old s_journal_inum. And the new
> s_journal_inum bypasses some of the checks in ext4_get_journal(), which
> may trigger a null pointer dereference problem. So if s_journal_inum
> changes after the journal replay, we ignore the change, and rewrite the
> current journal_inum to the superblock.
> 
> Link: https://bugzilla.kernel.org/show_bug.cgi?id=216541
> Reported-by: Luís Henriques <lhenriques@...e.de>
> Signed-off-by: Baokun Li <libaokun1@...wei.com>
> ---
>  fs/ext4/super.c | 7 +++++--
>  1 file changed, 5 insertions(+), 2 deletions(-)

Looks good. Feel free to add:

Reviewed-by: Jan Kara <jack@...e.cz>

								Honza


> 
> diff --git a/fs/ext4/super.c b/fs/ext4/super.c
> index 260c1b3e3ef2..3fe9dc19ff9c 100644
> --- a/fs/ext4/super.c
> +++ b/fs/ext4/super.c
> @@ -5953,8 +5953,11 @@ static int ext4_load_journal(struct super_block *sb,
>  	if (!really_read_only && journal_devnum &&
>  	    journal_devnum != le32_to_cpu(es->s_journal_dev)) {
>  		es->s_journal_dev = cpu_to_le32(journal_devnum);
> -
> -		/* Make sure we flush the recovery flag to disk. */
> +		ext4_commit_super(sb);
> +	}
> +	if (!really_read_only && journal_inum &&
> +	    journal_inum != le32_to_cpu(es->s_journal_inum)) {
> +		es->s_journal_inum = cpu_to_le32(journal_inum);
>  		ext4_commit_super(sb);
>  	}
>  
> -- 
> 2.31.1
> 
-- 
Jan Kara <jack@...e.com>
SUSE Labs, CR