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Date:   Wed, 18 Mar 2020 10:13:18 +0100
From:   Jan Kara <jack@suse.cz>
To:     Ritesh Harjani <riteshh@linux.ibm.com>
Cc:     linux-ext4@vger.kernel.org, tytso@mit.edu, jack@suse.cz,
        adilger.kernel@dilger.ca, linux-fsdevel@vger.kernel.org
Subject: Re: [PATCH] ext4: Unregister sysfs path before destroying jbd2
 journal
Message-ID: <20200318091318.GJ22684@quack2.suse.cz>
References: <20200318061301.4320-1-riteshh@linux.ibm.com>
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On Wed 18-03-20 11:43:01, Ritesh Harjani wrote:
> Call ext4_unregister_sysfs(), before destroying jbd2 journal,
> since below might cause, NULL pointer dereference issue.
> This got reported with LTP tests.
> 
> ext4_put_super() 		cat /sys/fs/ext4/loop2/journal_task
> 	| 				ext4_attr_show();
> ext4_jbd2_journal_destroy();  			|
>     	|				 journal_task_show()
> 	| 					|
> 	| 				task_pid_vnr(NULL);
> sbi->s_journal = NULL;
> 
> Signed-off-by: Ritesh Harjani <riteshh@linux.ibm.com>

Yeah, makes sence. Thanks for the patch! You can add:

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

								Honza

> ---
>  fs/ext4/super.c | 8 +++++++-
>  1 file changed, 7 insertions(+), 1 deletion(-)
> 
> diff --git a/fs/ext4/super.c b/fs/ext4/super.c
> index 5dc65b7583cb..27ab130a40d1 100644
> --- a/fs/ext4/super.c
> +++ b/fs/ext4/super.c
> @@ -1024,6 +1024,13 @@ static void ext4_put_super(struct super_block *sb)
>  
>  	destroy_workqueue(sbi->rsv_conversion_wq);
>  
> +	/*
> +	 * Unregister sysfs before destroying jbd2 journal.
> +	 * Since we could still access attr_journal_task attribute via sysfs
> +	 * path which could have sbi->s_journal->j_task as NULL
> +	 */
> +	ext4_unregister_sysfs(sb);
> +
>  	if (sbi->s_journal) {
>  		aborted = is_journal_aborted(sbi->s_journal);
>  		err = jbd2_journal_destroy(sbi->s_journal);
> @@ -1034,7 +1041,6 @@ static void ext4_put_super(struct super_block *sb)
>  		}
>  	}
>  
> -	ext4_unregister_sysfs(sb);
>  	ext4_es_unregister_shrinker(sbi);
>  	del_timer_sync(&sbi->s_err_report);
>  	ext4_release_system_zone(sb);
> -- 
> 2.21.0
> 
-- 
Jan Kara <jack@suse.com>
SUSE Labs, CR