linux-ext4 - Re: [PATCH v2] jbd2: fix data-race and null-ptr-deref in jbd2_journal_dirty

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Message-ID: <74flzxcuaj7sozun7bxbaxcv5wn7hnxg6kfmzzveb24ibufv2d@jycpstzyqfa2>
Date: Wed, 14 May 2025 17:57:15 +0200
From: Jan Kara <jack@...e.cz>
To: Jeongjun Park <aha310510@...il.com>
Cc: tytso@....edu, jack@...e.cz, linux-ext4@...r.kernel.org, 
	linux-kernel@...r.kernel.org, syzbot+de24c3fe3c4091051710@...kaller.appspotmail.com
Subject: Re: [PATCH v2] jbd2: fix data-race and null-ptr-deref in
 jbd2_journal_dirty_metadata()

On Wed 14-05-25 22:08:55, Jeongjun Park wrote:
> Since handle->h_transaction may be a NULL pointer, so we should change it
> to call is_handle_aborted(handle) first before dereferencing it.
> 
> And the following data-race was reported in my fuzzer:
> 
> ==================================================================
> BUG: KCSAN: data-race in jbd2_journal_dirty_metadata / jbd2_journal_dirty_metadata
> 
> write to 0xffff888011024104 of 4 bytes by task 10881 on cpu 1:
>  jbd2_journal_dirty_metadata+0x2a5/0x770 fs/jbd2/transaction.c:1556
>  __ext4_handle_dirty_metadata+0xe7/0x4b0 fs/ext4/ext4_jbd2.c:358
>  ext4_do_update_inode fs/ext4/inode.c:5220 [inline]
>  ext4_mark_iloc_dirty+0x32c/0xd50 fs/ext4/inode.c:5869
>  __ext4_mark_inode_dirty+0xe1/0x450 fs/ext4/inode.c:6074
>  ext4_dirty_inode+0x98/0xc0 fs/ext4/inode.c:6103
> ....
> 
> read to 0xffff888011024104 of 4 bytes by task 10880 on cpu 0:
>  jbd2_journal_dirty_metadata+0xf2/0x770 fs/jbd2/transaction.c:1512
>  __ext4_handle_dirty_metadata+0xe7/0x4b0 fs/ext4/ext4_jbd2.c:358
>  ext4_do_update_inode fs/ext4/inode.c:5220 [inline]
>  ext4_mark_iloc_dirty+0x32c/0xd50 fs/ext4/inode.c:5869
>  __ext4_mark_inode_dirty+0xe1/0x450 fs/ext4/inode.c:6074
>  ext4_dirty_inode+0x98/0xc0 fs/ext4/inode.c:6103
> ....
> 
> value changed: 0x00000000 -> 0x00000001
> ==================================================================
> 
> This issue is caused by missing data-race annotation for jh->b_modified.
> Therefore, the missing annotation needs to be added.
> 
> Reported-by: syzbot+de24c3fe3c4091051710@...kaller.appspotmail.com
> Closes: https://syzkaller.appspot.com/bug?extid=de24c3fe3c4091051710
> Fixes: 6e06ae88edae ("jbd2: speedup jbd2_journal_dirty_metadata()")
> Signed-off-by: Jeongjun Park <aha310510@...il.com>

Looks good now! Thanks! Feel free to add:

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

								Honza

> ---
> v2: Changed to annotate jh->b_modified to avoid performance overhead
> - Link to v1: https://lore.kernel.org/all/20250513170441.54658-1-aha310510@gmail.com/
> ---
>  fs/jbd2/transaction.c | 5 +++--
>  1 file changed, 3 insertions(+), 2 deletions(-)
> 
> diff --git a/fs/jbd2/transaction.c b/fs/jbd2/transaction.c
> index cbc4785462f5..c7867139af69 100644
> --- a/fs/jbd2/transaction.c
> +++ b/fs/jbd2/transaction.c
> @@ -1509,7 +1509,7 @@ int jbd2_journal_dirty_metadata(handle_t *handle, struct buffer_head *bh)
>  				jh->b_next_transaction == transaction);
>  		spin_unlock(&jh->b_state_lock);
>  	}
> -	if (jh->b_modified == 1) {
> +	if (data_race(jh->b_modified == 1)) {
>  		/* If it's in our transaction it must be in BJ_Metadata list. */
>  		if (data_race(jh->b_transaction == transaction &&
>  		    jh->b_jlist != BJ_Metadata)) {
> @@ -1528,7 +1528,6 @@ int jbd2_journal_dirty_metadata(handle_t *handle, struct buffer_head *bh)
>  		goto out;
>  	}
>  
> -	journal = transaction->t_journal;
>  	spin_lock(&jh->b_state_lock);
>  
>  	if (is_handle_aborted(handle)) {
> @@ -1543,6 +1542,8 @@ int jbd2_journal_dirty_metadata(handle_t *handle, struct buffer_head *bh)
>  		goto out_unlock_bh;
>  	}
>  
> +	journal = transaction->t_journal;
> +
>  	if (jh->b_modified == 0) {
>  		/*
>  		 * This buffer's got modified and becoming part
> --
-- 
Jan Kara <jack@...e.com>
SUSE Labs, CR