linux-ext4 - Re: [PATCH -next 2/2] jbd2: fix potential use-after-free in jbd2_fc_wait

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Date:   Wed, 14 Sep 2022 16:36:44 +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 -next 2/2] jbd2: fix potential use-after-free in
 jbd2_fc_wait_bufs

On Wed 14-09-22 18:08:12, Ye Bin wrote:
> In 'jbd2_fc_wait_bufs' use 'bh' after put buffer head reference count
> which may lead to use-after-free.
> So judge buffer if uptodate before put buffer head reference count.
> 
> Signed-off-by: Ye Bin <yebin10@...wei.com>

Looks good. Feel free to add:

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

								Honza

> ---
>  fs/jbd2/journal.c | 6 +++---
>  1 file changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/fs/jbd2/journal.c b/fs/jbd2/journal.c
> index 1c833d8cb0fe..4d49f629d06b 100644
> --- a/fs/jbd2/journal.c
> +++ b/fs/jbd2/journal.c
> @@ -923,16 +923,16 @@ int jbd2_fc_wait_bufs(journal_t *journal, int num_blks)
>  	for (i = j_fc_off - 1; i >= j_fc_off - num_blks; i--) {
>  		bh = journal->j_fc_wbuf[i];
>  		wait_on_buffer(bh);
> -		put_bh(bh);
> -		journal->j_fc_wbuf[i] = NULL;
>  		/*
>  		 * Update j_fc_off so jbd2_fc_release_bufs can release remain
>  		 * buffer head.
>  		 */
>  		if (unlikely(!buffer_uptodate(bh))) {
> -			journal->j_fc_off = i;
> +			journal->j_fc_off = i + 1;
>  			return -EIO;
>  		}
> +		put_bh(bh);
> +		journal->j_fc_wbuf[i] = NULL;
>  	}
>  
>  	return 0;
> -- 
> 2.31.1
> 
-- 
Jan Kara <jack@...e.com>
SUSE Labs, CR