linux-kernel - Re: [PATCH v2] ext4: don't order data when zeroing unwritten or delayed block

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [day] [month] [year] [list]

Message-ID: <cca2fc6c-3c54-418d-935e-779e60833f87@huawei.com>
Date: Wed, 31 Dec 2025 14:39:55 +0800
From: Baokun Li <libaokun1@...wei.com>
To: Zhang Yi <yi.zhang@...weicloud.com>, <linux-ext4@...r.kernel.org>
CC: <linux-fsdevel@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
	<tytso@....edu>, <adilger.kernel@...ger.ca>, <jack@...e.cz>,
	<ojaswin@...ux.ibm.com>, <ritesh.list@...il.com>, <yi.zhang@...wei.com>,
	<yizhang089@...il.com>, <yangerkun@...wei.com>, <yukuai@...as.com>
Subject: Re: [PATCH v2] ext4: don't order data when zeroing unwritten or
 delayed block

On 2025-12-23 09:19, Zhang Yi wrote:
> From: Zhang Yi <yi.zhang@...wei.com>
>
> When zeroing out a written partial block, it is necessary to order the
> data to prevent exposing stale data on disk. However, if the buffer is
> unwritten or delayed, it is not allocated as written, so ordering the
> data is not required. This can prevent strange and unnecessary ordered
> writes when appending data across a region within a block.
>
> Assume we have a 2K unwritten file on a filesystem with 4K blocksize,
> and buffered write from 3K to 4K. Before this patch,
> __ext4_block_zero_page_range() would add the range [2k,3k) to the
> ordered range, and then the JBD2 commit process would write back this
> block. However, it does nothing since the block is not mapped as
> written, this folio will be redirtied and written back agian through the
> normal write back process.
>
> Signed-off-by: Zhang Yi <yi.zhang@...wei.com>
> Reviewed-by: Jan Kara <jack@...e.cz>

Makes sense. Feel free to add:

Reviewed-by: Baokun Li <libaokun1@...wei.com>

> ---
>  fs/ext4/inode.c | 8 ++++++--
>  1 file changed, 6 insertions(+), 2 deletions(-)
>
> diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
> index 2e79b09fe2f0..f2d70c9af446 100644
> --- a/fs/ext4/inode.c
> +++ b/fs/ext4/inode.c
> @@ -4109,9 +4109,13 @@ static int __ext4_block_zero_page_range(handle_t *handle,
>  	if (ext4_should_journal_data(inode)) {
>  		err = ext4_dirty_journalled_data(handle, bh);
>  	} else {
> -		err = 0;
>  		mark_buffer_dirty(bh);
> -		if (ext4_should_order_data(inode))
> +		/*
> +		 * Only the written block requires ordered data to prevent
> +		 * exposing stale data.
> +		 */
> +		if (!buffer_unwritten(bh) && !buffer_delay(bh) &&
> +		    ext4_should_order_data(inode))
>  			err = ext4_jbd2_inode_add_write(handle, inode, from,
>  					length);
>  	}