linux-kernel - Re: [PATCH 2/2] ext4: refuse to create ea block when umounted

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Date:   Fri, 30 Dec 2022 12:13:25 -0800
From:   Eric Biggers <ebiggers@...nel.org>
To:     Jun Nie <jun.nie@...aro.org>
Cc:     tytso@....edu, adilger.kernel@...ger.ca,
        linux-ext4@...r.kernel.org, linux-kernel@...r.kernel.org,
        tudor.ambarus@...aro.org
Subject: Re: [PATCH 2/2] ext4: refuse to create ea block when umounted

On Fri, Dec 30, 2022 at 07:00:16PM +0800, Jun Nie wrote:
> The ea block expansion need to access s_root while it is
> already set as NULL when umount is triggered. Refuse this
> request to avoid panic.
> 
> Reported-by: syzbot+2dacb8f015bf1420155f@...kaller.appspotmail.com
> Link: https://syzkaller.appspot.com/bug?id=3613786cb88c93aa1c6a279b1df6a7b201347d08
> Signed-off-by: Jun Nie <jun.nie@...aro.org>
> ---
>  fs/ext4/xattr.c | 6 ++++++
>  1 file changed, 6 insertions(+)
> 
> diff --git a/fs/ext4/xattr.c b/fs/ext4/xattr.c
> index 235a517d9c17..ac58494e49b6 100644
> --- a/fs/ext4/xattr.c
> +++ b/fs/ext4/xattr.c
> @@ -1422,6 +1422,12 @@ static struct inode *ext4_xattr_inode_create(handle_t *handle,
>  	uid_t owner[2] = { i_uid_read(inode), i_gid_read(inode) };
>  	int err;
>  
> +	if (inode->i_sb->s_root == NULL) {
> +		ext4_error(inode->i_sb,
> +			   "refuse to create EA inode when umounting");
> +		return ERR_PTR(-EINVAL);
> +	}
> +

Why is an xattr being set during unmount?

- Eric