From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <linux-kernel-owner@vger.kernel.org>
Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand
	id S1752552AbbADC7y (ORCPT <rfc822;w@1wt.eu>);
	Sat, 3 Jan 2015 21:59:54 -0500
Received: from [119.145.14.66] ([119.145.14.66]:26896 "EHLO
	szxga03-in.huawei.com" rhost-flags-FAIL-FAIL-OK-OK) by vger.kernel.org
	with ESMTP id S1751765AbbADC7v (ORCPT
	<rfc822;linux-kernel@vger.kernel.org>);
	Sat, 3 Jan 2015 21:59:51 -0500
Message-ID: <54A8AC74.2060106@huawei.com>
Date: Sun, 4 Jan 2015 10:59:00 +0800
From: hujianyang <hujianyang@huawei.com>
User-Agent: Mozilla/5.0 (Windows NT 6.1; rv:17.0) Gecko/20130801 Thunderbird/17.0.8
MIME-Version: 1.0
To: Seunghun Lee <waydi1@gmail.com>
CC: <miklos@szeredi.hu>, <sedat.dilek@gmail.com>,
        <richard.weinberger@gmail.com>, <linux-fsdevel@vger.kernel.org>,
        <linux-kernel@vger.kernel.org>, <linux-unionfs@vger.kernel.org>
Subject: Re: [PATCH] ovl: Prevent rw remount when it should be ro mount
References: <1420219609-2568-1-git-send-email-waydi1@gmail.com>
In-Reply-To: <1420219609-2568-1-git-send-email-waydi1@gmail.com>
Content-Type: text/plain; charset="ISO-8859-1"
Content-Transfer-Encoding: 7bit
X-Originating-IP: [10.111.68.144]
X-CFilter-Loop: Reflected
X-Mirapoint-Virus-RAPID-Raw: score=unknown(0),
	refid=str=0001.0A020202.54A8AC92.0085,ss=1,re=0.001,recu=0.000,reip=0.000,cl=1,cld=1,fgs=0,
	ip=0.0.0.0,
	so=2013-05-26 15:14:31,
	dmn=2013-03-21 17:37:32
X-Mirapoint-Loop-Id: b9c480d4c56a30215294ee38fd8676fa
Sender: linux-kernel-owner@vger.kernel.org
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org

On 2015/1/3 1:26, Seunghun Lee wrote:
> Overlayfs should be mounted read-only when upper-fs is read-only or nonexistent.
> But now it can be remounted read-write and this can cause kernel panic.
> So we should prevent read-write remount when the above situation happens.
> 
> Signed-off-by: Seunghun Lee <waydi1@gmail.com>
> ---
>  fs/overlayfs/super.c | 11 +++++++++++
>  1 file changed, 11 insertions(+)
> 
> diff --git a/fs/overlayfs/super.c b/fs/overlayfs/super.c
> index 84f3144..8944651 100644
> --- a/fs/overlayfs/super.c
> +++ b/fs/overlayfs/super.c
> @@ -522,10 +522,21 @@ static int ovl_show_options(struct seq_file *m, struct dentry *dentry)
>  	return 0;
>  }
>  
> +static int ovl_remount(struct super_block *sb, int *flags, char *data)
> +{
> +	struct ovl_fs *ufs = sb->s_fs_info;
> +
> +	if (!ufs->upper_mnt || (ufs->upper_mnt->mnt_sb->s_flags & MS_RDONLY))
> +		*flags |= MS_RDONLY;
> +
> +	return 0;
> +}
> +
>  static const struct super_operations ovl_super_operations = {
>  	.put_super	= ovl_put_super,
>  	.statfs		= ovl_statfs,
>  	.show_options	= ovl_show_options,
> +	.remount_fs	= ovl_remount,
>  };
>  
>  enum {
> 

I think this exporting of .remount_fs may allow people in userspace
have the ability to remount a filesystem with a new set of mounting
options. Your new adding function do nothing with the passing in
parameters.

I'm not sure if it could be competent for remount case.

Add Cc linux-unionfs.