linux-kernel - Re: [PATCH] fs: allow clone_private_mount() for a path on real rootfs

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Message-ID: <9138a96b-3df0-455a-9059-287a98356c4c@nec.com>
Date: Wed, 14 May 2025 08:37:54 +0000
From: KONDO KAZUMA(近藤　和真)
	<kazuma-kondo@....com>
To: Al Viro <viro@...iv.linux.org.uk>
CC: "brauner@...nel.org" <brauner@...nel.org>, "jack@...e.cz" <jack@...e.cz>,
	"mike@...ynton.com" <mike@...ynton.com>, "miklos@...redi.hu"
	<miklos@...redi.hu>, "amir73il@...il.com" <amir73il@...il.com>,
	"linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
	"linux-unionfs@...r.kernel.org" <linux-unionfs@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	KONDO KAZUMA(近藤　和真) <kazuma-kondo@....com>
Subject: Re: [PATCH] fs: allow clone_private_mount() for a path on real rootfs

On 2025/05/14 11:43, Al Viro wrote:
> On Wed, May 14, 2025 at 12:25:58AM +0000, KONDO KAZUMA(近藤 和真) wrote:
> 
>> @@ -2482,17 +2482,13 @@ struct vfsmount *clone_private_mount(const struct path *path)
>>  	if (IS_MNT_UNBINDABLE(old_mnt))
>>  		return ERR_PTR(-EINVAL);
>>  
>> -	if (mnt_has_parent(old_mnt)) {
>> +	if (!is_mounted(&old_mnt->mnt))
>> +		return ERR_PTR(-EINVAL);
>> +
>> +	if (mnt_has_parent(old_mnt) || !is_anon_ns(old_mnt->mnt_ns)) {
>>  		if (!check_mnt(old_mnt))
>>  			return ERR_PTR(-EINVAL);
>>  	} else {
>> -		if (!is_mounted(&old_mnt->mnt))
>> -			return ERR_PTR(-EINVAL);
>> -
>> -		/* Make sure this isn't something purely kernel internal. */
>> -		if (!is_anon_ns(old_mnt->mnt_ns))
>> -			return ERR_PTR(-EINVAL);
>> -
>>  		/* Make sure we don't create mount namespace loops. */
>>  		if (!check_for_nsfs_mounts(old_mnt))
>>  			return ERR_PTR(-EINVAL);
> 
> Not the right way to do that.  What we want is
> 
> 	/* ours are always fine */
> 	if (!check_mnt(old_mnt)) {
> 		/* they'd better be mounted _somewhere */
> 		if (!is_mounted(old_mnt))
> 			return -EINVAL;
> 		/* no other real namespaces; only anon */
> 		if (!is_anon_ns(old_mnt->mnt_ns))
> 			return -EINVAL;
> 		/* ... and root of that anon */
> 		if (mnt_has_parent(old_mnt))
> 			return -EINVAL;
> 		/* Make sure we don't create mount namespace loops. */
> 		if (!check_for_nsfs_mounts(old_mnt))
> 			return ERR_PTR(-EINVAL);
> 	}

Hello Al Viro,

Thank you for your comment.
That code can solve my problem, and it seems to be better!

So, I will revise my patch and resend it.

Thanks,
Kazuma Kondo