linux-kernel - Re: [PATCH 1/2] fs: Allow bind mounts with locked children on permaenetly empty directories

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Message-ID: <20160309203239.GB3734@mail.hallyn.com>
Date:	Wed, 9 Mar 2016 14:32:39 -0600
From:	"Serge E. Hallyn" <serge@...lyn.com>
To:	Seth Forshee <seth.forshee@...onical.com>
Cc:	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Alexander Viro <viro@...iv.linux.org.uk>,
	"Serge E. Hallyn" <serge.hallyn@...ntu.com>,
	linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH 1/2] fs: Allow bind mounts with locked children on
 permaenetly empty directories

Quoting Seth Forshee (seth.forshee@...onical.com):
> Forbidding a bind mount due to a locked child on a permanently
> empty directory provides no security benefit since the
> directory cannot contain any contents which have been overmounted
> for security reasons.
> 
> Cc: stable@...r.kernel.org # v4.1+
> Signed-off-by: Seth Forshee <seth.forshee@...onical.com>

Acked-by: Serge Hallyn <serge.hallyn@...onical.com>

> ---
>  fs/namespace.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/fs/namespace.c b/fs/namespace.c
> index 4fb1691b4355..930f5557b1d1 100644
> --- a/fs/namespace.c
> +++ b/fs/namespace.c
> @@ -2065,6 +2065,8 @@ static bool has_locked_children(struct mount *mnt, struct dentry *dentry)
>  	list_for_each_entry(child, &mnt->mnt_mounts, mnt_child) {
>  		if (!is_subdir(child->mnt_mountpoint, dentry))
>  			continue;
> +		if (is_empty_dir_inode(child->mnt_mountpoint->d_inode))
> +			continue;
>  
>  		if (child->mnt.mnt_flags & MNT_LOCKED)
>  			return true;
> -- 
> 1.9.1