linux-kernel - Re: [REVIEW][PATCH 2/6] vfs: Allow userns root to call mknod on owned filesystems.

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Date:   Thu, 24 May 2018 21:12:32 +0200
From:   Christian Brauner <christian@...uner.io>
To:     "Eric W. Biederman" <ebiederm@...ssion.com>
Cc:     Linux Containers <containers@...ts.linux-foundation.org>,
        linux-fsdevel@...r.kernel.org,
        Seth Forshee <seth.forshee@...onical.com>,
        "Serge E. Hallyn" <serge@...lyn.com>, linux-kernel@...r.kernel.org
Subject: Re: [REVIEW][PATCH 2/6] vfs: Allow userns root to call mknod on
 owned filesystems.

On Wed, May 23, 2018 at 06:25:34PM -0500, Eric W. Biederman wrote:
> These filesystems already always set SB_I_NODEV so mknod will not be
> useful for gaining control of any devices no matter their permissions.
> This will allow overlayfs and applications to fakeroot to use device
> nodes to represent things on disk.

Excellent.

Acked-by: Christian Brauner <christian@...uner.io>

> 
> Signed-off-by: "Eric W. Biederman" <ebiederm@...ssion.com>
> ---
>  fs/namei.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/fs/namei.c b/fs/namei.c
> index 942c1f096f6b..20335896dcce 100644
> --- a/fs/namei.c
> +++ b/fs/namei.c
> @@ -3679,7 +3679,8 @@ int vfs_mknod(struct inode *dir, struct dentry *dentry, umode_t mode, dev_t dev)
>  	if (error)
>  		return error;
>  
> -	if ((S_ISCHR(mode) || S_ISBLK(mode)) && !capable(CAP_MKNOD))
> +	if ((S_ISCHR(mode) || S_ISBLK(mode)) &&
> +	    !ns_capable(dentry->d_sb->s_user_ns, CAP_MKNOD))
>  		return -EPERM;
>  
>  	if (!dir->i_op->mknod)
> -- 
> 2.14.1
>