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

Christian Brauner
2018-05-24T19:12:39Z

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@brauner.io>

>
> Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.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
>