mnt: Move the FS_USERNS_MOUNT check into sget_userns

Allowing a filesystem to be mounted by other than root in the initial
user namespace is a filesystem property not a mount namespace property
and as such should be checked in filesystem specific code.  Move the
FS_USERNS_MOUNT test into super.c:sget_userns().

Acked-by: Seth Forshee <seth.forshee@canonical.com>
Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>

1 files changed, 4 insertions, 0 deletions

diff --git a/fs/super.c b/fs/super.c
index 874c7e3..78790ad 100644
--- a/fs/super.c
+++ b/fs/super.c
@@ -466,6 +466,10 @@ struct super_block *sget_userns(struct file_system_type *type,
 	struct super_block *old;
 	int err;
 
+	if (!(flags & MS_KERNMOUNT) &&
+	    !(type->fs_flags & FS_USERNS_MOUNT) &&
+	    !capable(CAP_SYS_ADMIN))
+		return ERR_PTR(-EPERM);
 retry:
 	spin_lock(&sb_lock);
 	if (test) {