user namespaces: let user_ns be cloned with fairsched

fairsched creates a per-uid directory under /sys/kernel/uids/. So when you clone(CLONE_NEWUSER), it tries to create /sys/kernel/uids/0, which already exists, and you get back -ENOMEM.

This was supposed to be fixed by sysfs tagging, but that was postponed (ok, rejected until sysfs locking is fixed). So, just as with network namespaces, we just don't create those directories for user namespaces other than the init.

---

 kernel/user.c |    4 ++++
 1 files changed, 4 insertions(+), 0 deletions(-)

2d00643e7a4eda47526be7bca9600fda0d96c1c0

index 97202cb..6c924bc 100644
@@ -246,6 +246,8 @@ static int uids_user_create(struct user_
 	int error;
 
 	memset(kobj, 0, sizeof(struct kobject));
+	if (up->user_ns != &init_user_ns)
+		return 0;
 	kobj->kset = uids_kset;
 	error = kobject_init_and_add(kobj, &uids_ktype, NULL, "%d", up->uid);
 	if (error) {

@@ -281,6 +283,8 @@ static void remove_user_sysfs_dir(struct
 	unsigned long flags;
 	int remove_user = 0;
 
+	if (up->user_ns != &init_user_ns)
+		return;
 	/* Make uid_hash_remove() + sysfs_remove_file() + kobject_del()
 	 * atomic.
 	 */

1.1.6

Oops, sorry about that, it's a solitary patch. The 3/3 was a mistake.

-serge