Re: namespaces?: bug at mm/slub.c:2750

["Serge E. Hallyn" <serue-r/Jw6+rmf7HQT0dZR+AlfA@public.gmane.org>]

Quoting David Howells (dhowells-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org):
> Serge E. Hallyn <serue-r/Jw6+rmf7HQT0dZR+AlfA@public.gmane.org> wrote:
> 
> >  static void uid_hash_remove(struct user_struct *up)
> >  {
> > +	put_user_ns(up->user_ns);
> >  	hlist_del_init(&up->uidhash_node);
> >  }
> 
> Don't you need to do the hlist_del_init() first?  Otherwise, mightn't the
> put_user_ns() cause the namespace to be freed before hlist_del_init() removes
> the user_struct from it?

It's called under uidhash_lock spinlock so should be ok, but in
principle you're right so it's probably a good idea.

The main point is that without this patch, put_user_ns is done before
the hlist_del_init and *not* atomically under uidhash_lock.

thanks,
-serge