Re: [PATCH v3] mm: Add SLUB free list pointer obfuscation
From: Christoph Lameter
Date: Thu Jul 06 2017 - 09:43:52 EST
On Wed, 5 Jul 2017, Kees Cook wrote:
> @@ -3536,6 +3565,9 @@ static int kmem_cache_open(struct kmem_cache *s, unsigned long flags)
> s->flags = kmem_cache_flags(s->size, flags, s->name, s->ctor);
> s->reserved = 0;
> +#ifdef CONFIG_SLAB_FREELIST_HARDENED
> + s->random = get_random_long();
> if (need_reserve_slab_rcu && (s->flags & SLAB_TYPESAFE_BY_RCU))
> s->reserved = sizeof(struct rcu_head);
So if an attacker knows the internal structure of data then he can simply
dereference page->kmem_cache->random to decode the freepointer.
Assuming someone is already targeting a freelist pointer (which indicates
detailed knowledge of the internal structure) then I would think that
someone like that will also figure out how to follow the pointer links to
get to the random value.
Not seeing the point of all of this.