From mboxrd@z Thu Jan  1 00:00:00 1970
From: Christopher Lameter <cl@linux.com>
Subject: Re: [v3] mm: Add SLUB free list pointer obfuscation
Date: Wed, 26 Jul 2017 09:08:01 -0500 (CDT)
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To: Kees Cook <keescook@chromium.org>
Cc: Alexander Popov <alex.popov@linux.com>, Andrew Morton <akpm@linux-foundation.org>, Pekka Enberg <penberg@kernel.org>, David Rientjes <rientjes@google.com>, Joonsoo Kim <iamjoonsoo.kim@lge.com>, "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>, Ingo Molnar <mingo@kernel.org>, Josh Triplett <josh@joshtriplett.org>, Andy Lutomirski <luto@kernel.org>, Nicolas Pitre <nicolas.pitre@linaro.org>, Tejun Heo <tj@kernel.org>, Daniel Mack <daniel@zonque.org>, Sebastian Andrzej Siewior <bigeasy@linutronix.de>, Sergey Senozhatsky <sergey.senozhatsky@gmail.com>, Helge Deller <deller@gmx.de>, Rik van Riel <riel@redhat.com>, Linux-MM <linux-mm@kvack.org>, Tycho Andersen <tycho@docker.com>, LKML <linux-kernel@vger.kernel.org>"kernel-hardening@lists.openwall.com" <ke>
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On Tue, 25 Jul 2017, Kees Cook wrote:

> > @@ -290,6 +290,10 @@ static inline void set_freepointer(struct kmem_cache *s,
> > void *object, void *fp)
> >  {
> >         unsigned long freeptr_addr = (unsigned long)object + s->offset;
> >
> > +#ifdef CONFIG_SLAB_FREELIST_HARDENED
> > +       BUG_ON(object == fp); /* naive detection of double free or corruption */
> > +#endif
> > +
> >         *(void **)freeptr_addr = freelist_ptr(s, fp, freeptr_addr);
>
> What happens if, instead of BUG_ON, we do:
>
> if (unlikely(WARN_RATELIMIT(object == fp, "double-free detected"))
>         return;

This may work for the free fastpath but the set_freepointer function is
use in multiple other locations. Maybe just add this to the fastpath
instead of to this fucnction?