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Date: Wed, 26 Jul 2017 09:20:56 -0700
From: Kees Cook <keescook@...omium.org>
To: Christopher Lameter <cl@...ux.com>
Cc: Alexander Popov <alex.popov@...ux.com>, Andrew Morton <akpm@...ux-foundation.org>,
Pekka Enberg <penberg@...nel.org>, David Rientjes <rientjes@...gle.com>,
Joonsoo Kim <iamjoonsoo.kim@....com>, "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
Ingo Molnar <mingo@...nel.org>, Josh Triplett <josh@...htriplett.org>,
Andy Lutomirski <luto@...nel.org>, Nicolas Pitre <nicolas.pitre@...aro.org>, Tejun Heo <tj@...nel.org>,
Daniel Mack <daniel@...que.org>, Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
Sergey Senozhatsky <sergey.senozhatsky@...il.com>, Helge Deller <deller@....de>,
Rik van Riel <riel@...hat.com>, Linux-MM <linux-mm@...ck.org>, Tycho Andersen <tycho@...ker.com>,
LKML <linux-kernel@...r.kernel.org>,
"kernel-hardening@...ts.openwall.com" <kernel-hardening@...ts.openwall.com>
Subject: Re: [v3] mm: Add SLUB free list pointer obfuscation
On Wed, Jul 26, 2017 at 7:08 AM, Christopher Lameter <cl@...ux.com> wrote:
> 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?
Do you mean do_slab_free()?
-Kees
--
Kees Cook
Pixel Security
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