linux-kernel - Re: [x86/uaccess] 5b710f34e1: kernel BUG at mm/usercopy.c:75!

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Date:	Wed, 17 Aug 2016 14:53:46 -0700
From:	Kees Cook <keescook@...omium.org>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Rik van Riel <riel@...hat.com>,
	kernel test robot <xiaolong.ye@...el.com>, LKP <lkp@...org>,
	LKML <linux-kernel@...r.kernel.org>,
	Valdis Kletnieks <valdis.kletnieks@...edu>
Subject: Re: [x86/uaccess] 5b710f34e1: kernel BUG at mm/usercopy.c:75!

On Wed, Aug 17, 2016 at 2:52 PM, Linus Torvalds
<torvalds@...ux-foundation.org> wrote:
> On Wed, Aug 17, 2016 at 2:45 PM, Kees Cook <keescook@...omium.org> wrote:
>>
>> But PageSlab(page) should trip, returning __check_heap_object, which
>> for SLOB should just return NULL, skipping all the rest of the
>> checks...
>
> SLOB doesn't actually set that for all allocations.
>
> See "slob_alloc_node()", for example. It just returns a multi-order allocation.
>
> (See also kfree(), which uses PageSlab() to determine it it should do
> slob_free() or just free the pages directly).

Oooh, eww. Okay, that explains it. Alright, dropping all the
multi-page logic now...

-Kees

-- 
Kees Cook
Nexus Security