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

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Message-ID: <CAGXu5jLQKicH96W_jjvw_J3KTFpVsERQqhJphsq1oQ2t=OJ36Q@mail.gmail.com>
Date:	Wed, 17 Aug 2016 14:57:47 -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 2:55 PM, Linus Torvalds
<torvalds@...ux-foundation.org> wrote:
> On Wed, Aug 17, 2016 at 2:50 PM, Kees Cook <keescook@...omium.org> wrote:
>> On Wed, Aug 17, 2016 at 2:45 PM, Linus Torvalds
>>>
>>> Networking does, but seems to use __GFP_COMP, at least in the one case
>>> I checked (skbuff).
>>
>> Was this allocation really through kmalloc?
>
> The networking one I looked at, no. But they do __GFP_COMP.
>
> The task struct allocation generally is (alloc_task_struct_node()),
> but as Rik pointed out, SLOB doesn't actually necessarily do the slab
> book-keeping for multi-page allocations.

Perhaps I can just ifdef the multi-page checks with
CONFIG_HAVE_HARDENED_USERCOPY_ALLOCATOR. That way a SLOB build still
has basic bounds checking (which was my intention with that config),
and non-SLOB builds still get multi-page checking.

-Kees

-- 
Kees Cook
Nexus Security