linux-kernel - Re: [PATCH] usercopy: Skip multi-page bounds checking on SLOB

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Date:   Fri, 19 Aug 2016 13:07:53 -0700
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     Kees Cook <keescook@...omium.org>
Cc:     Rik van Riel <riel@...hat.com>,
        Laura Abbott <labbott@...oraproject.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-mm <linux-mm@...ck.org>,
        kernel test robot <xiaolong.ye@...el.com>
Subject: Re: [PATCH] usercopy: Skip multi-page bounds checking on SLOB

On Fri, Aug 19, 2016 at 1:03 PM, Kees Cook <keescook@...omium.org> wrote:
>
> Okay, I can live with that. I'd hoped to keep the general split
> between the other checks (i.e. stack) and the allocator, but if this
> is preferred, that's cool. :)

If it had been anything else than SLOB, I might have cared. As it was,
I didn't think it was worth worrying about SLOB together with
hardening.

It was also about the __check_object_size() modification just being
very ugly, with a "return NULL" in the middle of the function. I
looked at just splitting that function up, and having a part of it
that would just go away when the slab allocator wasn't smart enough,
but that would have been a bigger change that I'm not interested in
taking right now. So it could be a future improvement, and maybe we
could then re-instate SLOB with partial checking.

             Linus