Date: Fri, 8 Jul 2016 13:41:20 -0400 From: Kees Cook <keescook@...omium.org> To: Christoph Lameter <cl@...ux.com> Cc: Michael Ellerman <mpe@...erman.id.au>, "kernel-hardening@...ts.openwall.com" <kernel-hardening@...ts.openwall.com>, Jan Kara <jack@...e.cz>, Catalin Marinas <catalin.marinas@....com>, Will Deacon <will.deacon@....com>, Linux-MM <linux-mm@...ck.org>, sparclinux <sparclinux@...r.kernel.org>, linux-ia64@...r.kernel.org, Andrea Arcangeli <aarcange@...hat.com>, linux-arch <linux-arch@...r.kernel.org>, "x86@...nel.org" <x86@...nel.org>, Russell King <linux@...linux.org.uk>, PaX Team <pageexec@...email.hu>, Borislav Petkov <bp@...e.de>, Mathias Krause <minipli@...glemail.com>, Fenghua Yu <fenghua.yu@...el.com>, Rik van Riel <riel@...hat.com>, David Rientjes <rientjes@...gle.com>, Tony Luck <tony.luck@...el.com>, Andy Lutomirski <luto@...nel.org>, Joonsoo Kim <iamjoonsoo.kim@....com>, Dmitry Vyukov <dvyukov@...gle.com>, Laura Abbott <labbott@...oraproject.org>, Brad Spengler <spender@...ecurity.net>, Ard Biesheuvel <ard.biesheuvel@...aro.org>, LKML <linux-kernel@...r.kernel.org>, Pekka Enberg <penberg@...nel.org>, Case y Schauf ler <casey@...aufler-ca.com>, Andrew Morton <akpm@...ux-foundation.org>, "linuxppc-dev@...ts.ozlabs.org" <linuxppc-dev@...ts.ozlabs.org>, "David S. Miller" <davem@...emloft.net>, "linux-arm-kernel@...ts.infradead.org" <linux-arm-kernel@...ts.infradead.org> Subject: Re: Re: [PATCH 9/9] mm: SLUB hardened usercopy support On Fri, Jul 8, 2016 at 12:20 PM, Christoph Lameter <cl@...ux.com> wrote: > On Fri, 8 Jul 2016, Kees Cook wrote: > >> Is check_valid_pointer() making sure the pointer is within the usable >> size? It seemed like it was checking that it was within the slub >> object (checks against s->size, wants it above base after moving >> pointer to include redzone, etc). > > check_valid_pointer verifies that a pointer is pointing to the start of an > object. It is used to verify the internal points that SLUB used and > should not be modified to do anything different. Yup, no worries -- I won't touch it. :) I just wanted to verify my understanding. And after playing a bit more, I see that the only thing to the left is padding and redzone. SLUB layout, from what I saw: offset: what's there ------- start: padding, redzone red_left_pad: object itself inuse: rest of metadata size: start of next slub object (and object_size == inuse - red_left_pad) i.e. a pointer must be between red_left_pad and inuse, which is the same as pointer - ref_left_pad being less than object_size. So, as found already, the position in the usercopy check needs to be bumped down by red_left_pad, which is what Michael's fix does, so I'll include it in the next version. Thanks! -Kees -- Kees Cook Chrome OS & Brillo Security
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