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From:   Jann Horn <jannh@google.com>
Date:   Wed, 4 Mar 2020 01:23:17 +0100
Message-ID: <CAG48ez31PP--h6_FzVyfJ4H86QYczAFPdxtJHUEEan+7VJETAQ@mail.gmail.com>
Subject: SLUB: sysfs lets root force slab order below required minimum,
 causing memory corruption
To:     Christoph Lameter <cl@linux.com>,
        Pekka Enberg <penberg@kernel.org>,
        David Rientjes <rientjes@google.com>,
        Joonsoo Kim <iamjoonsoo.kim@lge.com>,
        Andrew Morton <akpm@linux-foundation.org>
Cc:     Linux-MM <linux-mm@kvack.org>,
        kernel list <linux-kernel@vger.kernel.org>,
        Kees Cook <keescook@chromium.org>,
        Matthew Garrett <mjg59@google.com>
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Hi!

FYI, I noticed that if you do something like the following as root,
the system blows up pretty quickly with error messages about stuff
like corrupt freelist pointers because SLUB actually allows root to
force a page order that is smaller than what is required to store a
single object:

    echo 0 > /sys/kernel/slab/task_struct/order

The other SLUB debugging options, like red_zone, also look kind of
suspicious with regards to races (either racing with other writes to
the SLUB debugging options, or with object allocations).