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Subject: Re: [PATCH v3] mm/slub: Fix incorrect interpretation of s->offset
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>,
        Kees Cook <keescook@chromium.org>
Cc:     linux-mm@kvack.org, linux-kernel@vger.kernel.org,
        Changbin Du <changbin.du@gmail.com>,
        Matthew Wilcox <willy@infradead.org>,
        Markus Elfring <Markus.Elfring@web.de>
References: <20200429135328.26976-1-longman@redhat.com>
From:   Waiman Long <longman@redhat.com>
Organization: Red Hat
Message-ID: <7530523e-749c-dac7-f6ab-f52dcb20ecb9@redhat.com>
Date:   Wed, 29 Apr 2020 09:55:21 -0400
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On 4/29/20 9:53 AM, Waiman Long wrote:
> In a couple of places in the slub memory allocator, the code uses
> "s->offset" as a check to see if the free pointer is put right after the
> object. That check is no longer true with commit 3202fa62fb43 ("slub:
> relocate freelist pointer to middle of object").
>
> As a result, echoing "1" into the validate sysfs file, e.g. of dentry,
> may cause a bunch of "Freepointer corrupt" error reports like the
> following to appear with the system in panic afterwards.
>
> [   38.579769] =============================================================================
> [   38.580845] BUG dentry(666:pmcd.service) (Tainted: G    B): Freepointer corrupt
> [   38.581948] -----------------------------------------------------------------------------
>
> To fix it, use the check "s->offset == s->inuse" in the new helper

Sorry, forgot to change the commit log to ">=". Anyway, this is a 
serious bug that needs to be fixed before v5.7 is released.

Cheers,
Longman