linux-kernel - Re: [PATCH v3] mm/slub: Fix incorrect interpretation of s->offset

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Date:   Wed, 29 Apr 2020 08:54:12 -0700
From:   Matthew Wilcox <willy@...radead.org>
To:     Waiman Long <longman@...hat.com>
Cc:     Christoph Lameter <cl@...ux.com>,
        Pekka Enberg <penberg@...nel.org>,
        David Rientjes <rientjes@...gle.com>,
        Joonsoo Kim <iamjoonsoo.kim@....com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Kees Cook <keescook@...omium.org>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, Changbin Du <changbin.du@...il.com>,
        Markus Elfring <Markus.Elfring@....de>
Subject: Re: [PATCH v3] mm/slub: Fix incorrect interpretation of s->offset

On Wed, Apr 29, 2020 at 09:53:28AM -0400, Waiman Long wrote:
> 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] -----------------------------------------------------------------------------

I might trim the timestamp and the === and --- from the commit message ...

> To fix it, use the check "s->offset == s->inuse" in the new helper
> function freeptr_outside_object() instead. Also add another helper function
> get_info_end() to return the end of info block (inuse + free pointer
> if not overlapping with object).
> 
> Fixes: 3202fa62fb43 ("slub: relocate freelist pointer to middle of object")
> Signed-off-by: Waiman Long <longman@...hat.com>

But the patch looks great.

Reviewed-by: Matthew Wilcox (Oracle) <willy@...radead.org>