linux-kernel - Re: [PATCH] slub/memcg: Cure the brainless abuse of sysfs attributes

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Date:   Sun, 21 May 2017 18:25:31 -0700 (PDT)
From:   David Rientjes <rientjes@...gle.com>
To:     Thomas Gleixner <tglx@...utronix.de>
cc:     LKML <linux-kernel@...r.kernel.org>, linux-mm@...ck.org,
        Johannes Weiner <hannes@...xchg.org>,
        Michal Hocko <mhocko@...nel.org>,
        Christoph Lameter <cl@...ux.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Peter Zijlstra <peterz@...radead.org>
Subject: Re: [PATCH] slub/memcg: Cure the brainless abuse of sysfs
 attributes

On Sat, 20 May 2017, Thomas Gleixner wrote:

> memcg_propagate_slab_attrs() abuses the sysfs attribute file functions to
> propagate settings from the root kmem_cache to a newly created
> kmem_cache. It does that with:
> 
>      attr->show(root, buf);
>      attr->store(new, buf, strlen(bug);
> 
> Aside of being a lazy and absurd hackery this is broken because it does not
> check the return value of the show() function.
> 
> Some of the show() functions return 0 w/o touching the buffer. That means in
> such a case the store function is called with the stale content of the
> previous show(). That causes nonsense like invoking kmem_cache_shrink() on
> a newly created kmem_cache. In the worst case it would cause handing in an
> uninitialized buffer.
> 
> This should be rewritten proper by adding a propagate() callback to those
> slub_attributes which must be propagated and avoid that insane conversion
> to and from ASCII, but that's too large for a hot fix.
> 
> Check at least the return value of the show() function, so calling store()
> with stale content is prevented.
> 
> Reported-by: Steven Rostedt <rostedt@...dmis.org>
> Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
> Cc: stable@...r.kernel.org

Acked-by: David Rientjes <rientjes@...gle.com>