linux-kernel - Re: [External] Re: [PATCH v5.4.y, v4.19.y] mm: memcg/slab: fix memory leak at non-root kmem

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <CAMZfGtVEiUmQYX61MT_oCymac+idXy16U8bAQoV21HcFrVXCxg@mail.gmail.com>
Date:   Wed, 15 Jul 2020 23:55:42 +0800
From:   Muchun Song <songmuchun@...edance.com>
To:     Vlastimil Babka <vbabka@...e.cz>
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>,
        Linux Memory Management List <linux-mm@...ck.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Shakeel Butt <shakeelb@...gle.com>,
        Roman Gushchin <guro@...com>
Subject: Re: [External] Re: [PATCH v5.4.y, v4.19.y] mm: memcg/slab: fix memory
 leak at non-root kmem_cache destroy

On Wed, Jul 15, 2020 at 11:43 PM Vlastimil Babka <vbabka@...e.cz> wrote:
>
> On 7/15/20 5:13 PM, Muchun Song wrote:
> > On Wed, Jul 15, 2020 at 7:32 PM Vlastimil Babka <vbabka@...e.cz> wrote:
> >>
> >> On 7/7/20 8:27 AM, Muchun Song wrote:
> >> > If the kmem_cache refcount is greater than one, we should not
> >> > mark the root kmem_cache as dying. If we mark the root kmem_cache
> >> > dying incorrectly, the non-root kmem_cache can never be destroyed.
> >> > It resulted in memory leak when memcg was destroyed. We can use the
> >> > following steps to reproduce.
> >> >
> >> >   1) Use kmem_cache_create() to create a new kmem_cache named A.
> >> >   2) Coincidentally, the kmem_cache A is an alias for kmem_cache B,
> >> >      so the refcount of B is just increased.
> >> >   3) Use kmem_cache_destroy() to destroy the kmem_cache A, just
> >> >      decrease the B's refcount but mark the B as dying.
> >> >   4) Create a new memory cgroup and alloc memory from the kmem_cache
> >> >      A. It leads to create a non-root kmem_cache for allocating.
> >> >   5) When destroy the memory cgroup created in the step 4), the
> >> >      non-root kmem_cache can never be destroyed.
> >> >
> >> > If we repeat steps 4) and 5), this will cause a lot of memory leak.
> >> > So only when refcount reach zero, we mark the root kmem_cache as dying.
> >> >
> >> > Fixes: 92ee383f6daa ("mm: fix race between kmem_cache destroy, create and deactivate")
> >> > Signed-off-by: Muchun Song <songmuchun@...edance.com>
> >>
> >> CC Roman, who worked in this area recently.
> >>
> >> Also why is this marked "[PATCH v5.4.y, v4.19.y]"? Has it been fixed otherwise
> >> in 5.5+ ?
> >
> > Because the memcg slab/slub is reworked by Roman since v5.8.
>
> That rework is in mmotm, so scheduled for 5.9, AFAIK. If you mean "The new
> cgroup slab memory controller" series.

Yeah, I mean "The new cgroup slab memory controller".

>
> > Therefore, this problem exists in v5.7 and below.
>
> Even 5.7 has a stable series, so no need to list only the LTS's.
> To sum up, the patch (once reviewed) should be queued for mainline as usual,
> perhaps sent before 5.8 is final, if deemed safe enough, and with added
>
> Cc: <stable@...r.kernel.org>
>
> and the Fixes: tag you provided, the applicable stable versions will pick it.

Got it. Thanks.

>
> Vlastimil



-- 
Yours,
Muchun