linux-kernel - Re: [PATCH] mm/slab_common: fix possiable double free of kmem

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Message-ID: <34b2bb18-ad64-ee10-37ad-3c2ab2387a0e@redhat.com>
Date:   Mon, 19 Sep 2022 09:34:10 -0400
From:   Waiman Long <longman@...hat.com>
To:     Feng Tang <feng.tang@...el.com>, 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>,
        Roman Gushchin <roman.gushchin@...ux.dev>,
        Hyeonggon Yoo <42.hyeyoo@...il.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "kasan-dev@...glegroups.com" <kasan-dev@...glegroups.com>
Subject: Re: [PATCH] mm/slab_common: fix possiable double free of kmem_cache

On 9/19/22 08:50, Feng Tang wrote:
> On Mon, Sep 19, 2022 at 05:12:38PM +0800, Vlastimil Babka wrote:
>> On 9/19/22 05:12, Feng Tang wrote:
> [...]
>>> The cause is inside kmem_cache_destroy():
>>>
>>> kmem_cache_destroy
>>>      acquire lock/mutex
>>>      shutdown_cache
>>>          schedule_work(kmem_cache_release) (if RCU flag set)
>>>      release lock/mutex
>>>      kmem_cache_release (if RCU flag set)
>> 				      ^ not set
>>
>> I've fixed that up.
> Oops.. Thanks for catching it!
>
>>> in some certain timing, the scheduled work could be run before
>>> the next RCU flag checking which will get a wrong state.
>>>
>>> Fix it by caching the RCU flag inside protected area, just like 'refcnt'
>>>
>>> Signed-off-by: Feng Tang <feng.tang@...el.com>
>> Thanks!
>>
>>> ---
>>>
>>> note:
>>>
>>> The error only happens on linux-next tree, and not in Linus' tree,
>>> which already has Waiman's commit:
>>> 0495e337b703 ("mm/slab_common: Deleting kobject in kmem_cache_destroy()
>>> without holding slab_mutex/cpu_hotplug_lock")
>> Actually that commit is already in Linus' rc5 too, so I will send your fix
>> this week too. Added a Fixes: 0495e337b703 (...) too.
> Got it, thanks
>
> - Feng

Thanks for catching this bug.

Reviewed-by: Waiman Long <longman@...hat.com>

Cheers,
Longman