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

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Date:   Mon, 19 Sep 2022 20:50:34 +0800
From:   Feng Tang <feng.tang@...el.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>,
        "Roman Gushchin" <roman.gushchin@...ux.dev>,
        Hyeonggon Yoo <42.hyeyoo@...il.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Waiman Long <longman@...hat.com>,
        "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 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