From: Henry Burns <henryburns@google.com>
To: Vitaly Wool <vitalywool@gmail.com>
Cc: Andrew Morton <akpm@linux-foundation.org>,
Vitaly Vul <vitaly.vul@sony.com>,
Mike Rapoport <rppt@linux.vnet.ibm.com>,
Xidong Wang <wangxidong_97@163.com>,
Shakeel Butt <shakeelb@google.com>,
Jonathan Adams <jwadams@google.com>,
Linux-MM <linux-mm@kvack.org>,
LKML <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] mm/z3fold: Fix z3fold_buddy_slots use after free
Date: Wed, 3 Jul 2019 10:18:37 -0700 [thread overview]
Message-ID: <CAGQXPThUgPA2gZkOiuFph43Qq_zFohbMcn_70dtjQZ_HxD41fQ@mail.gmail.com> (raw)
In-Reply-To: <CAMJBoFMBLv9OpXtQkOAyZ-vw5Ktk1tYtvfT=GPPx8jnKBN01rg@mail.gmail.com>
> > On Tue, Jul 2, 2019 at 12:45 AM Vitaly Wool <vitalywool@gmail.com> wrote:
> > >
> > > Hi Henry,
> > >
> > > On Mon, Jul 1, 2019 at 8:31 PM Henry Burns <henryburns@google.com> wrote:
> > > >
> > > > Running z3fold stress testing with address sanitization
> > > > showed zhdr->slots was being used after it was freed.
> > > >
> > > > z3fold_free(z3fold_pool, handle)
> > > > free_handle(handle)
> > > > kmem_cache_free(pool->c_handle, zhdr->slots)
> > > > release_z3fold_page_locked_list(kref)
> > > > __release_z3fold_page(zhdr, true)
> > > > zhdr_to_pool(zhdr)
> > > > slots_to_pool(zhdr->slots) *BOOM*
> > >
> > > Thanks for looking into this. I'm not entirely sure I'm all for
> > > splitting free_handle() but let me think about it.
> > >
> > > > Instead we split free_handle into two functions, release_handle()
> > > > and free_slots(). We use release_handle() in place of free_handle(),
> > > > and use free_slots() to call kmem_cache_free() after
> > > > __release_z3fold_page() is done.
> > >
> > > A little less intrusive solution would be to move backlink to pool
> > > from slots back to z3fold_header. Looks like it was a bad idea from
> > > the start.
> > >
> > > Best regards,
> > > Vitaly
> >
> > We still want z3fold pages to be movable though. Wouldn't moving
> > the backink to the pool from slots to z3fold_header prevent us from
> > enabling migration?
>
> That is a valid point but we can just add back pool pointer to
> z3fold_header. The thing here is, there's another patch in the
> pipeline that allows for a better (inter-page) compaction and it will
> somewhat complicate things, because sometimes slots will have to be
> released after z3fold page is released (because they will hold a
> handle to another z3fold page). I would prefer that we just added back
> pool to z3fold_header and changed zhdr_to_pool to just return
> zhdr->pool, then had the compaction patch valid again, and then we
> could come back to size optimization.
I see your point, patch incoming.
next prev parent reply other threads:[~2019-07-03 17:19 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-07-01 17:30 [PATCH] mm/z3fold: Fix z3fold_buddy_slots use after free Henry Burns
2019-07-02 7:45 ` Vitaly Wool
2019-07-02 16:56 ` Henry Burns
2019-07-03 6:02 ` Vitaly Wool
2019-07-03 17:18 ` Henry Burns [this message]
2019-07-03 20:14 ` Shakeel Butt
2019-07-04 6:59 ` Vitaly Wool
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