linux-kernel - Re: GPF in shm

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Date:	Sat, 2 Jan 2016 13:19:13 +0100
From:	Dmitry Vyukov <dvyukov@...gle.com>
To:	Manfred Spraul <manfred@...orfullife.com>
Cc:	syzkaller <syzkaller@...glegroups.com>,
	"Kirill A. Shutemov" <kirill@...temov.name>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Dave Hansen <dave.hansen@...ux.intel.com>,
	Hugh Dickins <hughd@...gle.com>, Joe Perches <joe@...ches.com>,
	sds@...ho.nsa.gov, Oleg Nesterov <oleg@...hat.com>,
	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
	Rik van Riel <riel@...hat.com>, mhocko@...e.cz,
	gang.chen.5i5j@...il.com, Peter Feiner <pfeiner@...gle.com>,
	Andrea Arcangeli <aarcange@...hat.com>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Kostya Serebryany <kcc@...gle.com>,
	Alexander Potapenko <glider@...gle.com>,
	Andrey Konovalov <andreyknvl@...gle.com>,
	Sasha Levin <sasha.levin@...cle.com>
Subject: Re: GPF in shm_lock ipc

On Sat, Jan 2, 2016 at 12:33 PM, Manfred Spraul
<manfred@...orfullife.com> wrote:
> Hi Dmitry,
>
> shm locking differs too much from msg/sem locking, I never looked at it in
> depth, so I'm not able to perform a proper review.
>
> Except for the obvious: Races that can be triggered from user space are
> inacceptable.
> Regardless if there is a BUG_ON, a WARN_ON or nothing at all.
>
> On 12/21/2015 04:44 PM, Dmitry Vyukov wrote:
>>>
>>> +
>>> +/* This is called by fork, once for every shm attach. */
>>> +static void shm_open(struct vm_area_struct *vma)
>>> +{
>>> +       int err = __shm_open(vma);
>>> +       /*
>>> +        * We raced in the idr lookup or with shm_destroy().
>>> +        * Either way, the ID is busted.
>>> +        */
>>> +       WARN_ON_ONCE(err);
>>>   }
>
> Is it possible to trigger this race? Parallel IPC_RMID & fork()?

Hi Manfred,

As far as I see my reproducer triggers exactly this warning (and later a crash).
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