linux-kernel - Re: GPF in shm

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Message-ID: <5687B576.7020303@colorfullife.com>
Date:	Sat, 2 Jan 2016 12:33:10 +0100
From:	Manfred Spraul <manfred@...orfullife.com>
To:	Dmitry Vyukov <dvyukov@...gle.com>,
	syzkaller <syzkaller@...glegroups.com>
Cc:	"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

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()?

--
     Manfred
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