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Subject: Re: GPF in shm_lock ipc
References: <CACT4Y+aqaR8QYk2nyN1n1iaSZWofBEkWuffvsfcqpvmGGQyMAw@mail.gmail.com>
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 <20151013031821.GA3052@linux-uzut.site> <20151013123028.GA12934@node>
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From: Manfred Spraul <manfred@colorfullife.com>
Message-ID: <5687B576.7020303@colorfullife.com>
Date: Sat, 2 Jan 2016 12:33:10 +0100
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To: Dmitry Vyukov <dvyukov@google.com>, syzkaller <syzkaller@googlegroups.com>
Cc: "Kirill A. Shutemov" <kirill@shutemov.name>, Andrew Morton <akpm@linux-foundation.org>, Dave Hansen <dave.hansen@linux.intel.com>, Hugh Dickins <hughd@google.com>, Joe Perches <joe@perches.com>, sds@tycho.nsa.gov, Oleg Nesterov <oleg@redhat.com>, "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>, Rik van Riel <riel@redhat.com>, mhocko@suse.cz, gang.chen.5i5j@gmail.com, Peter Feiner <pfeiner@google.com>, Andrea Arcangeli <aarcange@redhat.com>, "linux-mm@kvack.org" <linux-mm@kvack.org>, LKML <linux-kernel@vger.kernel.org>, Kostya Serebryany <kcc@google.com>, Alexander Potapenko <glider@google.com>, Andrey Konovalov <andreyknvl@google.com>, Sasha Levin <sasha.levin@oracle.com>

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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