Re: GPF in shm_lock ipc

[Dmitry Vyukov]

On Sat, Jan 2, 2016 at 12:33 PM, Manfred Spraul
<manfred@xxxxxxxxxxxxxxxx> 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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