Re: [PATCH 4/4] ipc,msg: prevent race with rmid in msgsnd,msgrcv

[Manfred Spraul]

Hi Andrew,

Could you include the patch in -mm and push it towards Linus?

On 09/16/2013 05:04 AM, Davidlohr Bueso wrote:
> This fixes a race in both msgrcv() and msgsnd() between finding the msg and
> actually dealing with the queue, as another thread can delete shmid
> underneath us if we are preempted before acquiring the kern_ipc_perm.lock.
>
> Manfred illustrates this nicely:
>
> Assume a preemptible kernel that is preempted just after
> > msq = msq_obtain_object_check(ns, msqid)
> in do_msgrcv().
> The only lock that is held is rcu_read_lock().
>
> Now the other thread processes IPC_RMID.
> When the first task is resumed, then it will happily wait for messages on a
> deleted queue.
>
> Fix this by checking for if the queue has been deleted after taking the lock.
>
> Reported-by: Manfred Spraul <manfred@xxxxxxxxxxxxxxxx>
> Cc: stable@xxxxxxxxxxxxxxx # for 3.11
> Signed-off-by: Davidlohr Bueso <davidlohr@xxxxxx>
Signed-off-by: Manfred Spraul <manfred@xxxxxxxxxxxxxxxx>

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