Re: [PATCH] [ipc/sem.c] fix race with concurrent semtimedop()timeouts and IPC_RMID

[Eric Dumazet]

Le mercredi 20 juillet 2011 Ã 23:58 -0700, Andrew Morton a Ãcrit :
> On Thu, 21 Jul 2011 08:42:53 +0200 Manfred Spraul <manfred@xxxxxxxxxxxxxxxx> wrote:
> 
> > If a semaphore array is removed and in parallel a sleeping task is woken up
> > (signal or timeout, does not matter), then the woken up task does not wait
> > until wake_up_sem_queue_do() is completed. This will cause crashes, because
> > wake_up_sem_queue_do() will read from a stale pointer.
> > 
> > The fix is simple: Regardless of anything, always call get_queue_result().
> > This function waits until wake_up_sem_queue_do() has finished it's task.
> > 
> > Andrew, could you please take care of merging the patch?
> 
> yup, thanks for this.  It's good to hear from you, and that you've
> still got what it takes :)
> 
> Do you know how long this bug has been around for?  Somewhere between
> 2.6.32 and 2.6.36, but that a large interval!

As I said, bug was introduced in commit
0a2b9d4c79671b05956806ede5d054e03ae56280
(ipc/sem.c: move wake_up_process out of the spinlock section)

(so first faulty kernel version is 2.6.35)

Please also add this bugzilla reference :

 https://bugzilla.kernel.org/show_bug.cgi?id=27142

Reported-by: Harald Laabs <kernelml@xxxxxxx>
Acked-by: Eric Dumazet <eric.dumazet@xxxxxxxxx>



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