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SubjectRe: [RFC, PATCH] fix SEM_UNDO with namespaces
Manfred Spraul wrote:
> Pavel Emelyanov wrote:
>> Manfred Spraul wrote:
>>
>>> Hi,
>>>
>>> the attached patch should fix the combination of CLONE_NEWIPC with
>>> shared sysv undo structures (the common case, just
>>> sys_unshare(CLONE_NEWIPC)):
>>> lookup_undo() now locates the undo array based on both semid and the
>>> namespace pointer.
>>>
>> If you start using any IPC object and then call unshare with CLONE_NEWIPC,
>> then it's your problem, but not the kernel.
>>
> The result is a kernel memory corruption, and kernel memory corruptions
> are always the kernel's problem.

Agree. Must be fixed, but I'm not sure we should try handling this
case by trying to de-op semaphores for former task namespace. I think
that destroying this list or returning -EBUSY for this case is OK.

> The code assumed that a semaphore id is globally unique. With
> namespaces, this is not true anymore.
> If two semaphore arrays exist with the same id, but different sizes,
> then semops will cause memory corruptions: The undo structure contains
> one element for each semaphore, thus the semop will write behind the end
> of the memory allocation.
>
>> I agree, that we should probably destroy this one when the task calls
>> unshare, but trying to keep this list relevant is useless.
>>
> A very tricky question: Let's assume we have a process with two threads.
> The undo structure is shared, as per opengroup standard.
> Now one thread calls unshare(CLONE_NEWIPC). What should happen? We
> cannot destroy the undo structure, the other thread might be still
> interested in it.
> If we allow sys_unshare() for multithreaded processes with CLONE_NEWIPC
> and without CLONE_SYSVSEM, then we must handle this case.

Hm... I'd simply disable creating any new namespaces for threads.
I think other namespaces developers agree with me. Serge, Suka, Eric
what do you think?

> --
> Manfred
>



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