> Quoting Pavel Emelyanov (
xemul@openvz.org):
> > 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?
>
> Absolutely.
>
