Re: [RFC, PATCH] fix SEM_UNDO with namespaces
From: Manfred Spraul
Date: Mon Mar 31 2008 - 12:15:02 EST
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.
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.
--
Manfred
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/