[patch] IPC/Message Queues

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cvanceat_private

Attached is a patch that corrects some problems with the handling of
Message Queues <ipc/msg.c>.

The previous IPC hooks were were not enforcing permissions on inline
msgrcv operations.  In sys_msgrcv, the previous msgrcv hook was placed
prior to the out_success label so that the message wasn't removed from the
queue prior to access decisions.  If there wasn't a message on the queue,
the process could wait for a message to become available (pipelined
receive) and possibly jump to a point after the msgrcv hook (the
out_success label).

In order to correct this oversight, I removed the test_message hook from
testmsg and placed hooks in the two locations that testmsg was being
called.  To check receive permissions, SELinux needs the task structure
for the receiving process. In the simple case, it is the current process,
in the pipelined send/receive case, it is the task from the wait queue.

Once these changes were made, the previous msgrcv hook is no longer
necessary, so I re-used the msgrcv hook name (with different parameters),
to indicate that we really are checking message receive permissions, and
no longer testing a single message.

Due to the surrounding kernel logic, we lose the security module's return
code, but I don't think this is a problem.

Opinions?  If there are no objections, I can have Stephen commit this
patch tomorrow.

chris.