Commit message: ipc,sem: fine grained locking for semtimedop

Introduce finer grained locking for semtimedop, to handle the common case
of a program wanting to manipulate one semaphore from an array with
multiple semaphores.

If the call is a semop manipulating just one semaphore in an array with
multiple semaphores, only take the lock for that semaphore itself.

If the call needs to manipulate multiple semaphores, or another caller is
in a transaction that manipulates multiple semaphores, the sem_array lock
is taken, as well as all the locks for the individual semaphores.

On a 24 CPU system, performance numbers with the semop-multi
test with N threads and N semaphores, look like this:

	vanilla		Davidlohr's	Davidlohr's +	Davidlohr's +
threads			patches		rwlock patches	v3 patches
10	610652		726325		1783589		2142206
20	341570		365699		1520453		1977878
30	288102		307037		1498167		2037995
40	290714		305955		1612665		2256484
50	288620		312890		1733453		2650292
60	289987		306043		1649360		2388008
70	291298		306347		1723167		2717486
80	290948		305662		1729545		2763582
90	290996		306680		1736021		2757524
100	292243		306700		1773700		3059159

[davidlohr.bueso@hp.com: do not call sem_lock when bogus sma]
[davidlohr.bueso@hp.com: make refcounter atomic]
Signed-off-by: Rik van Riel <riel@redhat.com>
Suggested-by: Linus Torvalds <torvalds@linux-foundation.org>
Acked-by: Davidlohr Bueso <davidlohr.bueso@hp.com>
Cc: Chegu Vinod <chegu_vinod@hp.com>
Cc: Jason Low <jason.low2@hp.com>
Reviewed-by: Michel Lespinasse <walken@google.com>
Cc: Peter Hurley <peter@hurleysoftware.com>
Cc: Stanislav Kinsbursky <skinsbursky@parallels.com>
Tested-by: Emmanuel Benisty <benisty.e@gmail.com>
Tested-by: Sedat Dilek <sedat.dilek@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
CVE: CVE-2013-4483
CWE: CWE-189
Vulnerability description: The ipc_rcu_putref function in ipc/util.c in the Linux kernel before 3.10 does not properly manage a reference count, which allows local users to cause a denial of service (memory consumption or system crash) via a crafted application.

Project: linux
File: sem.c

void exit_sem(struct task_struct *tsk)
{
	struct sem_undo_list *ulp;

	ulp = tsk->sysvsem.undo_list;
	if (!ulp)
		return;
	tsk->sysvsem.undo_list = NULL;

	if (!atomic_dec_and_test(&ulp->refcnt))
		return;

	for (;;) {
 		struct sem_array *sma;
 		struct sem_undo *un;
 		struct list_head tasks;
		int semid, i;
 
 		rcu_read_lock();
 		un = list_entry_rcu(ulp->list_proc.next,
				    struct sem_undo, list_proc);
		if (&un->list_proc == &ulp->list_proc)
 			semid = -1;
 		 else
 			semid = un->semid;
 
		if (semid == -1) {
			rcu_read_unlock();
 			break;
		}
 
		sma = sem_obtain_object_check(tsk->nsproxy->ipc_ns, un->semid);
 		/* exit_sem raced with IPC_RMID, nothing to do */
		if (IS_ERR(sma)) {
			rcu_read_unlock();
 			continue;
		}
 
		sem_lock(sma, NULL, -1);
 		un = __lookup_undo(ulp, semid);
 		if (un == NULL) {
 			/* exit_sem raced with IPC_RMID+semget() that created
 			 * exactly the same semid. Nothing to do.
 			 */
			sem_unlock(sma, -1);
 			continue;
 		}
 
		/* remove un from the linked lists */
		assert_spin_locked(&sma->sem_perm.lock);
		list_del(&un->list_id);

		spin_lock(&ulp->lock);
		list_del_rcu(&un->list_proc);
		spin_unlock(&ulp->lock);

		/* perform adjustments registered in un */
		for (i = 0; i < sma->sem_nsems; i++) {
			struct sem * semaphore = &sma->sem_base[i];
			if (un->semadj[i]) {
				semaphore->semval += un->semadj[i];
				/*
				 * Range checks of the new semaphore value,
				 * not defined by sus:
				 * - Some unices ignore the undo entirely
				 *   (e.g. HP UX 11i 11.22, Tru64 V5.1)
				 * - some cap the value (e.g. FreeBSD caps
				 *   at 0, but doesn't enforce SEMVMX)
				 *
				 * Linux caps the semaphore value, both at 0
				 * and at SEMVMX.
				 *
				 * 	Manfred <manfred@colorfullife.com>
				 */
				if (semaphore->semval < 0)
					semaphore->semval = 0;
				if (semaphore->semval > SEMVMX)
					semaphore->semval = SEMVMX;
				semaphore->sempid = task_tgid_vnr(current);
			}
		}
 		/* maybe some queued-up processes were waiting for this */
 		INIT_LIST_HEAD(&tasks);
 		do_smart_update(sma, NULL, 0, 1, &tasks);
		sem_unlock(sma, -1);
 		wake_up_sem_queue_do(&tasks);
 
 		kfree_rcu(un, rcu);
	}
	kfree(ulp);
}