Code: static int futex_wait_requeue_pi(u32 __user *uaddr, unsigned int flags,
				 u32 val, ktime_t *abs_time, u32 bitset,
				 u32 __user *uaddr2)
{
	struct hrtimer_sleeper timeout, *to = NULL;
	struct rt_mutex_waiter rt_waiter;
	struct rt_mutex *pi_mutex = NULL;
	struct futex_hash_bucket *hb;
	union futex_key key2 = FUTEX_KEY_INIT;
	struct futex_q q = futex_q_init;
	int res, ret;

	if (uaddr == uaddr2)
		return -EINVAL;

	if (!bitset)
		return -EINVAL;

	if (abs_time) {
		to = &timeout;
		hrtimer_init_on_stack(&to->timer, (flags & FLAGS_CLOCKRT) ?
				      CLOCK_REALTIME : CLOCK_MONOTONIC,
				      HRTIMER_MODE_ABS);
		hrtimer_init_sleeper(to, current);
		hrtimer_set_expires_range_ns(&to->timer, *abs_time,
					     current->timer_slack_ns);
	}

	/*
	 * The waiter is allocated on our stack, manipulated by the requeue
	 * code while we sleep on uaddr.
	 */
	debug_rt_mutex_init_waiter(&rt_waiter);
	RB_CLEAR_NODE(&rt_waiter.pi_tree_entry);
	RB_CLEAR_NODE(&rt_waiter.tree_entry);
	rt_waiter.task = NULL;

	ret = get_futex_key(uaddr2, flags & FLAGS_SHARED, &key2, VERIFY_WRITE);
	if (unlikely(ret != 0))
		goto out;

	q.bitset = bitset;
	q.rt_waiter = &rt_waiter;
	q.requeue_pi_key = &key2;

	/*
	 * Prepare to wait on uaddr. On success, increments q.key (key1) ref
	 * count.
	 */
	ret = futex_wait_setup(uaddr, val, flags, &q, &hb);
 	if (ret)
 		goto out_key2;
 
 	/* Queue the futex_q, drop the hb lock, wait for wakeup. */
 	futex_wait_queue_me(hb, &q, to);
 
	spin_lock(&hb->lock);
	ret = handle_early_requeue_pi_wakeup(hb, &q, &key2, to);
	spin_unlock(&hb->lock);
	if (ret)
		goto out_put_keys;

	/*
	 * In order for us to be here, we know our q.key == key2, and since
	 * we took the hb->lock above, we also know that futex_requeue() has
	 * completed and we no longer have to concern ourselves with a wakeup
	 * race with the atomic proxy lock acquisition by the requeue code. The
	 * futex_requeue dropped our key1 reference and incremented our key2
	 * reference count.
	 */

	/* Check if the requeue code acquired the second futex for us. */
	if (!q.rt_waiter) {
		/*
		 * Got the lock. We might not be the anticipated owner if we
		 * did a lock-steal - fix up the PI-state in that case.
		 */
		if (q.pi_state && (q.pi_state->owner != current)) {
			spin_lock(q.lock_ptr);
			ret = fixup_pi_state_owner(uaddr2, &q, current);
			spin_unlock(q.lock_ptr);
		}
	} else {
		/*
		 * We have been woken up by futex_unlock_pi(), a timeout, or a
		 * signal.  futex_unlock_pi() will not destroy the lock_ptr nor
		 * the pi_state.
		 */
		WARN_ON(!q.pi_state);
		pi_mutex = &q.pi_state->pi_mutex;
		ret = rt_mutex_finish_proxy_lock(pi_mutex, to, &rt_waiter, 1);
		debug_rt_mutex_free_waiter(&rt_waiter);

		spin_lock(q.lock_ptr);
		/*
		 * Fixup the pi_state owner and possibly acquire the lock if we
		 * haven't already.
		 */
		res = fixup_owner(uaddr2, &q, !ret);
		/*
		 * If fixup_owner() returned an error, proprogate that.  If it
		 * acquired the lock, clear -ETIMEDOUT or -EINTR.
		 */
		if (res)
			ret = (res < 0) ? res : 0;

		/* Unqueue and drop the lock. */
		unqueue_me_pi(&q);
	}

	/*
	 * If fixup_pi_state_owner() faulted and was unable to handle the
	 * fault, unlock the rt_mutex and return the fault to userspace.
	 */
	if (ret == -EFAULT) {
		if (pi_mutex && rt_mutex_owner(pi_mutex) == current)
			rt_mutex_unlock(pi_mutex);
	} else if (ret == -EINTR) {
		/*
		 * We've already been requeued, but cannot restart by calling
		 * futex_lock_pi() directly. We could restart this syscall, but
		 * it would detect that the user space "val" changed and return
		 * -EWOULDBLOCK.  Save the overhead of the restart and return
		 * -EWOULDBLOCK directly.
		 */
		ret = -EWOULDBLOCK;
	}

out_put_keys:
	put_futex_key(&q.key);
out_key2:
	put_futex_key(&key2);

out:
	if (to) {
		hrtimer_cancel(&to->timer);
		destroy_hrtimer_on_stack(&to->timer);
	}
	return ret;
}

Vulnerability Type: +Priv 
CWE ID: CWE-264
Summary: The futex_requeue function in kernel/futex.c in the Linux kernel through 3.14.5 does not ensure that calls have two different futex addresses, which allows local users to gain privileges via a crafted FUTEX_REQUEUE command that facilitates unsafe waiter modification.
Commit Message: futex-prevent-requeue-pi-on-same-futex.patch futex: Forbid uaddr == uaddr2 in futex_requeue(..., requeue_pi=1)

If uaddr == uaddr2, then we have broken the rule of only requeueing from
a non-pi futex to a pi futex with this call.  If we attempt this, then
dangling pointers may be left for rt_waiter resulting in an exploitable
condition.

This change brings futex_requeue() in line with futex_wait_requeue_pi()
which performs the same check as per commit 6f7b0a2a5c0f ("futex: Forbid
uaddr == uaddr2 in futex_wait_requeue_pi()")

[ tglx: Compare the resulting keys as well, as uaddrs might be
  	different depending on the mapping ]

Fixes CVE-2014-3153.

Reported-by: Pinkie Pie
Signed-off-by: Will Drewry <wad@chromium.org>
Signed-off-by: Kees Cook <keescook@chromium.org>
Cc: stable@vger.kernel.org
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Darren Hart <dvhart@linux.intel.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>