futex: Prevent overflow by strengthen input validation

UBSAN reports signed integer overflow in kernel/futex.c:

 UBSAN: Undefined behaviour in kernel/futex.c:2041:18
 signed integer overflow:
 0 - -2147483648 cannot be represented in type 'int'

Add a sanity check to catch negative values of nr_wake and nr_requeue.

Signed-off-by: Li Jinyue <lijinyue@huawei.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: peterz@infradead.org
Cc: dvhart@infradead.org
Cc: stable@vger.kernel.org
Link: https://lkml.kernel.org/r/1513242294-31786-1-git-send-email-lijinyue@huawei.com
static int lock_pi_update_atomic(u32 __user *uaddr, u32 uval, u32 newval)
{
	u32 uninitialized_var(curval);

	if (unlikely(should_fail_futex(true)))
		return -EFAULT;

	if (unlikely(cmpxchg_futex_value_locked(&curval, uaddr, uval, newval)))
		return -EFAULT;

	/* If user space value changed, let the caller retry */
	return curval != uval ? -EAGAIN : 0;
}

static int lock_pi_update_atomic(u32 __user *uaddr, u32 uval, u32 newval)
{
	u32 uninitialized_var(curval);

	if (unlikely(should_fail_futex(true)))
		return -EFAULT;

	if (unlikely(cmpxchg_futex_value_locked(&curval, uaddr, uval, newval)))
		return -EFAULT;

	/* If user space value changed, let the caller retry */
	return curval != uval ? -EAGAIN : 0;
}
