futex: Prevent overflow by strengthen input validation

futex: Prevent overflow by strengthen input validation

Orabug: 27539548
CVE: CVE-2018-6927

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
(cherry picked from commit fbe0e839d1e22d88810f3ee3e2f1479be4c0aa4a)
Signed-off-by: Brian Maly <brian.maly@oracle.com>
Conflicts:
        kernel/futex.c

Reviewed-by: Shan Hai <shan.hai@oracle.com>
Signed-off-by: Allen Pais <allen.pais@oracle.com>
Signed-off-by: Brian Maly <brian.maly@oracle.com>