[tip:locking/urgent] futex: Prevent overflow by strengthen input validation

[tip-bot for Li Jinyue <tipbot@zytor.com>]

Commit-ID:  fbe0e839d1e22d88810f3ee3e2f1479be4c0aa4a
Gitweb:     https://git.kernel.org/tip/fbe0e839d1e22d88810f3ee3e2f1479be4c0aa4a
Author:     Li Jinyue <lijinyue@huawei.com>
AuthorDate: Thu, 14 Dec 2017 17:04:54 +0800
Committer:  Thomas Gleixner <tglx@linutronix.de>
CommitDate: Sun, 14 Jan 2018 18:55:03 +0100

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

---
 kernel/futex.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/kernel/futex.c b/kernel/futex.c
index 9e69589..8c5424d 100644
--- a/kernel/futex.c
+++ b/kernel/futex.c
@@ -1878,6 +1878,9 @@ static int futex_requeue(u32 __user *uaddr1, unsigned int flags,
 	struct futex_q *this, *next;
 	DEFINE_WAKE_Q(wake_q);
 
+	if (nr_wake < 0 || nr_requeue < 0)
+		return -EINVAL;
+
 	/*
 	 * When PI not supported: return -ENOSYS if requeue_pi is true,
 	 * consequently the compiler knows requeue_pi is always false past