[PATCH 3.2 098/140] futex: Prevent overflow by strengthen input validation

[Ben Hutchings]

3.2.100-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Li Jinyue <lijinyue@xxxxxxxxxx>

commit fbe0e839d1e22d88810f3ee3e2f1479be4c0aa4a upstream.

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@xxxxxxxxxx>
Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: peterz@xxxxxxxxxxxxx
Cc: dvhart@xxxxxxxxxxxxx
Link: https://lkml.kernel.org/r/1513242294-31786-1-git-send-email-lijinyue@xxxxxxxxxx
[bwh: Backported to 3.2: adjust context]
Signed-off-by: Ben Hutchings <ben@xxxxxxxxxxxxxxx>
---
 kernel/futex.c | 3 +++
 1 file changed, 3 insertions(+)

--- a/kernel/futex.c
+++ b/kernel/futex.c
@@ -1376,6 +1376,9 @@ static int futex_requeue(u32 __user *uad
 	struct plist_head *head1;
 	struct futex_q *this, *next;
 
+	if (nr_wake < 0 || nr_requeue < 0)
+		return -EINVAL;
+
 	if (requeue_pi) {
 		/*
 		 * Requeue PI only works on two distinct uaddrs. This