From: Jiri Slaby <jslaby@suse.cz>
Date: Thu, 30 Nov 2017 15:35:44 +0100
Subject: futex: futex_wake_op, fix sign_extend32 sign bits
Git-commit: d70ef22892ed6c066e51e118b225923c9b74af34
Patch-mainline: v4.15-rc3
References: bnc#1064590

sign_extend32 counts the sign bit parameter from 0, not from 1.  So we
have to use "11" for 12th bit, not "12".

This mistake means we have not allowed negative op and cmp args since
commit 30d6e0a4190d ("futex: Remove duplicated code and fix undefined
behaviour") till now.

Fixes: 30d6e0a4190d ("futex: Remove duplicated code and fix undefined behaviour")
Signed-off-by: Jiri Slaby <jslaby@suse.cz>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Darren Hart <dvhart@infradead.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
---
 kernel/futex.c |    4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

--- a/kernel/futex.c
+++ b/kernel/futex.c
@@ -1578,8 +1578,8 @@ static int futex_atomic_op_inuser(unsign
 {
 	unsigned int op =	  (encoded_op & 0x70000000) >> 28;
 	unsigned int cmp =	  (encoded_op & 0x0f000000) >> 24;
-	int oparg = sign_extend32((encoded_op & 0x00fff000) >> 12, 12);
-	int cmparg = sign_extend32(encoded_op & 0x00000fff, 12);
+	int oparg = sign_extend32((encoded_op & 0x00fff000) >> 12, 11);
+	int cmparg = sign_extend32(encoded_op & 0x00000fff, 11);
 	int oldval, ret;
 
 	if (encoded_op & (FUTEX_OP_OPARG_SHIFT << 28)) {