From 9dd1c106b83fa1bbc95eac98713915ffcd1c4875 Mon Sep 17 00:00:00 2001
From: Chen Jie <chenjie6@huawei.com>
Date: Thu, 11 Apr 2019 10:29:20 -0700
Subject: [PATCH] futex: Ensure that futex address is aligned in handle_futex_death()
Git-commit: 5a07168d8d89b00fe1760120714378175b3ef992
Patch-mainline: v5.1-rc2
References: bsc#1050549 

The futex code requires that the user space addresses of futexes are 32bit
aligned. sys_futex() checks this in futex_get_keys() but the robust list
code has no alignment check in place.

As a consequence the kernel crashes on architectures with strict alignment
requirements in handle_futex_death() when trying to cmpxchg() on an
unaligned futex address which was retrieved from the robust list.

[ tglx: Rewrote changelog, proper sizeof() based alignement check and add
  	comment ]

Fixes: 0771dfefc9e5 ("[PATCH] lightweight robust futexes: core")
Signed-off-by: Chen Jie <chenjie6@huawei.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: <dvhart@infradead.org>
Cc: <peterz@infradead.org>
Cc: <zengweilin@huawei.com>
Cc: stable@vger.kernel.org
Link: https://lkml.kernel.org/r/1552621478-119787-1-git-send-email-chenjie6@huawei.com
Signed-off-by: Davidlohr Bueso <dbueso@suse.de>

---
 kernel/futex.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/kernel/futex.c b/kernel/futex.c
index ef9a165e4159..280c148acb2a 100644
--- a/kernel/futex.c
+++ b/kernel/futex.c
@@ -3370,6 +3370,10 @@ int handle_futex_death(u32 __user *uaddr, struct task_struct *curr, int pi)
 {
 	u32 uval, uninitialized_var(nval), mval;
 
+	/* Futex address must be 32bit aligned */
+	if ((((unsigned long)uaddr) % sizeof(*uaddr)) != 0)
+		return -1;
+
 retry:
 	if (get_user(uval, uaddr))
 		return -1;
-- 
2.16.4