linux-kernel - [PATCH 3.16 039/157] futex: Ensure that futex address is aligned in handle_futex

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Message-ID: <lsq.1565469607.880857944@decadent.org.uk>
Date:   Sat, 10 Aug 2019 21:40:07 +0100
From:   Ben Hutchings <ben@...adent.org.uk>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:     akpm@...ux-foundation.org, Denis Kirjanov <kda@...ux-powerpc.org>,
        "" <peterz@...radead.org>, "Chen Jie" <chenjie6@...wei.com>,
        "" <dvhart@...radead.org>, "" <zengweilin@...wei.com>,
        "Thomas Gleixner" <tglx@...utronix.de>
Subject: [PATCH 3.16 039/157] futex: Ensure that futex address is aligned
 in handle_futex_death()

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

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

From: Chen Jie <chenjie6@...wei.com>

commit 5a07168d8d89b00fe1760120714378175b3ef992 upstream.

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@...wei.com>
Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
Cc: <dvhart@...radead.org>
Cc: <peterz@...radead.org>
Cc: <zengweilin@...wei.com>
Link: https://lkml.kernel.org/r/1552621478-119787-1-git-send-email-chenjie6@huawei.com
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 kernel/futex.c | 4 ++++
 1 file changed, 4 insertions(+)

--- a/kernel/futex.c
+++ b/kernel/futex.c
@@ -2909,6 +2909,10 @@ int handle_futex_death(u32 __user *uaddr
 {
 	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;