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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@huawei.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@huawei.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: <dvhart@infradead.org>
Cc: <peterz@infradead.org>
Cc: <zengweilin@huawei.com>
Link: https://lkml.kernel.org/r/1552621478-119787-1-git-send-email-chenjie6@huawei.com
Signed-off-by: Ben Hutchings <ben@decadent.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;
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