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Subject[tip:locking/urgent] futex: Ensure that futex address is aligned in handle_futex_death()
Commit-ID:  5a07168d8d89b00fe1760120714378175b3ef992
Gitweb: https://git.kernel.org/tip/5a07168d8d89b00fe1760120714378175b3ef992
Author: Chen Jie <chenjie6@huawei.com>
AuthorDate: Fri, 15 Mar 2019 03:44:38 +0000
Committer: Thomas Gleixner <tglx@linutronix.de>
CommitDate: Fri, 22 Mar 2019 13:05:26 +0100

futex: Ensure that futex address is aligned in handle_futex_death()

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

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

diff --git a/kernel/futex.c b/kernel/futex.c
index c3b73b0311bc..9e40cf7be606 100644
--- a/kernel/futex.c
+++ b/kernel/futex.c
@@ -3436,6 +3436,10 @@ static int handle_futex_death(u32 __user *uaddr, struct task_struct *curr, int p
{
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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