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

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>

diff --git a/kernel/futex.c b/kernel/futex.c
index 0ee2f54d74fbd76f3e466b84a6fe5d7fe921afe0..99679c0040cc4eb8d54369768b38170679bb44ed 100644 (file)
--- a/kernel/futex.c
+++ b/kernel/futex.c
@@ -2909,6 +2909,10 @@ 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;