[PATCH 4.14 11/41] futex: Ensure that futex address is aligned in handle_futex_death()

From: Greg Kroah-Hartman
Date: Tue Mar 26 2019 - 02:33:09 EST

4.14-stable review patch. If anyone has any objections, please let me know.


From: Chen Jie <chenjie6@xxxxxxxxxx>

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@xxxxxxxxxx>
Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: <dvhart@xxxxxxxxxxxxx>
Cc: <peterz@xxxxxxxxxxxxx>
Cc: <zengweilin@xxxxxxxxxx>
Cc: stable@xxxxxxxxxxxxxxx
Link: https://lkml.kernel.org/r/1552621478-119787-1-git-send-email-chenjie6@xxxxxxxxxx
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

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

--- a/kernel/futex.c
+++ b/kernel/futex.c
@@ -3450,6 +3450,10 @@ 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;
if (get_user(uval, uaddr))
return -1;