[PATCH AUTOSEL for 4.4 093/101] pty: cancel pty slave port buf's work in tty_release

Sasha Levin
2018-03-08T05:02:14Z

From: Sahara <keun-o.park@darkmatter.ae>

[ Upstream commit 2b022ab7542df60021ab57854b3faaaf42552eaf ]

In case that CONFIG_SLUB_DEBUG is on and pty is used, races between
release_one_tty and flush_to_ldisc work threads may happen and lead
to use-after-free condition on tty->link->port. Because SLUB_DEBUG
is turned on, freed tty->link->port is filled with POISON_FREE value.
So far without SLUB_DEBUG, port was filled with zero and flush_to_ldisc
could return without a problem by checking if tty is NULL.

CPU 0 CPU 1
----- -----
release_tty pty_write
cancel_work_sync(tty) to = tty->link
tty_kref_put(tty->link) tty_schedule_flip(to->port)
<< workqueue >> ...
release_one_tty ...
pty_cleanup ...
kfree(tty->link->port) << workqueue >>
flush_to_ldisc
tty = READ_ONCE(port->itty)
tty is 0x6b6b6b6b6b6b6b6b
!!PANIC!! access tty->ldisc

Unable to handle kernel paging request at virtual address 6b6b6b6b6b6b6b93
pgd = ffffffc0eb1c3000
[6b6b6b6b6b6b6b93] *pgd=0000000000000000, *pud=0000000000000000
------------[ cut here ]------------
Kernel BUG at ffffff800851154c [verbose debug info unavailable]
Internal error: Oops - BUG: 96000004 [#1] PREEMPT SMP
CPU: 3 PID: 265 Comm: kworker/u8:9 Tainted: G W 3.18.31-g0a58eeb #1
Hardware name: Qualcomm Technologies, Inc. MSM 8996pro v1.1 + PMI8996 Carbide (DT)
Workqueue: events_unbound flush_to_ldisc
task: ffffffc0ed610ec0 ti: ffffffc0ed624000 task.ti: ffffffc0ed624000
PC is at ldsem_down_read_trylock+0x0/0x4c
LR is at tty_ldisc_ref+0x24/0x4c
pc : [<ffffff800851154c>] lr : [<ffffff800850f6c0>] pstate: 80400145
sp : ffffffc0ed627cd0
x29: ffffffc0ed627cd0 x28: 0000000000000000
x27: ffffff8009e05000 x26: ffffffc0d382cfa0
x25: 0000000000000000 x24: ffffff800a012f08
x23: 0000000000000000 x22: ffffffc0703fbc88
x21: 6b6b6b6b6b6b6b6b x20: 6b6b6b6b6b6b6b93
x19: 0000000000000000 x18: 0000000000000001
x17: 00e80000f80d6f53 x16: 0000000000000001
x15: 0000007f7d826fff x14: 00000000000000a0
x13: 0000000000000000 x12: 0000000000000109
x11: 0000000000000000 x10: 0000000000000000
x9 : ffffffc0ed624000 x8 : ffffffc0ed611580
x7 : 0000000000000000 x6 : ffffff800a42e000
x5 : 00000000000003fc x4 : 0000000003bd1201
x3 : 0000000000000001 x2 : 0000000000000001
x1 : ffffff800851004c x0 : 6b6b6b6b6b6b6b93

Signed-off-by: Sahara <keun-o.park@darkmatter.ae>

Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Signed-off-by: Sasha Levin <alexander.levin@microsoft.com>
---
drivers/tty/tty_io.c | 2 ++
1 file changed, 2 insertions(+)

diff --git a/drivers/tty/tty_io.c b/drivers/tty/tty_io.c
index 1bb629ab8ecc..a638c1738547 100644
--- a/drivers/tty/tty_io.c
+++ b/drivers/tty/tty_io.c
@@ -1694,6 +1694,8 @@ static void release_tty(struct tty_struct *tty, int idx)
if (tty->link)
tty->link->port->itty = NULL;
tty_buffer_cancel_work(tty->port);
+ if (tty->link)
+ tty_buffer_cancel_work(tty->link->port);

tty_kref_put(tty->link);
tty_kref_put(tty);
--
2.14.1