This is a note to let you know that I've just added the patch titled
tty: fix data race in tty_ldisc_ref_wait()
to the 4.9-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
tty-fix-data-race-in-tty_ldisc_ref_wait.patch
and it can be found in the queue-4.9 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From foo@baz Mon Dec 18 14:12:34 CET 2017
From: Dmitry Vyukov <dvyukov@xxxxxxxxxx>
Date: Sat, 4 Mar 2017 13:46:12 +0100
Subject: tty: fix data race in tty_ldisc_ref_wait()
From: Dmitry Vyukov <dvyukov@xxxxxxxxxx>
[ Upstream commit a4a3e061149f09c075f108b6f1cf04d9739a6bc2 ]
tty_ldisc_ref_wait() checks tty->ldisc under tty->ldisc_sem.
But if ldisc==NULL it releases them sem and reloads
tty->ldisc without holding the sem. This is wrong and
can lead to returning non-NULL ldisc without protection.
Don't reload tty->ldisc second time.
Signed-off-by: Dmitry Vyukov <dvyukov@xxxxxxxxxx>
Cc: syzkaller@xxxxxxxxxxxxxxxx
Cc: linux-kernel@xxxxxxxxxxxxxxx
Cc: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
Cc: Jiri Slaby <jslaby@xxxxxxxx>
Cc: Peter Hurley <peter@xxxxxxxxxxxxxxxxxx>
Cc: One Thousand Gnomes <gnomes@xxxxxxxxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
Signed-off-by: Sasha Levin <alexander.levin@xxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
drivers/tty/tty_ldisc.c | 7 +++++--
1 file changed, 5 insertions(+), 2 deletions(-)
--- a/drivers/tty/tty_ldisc.c
+++ b/drivers/tty/tty_ldisc.c
@@ -271,10 +271,13 @@ const struct file_operations tty_ldiscs_
struct tty_ldisc *tty_ldisc_ref_wait(struct tty_struct *tty)
{
+ struct tty_ldisc *ld;
+
ldsem_down_read(&tty->ldisc_sem, MAX_SCHEDULE_TIMEOUT);
- if (!tty->ldisc)
+ ld = tty->ldisc;
+ if (!ld)
ldsem_up_read(&tty->ldisc_sem);
- return tty->ldisc;
+ return ld;
}
EXPORT_SYMBOL_GPL(tty_ldisc_ref_wait);
Patches currently in stable-queue which might be from dvyukov@xxxxxxxxxx are
queue-4.9/tty-fix-data-race-in-tty_ldisc_ref_wait.patch
queue-4.9/kvm-nvmx-do-not-warn-when-msr-bitmap-address-is-not-backed.patch
queue-4.9/userfaultfd-shmem-__do_fault-requires-vm_fault_nopage.patch
queue-4.9/tty-don-t-panic-on-oom-in-tty_set_ldisc.patch