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%3Ba=su...

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@vger.kernel.org know about it.

From foo@baz Mon Dec 18 14:12:34 CET 2017

From: Dmitry Vyukov dvyukov@google.com Date: Sat, 4 Mar 2017 13:46:12 +0100 Subject: tty: fix data race in tty_ldisc_ref_wait()

From: Dmitry Vyukov dvyukov@google.com

[ 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@google.com Cc: syzkaller@googlegroups.com Cc: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman gregkh@linuxfoundation.org Cc: Jiri Slaby jslaby@suse.com Cc: Peter Hurley peter@hurleysoftware.com Cc: One Thousand Gnomes gnomes@lxorguk.ukuu.org.uk Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org Signed-off-by: Sasha Levin alexander.levin@verizon.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- 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@google.com 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