From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756784AbdLGRQf (ORCPT ); Thu, 7 Dec 2017 12:16:35 -0500 Received: from fldsmtpe03.verizon.com ([140.108.26.142]:49829 "EHLO fldsmtpe03.verizon.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756263AbdLGPwU (ORCPT ); Thu, 7 Dec 2017 10:52:20 -0500 From: alexander.levin@verizon.com Cc: Dmitry Vyukov , "syzkaller@googlegroups.com" , Greg Kroah-Hartman , Jiri Slaby , Peter Hurley , One Thousand Gnomes , alexander.levin@verizon.com X-Host: surveyor.tdc.vzwcorp.com To: "linux-kernel@vger.kernel.org" , "stable@vger.kernel.org" Subject: [PATCH AUTOSEL for 4.9 075/156] tty: fix data race in tty_ldisc_ref_wait() Thread-Topic: [PATCH AUTOSEL for 4.9 075/156] tty: fix data race in tty_ldisc_ref_wait() Thread-Index: AQHTb3LuIAoB30lyJECj8emQIOGGKw== Date: Thu, 7 Dec 2017 15:49:13 +0000 Message-ID: <20171207154845.4814-75-alexander.levin@verizon.com> References: <20171207154845.4814-1-alexander.levin@verizon.com> In-Reply-To: <20171207154845.4814-1-alexander.levin@verizon.com> Accept-Language: en-US Content-Language: en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: x-ms-exchange-messagesentrepresentingtype: 1 x-ms-exchange-transport-fromentityheader: Hosted x-originating-ip: [10.144.60.250] Content-Type: text/plain; charset="iso-8859-1" MIME-Version: 1.0 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Transfer-Encoding: 8bit X-MIME-Autoconverted: from quoted-printable to 8bit by nfs id vB7HGrqa025632 From: Dmitry Vyukov [ 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 Cc: syzkaller@googlegroups.com Cc: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman Cc: Jiri Slaby Cc: Peter Hurley Cc: One Thousand Gnomes Signed-off-by: Greg Kroah-Hartman Signed-off-by: Sasha Levin --- drivers/tty/tty_ldisc.c | 7 +++++-- 1 file changed, 5 insertions(+), 2 deletions(-) diff --git a/drivers/tty/tty_ldisc.c b/drivers/tty/tty_ldisc.c index c3956ca022e4..b0500a0a87b8 100644 --- a/drivers/tty/tty_ldisc.c +++ b/drivers/tty/tty_ldisc.c @@ -271,10 +271,13 @@ const struct file_operations tty_ldiscs_proc_fops = { 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); -- 2.11.0