From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-3.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_PASS,URIBL_BLOCKED autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 11E5BC7112A for ; Sun, 14 Oct 2018 15:34:22 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id D4C1E20835 for ; Sun, 14 Oct 2018 15:34:21 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org D4C1E20835 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=decadent.org.uk Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728764AbeJNXPj (ORCPT ); Sun, 14 Oct 2018 19:15:39 -0400 Received: from shadbolt.e.decadent.org.uk ([88.96.1.126]:36577 "EHLO shadbolt.e.decadent.org.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728174AbeJNXPi (ORCPT ); Sun, 14 Oct 2018 19:15:38 -0400 Received: from [2a02:8011:400e:2:cbab:f00:c93f:614] (helo=deadeye) by shadbolt.decadent.org.uk with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.84_2) (envelope-from ) id 1gBiLx-0004cW-Ec; Sun, 14 Oct 2018 16:30:49 +0100 Received: from ben by deadeye with local (Exim 4.91) (envelope-from ) id 1gBiLU-0000PG-Or; Sun, 14 Oct 2018 16:30:20 +0100 Content-Type: text/plain; charset="UTF-8" Content-Disposition: inline Content-Transfer-Encoding: 8bit MIME-Version: 1.0 From: Ben Hutchings To: linux-kernel@vger.kernel.org, stable@vger.kernel.org CC: akpm@linux-foundation.org, "Johannes Weiner" , "Michal Hocko" , "Tetsuo Handa" , "Greg Kroah-Hartman" , "Jiri Slaby" , "Dmitry Vyukov" , "Alan Cox" , syzbot+40b7287c2dc987c48c81@syzkaller.appspotmail.com, "Christoph Hellwig" Date: Sun, 14 Oct 2018 16:25:41 +0100 Message-ID: X-Mailer: LinuxStableQueue (scripts by bwh) Subject: [PATCH 3.16 196/366] tty: Avoid possible error pointer dereference at tty_ldisc_restore(). In-Reply-To: X-SA-Exim-Connect-IP: 2a02:8011:400e:2:cbab:f00:c93f:614 X-SA-Exim-Mail-From: ben@decadent.org.uk X-SA-Exim-Scanned: No (on shadbolt.decadent.org.uk); SAEximRunCond expanded to false Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 3.16.60-rc1 review patch. If anyone has any objections, please let me know. ------------------ From: Tetsuo Handa commit 598c2d41ff44889dd8eced4f117403e472158d85 upstream. syzbot is reporting crashes [1] triggered by memory allocation failure at tty_ldisc_get() from tty_ldisc_restore(). While syzbot stops at WARN_ON() due to panic_on_warn == true, panic_on_warn == false will after all trigger an OOPS by dereferencing old->ops->num if IS_ERR(old) == true. We can simplify tty_ldisc_restore() as three calls (old->ops->num, N_TTY, N_NULL) to tty_ldisc_failto() in addition to avoiding possible error pointer dereference. If someone reports kernel panic triggered by forcing all memory allocations for tty_ldisc_restore() to fail, we can consider adding __GFP_NOFAIL for tty_ldisc_restore() case. [1] https://syzkaller.appspot.com/bug?id=6ac359c61e71d22e06db7f8f88243feb11d927e7 Reported-by: syzbot+40b7287c2dc987c48c81@syzkaller.appspotmail.com Signed-off-by: Tetsuo Handa Cc: Greg Kroah-Hartman Cc: Jiri Slaby Cc: Dmitry Vyukov Cc: Johannes Weiner Cc: Alan Cox Cc: Christoph Hellwig Cc: Michal Hocko Signed-off-by: Greg Kroah-Hartman [bwh: Backported to 3.16: tty_name() requires a buffer] Signed-off-by: Ben Hutchings --- drivers/tty/tty_ldisc.c | 13 +++++-------- 1 file changed, 5 insertions(+), 8 deletions(-) --- a/drivers/tty/tty_ldisc.c +++ b/drivers/tty/tty_ldisc.c @@ -510,19 +510,16 @@ static void tty_ldisc_restore(struct tty char buf[64]; /* There is an outstanding reference here so this is safe */ - old = tty_ldisc_get(tty, old->ops->num); - WARN_ON(IS_ERR(old)); - tty->ldisc = old; - tty_set_termios_ldisc(tty, old->ops->num); - if (tty_ldisc_open(tty, old) < 0) { - tty_ldisc_put(old); + if (tty_ldisc_failto(tty, old->ops->num) < 0) { + const char *name = tty_name(tty, buf); + + pr_warn("Falling back ldisc for %s.\n", name); /* The traditional behaviour is to fall back to N_TTY, we want to avoid falling back to N_NULL unless we have no choice to avoid the risk of breaking anything */ if (tty_ldisc_failto(tty, N_TTY) < 0 && tty_ldisc_failto(tty, N_NULL) < 0) - panic("Couldn't open N_NULL ldisc for %s.", - tty_name(tty, buf)); + panic("Couldn't open N_NULL ldisc for %s.", name); } }