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_HELO_NONE,SPF_PASS,URIBL_BLOCKED autolearn=no 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 B286FC54FD0 for ; Thu, 23 Apr 2020 23:08:34 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 9977B2087E for ; Thu, 23 Apr 2020 23:08:34 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728983AbgDWXIc (ORCPT ); Thu, 23 Apr 2020 19:08:32 -0400 Received: from shadbolt.e.decadent.org.uk ([88.96.1.126]:50980 "EHLO shadbolt.e.decadent.org.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728666AbgDWXG7 (ORCPT ); Thu, 23 Apr 2020 19:06:59 -0400 Received: from [192.168.4.242] (helo=deadeye) by shadbolt.decadent.org.uk with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.89) (envelope-from ) id 1jRkvc-0004n0-LE; Fri, 24 Apr 2020 00:06:44 +0100 Received: from ben by deadeye with local (Exim 4.93) (envelope-from ) id 1jRkvY-00E6y9-63; Fri, 24 Apr 2020 00:06:40 +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, Denis Kirjanov , "David S. Miller" , netdev@vger.kernel.org, "Marc Kleine-Budde" , "Richard Palethorpe" , "Wolfgang Grandegger" , syzkaller@googlegroups.com, linux-can@vger.kernel.org, syzbot+017e491ae13c0068598a@syzkaller.appspotmail.com, "Tyler Hall" Date: Fri, 24 Apr 2020 00:07:08 +0100 Message-ID: X-Mailer: LinuxStableQueue (scripts by bwh) X-Patchwork-Hint: ignore Subject: [PATCH 3.16 201/245] can, slip: Protect tty->disc_data in write_wakeup and close with RCU In-Reply-To: X-SA-Exim-Connect-IP: 192.168.4.242 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 3.16.83-rc1 review patch. If anyone has any objections, please let me know. ------------------ From: Richard Palethorpe commit 0ace17d56824165c7f4c68785d6b58971db954dd upstream. write_wakeup can happen in parallel with close/hangup where tty->disc_data is set to NULL and the netdevice is freed thus also freeing disc_data. write_wakeup accesses disc_data so we must prevent close from freeing the netdev while write_wakeup has a non-NULL view of tty->disc_data. We also need to make sure that accesses to disc_data are atomic. Which can all be done with RCU. This problem was found by Syzkaller on SLCAN, but the same issue is reproducible with the SLIP line discipline using an LTP test based on the Syzkaller reproducer. A fix which didn't use RCU was posted by Hillf Danton. Fixes: 661f7fda21b1 ("slip: Fix deadlock in write_wakeup") Fixes: a8e83b17536a ("slcan: Port write_wakeup deadlock fix from slip") Reported-by: syzbot+017e491ae13c0068598a@syzkaller.appspotmail.com Signed-off-by: Richard Palethorpe Cc: Wolfgang Grandegger Cc: Marc Kleine-Budde Cc: "David S. Miller" Cc: Tyler Hall Cc: linux-can@vger.kernel.org Cc: netdev@vger.kernel.org Cc: linux-kernel@vger.kernel.org Cc: syzkaller@googlegroups.com Signed-off-by: David S. Miller Signed-off-by: Ben Hutchings --- drivers/net/can/slcan.c | 12 ++++++++++-- drivers/net/slip/slip.c | 12 ++++++++++-- 2 files changed, 20 insertions(+), 4 deletions(-) --- a/drivers/net/can/slcan.c +++ b/drivers/net/can/slcan.c @@ -346,9 +346,16 @@ static void slcan_transmit(struct work_s */ static void slcan_write_wakeup(struct tty_struct *tty) { - struct slcan *sl = tty->disc_data; + struct slcan *sl; + + rcu_read_lock(); + sl = rcu_dereference(tty->disc_data); + if (!sl) + goto out; schedule_work(&sl->tx_work); +out: + rcu_read_unlock(); } /* Send a can_frame to a TTY queue. */ @@ -640,10 +647,11 @@ static void slcan_close(struct tty_struc return; spin_lock_bh(&sl->lock); - tty->disc_data = NULL; + rcu_assign_pointer(tty->disc_data, NULL); sl->tty = NULL; spin_unlock_bh(&sl->lock); + synchronize_rcu(); flush_work(&sl->tx_work); /* Flush network side */ --- a/drivers/net/slip/slip.c +++ b/drivers/net/slip/slip.c @@ -452,9 +452,16 @@ static void slip_transmit(struct work_st */ static void slip_write_wakeup(struct tty_struct *tty) { - struct slip *sl = tty->disc_data; + struct slip *sl; + + rcu_read_lock(); + sl = rcu_dereference(tty->disc_data); + if (!sl) + goto out; schedule_work(&sl->tx_work); +out: + rcu_read_unlock(); } static void sl_tx_timeout(struct net_device *dev) @@ -885,10 +892,11 @@ static void slip_close(struct tty_struct return; spin_lock_bh(&sl->lock); - tty->disc_data = NULL; + rcu_assign_pointer(tty->disc_data, NULL); sl->tty = NULL; spin_unlock_bh(&sl->lock); + synchronize_rcu(); flush_work(&sl->tx_work); /* VSV = very important to remove timers */