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=-6.8 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_HELO_NONE,SPF_PASS,USER_AGENT_GIT autolearn=unavailable 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 418BEC3F68F for ; Tue, 28 Jan 2020 14:25:57 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 1A12621739 for ; Tue, 28 Jan 2020 14:25:57 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1580221557; bh=N53L2593G9AItP5Hfi5f6AE/8lIDgtBvs63EpGa8FJM=; h=From:To:Cc:Subject:Date:In-Reply-To:References:List-ID:From; b=Rq8Gt8Skjr2emfFTxZJJeGNAmLxYrvHYI+L6n+Zk+8sCzrMoUljaZ0UOG7mlRCrhR QidUEibALeUkfqfZ6dfw9uHQd+IosH3CArqleAxnjBiAPiG6O0FM29UO/uR1lQdjlS 6F8t8tJ4YkRjhk7X9CPTAhgpESPWsvZSCHfanfeY= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1733102AbgA1OZ4 (ORCPT ); Tue, 28 Jan 2020 09:25:56 -0500 Received: from mail.kernel.org ([198.145.29.99]:53022 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1730766AbgA1OZx (ORCPT ); Tue, 28 Jan 2020 09:25:53 -0500 Received: from localhost (83-86-89-107.cable.dynamic.v4.ziggo.nl [83.86.89.107]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 4BC3224686; Tue, 28 Jan 2020 14:25:52 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1580221552; bh=N53L2593G9AItP5Hfi5f6AE/8lIDgtBvs63EpGa8FJM=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=pQT6KO8YfrkCE3fqpJLz480OFcjDxuk8e5gt99WfhlLXrmnUpRNoNhymUTVrbKhUs C/b6O3Ll3SCixCG2EHLG6CXvwkA47KnPhkRWp/uq2i7XTBhwugmIbI0KoB/byEAoKa QgBRCbwUEJBsa0AMRtQtyHCBBLl/r0N09FfidYiI= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, syzbot+017e491ae13c0068598a@syzkaller.appspotmail.com, Richard Palethorpe , Wolfgang Grandegger , Marc Kleine-Budde , "David S. Miller" , Tyler Hall , linux-can@vger.kernel.org, netdev@vger.kernel.org, syzkaller@googlegroups.com Subject: [PATCH 4.9 234/271] can, slip: Protect tty->disc_data in write_wakeup and close with RCU Date: Tue, 28 Jan 2020 15:06:23 +0100 Message-Id: <20200128135909.978871848@linuxfoundation.org> X-Mailer: git-send-email 2.25.0 In-Reply-To: <20200128135852.449088278@linuxfoundation.org> References: <20200128135852.449088278@linuxfoundation.org> User-Agent: quilt/0.66 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Richard Palethorpe [ Upstream commit 0ace17d56824165c7f4c68785d6b58971db954dd ] 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: Greg Kroah-Hartman --- 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 @@ -344,9 +344,16 @@ 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) @@ -887,10 +894,11 @@ 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 */