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=-9.5 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH, MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_PASS,URIBL_BLOCKED,USER_AGENT_GIT 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 C1CA3ECE563 for ; Mon, 17 Sep 2018 23:53:34 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 792DC20C0E for ; Mon, 17 Sep 2018 23:53:34 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=arista.com header.i=@arista.com header.b="NVqy7+8l" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 792DC20C0E Authentication-Results: mail.kernel.org; dmarc=fail (p=quarantine dis=none) header.from=arista.com 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 S1729023AbeIRFXO (ORCPT ); Tue, 18 Sep 2018 01:23:14 -0400 Received: from mail-ed1-f65.google.com ([209.85.208.65]:33619 "EHLO mail-ed1-f65.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728689AbeIRFWs (ORCPT ); Tue, 18 Sep 2018 01:22:48 -0400 Received: by mail-ed1-f65.google.com with SMTP id d8-v6so411622edv.0 for ; Mon, 17 Sep 2018 16:53:06 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=arista.com; s=googlenew; h=from:to:cc:subject:date:message-id:in-reply-to:references; bh=Dcu5K2A3gkhR5xavIBmd5tcJGwCobJLSptYeQ9hDahw=; b=NVqy7+8l2Se1UnsAobAEbwMv+NUphoij58ArZHoXjjtnd+TvVlVRmNZ5ZD9CIkWHuf 9UOay+bREjg2IMtN4Rk/YwUm78Hxy0yYx0m35SLSE/ksv4ODOQa8VdwWtrfAGhifyA3H 726/vKhmQyTaS4d/L/3DCZL/2a7tBkls5tpcRvGVTg15rlNj2frvgzmHCvfPULDm7t/4 lhjLMhdz/pxO14QdYaZn0QPLxjS9Wqvn3YewmUjVBXI6nl4v6CYDg/E/CRTUx+13FXXK 5K8/7gJVGbcwTjPNLLTdRIWG40Z1AKXGPFy+aW3t5znVkSQi8c5QjfItsbnCLPI95Yql 5OXw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:from:to:cc:subject:date:message-id:in-reply-to :references; bh=Dcu5K2A3gkhR5xavIBmd5tcJGwCobJLSptYeQ9hDahw=; b=XSlRKRhdNz6jruu1o2LvpLHWbpXBIbmIYyftk3OLaTxUmEYGxfTdq6qkriDDU6/Umq ZLGSlsrkGR9/zwkLHbgKfNYWhCm+K81/zpvVq9EqVpoDyk5ZYiTRoqo46koatvK2FRun oPeglkYoLrGMCB7HxMsEIv+Q1ovrY0m/X180JmWT8u8cvEdiftYxwveZ59cuzztQ+tXW 4tQsMMw37nMWvEpBrad+hDrn8/HiGNC1qNyUF7cp277m4F4Zod0kbPakPvjmMDm78xS4 BWjOzvZAsdFC/NF68zDO+tcFH8U2S6FHEHiG1G2dz3aA2EVFxRq/brM3wflRGJMN24YW 6Hrw== X-Gm-Message-State: APzg51Aa1uezFGZ6PtrtwJaMeZetyRfjTCCwA2i/ULsyJEgrcCc537JW btqgze52PVZjpw8zWy9vIBkVQ6VnHsc= X-Google-Smtp-Source: ANB0VdZo0j5UI32eo7/Sw2L5tTb9k7De92W3PbQYrkxliA3Cgeew7uAowMgM3wReCCijTmdRptR3LA== X-Received: by 2002:a50:fd10:: with SMTP id i16-v6mr9074482eds.253.1537228384796; Mon, 17 Sep 2018 16:53:04 -0700 (PDT) Received: from dhcp.ire.aristanetworks.com ([217.173.96.166]) by smtp.gmail.com with ESMTPSA id r35-v6sm7193912edr.59.2018.09.17.16.53.03 (version=TLS1_2 cipher=ECDHE-RSA-CHACHA20-POLY1305 bits=256/256); Mon, 17 Sep 2018 16:53:04 -0700 (PDT) From: Dmitry Safonov To: linux-kernel@vger.kernel.org Cc: Dmitry Safonov <0x7f454c46@gmail.com>, Dmitry Safonov , Daniel Axtens , Dmitry Vyukov , Mark Rutland , Michael Neuling , Mikulas Patocka , Nathan March , =?UTF-8?q?Pasi=20K=C3=A4rkk=C3=A4inen?= , Peter Hurley , Peter Zijlstra , "Rong, Chen" , Sergey Senozhatsky , Tan Xiaojun , Tetsuo Handa , Jiri Slaby , syzbot+3aa9784721dfb90e984d@syzkaller.appspotmail.com, Tetsuo Handa , stable@vger.kernel.org, Greg Kroah-Hartman , Jiri Slaby Subject: [PATCHv5 3/7] tty: Hold tty_ldisc_lock() during tty_reopen() Date: Tue, 18 Sep 2018 00:52:54 +0100 Message-Id: <20180917235258.5719-4-dima@arista.com> X-Mailer: git-send-email 2.13.6 In-Reply-To: <20180917235258.5719-1-dima@arista.com> References: <20180917235258.5719-1-dima@arista.com> Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org tty_ldisc_reinit() doesn't race with neither tty_ldisc_hangup() nor set_ldisc() nor tty_ldisc_release() as they use tty lock. But it races with anyone who expects line discipline to be the same after hoding read semaphore in tty_ldisc_ref(). We've seen the following crash on v4.9.108 stable: BUG: unable to handle kernel paging request at 0000000000002260 IP: [..] n_tty_receive_buf_common+0x5f/0x86d Workqueue: events_unbound flush_to_ldisc Call Trace: [..] n_tty_receive_buf2 [..] tty_ldisc_receive_buf [..] flush_to_ldisc [..] process_one_work [..] worker_thread [..] kthread [..] ret_from_fork tty_ldisc_reinit() should be called with ldisc_sem hold for writing, which will protect any reader against line discipline changes. Backport-first: b027e2298bd5 ("tty: fix data race between tty_init_dev and flush of buf") Cc: stable@vger.kernel.org Cc: Greg Kroah-Hartman Cc: Jiri Slaby Reviewed-by: Jiri Slaby Reported-by: syzbot+3aa9784721dfb90e984d@syzkaller.appspotmail.com Tested-by: Mark Rutland Tested-by: Tetsuo Handa Signed-off-by: Dmitry Safonov --- drivers/tty/tty_io.c | 9 +++++++-- 1 file changed, 7 insertions(+), 2 deletions(-) diff --git a/drivers/tty/tty_io.c b/drivers/tty/tty_io.c index 5e5da9acaf0a..3ef8b977b167 100644 --- a/drivers/tty/tty_io.c +++ b/drivers/tty/tty_io.c @@ -1267,15 +1267,20 @@ static int tty_reopen(struct tty_struct *tty) if (test_bit(TTY_EXCLUSIVE, &tty->flags) && !capable(CAP_SYS_ADMIN)) return -EBUSY; - tty->count++; + retval = tty_ldisc_lock(tty, 5 * HZ); + if (retval) + return retval; + tty->count++; if (tty->ldisc) - return 0; + goto out_unlock; retval = tty_ldisc_reinit(tty, tty->termios.c_line); if (retval) tty->count--; +out_unlock: + tty_ldisc_unlock(tty); return retval; } -- 2.13.6