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=-9.3 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 1EF94C0044C for ; Thu, 1 Nov 2018 00:25:04 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id D6E732064C for ; Thu, 1 Nov 2018 00:25:03 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=arista.com header.i=@arista.com header.b="J8RsfFya" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org D6E732064C 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 S1727244AbeKAJZd (ORCPT ); Thu, 1 Nov 2018 05:25:33 -0400 Received: from mail-ed1-f65.google.com ([209.85.208.65]:44891 "EHLO mail-ed1-f65.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726322AbeKAJZc (ORCPT ); Thu, 1 Nov 2018 05:25:32 -0400 Received: by mail-ed1-f65.google.com with SMTP id n19-v6so4213254edq.11 for ; Wed, 31 Oct 2018 17:24:59 -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 :mime-version:content-transfer-encoding; bh=KTTxNUpzV2y7L2vECJT+5rBRgLaIPcy7D5Gk0Z/6hQE=; b=J8RsfFyaPnyYR+lv7UzQBtIzVlaXudg3v88jCXiwvaYQJgaXo3FW1BkNrHLCkfyat/ dHXoW/bXr/JQcRHXDJMlHsXliISk22f4gSR8fXST7wUsQ+u2fMv+D62JNbwZI7oWQPDa 8ilquwE44ZPeAxBU7s1fAw/0nWvNky0f7hzf70iATlTO+jPeNBgLUd/zQPPN9LuD8Cx0 jogkLs2i9NrkXume9b+3CT+e71wC7WmgyDQdbH7fhoaLmG/aEnmTNk3kaR0egp1TdoaB 1FJS4Zg9YrbcsfxvcDuQy8fx5e5OLtxnCF7+gdc/lwp4aHZEZnpBLTT7C6rpQbXOla0K Qz6g== 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:mime-version:content-transfer-encoding; bh=KTTxNUpzV2y7L2vECJT+5rBRgLaIPcy7D5Gk0Z/6hQE=; b=GxHQ3orcc2OtP9+d6NWbb7RDPv+C71oH6t2Y2gQ5c0cEhYoZD1aTAzQnVrma0Z28L4 DA6jhG29Lf3wtrc/b3mvGk58gm1ejEwhvv6KoG6515QEKkx9BNrDV1gDJZd3666wMT19 xX10IIYZptYYHRxJa3oplZ8n+UIu+yOymvCspg9IVl0NfgiNJRsIdc1WiTiMhDVf8S46 +TLNkq9q47OFsxxcTCITmp2ds2S3su2X0mOh5yK9couy+y8CxSGiu+XfM0p/mM4utXUs LhVpRrQxghtEUoXpn1uTjlGzzo6uRFkAHgUajR24CgkP+IIrV6X6ZmClEZi3/dUmRJXn rR8Q== X-Gm-Message-State: AGRZ1gLuBBGSMASuBSnhw+vpwy9ki+YbLyfbpFnWHmyLE/2DN8OHehxv KoJYXflKo++dWke4qwnHCKJB+DsZrgk= X-Google-Smtp-Source: AJdET5fCZPOl2FydWzaVSktfugyxwnORlD8YHAtmD0D3QaOeH1sYR3pZybSHlZGK5Um08eIJcBw3pA== X-Received: by 2002:a50:e68d:: with SMTP id z13-v6mr3538147edm.275.1541031898177; Wed, 31 Oct 2018 17:24:58 -0700 (PDT) Received: from Mindolluin.ire.aristanetworks.com ([217.173.96.166]) by smtp.gmail.com with ESMTPSA id s12-v6sm10188175edd.39.2018.10.31.17.24.56 (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Wed, 31 Oct 2018 17:24:57 -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 , Greg Kroah-Hartman , Jiri Slaby , stable@vger.kernel.org Subject: [PATCHv6 2/7] tty: Hold tty_ldisc_lock() during tty_reopen() Date: Thu, 1 Nov 2018 00:24:47 +0000 Message-Id: <20181101002452.5483-3-dima@arista.com> X-Mailer: git-send-email 2.19.1 In-Reply-To: <20181101002452.5483-1-dima@arista.com> References: <20181101002452.5483-1-dima@arista.com> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 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. Cc: Greg Kroah-Hartman Cc: Jiri Slaby Cc: stable@vger.kernel.org # b027e2298bd5 ("tty: fix data race between tty_init_dev and flush of buf") 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 ee80dfbd5442..f73d8fa7f02b 100644 --- a/drivers/tty/tty_io.c +++ b/drivers/tty/tty_io.c @@ -1268,15 +1268,20 @@ 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; } -- 2.19.1