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=-2.8 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, 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 CAF60ECDFC0 for ; Wed, 12 Sep 2018 00:17:13 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 822AC20866 for ; Wed, 12 Sep 2018 00:17:13 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=arista.com header.i=@arista.com header.b="XbMM+QW6" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 822AC20866 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 S1727798AbeILFSz (ORCPT ); Wed, 12 Sep 2018 01:18:55 -0400 Received: from mail-ed1-f65.google.com ([209.85.208.65]:35779 "EHLO mail-ed1-f65.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726885AbeILFSy (ORCPT ); Wed, 12 Sep 2018 01:18:54 -0400 Received: by mail-ed1-f65.google.com with SMTP id y20-v6so362479edq.2 for ; Tue, 11 Sep 2018 17:17:09 -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=IG4AuSRFxAsZ+FcIpFPikBp4Rr2AKaPnrBwREdUxh6U=; b=XbMM+QW6ciCaxAiqFWIxd8390CymJPUDnfKBG1ERTGt9/51OvvkKnpuO6K9PNQRoM0 3uoRKdJftyJ6Ls7lb79s0slSG0vhjDJ3E6Ww5a11YdyqMC0mbLoY1ZtDfmx/D6Lcta7a ctLKTVeL/eLEJbiBGAd3Kpds627xruwPZVs1r6V6MM3fuFreZO1vElmOt7yQEWKwE/Qa 6meAmmJWofsr4gwHRj/RERYnEG0Plg3oGI5jfsLZPNDiOEzzB5Ro9ULxuCcl/RF2uqOz QDv8+cJU2KdUkELQtfq/ykI7UoTJNllLcEQZGWzoYfTM/Xp6tWT+KBDR/cT0tIbZgSH7 TiRw== 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=IG4AuSRFxAsZ+FcIpFPikBp4Rr2AKaPnrBwREdUxh6U=; b=XLbWdv/9OAc6vCkvT0U5vDMPJpVL/NdhWEwEbV+ddJmIoFljuRW4LXL52PgPpdDSXp /nwiwSDp0Z/4k90kb72a0Vpr45OkWg5SJSzuCQryDU7J0ItyvXkz2dkN8VMtRjaqIqoX vKVRDx9LaSkRYvOOgGVg4f8b3P9oHC90xj7HWVBfK5hfGYC6HoKT6zUHt7h379VTVacy HEqVAm3FhVu4kma2v0kAg6FRlRtGinh8e80P7XGvLDKiOm9qjlCbJMYO+pZyTNw34U+G OSu/ra7gsB0HD1CpoyNX4wmZFg2zPzI7ReNJQpJFUiO0llI4kRtIpkWK/vzaUrrLMuhE Wlfg== X-Gm-Message-State: APzg51CgF6XsZ4c5Tz8t8KS4BESknNwrv1qYwAegyyH7eUXIRWNgdwSz dX+SsHt3otgrMxumYqzwf9UMg9DZBas= X-Google-Smtp-Source: ANB0VdbswXIEGtOdnnbc3DC9ySwkr5SzcWpV5pSn9XDFibb51QS+2yo6meBsWFmmXa7enMADue3vng== X-Received: by 2002:a50:cf42:: with SMTP id d2-v6mr31526449edk.242.1536711428577; Tue, 11 Sep 2018 17:17:08 -0700 (PDT) Received: from dhcp.ire.aristanetworks.com ([217.173.96.166]) by smtp.gmail.com with ESMTPSA id l16-v6sm10380593edb.41.2018.09.11.17.17.06 (version=TLS1_2 cipher=ECDHE-RSA-CHACHA20-POLY1305 bits=256/256); Tue, 11 Sep 2018 17:17:07 -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: [PATCHv4 2/7] tty: Hold tty_ldisc_lock() during tty_reopen() Date: Wed, 12 Sep 2018 01:16:56 +0100 Message-Id: <20180912001702.18522-3-dima@arista.com> X-Mailer: git-send-email 2.13.6 In-Reply-To: <20180912001702.18522-1-dima@arista.com> References: <20180912001702.18522-1-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, 6 insertions(+), 3 deletions(-) diff --git a/drivers/tty/tty_io.c b/drivers/tty/tty_io.c index 5e5da9acaf0a..a947719b4626 100644 --- a/drivers/tty/tty_io.c +++ b/drivers/tty/tty_io.c @@ -1255,7 +1255,7 @@ static void tty_driver_remove_tty(struct tty_driver *driver, struct tty_struct * static int tty_reopen(struct tty_struct *tty) { struct tty_driver *driver = tty->driver; - int retval; + int retval = 0; if (driver->type == TTY_DRIVER_TYPE_PTY && driver->subtype == PTY_TYPE_MASTER) @@ -1267,15 +1267,18 @@ static int tty_reopen(struct tty_struct *tty) if (test_bit(TTY_EXCLUSIVE, &tty->flags) && !capable(CAP_SYS_ADMIN)) return -EBUSY; - tty->count++; + tty_ldisc_lock(tty, MAX_SCHEDULE_TIMEOUT); + 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