From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751956AbbIQKjn (ORCPT ); Thu, 17 Sep 2015 06:39:43 -0400 Received: from mail-wi0-f169.google.com ([209.85.212.169]:38499 "EHLO mail-wi0-f169.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751813AbbIQKjl (ORCPT ); Thu, 17 Sep 2015 06:39:41 -0400 From: Dmitry Vyukov To: gregkh@linuxfoundation.org, peter@hurleysoftware.com, jslaby@suse.com, linux-kernel@vger.kernel.org Cc: jslaby@suse.cz, andreyknvl@google.com, kcc@google.com, glider@google.com, paulmck@linux.vnet.ibm.com, hboehm@google.com, Dmitry Vyukov Subject: [PATCH v2] tty: fix data race in flush_to_ldisc Date: Thu, 17 Sep 2015 12:39:36 +0200 Message-Id: <1442486376-115369-1-git-send-email-dvyukov@google.com> X-Mailer: git-send-email 2.6.0.rc0.131.gf624c3d Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org flush_to_ldisc reads port->itty and checks that it is not NULL, concurrently release_tty sets port->itty to NULL. It is possible that flush_to_ldisc loads port->itty once, ensures that it is not NULL, but then reloads it again and uses. The second load can already return NULL, which will cause a crash. Use READ_ONCE to read port->itty. The data race was found with KernelThreadSanitizer (KTSAN). Signed-off-by: Dmitry Vyukov --- Changed since first version: - remove WRITE_ONCE when updating port->itty --- drivers/tty/tty_buffer.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/drivers/tty/tty_buffer.c b/drivers/tty/tty_buffer.c index 5a3fa89..23de97d 100644 --- a/drivers/tty/tty_buffer.c +++ b/drivers/tty/tty_buffer.c @@ -467,7 +467,7 @@ static void flush_to_ldisc(struct work_struct *work) struct tty_struct *tty; struct tty_ldisc *disc; - tty = port->itty; + tty = READ_ONCE(port->itty); if (tty == NULL) return; -- 2.6.0.rc0.131.gf624c3d