From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753323AbcAGPdN (ORCPT ); Thu, 7 Jan 2016 10:33:13 -0500 Received: from mail.linuxfoundation.org ([140.211.169.12]:57670 "EHLO mail.linuxfoundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750756AbcAGPdL (ORCPT ); Thu, 7 Jan 2016 10:33:11 -0500 Date: Thu, 7 Jan 2016 07:33:10 -0800 From: Greg Kroah-Hartman To: Mateusz Guzik Cc: Jiri Slaby , stable@vger.kernel.org, linux-kernel@vger.kernel.org, security@kernel.org, milos@redhat.com Subject: Re: [PATCH] tty: plug a use-after-free in TIOCGETD ioctl Message-ID: <20160107153310.GA26031@kroah.com> References: <1452178680-30284-1-git-send-email-mguzik@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1452178680-30284-1-git-send-email-mguzik@redhat.com> User-Agent: Mutt/1.5.24 (2015-08-30) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Jan 07, 2016 at 03:58:00PM +0100, Mateusz Guzik wrote: > When the line discipline is being changed, the old one is freed. > However, the handler for TIOCGETD would dereference it without taking > any locks, in effect possibly reading freed memory. > > Line discipline changes are protected with tty lock. Use it on reader > side as well. > > CVE: CVE-2016-0723 Why a cve tag? > Found-by: Milos Vyletel > Signed-off-by: Mateusz Guzik > --- > drivers/tty/tty_io.c | 23 ++++++++++++++++++++++- > 1 file changed, 22 insertions(+), 1 deletion(-) > > diff --git a/drivers/tty/tty_io.c b/drivers/tty/tty_io.c > index 892c923..1b10469 100644 > --- a/drivers/tty/tty_io.c > +++ b/drivers/tty/tty_io.c > @@ -2626,6 +2626,27 @@ static int tiocgsid(struct tty_struct *tty, struct tty_struct *real_tty, pid_t _ > } > > /** > + * tiocgetd - get line discipline > + * @tty: tty device > + * @p: pointer to returned line discipline > + * > + * Get the line discipline associated with the tty. > + * > + * Locking: none > + */ > + > +static int tiocgetd(struct tty_struct *tty, int __user *p) > +{ > + int ldisc; > + > + tty_lock(tty); > + ldisc = tty->ldisc->ops->num; > + tty_unlock(tty); > + > + return put_user(ldisc, p); Does this really protect anything? What is preventing ldisc from going away right after the tty_unlock call? And how are you able to trigger the tty to go away while the file is still held open and this ioctl is being called? thanks, greg k-h