From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933430AbcAKOIX (ORCPT ); Mon, 11 Jan 2016 09:08:23 -0500 Received: from mx1.redhat.com ([209.132.183.28]:44727 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S933264AbcAKOHs (ORCPT ); Mon, 11 Jan 2016 09:07:48 -0500 From: "Herton R. Krzesinski" To: linux-kernel@vger.kernel.org Cc: Peter Hurley , Alan Cox , Greg Kroah-Hartman , Jiri Slaby , Andrew Morton , Josh Triplett , Al Viro , David Howells Subject: [PATCH 1/2 v2] pty: fix possible use after free of tty->driver_data Date: Mon, 11 Jan 2016 12:07:43 -0200 Message-Id: <1452521264-21766-2-git-send-email-herton@redhat.com> In-Reply-To: <1452521264-21766-1-git-send-email-herton@redhat.com> References: <1452521264-21766-1-git-send-email-herton@redhat.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org This change fixes a bug for a corner case where we have the the last release from a pty master/slave coming from a previously opened /dev/tty file. When this happens, the tty->driver_data can be stale, due to all ptmx or pts/N files having already been closed before (and thus the inode related to these files, which tty->driver_data points to, being already freed/destroyed). The fix here is to keep a reference on the opened master ptmx inode. We maintain the inode referenced until the final pty_unix98_shutdown, and only pass this inode to devpts_kill_index. Signed-off-by: Herton R. Krzesinski Cc: # 2.6.29+ --- drivers/tty/pty.c | 18 +++++++++++++++++- 1 file changed, 17 insertions(+), 1 deletion(-) v2: fixed patch changelog diff --git a/drivers/tty/pty.c b/drivers/tty/pty.c index a45660f..96016e5 100644 --- a/drivers/tty/pty.c +++ b/drivers/tty/pty.c @@ -681,7 +681,14 @@ static void pty_unix98_remove(struct tty_driver *driver, struct tty_struct *tty) /* this is called once with whichever end is closed last */ static void pty_unix98_shutdown(struct tty_struct *tty) { - devpts_kill_index(tty->driver_data, tty->index); + struct inode *ptmx_inode; + + if (tty->driver->subtype == PTY_TYPE_MASTER) + ptmx_inode = tty->driver_data; + else + ptmx_inode = tty->link->driver_data; + devpts_kill_index(ptmx_inode, tty->index); + iput(ptmx_inode); /* drop reference we acquired at ptmx_open */ } static const struct tty_operations ptm_unix98_ops = { @@ -773,6 +780,15 @@ static int ptmx_open(struct inode *inode, struct file *filp) set_bit(TTY_PTY_LOCK, &tty->flags); /* LOCK THE SLAVE */ tty->driver_data = inode; + /* + * In the case where all references to ptmx inode are dropped and we + * still have /dev/tty opened pointing to the master/slave pair (ptmx + * is closed/released before /dev/tty), we must make sure that the inode + * is still valid when we call the final pty_unix98_shutdown, thus we + * hold an additional reference to the ptmx inode + */ + ihold(inode); + tty_add_file(tty, filp); slave_inode = devpts_pty_new(inode, -- 2.4.3