From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756787Ab3BEUWr (ORCPT ); Tue, 5 Feb 2013 15:22:47 -0500 Received: from mailout39.mail01.mtsvc.net ([216.70.64.83]:60085 "EHLO n12.mail01.mtsvc.net" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1756737Ab3BEUWn (ORCPT ); Tue, 5 Feb 2013 15:22:43 -0500 From: Peter Hurley To: Greg Kroah-Hartman , Alan Cox , Jiri Slaby , Sasha Levin , Sebastian Andrzej Siewior Cc: linux-serial@vger.kernel.org, linux-kernel@vger.kernel.org, Ilya Zykov , Dave Jones , Peter Hurley Subject: [PATCH v3 08/23] tty: Halt both ldiscs concurrently Date: Tue, 5 Feb 2013 15:20:23 -0500 Message-Id: <1360095638-6624-9-git-send-email-peter@hurleysoftware.com> X-Mailer: git-send-email 1.8.1.2 In-Reply-To: <1360095638-6624-1-git-send-email-peter@hurleysoftware.com> References: <1355509370-5883-1-git-send-email-peter@hurleysoftware.com> <1360095638-6624-1-git-send-email-peter@hurleysoftware.com> X-Authenticated-User: 125194 peter@hurleysoftware.com X-MT-ID: 8fa290c2a27252aacf65dbc4a42f3ce3735fb2a4 X-MT-INTERNAL-ID: 8fa290c2a27252aacf65dbc4a42f3ce3735fb2a4 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org The pty driver does not obtain an ldisc reference to the linked tty when writing. When the ldiscs are sequentially halted, it is possible for one ldisc to be halted, and before the second ldisc can be halted, a concurrent write schedules buffer work on the first ldisc. This can lead to an access-after-free error when the scheduled buffer work starts on the closed ldisc. Prevent subsequent use after halt by performing each stage of the halt on both ttys. Signed-off-by: Peter Hurley --- drivers/tty/tty_ldisc.c | 38 +++++++++++++++++++++++++------------- 1 file changed, 25 insertions(+), 13 deletions(-) diff --git a/drivers/tty/tty_ldisc.c b/drivers/tty/tty_ldisc.c index 76a5741..8d3eec1 100644 --- a/drivers/tty/tty_ldisc.c +++ b/drivers/tty/tty_ldisc.c @@ -530,14 +530,17 @@ static int tty_ldisc_wait_idle(struct tty_struct *tty, long timeout) /** * tty_ldisc_halt - shut down the line discipline * @tty: tty device + * @o_tty: paired pty device (can be NULL) * @pending: returns true if work was scheduled when cancelled * (can be set to NULL) + * @o_pending: returns true if work was scheduled when cancelled + * (can be set to NULL) * @timeout: # of jiffies to wait for ldisc refs to be released * - * Shut down the line discipline and work queue for this tty device. - * The TTY_LDISC flag being cleared ensures no further references can - * be obtained while the delayed work queue halt ensures that no more - * data is fed to the ldisc. + * Shut down the line discipline and work queue for this tty device and + * its paired pty (if exists). Clearing the TTY_LDISC flag ensures + * no further references can be obtained while the work queue halt + * ensures that no more data is fed to the ldisc. * * Furthermore, guarantee that existing ldisc references have been * released, which in turn, guarantees that no future buffer work @@ -548,19 +551,32 @@ static int tty_ldisc_wait_idle(struct tty_struct *tty, long timeout) * flushed. */ -static int tty_ldisc_halt(struct tty_struct *tty, int *pending, long timeout) +static int tty_ldisc_halt(struct tty_struct *tty, struct tty_struct *o_tty, + int *pending, int *o_pending, long timeout) { - int scheduled, retval; + int scheduled, o_scheduled, retval; clear_bit(TTY_LDISC, &tty->flags); + if (o_tty) + clear_bit(TTY_LDISC, &o_tty->flags); + retval = tty_ldisc_wait_idle(tty, timeout); + if (!retval && o_tty) + retval = tty_ldisc_wait_idle(o_tty, timeout); if (retval) return retval; scheduled = cancel_work_sync(&tty->port->buf.work); set_bit(TTY_LDISC_HALTED, &tty->flags); + if (o_tty) { + o_scheduled = cancel_work_sync(&o_tty->port->buf.work); + set_bit(TTY_LDISC_HALTED, &o_tty->flags); + } + if (pending) *pending = scheduled; + if (o_tty && o_pending) + *o_pending = o_scheduled; return 0; } @@ -702,9 +718,7 @@ int tty_set_ldisc(struct tty_struct *tty, int ldisc) * parallel to the change and re-referencing the tty. */ - retval = tty_ldisc_halt(tty, &work, 5 * HZ); - if (o_tty) - tty_ldisc_halt(o_tty, &o_work, 0); + retval = tty_ldisc_halt(tty, o_tty, &work, &o_work, 5 * HZ); /* * Wait for ->hangup_work and ->buf.work handlers to terminate. @@ -965,12 +979,10 @@ void tty_ldisc_release(struct tty_struct *tty, struct tty_struct *o_tty) * race with the set_ldisc code path. */ - tty_ldisc_halt(tty, NULL, MAX_SCHEDULE_TIMEOUT); + tty_ldisc_halt(tty, o_tty, NULL, NULL, MAX_SCHEDULE_TIMEOUT); tty_ldisc_flush_works(tty); - if (o_tty) { - tty_ldisc_halt(o_tty, NULL, MAX_SCHEDULE_TIMEOUT); + if (o_tty) tty_ldisc_flush_works(o_tty); - } tty_lock_pair(tty, o_tty); /* This will need doing differently if we need to lock */ -- 1.8.1.2