Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753064AbbDNGte (ORCPT ); Tue, 14 Apr 2015 02:49:34 -0400 Received: from mail-wi0-f179.google.com ([209.85.212.179]:37803 "EHLO mail-wi0-f179.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752815AbbDNGtT (ORCPT ); Tue, 14 Apr 2015 02:49:19 -0400 Date: Tue, 14 Apr 2015 08:50:01 +0200 From: Olivier Sobrie To: NeilBrown Cc: "David S. Miller" , Jan Dumon , linux-usb@vger.kernel.org, netdev@vger.kernel.org, linux-kernel@vger.kernel.org, GTA04 owners Subject: Re: [PATCH] hso: fix refcnt leak in recent patch. Message-ID: <20150414065001.GA23791@thinkoso.home> Reply-To: Olivier Sobrie References: <20150414093634.4fe24ba3@notabene.brown> <20150414110303.66edcfee@notabene.brown> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20150414110303.66edcfee@notabene.brown> X-PGP-Key: http://olivier.sobrie.be/pgp/public.key User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3949 Lines: 123 Hello Neil, On Tue, Apr 14, 2015 at 11:03:03AM +1000, NeilBrown wrote: > On Tue, 14 Apr 2015 09:36:34 +1000 NeilBrown wrote: > > > > > > > Prior to > > commit 29bd3bc1194c624ce863cab2a7da9bc1f0c3b47b > > hso: fix crash when device disappears while serial port is open > > > > hso_serial_open would always kref_get(&serial->parent->ref) before > > returning zero. > > Since that commit, it only calls kref_get when returning 0 if > > serial->port.count was zero. > > > > This results in calls to > > kref_put(&serial->parent->ref, hso_serial_ref_free); > > > > after hso_serial_ref_free has been called, which dereferences a freed > > pointer. > > > > This patch adds the missing kref_get(). > > > > Fixes: commit 29bd3bc1194c624ce863cab2a7da9bc1f0c3b47b > > Cc: stable@vger.kernel.org (v4.0) > > Cc: Olivier Sobrie > > Signed-off-by: NeilBrown > > > > diff --git a/drivers/net/usb/hso.c b/drivers/net/usb/hso.c > > index 75befc1bd816..6848fc903340 100644 > > --- a/drivers/net/usb/hso.c > > +++ b/drivers/net/usb/hso.c > > @@ -1299,6 +1299,7 @@ static int hso_serial_open(struct tty_struct *tty, struct file *filp) > > } > > } else { > > D1("Port was already open"); > > + kref_get(&serial->parent->ref); > > } > > > > usb_autopm_put_interface(serial->parent->interface); > > > Sorry - that was wrong. > I'm getting crashes which strongly suggest the kref_put is being called extra > times, but I misunderstood the code and was hasty. > > Maybe this instead? Indeed, if I undestand correctly the code in tty_io.c, cleanup() method is also called when the open fails while kref_get is only done if the open succeeds. Sorry for that mess. I assume you get that crash when hso_start_serial_device() returns an error? At first sight, the patch below looks good to me. I'll test it in the next days. Thank you, Olivier > > Thanks, > NeilBrown > > From: NeilBrown > Date: Tue, 14 Apr 2015 09:33:03 +1000 > Subject: [PATCH] hso: fix refcnt leak in recent patch. > > Prior to > commit 29bd3bc1194c624ce863cab2a7da9bc1f0c3b47b > hso: fix crash when device disappears while serial port is open > > a kref_get on serial->parent->ref would be taken on each open, > and it would be kref_put on each close. > > Now the kref_put happens when the tty_struct is finally put (via > the 'cleanup') providing tty->driver_data has been set. > So the kref_get must be called exact once when tty->driver_data is > set. > > With the current code, if the first open fails the kref_get() is never > called, but the kref_put() is called, leaving to a crash. > > So change the kref_get call to happen exactly when ->driver_data is > changed from NULL to non-NULL. > > Fixes: commit 29bd3bc1194c624ce863cab2a7da9bc1f0c3b47b > Cc: stable@vger.kernel.org (v4.0) > Cc: Olivier Sobrie > Signed-off-by: NeilBrown > > diff --git a/drivers/net/usb/hso.c b/drivers/net/usb/hso.c > index 75befc1bd816..17fd3820263a 100644 > --- a/drivers/net/usb/hso.c > +++ b/drivers/net/usb/hso.c > @@ -1278,6 +1278,8 @@ static int hso_serial_open(struct tty_struct *tty, struct file *filp) > D1("Opening %d", serial->minor); > > /* setup */ > + if (tty->driver_data == NULL) > + kref_get(&serial->parent->ref); > tty->driver_data = serial; > tty_port_tty_set(&serial->port, tty); > > @@ -1294,8 +1296,6 @@ static int hso_serial_open(struct tty_struct *tty, struct file *filp) > if (result) { > hso_stop_serial_device(serial->parent); > serial->port.count--; > - } else { > - kref_get(&serial->parent->ref); > } > } else { > D1("Port was already open"); -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/