From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S934467Ab3AOW5o (ORCPT ); Tue, 15 Jan 2013 17:57:44 -0500 Received: from mail.kernel.org ([198.145.19.201]:48644 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S934446Ab3AOW5j (ORCPT ); Tue, 15 Jan 2013 17:57:39 -0500 From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org, stable@vger.kernel.org Cc: Greg Kroah-Hartman , alan@lxorguk.ukuu.org.uk, Ian Abbott , =?ISO-8859-15?q?=C3=89ric=20Piel?= Subject: [ 50/71] staging: comedi: comedi_test: fix race when cancelling command Date: Tue, 15 Jan 2013 14:54:47 -0800 Message-Id: <20130115225344.018333401@linuxfoundation.org> X-Mailer: git-send-email 1.8.1.336.g94702dd In-Reply-To: <20130115225340.367496998@linuxfoundation.org> References: <20130115225340.367496998@linuxfoundation.org> User-Agent: quilt/0.60-1 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 3.0-stable review patch. If anyone has any objections, please let me know. ------------------ From: Ian Abbott commit c0729eeefdcd76db338f635162bf0739fd2c5f6f upstream. Éric Piel reported a kernel oops in the "comedi_test" module. It was a NULL pointer dereference within `waveform_ai_interrupt()` (actually a timer function) that sometimes occurred when a running asynchronous command is cancelled (either by the `COMEDI_CANCEL` ioctl or by closing the device file). This seems to be a race between the caller of `waveform_ai_cancel()` which on return from that function goes and tears down the running command, and the timer function which uses the command. In particular, `async->cmd.chanlist` gets freed (and the pointer set to NULL) by `do_become_nonbusy()` in "comedi_fops.c" but a previously scheduled `waveform_ai_interrupt()` timer function will dereference that pointer regardless, leading to the oops. Fix it by replacing the `del_timer()` call in `waveform_ai_cancel()` with `del_timer_sync()`. Signed-off-by: Ian Abbott Reported-by: Éric Piel Signed-off-by: Greg Kroah-Hartman --- drivers/staging/comedi/drivers/comedi_test.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) --- a/drivers/staging/comedi/drivers/comedi_test.c +++ b/drivers/staging/comedi/drivers/comedi_test.c @@ -461,7 +461,7 @@ static int waveform_ai_cancel(struct com struct comedi_subdevice *s) { devpriv->timer_running = 0; - del_timer(&devpriv->timer); + del_timer_sync(&devpriv->timer); return 0; }