From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755321AbcC1SVL (ORCPT ); Mon, 28 Mar 2016 14:21:11 -0400 Received: from [198.137.202.9] ([198.137.202.9]:52215 "EHLO bombadil.infradead.org" rhost-flags-FAIL-FAIL-OK-OK) by vger.kernel.org with ESMTP id S1753852AbcC1SVH (ORCPT ); Mon, 28 Mar 2016 14:21:07 -0400 Date: Mon, 28 Mar 2016 11:18:05 -0700 From: Darren Hart To: Colin King , Rafael Wysocki Cc: Sujith Thomas , platform-driver-x86@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] intel_menlow: set cdev after null device check to avoid null pointer dereference Message-ID: <20160328181805.GC26086@dvhart-mobl5.amr.corp.intel.com> References: <1459181919-13825-1-git-send-email-colin.king@canonical.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1459181919-13825-1-git-send-email-colin.king@canonical.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 Mon, Mar 28, 2016 at 05:18:39PM +0100, Colin King wrote: > From: Colin Ian King > > intel_menlow_memory_remove sanity checks to see if device is null, however, > this check is performed after we have already passed device into a call > to acpi_driver_data. If device is null, then acpi_driver_data will produce > a null pointer dereference on device. The correct action is to sanity check > device, then assign cdev, then check if cdev is null. > Hrm, looking at this locally, that all makes sense. Taking a step back however, I notice that intel_menlow_memory_remove is an ops function pointer inside the acpi_driver structure itself, which is called from acpi_device_remove() (and probe) (drivers/acpi/bus.c). This already verifies acpi_driver is not NULL and can't get acpi_driver if acpi_device is NULL. So unless there is some other use case for this callback I'm unaware of (certainly possible) it appears to be totally redundant to do this checking here. +Rafael - is there a best practices for these acpi callbacks with respect to input validation? > Signed-off-by: Colin Ian King > --- > drivers/platform/x86/intel_menlow.c | 8 ++++++-- > 1 file changed, 6 insertions(+), 2 deletions(-) > > diff --git a/drivers/platform/x86/intel_menlow.c b/drivers/platform/x86/intel_menlow.c > index 0a919d8..185a1bd 100644 > --- a/drivers/platform/x86/intel_menlow.c > +++ b/drivers/platform/x86/intel_menlow.c > @@ -196,9 +196,13 @@ static int intel_menlow_memory_add(struct acpi_device *device) > > static int intel_menlow_memory_remove(struct acpi_device *device) > { > - struct thermal_cooling_device *cdev = acpi_driver_data(device); > + struct thermal_cooling_device *cdev; > + > + if (!device) > + return -EINVAL; > > - if (!device || !cdev) > + cdev = acpi_driver_data(device); > + if (!cdev) > return -EINVAL; > > sysfs_remove_link(&device->dev.kobj, "thermal_cooling"); > -- > 2.7.4 > > -- Darren Hart Intel Open Source Technology Center