From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754684Ab2DCNQB (ORCPT ); Tue, 3 Apr 2012 09:16:01 -0400 Received: from e23smtp05.au.ibm.com ([202.81.31.147]:46398 "EHLO e23smtp05.au.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754367Ab2DCNQA (ORCPT ); Tue, 3 Apr 2012 09:16:00 -0400 Message-ID: <4F7AF7FE.5070307@linux.vnet.ibm.com> Date: Tue, 03 Apr 2012 18:45:42 +0530 From: "Srivatsa S. Bhat" User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:11.0) Gecko/20120329 Thunderbird/11.0.1 MIME-Version: 1.0 To: lenb@kernel.org CC: Daniel Lezcano , khilman@ti.com, deepthi@linux.vnet.ibm.com, g.trinabh@gmail.com, arjan@infradead.org, linux-kernel@vger.kernel.org, linux-pm@vger.kernel.org, amit.kucheria@linaro.org Subject: Re: [PATCH] cpuidle: Avoid possible NULL pointer dereference in __cpuidle_register_device() References: <20120402144422.11574.83174.stgit@srivatsabhat.in.ibm.com> <4F79FE8F.1040708@linaro.org> <4F7AE42F.9080800@linux.vnet.ibm.com> <4F7AE831.507@linaro.org> In-Reply-To: <4F7AE831.507@linaro.org> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit x-cbid: 12040303-1396-0000-0000-000000E8F5A4 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 04/03/2012 05:38 PM, Daniel Lezcano wrote: > On 04/03/2012 01:51 PM, Srivatsa S. Bhat wrote: >> On 04/03/2012 01:01 AM, Daniel Lezcano wrote: >> >>> On 04/02/2012 04:44 PM, Srivatsa S. Bhat wrote: >>>> In __cpuidle_register_device(), "dev->cpu" is used before checking if >>>> dev is >>>> non-NULL. Fix it. >>>> >>>> Signed-off-by: Srivatsa S. Bhat >>>> --- >>> >>> That should be fixed at the caller level. Usually, static function does >>> not check the function parameters, it is up to the exported function to >>> do that. It is supposed the static functions are called with valid >>> parameters. >>> >> >> >> Ok, good point! I hadn't thought about that.. I just happened to notice >> that in __cpuidle_register_device(), the dev == NULL check is performed >> _after_ dereferencing it, which made the check useless. So I tried to >> fix that within that function. But thanks for pointing out the >> semantics.. >> >>> There are two callers for __cpuidle_register_device: >>> * cpuidle_register_device >>> * cpuidle_enable_device >>> >>> Both of them do not check 'dev' is a valid parameter. They should as >>> they are exported and could be used by an external module. IMHO, BUG_ON >>> could be used here if dev == NULL. >>> >> >> >> BUG_ON? That would crash the system.. which might be unnecessary.. > > Mmh, yes, I agree. never mind. > >> How about checking if dev == NULL in the 2 callers like you suggested >> and returning -EINVAL if dev is indeed NULL? >> (And of course no checks for dev == NULL in __cpuidle_register_device). > > Ok for me. > Great! Here is the updated patch: --- From: Srivatsa S. Bhat Subject: [PATCH v2] cpuidle: Add checks to avoid NULL pointer dereference The existing check for dev == NULL in __cpuidle_register_device() is rendered useless because dev is dereferenced before the check itself. Moreover, correctly speaking, it is the job of the callers of this function, i.e., cpuidle_register_device() & cpuidle_enable_device() (which also happen to be exported functions) to ensure that __cpuidle_register_device() is called with a non-NULL dev. So add the necessary dev == NULL checks in the two callers and remove the (useless) check from __cpuidle_register_device(). Signed-off-by: Srivatsa S. Bhat --- drivers/cpuidle/cpuidle.c | 8 ++++++-- 1 files changed, 6 insertions(+), 2 deletions(-) diff --git a/drivers/cpuidle/cpuidle.c b/drivers/cpuidle/cpuidle.c index 87411ce..eae2f11 100644 --- a/drivers/cpuidle/cpuidle.c +++ b/drivers/cpuidle/cpuidle.c @@ -291,6 +291,9 @@ int cpuidle_enable_device(struct cpuidle_device *dev) int ret, i; struct cpuidle_driver *drv = cpuidle_get_driver(); + if (!dev) + return -EINVAL; + if (dev->enabled) return 0; if (!drv || !cpuidle_curr_governor) @@ -375,8 +378,6 @@ static int __cpuidle_register_device(struct cpuidle_device *dev) struct device *cpu_dev = get_cpu_device((unsigned long)dev->cpu); struct cpuidle_driver *cpuidle_driver = cpuidle_get_driver(); - if (!dev) - return -EINVAL; if (!try_module_get(cpuidle_driver->owner)) return -EINVAL; @@ -401,6 +402,9 @@ int cpuidle_register_device(struct cpuidle_device *dev) { int ret; + if (!dev) + return -EINVAL; + mutex_lock(&cpuidle_lock); if ((ret = __cpuidle_register_device(dev))) {