From mboxrd@z Thu Jan 1 00:00:00 1970 From: Dmitry Torokhov Subject: Re: [PATCH] PM / clock_ops: Fix clock error check in __pm_clk_add() Date: Tue, 12 May 2015 11:07:33 -0700 Message-ID: <20150512180733.GB20725@dtor-ws> References: <1431074863-19124-1-git-send-email-geert+renesas@glider.be> <20150508171955.GA38039@dtor-ws> <20150508210557.GC38039@dtor-ws> <5552065B.1020501@linaro.org> <20150512164254.GA20725@dtor-ws> <55523F67.9040100@linaro.org> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Received: from mail-ie0-f182.google.com ([209.85.223.182]:35776 "EHLO mail-ie0-f182.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932639AbbELSHi (ORCPT ); Tue, 12 May 2015 14:07:38 -0400 Content-Disposition: inline In-Reply-To: <55523F67.9040100@linaro.org> Sender: linux-pm-owner@vger.kernel.org List-Id: linux-pm@vger.kernel.org To: "Grygorii.Strashko@linaro.org" Cc: Geert Uytterhoeven , Geert Uytterhoeven , "Rafael J. Wysocki" , Kevin Hilman , Santosh Shilimkar , Linux PM list , "linux-kernel@vger.kernel.org" On Tue, May 12, 2015 at 08:59:03PM +0300, Grygorii.Strashko@linaro.org wrote: > On 05/12/2015 07:42 PM, Dmitry Torokhov wrote: > > On Tue, May 12, 2015 at 04:55:39PM +0300, Grygorii.Strashko@linaro.org wrote: > >> On 05/09/2015 12:05 AM, Dmitry Torokhov wrote: > >>> On Fri, May 08, 2015 at 10:59:04PM +0200, Geert Uytterhoeven wrote: > >>>> On Fri, May 8, 2015 at 7:19 PM, Dmitry Torokhov > >>>> wrote: > >>>>> On Fri, May 08, 2015 at 10:47:43AM +0200, Geert Uytterhoeven wrote: > >>>>>> In the final iteration of commit 245bd6f6af8a62a2 ("PM / clock_ops: Add > >>>>>> pm_clk_add_clk()"), a refcount increment was added by Grygorii Strashko. > >>>>>> However, the accompanying IS_ERR() check operates on the wrong clock > >>>>>> pointer, which is always zero at this point, i.e. not an error. > >>>>>> This may lead to a NULL pointer dereference later, when __clk_get() > >>>>>> tries to dereference an error pointer. > >>>>>> > >>>>>> Check the passed clock pointer instead to fix this. > >>>>> > >>>>> Frankly I would remove the check altogether. Why do we only check for > >>>>> IS_ERR and not NULL or otherwise validate the pointer? The clk is passed > >>>> > >>>> __clk_get() does the NULL check. > >>> > >>> No, not really. It _handles_ clk being NULL and returns "everything is > >>> fine". In any case it is __clk_get's decision what to do. > >>> > >>> I dislike gratuitous checks of arguments passed in. Instead of relying > >>> on APIs refusing grabage we better not pass garbage to these APIs in the > >>> first place. So I'd change it to trust that we are given a usable > >>> pointer and simply do: > >>> > >>> if (!__clk_get(clk)) { > >>> kfree(ce); > >>> return -ENOENTl > >>> } > >> > >> Not sure this is right thing to do, because this API initially > >> was intended to be used as below [1]: > >> clk = of_clk_get(dev->of_node, i)); > >> ret = pm_clk_add_clk(dev, clk); > >> clk_put(clk); > >> > >> and of_clk_get may return ERR_PTR(). > > > > Jeez, that sequence was not meant to be taken literally, it does miss > > error handling completely. If you notice the majority of users of this > > API do something like below: > > > > i = 0; > > while ((clk = of_clk_get(dev->of_node, i++)) && !IS_ERR(clk)) { > > dev_dbg(dev, "adding clock '%s' to list of PM clocks\n", > > __clk_get_name(clk)); > > error = pm_clk_add_clk(dev, clk); > > clk_put(clk); > > if (error) { > > dev_err(dev, "pm_clk_add_clk failed %d\n", error); > > pm_clk_destroy(dev); > > return error; > > } > > } > > > > i.e. it already validates clk pointer before passing it on since it > > needs to know when to stop iterating. > > np. It's just my opinion - if you agree that code will just crash > in case of passing invalid @clk argument (in worst case:) > > int __clk_get(struct clk *clk) > { > struct clk_core *core = !clk ? NULL : clk->core; > ^^^ here Yes, it will crash if you pass invalid pointer here, be it ERR_PTR-encoded value, or, for example, 0x1, or maybe (void *)random_32(). The latter will probably not crash right away, but cause some random damage that will manifest later. Thanks. -- Dmitry