Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933461AbbELR7K (ORCPT ); Tue, 12 May 2015 13:59:10 -0400 Received: from mail-wg0-f53.google.com ([74.125.82.53]:33544 "EHLO mail-wg0-f53.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932788AbbELR7G (ORCPT ); Tue, 12 May 2015 13:59:06 -0400 From: "Grygorii.Strashko@linaro.org" X-Google-Original-From: "Grygorii.Strashko@linaro.org" Message-ID: <55523F67.9040100@linaro.org> Date: Tue, 12 May 2015 20:59:03 +0300 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.6.0 MIME-Version: 1.0 To: Dmitry Torokhov CC: Geert Uytterhoeven , Geert Uytterhoeven , "Rafael J. Wysocki" , Kevin Hilman , Santosh Shilimkar , Linux PM list , "linux-kernel@vger.kernel.org" Subject: Re: [PATCH] PM / clock_ops: Fix clock error check in __pm_clk_add() 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> In-Reply-To: <20150512164254.GA20725@dtor-ws> Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2986 Lines: 80 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 let it be. -- regards, -grygorii -- 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/