Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S964978AbbEMAch (ORCPT ); Tue, 12 May 2015 20:32:37 -0400 Received: from mail-ie0-f179.google.com ([209.85.223.179]:36842 "EHLO mail-ie0-f179.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S964895AbbEMAce (ORCPT ); Tue, 12 May 2015 20:32:34 -0400 Date: Tue, 12 May 2015 17:32:29 -0700 From: Dmitry Torokhov To: "Rafael J. Wysocki" Cc: "Grygorii.Strashko@linaro.org" , Geert Uytterhoeven , Geert Uytterhoeven , 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() Message-ID: <20150513003229.GH20725@dtor-ws> References: <1431074863-19124-1-git-send-email-geert+renesas@glider.be> <55523F67.9040100@linaro.org> <20150512180733.GB20725@dtor-ws> <2196912.kiJqTqq7oO@vostro.rjw.lan> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <2196912.kiJqTqq7oO@vostro.rjw.lan> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 4541 Lines: 104 On Wed, May 13, 2015 at 02:22:50AM +0200, Rafael J. Wysocki wrote: > On Tuesday, May 12, 2015 11:07:33 AM Dmitry Torokhov wrote: > > 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. > > Oh well. Shouldn't we actually do: > > int __clk_get(struct clk *clk) > { > struct clk_core *core = IS_ERR_OR_NULL(clk) ? NULL : clk->core; > > and remove the check from __pm_clk_add() at the same time? > > Knowingly crashing on an error encoded as a pointer is kind of disgusting to me > and the difference between that and a random invalid pointer is that poeple who > pass error values encoded as pointers up the stack usually expect them to be > handled cleanly. I think the operative work here is "up". Returning ERR_PTR-encoded pointer is fine, checking it fine as well, blindly passing it *down* into a random API is not fine and we should not try to accommodate this. Thanks. -- Dmitry -- 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/