From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-8.5 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_PASS,USER_AGENT_MUTT autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 94FE7C04EB8 for ; Tue, 4 Dec 2018 14:36:42 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 6522D20672 for ; Tue, 4 Dec 2018 14:36:42 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 6522D20672 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=hofr.at Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726559AbeLDOgl (ORCPT ); Tue, 4 Dec 2018 09:36:41 -0500 Received: from 178.115.242.59.static.drei.at ([178.115.242.59]:37945 "EHLO mail.osadl.at" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725910AbeLDOgl (ORCPT ); Tue, 4 Dec 2018 09:36:41 -0500 Received: by mail.osadl.at (Postfix, from userid 1001) id 00E435C0FF8; Tue, 4 Dec 2018 14:36:00 +0000 (UTC) Date: Tue, 4 Dec 2018 15:36:00 +0100 From: Nicholas Mc Guire To: Peter Rosin Cc: Nicholas Mc Guire , Wolfram Sang , "linux-i2c@vger.kernel.org" , "linux-kernel@vger.kernel.org" Subject: Re: [PATCH] i2c: mux: demux-pinctrl: handle failure case of devm_kstrdup() Message-ID: <20181204143600.GB16001@osadl.at> References: <1543658470-20887-1-git-send-email-hofrat@osadl.org> <37b8709c-0b58-7bc9-22c5-e01953593d06@axentia.se> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <37b8709c-0b58-7bc9-22c5-e01953593d06@axentia.se> User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Dec 04, 2018 at 02:11:33PM +0000, Peter Rosin wrote: > Ho hmm. Had another look at this patch, or rather, the context of the > patch so not really related, but... > > On 2018-12-01 11:01, Nicholas Mc Guire wrote: > > devm_kstrdup() may return NULL if internal allocation failed. > > Thus using name, value is unsafe without being checked. As > > i2c_demux_pinctrl_probe() can return -ENOMEM in other cases > > a dev_err() message is included to make the failure location > > clear. > > > > Signed-off-by: Nicholas Mc Guire > > Fixes: e35478eac030 ("i2c: mux: demux-pinctrl: run properly with multiple instances") > > --- > > > > Problem located with experimental coccinelle script > > > > Q: The use of devm_kstrdup() seems a bit odd while technically not wrong, > > personally I think devm_kasprintf() would be more suitable here. > > > > Patch was compile tested with: multi_v7_defconfig > > (implies I2C_DEMUX_PINCTRL=y) > > > > Patch is against 4.20-rc4 (localversion-next is next-20181130) > > > > drivers/i2c/muxes/i2c-demux-pinctrl.c | 6 ++++++ > > 1 file changed, 6 insertions(+) > > > > diff --git a/drivers/i2c/muxes/i2c-demux-pinctrl.c b/drivers/i2c/muxes/i2c-demux-pinctrl.c > > index 035032e..c466999 100644 > > --- a/drivers/i2c/muxes/i2c-demux-pinctrl.c > > +++ b/drivers/i2c/muxes/i2c-demux-pinctrl.c > > @@ -244,6 +244,12 @@ static int i2c_demux_pinctrl_probe(struct platform_device *pdev) > > > > props[i].name = devm_kstrdup(&pdev->dev, "status", GFP_KERNEL); > > props[i].value = devm_kstrdup(&pdev->dev, "ok", GFP_KERNEL); > > It seemed very dubious to use devm_kstrdup here, since > yup - which is where the question in the initial pach came from I felt that this should better be a devm_kasprint() - I did not understand why it was kstrdup here in the first place - technically it is not wrong though as the source is not RO so it will allocate and copy the original string and thus effectively it behaves like devm_kasprintf > 1. if the consumer is not freeing the strings it would be sufficient with just > props[i].name = "status"; > props[i].value = "ok"; > > 2. if the consumer is freeing the strings, it is very bad to free them twice > which is what happens with the devm_ prefix. Why would it be freed twice ? the pointer returned is a seperately allocated objects ? that needs to be indepdently freed (this is not the devm_kstrdup_const() case) > > So, there is no case, AFAICT, where it is sane to use devm_kstrdup. I think the only technical difference between devm_kstrdup and devm_kasprintf is effectively a memcpy vs vsnprintf - so here I think devm_kasprintf would also be the more suitable call to use. thx! hofrat > > Therefore I had a look at the code, and to me it seems as if the consumer > very much frees the strings, which means that we are in case 2, and that > the above should be ordinary kstrdup calls. > > Am I missing something? > > Cheers, > Peter > > > + if (!props[i].name || !props[i].value) { > > + dev_err(&pdev->dev, > > + "chan %d name, value allocation failed\n", i); > > + err = -ENOMEM; > > + goto err_rollback; > > + } > > props[i].length = 3; > > > > of_changeset_init(&priv->chan[i].chgset); > > >