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=-15.6 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,NICE_REPLY_A,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 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 F30E8C07E95 for ; Tue, 13 Jul 2021 16:16:31 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id D962461166 for ; Tue, 13 Jul 2021 16:16:31 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229902AbhGMQTU (ORCPT ); Tue, 13 Jul 2021 12:19:20 -0400 Received: from foss.arm.com ([217.140.110.172]:46492 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229604AbhGMQTT (ORCPT ); Tue, 13 Jul 2021 12:19:19 -0400 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 6E1DE6D; Tue, 13 Jul 2021 09:16:29 -0700 (PDT) Received: from [192.168.1.179] (unknown [172.31.20.19]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 228D33F7D8; Tue, 13 Jul 2021 09:16:28 -0700 (PDT) Subject: Re: [PATCH] drm/of: free the iterator object on failure To: Laurent Pinchart Cc: Daniel Vetter , David Airlie , Maarten Lankhorst , Maxime Ripard , Thomas Zimmermann , dri-devel@lists.freedesktop.org, linux-kernel@vger.kernel.org, Biju Das References: <20210712155758.48286-1-steven.price@arm.com> From: Steven Price Message-ID: <5c3db755-c3fb-dfe7-3d23-bbbcc81af3d8@arm.com> Date: Tue, 13 Jul 2021 17:16:16 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.11.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Language: en-GB Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 12/07/2021 22:55, Laurent Pinchart wrote: > Hi Steven, Hi Laurent, > On Mon, Jul 12, 2021 at 10:31:52PM +0100, Steven Price wrote: >> On 12/07/2021 17:50, Laurent Pinchart wrote: >>> On Mon, Jul 12, 2021 at 04:57:58PM +0100, Steven Price wrote: >>>> When bailing out due to the sanity check the iterator value needs to be >>>> freed because the early return prevents for_each_child_of_node() from >>>> doing the dereference itself. >>>> >>>> Fixes: 4ee48cc5586b ("drm: of: Fix double-free bug") >>> >>> I don't think the Fixes tag is correct, the issue was already present >>> before 4ee48cc5586b. The fix looks right though. >> >> I'm not sure quite what you mean by "already present". As I understand >> it the timeline was: >> >> 1. 6529007522de drm: of: Add drm_of_lvds_get_dual_link_pixel_order >> The function was originally added. This made the mistake twice of >> calling of_node_put() on the wrong variable (remote_port rather than >> endpoint). > > Correct. > >> 2. 4ee48cc5586b drm: of: Fix double-free bug >> One of the of_node_put() calls was removed as it was a double-free. >> This left the first incorrect of_node_put() in place, and the second >> is now a straight leak. > > That's right, but this commit didn't introduce the leak, it was already > there in 6529007522de (in addition to the double-free). Ah, I see what you mean. My thought process was that the original comment had the bug "using the wrong variable", and (2) (partially) fixed that but in the process introduced a new bug (a memory leak). But I guess technically the memory leak was there from the beginning. The other reason I referenced (2) in the Fixes line is because this patch depends on patch (2), whereas it won't apply cleanly without. However I don't think it really matters either way: (2) has already been backported, and either way this needs fixing if either (1) or (2) are present. Would you like me to resend with a "Fixes: 6529007522de drm: of: Add drm_of_lvds_get_dual_link_pixel_order", or are you happy to just fix this up when merging? Thanks, Steve >> 3. b557a5f8da57 drm/of: free the right object >> This (correctly) fixes the first of_node_put() to free endpoint. And >> the post from Daniel was what caused me to look. >> >> 4. This patch >> Reintroduces the of_node_put() removed in (2) but putting endpoint >> rather than remote_port. >> >> I've put (2) in the Fixes line as this patch is fixing the leak >> introduced by that patch, but that in itself was of course 'fixing' the >> double free of the original patch. >> >>>> Signed-off-by: Steven Price >>>> --- >>>> drivers/gpu/drm/drm_of.c | 4 +++- >>>> 1 file changed, 3 insertions(+), 1 deletion(-) >>>> >>>> Daniel's email[1] made me take a look at this function and it appears >>>> that for_each_child_of_node()'s interface had caused a bad bug fix due >>>> to the hidden reference counting in the iterator. >>>> >>>> [1] https://lore.kernel.org/r/YOxQ5TbkNrqCGBDJ%40phenom.ffwll.local >>>> >>>> diff --git a/drivers/gpu/drm/drm_of.c b/drivers/gpu/drm/drm_of.c >>>> index 197c57477344..997b8827fed2 100644 >>>> --- a/drivers/gpu/drm/drm_of.c >>>> +++ b/drivers/gpu/drm/drm_of.c >>>> @@ -331,8 +331,10 @@ static int drm_of_lvds_get_remote_pixels_type( >>>> * configurations by passing the endpoints explicitly to >>>> * drm_of_lvds_get_dual_link_pixel_order(). >>>> */ >>>> - if (!current_pt || pixels_type != current_pt) >>>> + if (!current_pt || pixels_type != current_pt) { >>>> + of_node_put(endpoint); >>>> return -EINVAL; >>>> + } >>>> } >>>> >>>> return pixels_type; >