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=-15.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER, INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED autolearn=unavailable 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 8184AC07E99 for ; Mon, 12 Jul 2021 21:56:26 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 5DAC06117A for ; Mon, 12 Jul 2021 21:56:26 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230122AbhGLV7N (ORCPT ); Mon, 12 Jul 2021 17:59:13 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:46610 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229571AbhGLV7M (ORCPT ); Mon, 12 Jul 2021 17:59:12 -0400 Received: from perceval.ideasonboard.com (perceval.ideasonboard.com [IPv6:2001:4b98:dc2:55:216:3eff:fef7:d647]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 78B67C0613DD for ; Mon, 12 Jul 2021 14:56:23 -0700 (PDT) Received: from pendragon.ideasonboard.com (62-78-145-57.bb.dnainternet.fi [62.78.145.57]) by perceval.ideasonboard.com (Postfix) with ESMTPSA id BA1B2CC; Mon, 12 Jul 2021 23:56:19 +0200 (CEST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=ideasonboard.com; s=mail; t=1626126979; bh=+d8YmarxqieQLIrWWfUj888qjlOdg83gqF6/rmhuzng=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=sKGPXvlp5fN9Nh+8sOS1EV8yWEPE9bwH7owAA3bsoKZncpHSvV6TpGpoRfDXh6ksL /cTysgd1UwzTaxWwxzAKusz0Eronc0bTFgtv0oh7wqRuGf7x1JKJG4mA44B3/9p0ob l8Yl59ETdw/3+eejNTN39IkglMgK2w742R2Tyv1Q= Date: Tue, 13 Jul 2021 00:55:33 +0300 From: Laurent Pinchart To: Steven Price Cc: Daniel Vetter , David Airlie , Maarten Lankhorst , Maxime Ripard , Thomas Zimmermann , dri-devel@lists.freedesktop.org, linux-kernel@vger.kernel.org, Biju Das Subject: Re: [PATCH] drm/of: free the iterator object on failure Message-ID: References: <20210712155758.48286-1-steven.price@arm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Steven, 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). > 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; -- Regards, Laurent Pinchart