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=-10.0 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_HELO_NONE,SPF_PASS 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 4336AC433E0 for ; Sun, 19 Jul 2020 13:39:58 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 1EC3922BEF for ; Sun, 19 Jul 2020 13:39:58 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1725988AbgGSNj5 (ORCPT ); Sun, 19 Jul 2020 09:39:57 -0400 Received: from asavdk4.altibox.net ([109.247.116.15]:42358 "EHLO asavdk4.altibox.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726038AbgGSNj5 (ORCPT ); Sun, 19 Jul 2020 09:39:57 -0400 Received: from ravnborg.org (unknown [188.228.123.71]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by asavdk4.altibox.net (Postfix) with ESMTPS id DFA79804DA; Sun, 19 Jul 2020 15:39:53 +0200 (CEST) Date: Sun, 19 Jul 2020 15:39:52 +0200 From: Sam Ravnborg To: Steve Cohen Cc: adelva@google.com, linux-arm-msm@vger.kernel.org, dri-devel@lists.freedesktop.org, pdhaval@codeaurora.org, seanpaul@chromium.org, freedreno@lists.freedesktop.org Subject: Re: [PATCH] drm: hold gem reference until object is no longer accessed Message-ID: <20200719133952.GA40646@ravnborg.org> References: <1594420826-4897-1-git-send-email-cohens@codeaurora.org> <20200716202952.GF2254583@ravnborg.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200716202952.GF2254583@ravnborg.org> X-CMAE-Score: 0 X-CMAE-Analysis: v=2.3 cv=aP3eV41m c=1 sm=1 tr=0 a=S6zTFyMACwkrwXSdXUNehg==:117 a=S6zTFyMACwkrwXSdXUNehg==:17 a=kj9zAlcOel0A:10 a=LpQP-O61AAAA:8 a=7gkXJVJtAAAA:8 a=e5mUnYsNAAAA:8 a=T2CN4U7q9iM9Igr8EeIA:9 a=CjuIK1q_8ugA:10 a=pioyyrs4ZptJ924tMmac:22 a=E9Po1WZjFZOl8hwRPBS3:22 a=Vxmtnl_E_bksehYqCbjh:22 Sender: linux-arm-msm-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-arm-msm@vger.kernel.org Hi Steve. On Thu, Jul 16, 2020 at 10:29:52PM +0200, Sam Ravnborg wrote: > Hi Steve and others. > > On Fri, Jul 10, 2020 at 06:40:26PM -0400, Steve Cohen wrote: > > BUG: KASAN: use-after-free in drm_gem_open_ioctl > > > > There is potential for use-after-free here if the GEM object > > handle is closed between the idr lookup and retrieving the size > > from the object since a local reference is not being held at that > > point. Hold the local reference while the object can still be > > accessed to resolve this. > > > > Signed-off-by: Steve Cohen > > --- > > drivers/gpu/drm/drm_gem.c | 7 ++++--- > > 1 file changed, 4 insertions(+), 3 deletions(-) > > > > diff --git a/drivers/gpu/drm/drm_gem.c b/drivers/gpu/drm/drm_gem.c > > index 7bf628e..4b2891c 100644 > > --- a/drivers/gpu/drm/drm_gem.c > > +++ b/drivers/gpu/drm/drm_gem.c > > @@ -898,14 +898,15 @@ drm_gem_open_ioctl(struct drm_device *dev, void *data, > > > > /* drm_gem_handle_create_tail unlocks dev->object_name_lock. */ > > ret = drm_gem_handle_create_tail(file_priv, obj, &handle); > > - drm_gem_object_put_unlocked(obj); > > if (ret) > > - return ret; > > + goto out; > > > > args->handle = handle; > > args->size = obj->size; > > > > - return 0; > > +out: > > + drm_gem_object_put_unlocked(obj); > > + return ret; > > Lookign at drm_gem_flink_ioctl() that is implmented just above this > functions there are two things that I noted. > > 1) In drm_gem_flink_ioctl() the label is named "err:" - and my OCD likes > that similar labels have the same name. > > 2) The function takes the object_name_lock but fails to release it in > the error situation. Daniel pointed out on irc that drm_gem_handle_create_tail releases the lock. If I had read the comment I would have noticed too - sigh. With the label name fixed to "err:" like used in the function above: Reviewed-by: Sam Ravnborg Please re-submit. Sam > > Danile Vetter updated the locking in > 20228c447846da9399ead53fdbbc8ab69b47788a ("drm/gem: completely close gem_open vs. gem_close races") > > but I failed to follow it all. > > Sam > > > } > > > > /** > > -- > > The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum, > > a Linux Foundation Collaborative Project > > > > _______________________________________________ > > dri-devel mailing list > > dri-devel@lists.freedesktop.org > > https://lists.freedesktop.org/mailman/listinfo/dri-devel > _______________________________________________ > dri-devel mailing list > dri-devel@lists.freedesktop.org > https://lists.freedesktop.org/mailman/listinfo/dri-devel