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 Received: from gabe.freedesktop.org (gabe.freedesktop.org [131.252.210.177]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id D21B9C77B7A for ; Wed, 31 May 2023 12:05:40 +0000 (UTC) Received: from gabe.freedesktop.org (localhost [127.0.0.1]) by gabe.freedesktop.org (Postfix) with ESMTP id 90A3B10E0BE; Wed, 31 May 2023 12:05:39 +0000 (UTC) Received: from dfw.source.kernel.org (dfw.source.kernel.org [139.178.84.217]) by gabe.freedesktop.org (Postfix) with ESMTPS id D6A1410E0BE for ; Wed, 31 May 2023 12:05:36 +0000 (UTC) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by dfw.source.kernel.org (Postfix) with ESMTPS id 6B32A628FE; Wed, 31 May 2023 12:05:35 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 60FB0C433EF; Wed, 31 May 2023 12:05:34 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1685534734; bh=hiP3hANCfLtuDbbmwGCMplIx6+2peQpDiyNeqRnML+c=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=O7b4MhqL3hr/VMDYGhPvcUH2Fm9O3XqBiopsX+faEUK8/bXrq4fdXBfuOotXIOMxl 4/sLGBr/8HEV8KNJvNumIBxwNhGd0t3gd0NTZBdhgvy+937e7rt2A5kg7x08alkt+z HWY78DOpz23IpOfvtYBgZpelkpj7k3hyMkjkIzrjv3e4e8HkMJwGGEX/vDPZfWzLxZ WHE06+2UIWWA6t1my732z+3nWqno3rbHc001rpBBvC5z3g6OExsYbWMm3G5i1sZ4EQ U72/UWykHao6EKyuM346UKEy2ZCBzXPhurvPil3Ty06RfnAG6BPIwjBEHHaY3ldtsD JtGx1VaOLLinA== Date: Wed, 31 May 2023 14:05:31 +0200 From: Andi Shyti To: lm0963 Subject: Re: [PATCH] drm/exynos: fix race condition UAF in exynos_g2d_exec_ioctl Message-ID: <20230531120531.dynd3iyggauucly7@intel.intel> References: <20230526130131.16521-1-lm0963hack@gmail.com> <20230530222150.24oogloda6wtvpvm@intel.intel> <20230531081917.grx3qqqm7usaqoa5@intel.intel> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: X-BeenThere: dri-devel@lists.freedesktop.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Direct Rendering Infrastructure - Development List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: linux-samsung-soc@vger.kernel.org, alim.akhtar@samsung.com, sw0312.kim@samsung.com, krzysztof.kozlowski@linaro.org, dri-devel@lists.freedesktop.org, linux-kernel@vger.kernel.org, kyungmin.park@samsung.com, linux-arm-kernel@lists.infradead.org Errors-To: dri-devel-bounces@lists.freedesktop.org Sender: "dri-devel" Hi Min, On Wed, May 31, 2023 at 06:54:34PM +0800, lm0963 wrote: > Hi Andi, > > On Wed, May 31, 2023 at 4:19 PM Andi Shyti wrote: > > > > Hi Min, > > > > > > > If it is async, runqueue_node is freed in g2d_runqueue_worker on another > > > > > worker thread. So in extreme cases, if g2d_runqueue_worker runs first, and > > > > > then executes the following if statement, there will be use-after-free. > > > > > > > > > > Signed-off-by: Min Li > > > > > --- > > > > > drivers/gpu/drm/exynos/exynos_drm_g2d.c | 2 +- > > > > > 1 file changed, 1 insertion(+), 1 deletion(-) > > > > > > > > > > diff --git a/drivers/gpu/drm/exynos/exynos_drm_g2d.c b/drivers/gpu/drm/exynos/exynos_drm_g2d.c > > > > > index ec784e58da5c..414e585ec7dd 100644 > > > > > --- a/drivers/gpu/drm/exynos/exynos_drm_g2d.c > > > > > +++ b/drivers/gpu/drm/exynos/exynos_drm_g2d.c > > > > > @@ -1335,7 +1335,7 @@ int exynos_g2d_exec_ioctl(struct drm_device *drm_dev, void *data, > > > > > /* Let the runqueue know that there is work to do. */ > > > > > queue_work(g2d->g2d_workq, &g2d->runqueue_work); > > > > > > > > > > - if (runqueue_node->async) > > > > > + if (req->async) > > > > > > > > did you actually hit this? If you did, then the fix is not OK. > > > > > > No, I didn't actually hit this. I found it through code review. This > > > is only a theoretical issue that can only be triggered in extreme > > > cases. > > > > first of all runqueue is used again two lines below this, which > > means that if you don't hit the uaf here you will hit it > > immediately after. > > No, if async is true, then it will goto out, which will directly return. > > if (runqueue_node->async) > goto out; // here, go to out, will directly return > > wait_for_completion(&runqueue_node->complete); // not hit > g2d_free_runqueue_node(g2d, runqueue_node); > > out: > return 0; that's right, sorry, I misread it. > > Second, if runqueue is freed, than we need to remove the part > > where it's freed because it doesn't make sense to free runqueue > > at this stage. > > It is freed by g2d_free_runqueue_node in g2d_runqueue_worker > > static void g2d_runqueue_worker(struct work_struct *work) > { > ...... > if (runqueue_node) { > pm_runtime_mark_last_busy(g2d->dev); > pm_runtime_put_autosuspend(g2d->dev); > > complete(&runqueue_node->complete); > if (runqueue_node->async) > g2d_free_runqueue_node(g2d, runqueue_node); // freed here this is what I'm wondering: is it correct to free a resource here? The design looks to me a bit fragile and prone to mistakes. The patch per se is OK. It doesn't make much difference to me where you actually read async, although this patch looks a bit safer: Reviewed-by: Andi Shyti However some refactoring might be needed to make it a bit more robust. Thanks, Andi > } > > > > > Finally, can you elaborate on the code review that you did so > > that we all understand it? > > queue_work(g2d->g2d_workq, &g2d->runqueue_work); > msleep(100); // add sleep here to let g2d_runqueue_worker run first > if (runqueue_node->async) > goto out; > > > > > > Andi > > > > -- > Min Li