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 vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 88574C77B7E for ; Thu, 1 Jun 2023 08:36:45 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232357AbjFAIgn (ORCPT ); Thu, 1 Jun 2023 04:36:43 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:44110 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232083AbjFAIgA (ORCPT ); Thu, 1 Jun 2023 04:36:00 -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 675011BF; Thu, 1 Jun 2023 01:34:44 -0700 (PDT) Received: from pendragon.ideasonboard.com (om126205251136.34.openmobile.ne.jp [126.205.251.136]) by perceval.ideasonboard.com (Postfix) with ESMTPSA id 14E272B6; Thu, 1 Jun 2023 10:34:19 +0200 (CEST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=ideasonboard.com; s=mail; t=1685608460; bh=gjjeif7oGjHL6hoGkZVclWwy0gG6mXm12g9c6do6TMY=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=JUUnACbDpEB6bOR3h2O5ln8qOzpTqf9VBhkZ21myMqir6gqWJBUH2lhbgPljo3AUr ZLmbW7sTAYzT5ej8JCl0YnN2x2g7F+RvAmu0lgbeX4QT61LRIobNk04EA1PyP66ClH YW/Xq3c4rgNzXp9p+1Ol32sfvdB3/t8nHUJEqQMg= Date: Thu, 1 Jun 2023 11:34:38 +0300 From: Laurent Pinchart To: Benjamin Gaignard Cc: Hans Verkuil , tfiga@chromium.org, m.szyprowski@samsung.com, mchehab@kernel.org, ming.qian@nxp.com, shijie.qin@nxp.com, eagle.zhou@nxp.com, bin.liu@mediatek.com, matthias.bgg@gmail.com, angelogioacchino.delregno@collabora.com, tiffany.lin@mediatek.com, andrew-ct.chen@mediatek.com, yunfei.dong@mediatek.com, stanimir.k.varbanov@gmail.com, quic_vgarodia@quicinc.com, agross@kernel.org, andersson@kernel.org, konrad.dybcio@linaro.org, ezequiel@vanguardiasur.com.ar, p.zabel@pengutronix.de, daniel.almeida@collabora.com, linux-media@vger.kernel.org, linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-mediatek@lists.infradead.org, linux-arm-msm@vger.kernel.org, linux-rockchip@lists.infradead.org, kernel@collabora.com Subject: Re: [PATCH v2 3/8] media: videobuf2: Add a module param to limit vb2 queue buffer storage Message-ID: <20230601083438.GE22609@pendragon.ideasonboard.com> References: <20230321102855.346732-1-benjamin.gaignard@collabora.com> <20230321102855.346732-4-benjamin.gaignard@collabora.com> <6c4658fd-3a64-b3f8-67cd-17ed2d7d3567@xs4all.nl> <20230531080331.GB6496@pendragon.ideasonboard.com> <608ae7d6-3f3b-137d-08d2-d41a240be2c4@xs4all.nl> <20230531123945.GF27043@pendragon.ideasonboard.com> <6f53b5f6-6649-f194-1808-5f5757b449f4@collabora.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <6f53b5f6-6649-f194-1808-5f5757b449f4@collabora.com> Precedence: bulk List-ID: X-Mailing-List: linux-media@vger.kernel.org Hi Benjamin, On Thu, Jun 01, 2023 at 10:03:39AM +0200, Benjamin Gaignard wrote: > Le 31/05/2023 à 14:39, Laurent Pinchart a écrit : > > On Wed, May 31, 2023 at 10:30:36AM +0200, Hans Verkuil wrote: > >> On 5/31/23 10:03, Laurent Pinchart wrote: > >>> On Wed, May 31, 2023 at 08:36:59AM +0200, Hans Verkuil wrote: > >>>> On 21/03/2023 11:28, Benjamin Gaignard wrote: > >>>>> Add module parameter "max_vb_buffer_per_queue" to be able to limit > >>>>> the number of vb2 buffers store in queue. > >>>>> > >>>>> Signed-off-by: Benjamin Gaignard > >>>>> --- > >>>>> drivers/media/common/videobuf2/videobuf2-core.c | 15 +++------------ > >>>>> include/media/videobuf2-core.h | 11 +++++++++-- > >>>>> 2 files changed, 12 insertions(+), 14 deletions(-) > >>>>> > >>>>> diff --git a/drivers/media/common/videobuf2/videobuf2-core.c b/drivers/media/common/videobuf2/videobuf2-core.c > >>>>> index ae9d72f4d181..f4da917ccf3f 100644 > >>>>> --- a/drivers/media/common/videobuf2/videobuf2-core.c > >>>>> +++ b/drivers/media/common/videobuf2/videobuf2-core.c > >>>>> @@ -34,6 +34,8 @@ > >>>>> static int debug; > >>>>> module_param(debug, int, 0644); > >>>>> > >>>>> +module_param(max_vb_buffer_per_queue, ulong, 0644); > >>>> There is no MODULE_PARM_DESC here? Please add. I see it is not there for > >>>> the debug param either, it should be added for that as well. > >>> Would this be the right time to consider resource accounting in V4L2 for > >>> buffers ? Having a module parameter doesn't sound very useful, an > >>> application could easily allocate more buffers by using buffer orphaning > >>> (allocating buffers, exporting them as dmabuf objects, and freeing them, > >>> which leaves the memory allocated). Repeating allocation cycles up to > >>> max_vb_buffer_per_queue will allow allocating an unbounded number of > >>> buffers, using all the available system memory. I'd rather not add a > >>> module argument that only gives the impression of some kind of safety > >>> without actually providing any value. > >> Does dmabuf itself provide some accounting mechanism? Just wondering. > >> > >> More specific to V4L2: I'm not so sure about this module parameter either. > >> It makes sense to have a check somewhere against ridiculous values (i.e. > >> allocating MAXINT buffers), but that can be a define as well. But otherwise > >> I am fine with allowing applications to allocate buffers until the memory > >> is full. > >> > >> The question is really: what is this parameter supposed to do? The only > >> thing it does is to sanitize unlikely inputs (e.g. allocating MAXINT buffers). > >> > >> I prefer that as a define, to be honest. > >> > >> I think it is perfectly fine for users to try to request more buffers than > >> memory allows. It will just fail in that case, not a problem. > >> > >> And if an application is doing silly things like buffer orphaning, then so > >> what? Is that any different than allocating memory and not freeing it? > >> Eventually it will run out of memory and crash, which is normal. > > > > Linux provides APIs to account for and limit usage of resources, > > including memory. A system administrator can prevent rogue processes > > from starving system resources. The memory consumed by vb2 buffer isn't > > taken into account, making V4L2 essentially unsafe for untrusted > > processes. > > > > Now, to be fair, there are many reasons why allowing access to v4L2 > > devices to untrusted applications is a bad idea, and memory consumption > > is likely not even the worst one. Still, is this something we want to > > fix, or do we want to consider V4L2 to be priviledged API only ? Right > > now we can't do so, but with many Linux systems moving towards pipewire, > > we could possibly have a system daemon isolating untrusted applications > > from the rest of the system. We may thus not need to fix this in the > > V4L2 API. > > I'm working in v3 where I'm using Xarray API. > > Just to be sure to understand you well: > I can just remove VB2_MAX_FRAME limit without adding a new one ? As long as the code is protected against overflows (e.g. if it uses num_buffers + 1 in some calculations and allows num_buffers to be UINT_MAX, you'll have an issue), it should be fine for the vb2 and V4L2 core. Limiting the number of buffers doesn't really protect against much. -- Regards, Laurent Pinchart