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[23.128.96.18]) by mx.google.com with ESMTP id a21si6785937jab.23.2021.06.17.01.03.54; Thu, 17 Jun 2021 01:04:05 -0700 (PDT) Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18; Authentication-Results: mx.google.com; dkim=pass header.i=@foss.st.com header.s=selector1 header.b=Mv1eFLHU; spf=pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) smtp.mailfrom=linux-kernel-owner@vger.kernel.org; dmarc=pass (p=NONE sp=NONE dis=NONE) header.from=foss.st.com Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230238AbhFQIE0 (ORCPT + 99 others); Thu, 17 Jun 2021 04:04:26 -0400 Received: from mx07-00178001.pphosted.com ([185.132.182.106]:8524 "EHLO mx07-00178001.pphosted.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229716AbhFQIEZ (ORCPT ); Thu, 17 Jun 2021 04:04:25 -0400 Received: from pps.filterd (m0046668.ppops.net [127.0.0.1]) by mx07-00178001.pphosted.com (8.16.0.43/8.16.0.43) with SMTP id 15H7vCEg018983; Thu, 17 Jun 2021 10:02:16 +0200 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=foss.st.com; h=subject : to : cc : references : from : message-id : date : mime-version : in-reply-to : content-type : content-transfer-encoding; s=selector1; bh=mkIffYA2IIRDHWHO2j0eKvCtgWPyW1DH7iVGn8lTvJY=; b=Mv1eFLHUNbNnqzh7jnk5dexzM59khgCCu/dvNeH+lkV5Tn1ynQZ5l2hy4ZOEvV8s+5+A R4B0RDGyeRU98nlBdtTHQjnZ7RBr3s32RdsupW2tPXQB5pnLTyTnmZ+/QyikYY4A2Kyf A+E6oymSsUZdifJ/QZpVuN0pmCi8q5XRyJJGuoebyRzts8x5Z30UhfwzvSxvYkaKki3D +m6daNk3yAAx27O5Ltfw08O7+hRfhtAusNto8O7Kxu66xPxlUY1CNX1oIxL3Q9Tl7OhK uihAI79m7Rc4MVbNC7LhI4sNTdqTTWOMuOkXxeTnB2DM+rO4cINKNRigqF1ekopmCLtO 0w== Received: from beta.dmz-eu.st.com (beta.dmz-eu.st.com [164.129.1.35]) by mx07-00178001.pphosted.com with ESMTP id 3980uarq13-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=NOT); Thu, 17 Jun 2021 10:02:16 +0200 Received: from euls16034.sgp.st.com (euls16034.sgp.st.com [10.75.44.20]) by beta.dmz-eu.st.com (STMicroelectronics) with ESMTP id 3097A10002A; Thu, 17 Jun 2021 10:02:15 +0200 (CEST) Received: from Webmail-eu.st.com (sfhdag2node3.st.com [10.75.127.6]) by euls16034.sgp.st.com (STMicroelectronics) with ESMTP id 1966E217371; Thu, 17 Jun 2021 10:02:15 +0200 (CEST) Received: from lmecxl0889.lme.st.com (10.75.127.46) by SFHDAG2NODE3.st.com (10.75.127.6) with Microsoft SMTP Server (TLS) id 15.0.1497.2; Thu, 17 Jun 2021 10:02:14 +0200 Subject: Re: [PATCH 3/4] rpmsg: ctrl: Add check on rpmsg device removability from user space To: Mathieu Poirier CC: Bjorn Andersson , Ohad Ben-Cohen , , , References: <20210604091406.15901-1-arnaud.pouliquen@foss.st.com> <20210604091406.15901-4-arnaud.pouliquen@foss.st.com> <20210615174634.GB604521@p14s> <20210616171524.GA637642@p14s> From: Arnaud POULIQUEN Message-ID: Date: Thu, 17 Jun 2021 10:02:14 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.8.1 MIME-Version: 1.0 In-Reply-To: <20210616171524.GA637642@p14s> Content-Type: text/plain; charset="utf-8" Content-Language: en-US Content-Transfer-Encoding: 7bit X-Originating-IP: [10.75.127.46] X-ClientProxiedBy: SFHDAG1NODE3.st.com (10.75.127.3) To SFHDAG2NODE3.st.com (10.75.127.6) X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:6.0.391,18.0.790 definitions=2021-06-17_02:2021-06-15,2021-06-17 signatures=0 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hello Mathieu, On 6/16/21 7:15 PM, Mathieu Poirier wrote: > On Wed, Jun 16, 2021 at 11:30:51AM +0200, Arnaud POULIQUEN wrote: >> >> >> On 6/15/21 7:46 PM, Mathieu Poirier wrote: >>> On Fri, Jun 04, 2021 at 11:14:05AM +0200, Arnaud Pouliquen wrote: >>>> Using the RPMSG_RELEASE_DEV_IOCTL is possible to remove any >>>> rpmsg device (such as the rpmsg ns or the rpmsg ctrldev). >>>> >>>> Add a new field to store the removability of the device. >>>> >>>> By default the rpmsg device can not be removed by user space. It is >>>> set to 1 by the rpmsg ctrl on RPMSG_CREATE_DEV_IOCTL request, but >>>> could also be set by an rpmsg driver during probe. >>>> >>>> Signed-off-by: Arnaud Pouliquen >>>> --- >>>> drivers/rpmsg/rpmsg_ctrl.c | 17 ++++++++++++++++- >>>> include/linux/rpmsg.h | 2 ++ >>>> 2 files changed, 18 insertions(+), 1 deletion(-) >>>> >>>> diff --git a/drivers/rpmsg/rpmsg_ctrl.c b/drivers/rpmsg/rpmsg_ctrl.c >>>> index cb19e32d05e1..e93c6ec49038 100644 >>>> --- a/drivers/rpmsg/rpmsg_ctrl.c >>>> +++ b/drivers/rpmsg/rpmsg_ctrl.c >>>> @@ -74,6 +74,7 @@ static long rpmsg_ctrldev_ioctl(struct file *fp, unsigned int cmd, >>>> struct rpmsg_endpoint_info eptinfo; >>>> struct rpmsg_channel_info chinfo; >>>> struct rpmsg_device *rpdev; >>>> + struct device *dev; >>>> int ret = 0; >>>> >>>> if (copy_from_user(&eptinfo, argp, sizeof(eptinfo))) >>>> @@ -95,11 +96,25 @@ static long rpmsg_ctrldev_ioctl(struct file *fp, unsigned int cmd, >>>> if (!rpdev) { >>>> dev_err(&ctrldev->dev, "failed to create %s channel\n", chinfo.name); >>>> ret = -ENXIO; >>>> + } else { >>>> + /* Allow user space to release the device. */ >>>> + rpdev->us_removable = 1; >>> >>> As a rule of thumb I try really hard to avoid introducing new flags. In this case we >>> can attain the same result by looking at chinfo->name, chinfo->src and >>> chinfo->dst. I would introduce a new inline function in rpmsg_internal.h, >>> something like rpmsg_chrdev_is_ctrl_dev(), and compare the specifics in chinfo >>> to rpdev->id.name, rpdev->src and rpdev->dst. If they all match then the >>> operation is refused. >> >> Something must have escaped me, because i turn around your your proposal, >> without understand it. >> >> The "us_removable" flag is not only for the rpmsg_ctrl, but for any rpmsg device >> that have not to be released by user application. Either because there are core >> ( rpmsg_ctrl, rpmsg_ns) or because a rpmsg driver don't allow to unbind its >> rpmsg devices. >> > > I don't see how the current patch would allow a driver to prevent user space > from releasing a rpmsg device since the sysfs attribute can be changed at will. > So even if the driver sets the flag user space can still revert it. The patch [4/4] define the a read only attribute using the rpmsg_show_attr declaration[1]. So the userspace can't change it. This also has the advantage of not allowing the new IOCTRL API to be used by default for legacy RPMSg devices without a specific patch. [1] https://elixir.bootlin.com/linux/latest/source/drivers/rpmsg/rpmsg_core.c#L362 > >> look to me that rpmsg_chrdev_is_ctrl_dev just prevents rpmsg ctrl to be released >> by the RPMSG_RELEASE_DEV_IOCTL. > > That is correct. I did not address rpmsg_ns to keep things simple but it would > also have to be handled properly. > >> >> Please, could you clarify what you have in mind here? > > Other than rpmsg_ctrl and rpmsg_ns I don't think we should introduce any > mechanism to prevent users from releasing an rpmsg. Doing so needs root access > - if a user space process with root privileges can't be trusted then we have > bigger problems than unwanted releases of registered rpmsg devices. That's make sense. If we go on this way we could also trust the root application for the rpmsg_ns and only protect the rpmsg_ctrl which can not release itself, as you proposed. Thanks, Arnaud > >> >> Thanks, >> Arnaud >> >>> >>> That way we don't introduce a new flag and there is also no need to call >>> rpmsg_find_device() twice. >> >> >> >>> >>> Thanks, >>> Mathieu >>> >>>> } >>>> break; >>>> >>>> case RPMSG_RELEASE_DEV_IOCTL: >>>> - ret = rpmsg_release_channel(ctrldev->rpdev, &chinfo); >>>> + dev = rpmsg_find_device(ctrldev->rpdev->dev.parent, &chinfo); >>>> + if (!dev) >>>> + ret = -ENXIO; >>>> + >>>> + /* Verify that rpmsg device removal is allowed. */ >>>> + if (!ret) { >>>> + rpdev = to_rpmsg_device(dev); >>>> + if (!rpdev->us_removable) >>>> + ret = -EACCES; >>>> + } >>>> + if (!ret) >>>> + ret = rpmsg_release_channel(ctrldev->rpdev, &chinfo); >>>> if (ret) >>>> dev_err(&ctrldev->dev, "failed to release %s channel (%d)\n", >>>> chinfo.name, ret); >>>> diff --git a/include/linux/rpmsg.h b/include/linux/rpmsg.h >>>> index d97dcd049f18..3642aad1a789 100644 >>>> --- a/include/linux/rpmsg.h >>>> +++ b/include/linux/rpmsg.h >>>> @@ -47,6 +47,7 @@ struct rpmsg_channel_info { >>>> * @ept: the rpmsg endpoint of this channel >>>> * @announce: if set, rpmsg will announce the creation/removal of this channel >>>> * @little_endian: True if transport is using little endian byte representation >>>> + * @us_removable: True if userspace application has permission to remove the rpmsg device >>>> */ >>>> struct rpmsg_device { >>>> struct device dev; >>>> @@ -57,6 +58,7 @@ struct rpmsg_device { >>>> struct rpmsg_endpoint *ept; >>>> bool announce; >>>> bool little_endian; >>>> + bool us_removable; >>>> >>>> const struct rpmsg_device_ops *ops; >>>> }; >>>> -- >>>> 2.17.1 >>>>