From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id E3FBB76056; Fri, 31 May 2024 14:52:04 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1717167125; cv=none; b=LSmWbGFEDRAbHQTKutojinbVZb5BU+yeF1VXst0IvDi9RKcl8Z6kg9sOamgfGHLtW0mo4Wx5KsGy/B1vPw8+if/fhfKLcjbmnNStckicYE84Gj6WEIxTKQPMGKxTAmBAgohaH1F087HGvQZDfwRUOudiJ6tpIXi00UMOVlLP9zk= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1717167125; c=relaxed/simple; bh=hzo9KAzzzXmogiiArl5dNeq1whTMmlBGgy2PXnwl1Gs=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=MGEOngzhNPDLp1pDBzdUPtCCn4VKkv+NhPLeS5tUaZQNb1BXDz135oQYbq0nkNkXAP/ejvuLA3VL49eW2Iatih6WC4eohqECwNIoLdRiOGIaFtn+ep5cie/WqXL4INhNaKs9hnP7+HMF7NUCGWCPyQcPu192d1ybiuxUxqNYv0s= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=MlLNKRne; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="MlLNKRne" Received: by smtp.kernel.org (Postfix) with ESMTPSA id BA75AC116B1; Fri, 31 May 2024 14:52:04 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1717167124; bh=hzo9KAzzzXmogiiArl5dNeq1whTMmlBGgy2PXnwl1Gs=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=MlLNKRneXjOIFxaxoz4i1wecJfTu6d0fk6gEGRm1chmrFbeOvRygmVe8aFwayzQ4N UHiuqX+YMmuSOvlMjQeCunisAbCQVD5b5z/VsaRsqxCHdnZR411UXfTQQoHmQN9s2C zuCOWL1NsRc34LRvAu8qhZSNXME1zSe47lzgTQ6RSu7qWFTJv2K8RWjYiOPyNXuzPm hULHSctfCHue6ajBNjGuQ+BgT4w68AKNl3J4/wkMVvHVbJmFSaIHdENiDt+75i64rz Y0rmTd7tsM6iWvg2NhKoWuZgmF7/G9Znu4yGsK0YafLvwtH8P/BXgXIa+/9REBs4Y6 1G97GswnEu4Mg== Date: Fri, 31 May 2024 07:52:04 -0700 From: "Darrick J. Wong" To: Jan Kara Cc: Andrey Albershteyn , linux-fsdevel@vger.kernel.org, linux-xfs@vger.kernel.org, Alexander Viro , Christian Brauner Subject: Re: [PATCH v2 2/4] fs: add FS_IOC_FSSETXATTRAT and FS_IOC_FSGETXATTRAT Message-ID: <20240531145204.GJ52987@frogsfrogsfrogs> References: <20240520164624.665269-2-aalbersh@redhat.com> <20240520164624.665269-4-aalbersh@redhat.com> <20240522100007.zqpa5fxsele5m7wo@quack3> <20240523074828.7ut55rhhbawsqrn4@quack3> <20240524161101.yyqacjob42qjcbnb@quack3> Precedence: bulk X-Mailing-List: linux-fsdevel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20240524161101.yyqacjob42qjcbnb@quack3> On Fri, May 24, 2024 at 06:11:01PM +0200, Jan Kara wrote: > On Thu 23-05-24 13:16:48, Andrey Albershteyn wrote: > > On 2024-05-23 09:48:28, Jan Kara wrote: > > > Hi! > > > > > > On Wed 22-05-24 12:45:09, Andrey Albershteyn wrote: > > > > On 2024-05-22 12:00:07, Jan Kara wrote: > > > > > Hello! > > > > > > > > > > On Mon 20-05-24 18:46:21, Andrey Albershteyn wrote: > > > > > > XFS has project quotas which could be attached to a directory. All > > > > > > new inodes in these directories inherit project ID set on parent > > > > > > directory. > > > > > > > > > > > > The project is created from userspace by opening and calling > > > > > > FS_IOC_FSSETXATTR on each inode. This is not possible for special > > > > > > files such as FIFO, SOCK, BLK etc. as opening them returns a special > > > > > > inode from VFS. Therefore, some inodes are left with empty project > > > > > > ID. Those inodes then are not shown in the quota accounting but > > > > > > still exist in the directory. > > > > > > > > > > > > This patch adds two new ioctls which allows userspace, such as > > > > > > xfs_quota, to set project ID on special files by using parent > > > > > > directory to open FS inode. This will let xfs_quota set ID on all > > > > > > inodes and also reset it when project is removed. Also, as > > > > > > vfs_fileattr_set() is now will called on special files too, let's > > > > > > forbid any other attributes except projid and nextents (symlink can > > > > > > have one). > > > > > > > > > > > > Signed-off-by: Andrey Albershteyn > > > > > > > > > > I'd like to understand one thing. Is it practically useful to set project > > > > > IDs for special inodes? There is no significant disk space usage associated > > > > > with them so wrt quotas we are speaking only about the inode itself. So is > > > > > the concern that user could escape inode project quota accounting and > > > > > perform some DoS? Or why do we bother with two new somewhat hairy ioctls > > > > > for something that seems as a small corner case to me? > > > > > > > > So there's few things: > > > > - Quota accounting is missing only some special files. Special files > > > > created after quota project is setup inherit ID from the project > > > > directory. > > > > - For special files created after the project is setup there's no > > > > way to make them project-less. Therefore, creating a new project > > > > over those will fail due to project ID miss match. > > > > - It wasn't possible to hardlink/rename project-less special files > > > > inside a project due to ID miss match. The linking is fixed, and > > > > renaming is worked around in first patch. > > > > > > > > The initial report I got was about second and last point, an > > > > application was failing to create a new project after "restart" and > > > > wasn't able to link special files created beforehand. > > > > > > I see. OK, but wouldn't it then be an easier fix to make sure we *never* > > > inherit project id for special inodes? And make sure inodes with unset > > > project ID don't fail to be linked, renamed, etc... > > > > But then, in set up project, you can cross-link between projects and > > escape quota this way. During linking/renaming if source inode has > > ID but target one doesn't, we won't be able to tell that this link > > is within the project. > > Well, I didn't want to charge these special inodes to project quota at all > so "escaping quota" was pretty much what I suggested to do. But my point > was that since the only thing that's really charged for these inodes is the > inodes itself then does this small inaccuracy really matter in practice? > Are we afraid the user is going to fill the filesystem with symlinks? I thought the worry here is that you can't fully reassign the project id for a directory tree unless you have an *at() version of the ioctl to handle the special files that you can't open directly? So you start with a directory tree that's (say) 2% symlinks and project id 5. Later you want to set project id 7 on that subtree, but after the incomplete change, projid 7 is charged for 98% of the tree, and 2% are still stuck on projid 5. This is a mess, and if enforcement is enabled you've just broken it in a way that can't be fixed aside from recreating those files. --D > Honza > -- > Jan Kara > SUSE Labs, CR >