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 4DBFE17D2; Wed, 5 Jun 2024 00:37:56 +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=1717547877; cv=none; b=MSpyo0znv34+B+tOMgHNCmmM1ppYanlh4p3pqWwQ/CFtnGLmVeSdZAOz+1mR/eXvb9RR6NI7nOxKvjANSjnAR/IJiSi3EEY1Oww+UZOxUYfteb1VArfYyqOyX42QJwcHOpcu7nd+aGB4tN7HwCnvnbN0vTHiTR3gjQcJU3drELg= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1717547877; c=relaxed/simple; bh=MsU08HHsxHeQbGD4Wl3i5+Z2PYwo6GFP1KcWDbVKV88=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=X7yRQaxVKvl2imkX+XJgxq8NsVE8ZbWbTAZ+EBqKeZeWDM6W7QywL0LpgdCViIGJnQcdXSBgdfGrWNwGTWOCnwLZNwY6PiT6JgNZU1DYkFXZvGdBtqJCNVXvo89azNiJojpFNPscXtOFZJRc6lXs3p+8yhvCPST3DRh0edhO6nU= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=L/frZdgH; 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="L/frZdgH" Received: by smtp.kernel.org (Postfix) with ESMTPSA id C32AFC2BBFC; Wed, 5 Jun 2024 00:37:56 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1717547876; bh=MsU08HHsxHeQbGD4Wl3i5+Z2PYwo6GFP1KcWDbVKV88=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=L/frZdgH0L5glNRtkd+VGSbcRoaab/BbN3mnFVTca3Pvog5722ZbMw2o5sEjcdhgr EprBZHpVD65HJFVKeSOJzVtTqylCXynhygqCvXpgmuyxiQouwqHFBzNjifWUPBBx9o btgWevO5quotw1I/TWS/E9HNroTANJ0jGI5oBwKw11RgjTXX/1XROfSks2cSMhtUc2 YVo+0CTT2z8j0zynrHFGO9TGjmAkXHfZboKG2AObLdc8YMVECHJorOsXwjHZ7d08MA muIOYB9NukKa4oEmifc3qtqh/gGHscK2L+Zh6iDNvQPptNZ8RcKJU08KZU6Q/pBE2U cqljDPyTywrNQ== Date: Tue, 4 Jun 2024 17:37:56 -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: <20240605003756.GH52987@frogsfrogsfrogs> References: <20240522100007.zqpa5fxsele5m7wo@quack3> <20240523074828.7ut55rhhbawsqrn4@quack3> <20240524161101.yyqacjob42qjcbnb@quack3> <20240531145204.GJ52987@frogsfrogsfrogs> <20240603104259.gii7lfz2fg7lyrcw@quack3> <20240603174259.GB52987@frogsfrogsfrogs> <20240604085843.q6qtmtitgefioj5m@quack3> Precedence: bulk X-Mailing-List: linux-xfs@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: <20240604085843.q6qtmtitgefioj5m@quack3> On Tue, Jun 04, 2024 at 10:58:43AM +0200, Jan Kara wrote: > On Mon 03-06-24 10:42:59, Darrick J. Wong wrote: > > On Mon, Jun 03, 2024 at 06:28:47PM +0200, Andrey Albershteyn wrote: > > > On 2024-06-03 12:42:59, Jan Kara wrote: > > > > On Fri 31-05-24 07:52:04, Darrick J. Wong wrote: > > > > > 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. > > > > > > > > So the idea I'm trying to propose (and apparently I'm failing to explain it > > > > properly) is: > > > > > > > > When creating special inode, set i_projid = 0 regardless of directory > > > > settings. > > > > > > > > When creating hardlink or doing rename, if i_projid of dentry is 0, we > > > > allow the operation. > > > > > > > > Teach fsck to set i_projid to 0 when inode is special. > > > > > > > > As a result, AFAICT no problem with hardlinks, renames or similar. No need > > > > for special new ioctl or syscall. The downside is special inodes escape > > > > project quota accounting. Do we care? > > > > > > I see. But is it fine to allow fill filesystem with special inodes? > > > Don't know if it can be used somehow but this is exception from > > > isoft/ihard limits then. > > > > > > I don't see issues with this approach also, if others don't have > > > other points or other uses for those new syscalls, I can go with > > > this approach. > > > > I do -- allowing unpriviledged users to create symlinks that consume > > icount (and possibly bcount) in the root project breaks the entire > > enforcement mechanism. That's not the way that project quota has worked > > on xfs and it would be quite rude to nullify the PROJINHERIT flag bit > > only for these special cases. > > OK, fair enough. I though someone will hate this. I'd just like to > understand one thing: Owner of the inode can change the project ID to 0 > anyway so project quotas are more like a cooperative space tracking scheme > anyway. If you want to escape it, you can. So what are you exactly worried > about? Is it the container usecase where from within the user namespace you > cannot change project IDs? Yep. > Anyway I just wanted to have an explicit decision that the simple solution > is not good enough before we go the more complex route ;). Also, every now and then someone comes along and half-proposes making it so that non-root cannot change project ids anymore. Maybe some day that will succeed. --D > Honza > -- > Jan Kara > SUSE Labs, CR >