On Wed, Jun 5, 2024 at 3:38 AM Darrick J. Wong <djwong@xxxxxxxxxx> wrote: > > 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 <aalbersh@xxxxxxxxxx> > > > > > > > > > > > > > > > > > > > > > > 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. > I'd just like to point out that the purpose of the project quotas feature as I understand it, is to apply quotas to subtrees, where container storage is a very common private case of project subtree. The purpose is NOT to create a "project" of random files in random paths. My point is that changing the project id of a non-dir child to be different from the project id of its parent is a pretty rare use case (I think?). If changing the projid of non-dir is needed for moving it to a different subtree, we could allow renameat2(2) of non-dir with no hardlinks to implicitly change its inherited project id or explicitly with a flag for a hardlink, e.g.: renameat2(olddirfd, name, newdirfd, name, RENAME_NEW_PROJID). Which leaves us only with the use cases of: 1. Share some inode (as hardlinks) among projects 2. Recursively changing a subtree projid #1 could be allowed with a flag to linkat(2) or hardlink within a shared project subtree and rename the hardlink out of the shared project subtree with renameat2(2) and explicit flag, e.g.: renameat2(olddirfd, name, newdirfd, name, RENAME_OLD_PROJID). #2 *could technically* be done by the same rename flag that will allow rename to the same path, e.g: renameat2(dirfd, name, dirfd, name, RENAME_NEW_PROJID). It's not pretty and I personally prefer the syscall solution. Just wanted to put it out there. Thanks, Amir.
