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? Honza -- Jan Kara <jack@xxxxxxxx> SUSE Labs, CR
