Hi, 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. -- - Andrey
