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. -- - Andrey
