Question (related to UBUNTU: SAUCE: fs: Refuse uid/gid changes which don't map into s_user_ns) ---------------------------
When an overlayfs is mounted inside a user-namespace, should it permit the creation of inodes in the upper layer with uids that are outside the user-namespace? My Tentative Answer ------------------- (TLDR; yes) If a directory D is granted world-write permissions (in the initial namespace) via 'chmod -R a+rwX', then any user is permitted to edit or delete files in D, even if the files and D are owned by root. If we subsequently enter a user-namespace, then we are still permitted to edit files in D. But if we enter a user-namespace and subsequently utilize D as the lower layer of an overlayfs, then editing files in D necessitates the creation of files in the upper layer with uids which are outside the user namespace. While restriciting the permissible range of uids in the upper layer may well enhance security, it also limits the utility of overlayfs. overlayfs will sometimes deny permissions which were granted in the initial namespace. overlayfs will remain useful for mounting a rootfs (since all uids are within the user-namespace), but not for mounting directories onto the rootfs. -- You received this bug notification because you are a member of Ubuntu Bugs, which is subscribed to Ubuntu. https://bugs.launchpad.net/bugs/1617388 Title: When using overlayfs with kernel 4.4, some files cannot be deleted. To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1617388/+subscriptions -- ubuntu-bugs mailing list [email protected] https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs
