I'm pretty sure this is related to copy up. For some reason, when unlinking a file in the lowerdir that isn't in the upperdir overlayfs first copies up the file from the lowerdir, then replaces it with a whiteout. There are a couple of problems with letting the user create the inode in the upperdir though.
First, starting in xenial the tmpfs mount isn't going to allow any inodes to be created in it that are not mapped into the user namespace. This is generally a sensible policy as it presents users from inserting inodes into the system owned by users over which they have no privileges. Second, even if the upperdir wasn't limited in this matter, it's not really a good idea to let a user create inodes owned by another user without having privileges towards that user. In this case it's under kernel control and immediately replaced by a whiteout, so it probably doesn't pose a problem in reality. But generally allowing copy up of such an inode to a mount over which the user is privileged could be problematic. So I'm going to have to think about this as we need to proceed very carefully. Ideally we can just avoid the copy up and write the whiteout directly, but I assume there must be some reason the code doesn't already work that way. -- You received this bug notification because you are a member of Kernel Packages, which is subscribed to linux in Ubuntu. https://bugs.launchpad.net/bugs/1617388 Title: When using overlayfs with kernel 4.4, some files cannot be deleted. Status in linux package in Ubuntu: Triaged Bug description: #!/bin/bash # --------------------------------------------------------------------- # This script exhibits a bug in overlayfs in kernel 4.4. # The bug is not present in kernel 4.2. # The bug can be reproduced in an x86_64 virtual-machine; # 32-bit has not been tested. # # With kernel 4.2, the script output ends with: # "script completed without encountering a kernel bug" # # With kernel 4.4, the script output ends with: # "rm: cannot remove ‘mnt_ovl/sub/sub.txt’: # Value too large for defined data type" # # The script depends upon lxc-usernsexec (part of the lxc1 package) to # create a user-namespace. # # The script should be run as a normal user (not root), in a directory where # the user has write-permission: # ./script # -------------------------------------------------------------------- cleanup() { [[ -d "$storedir" ]] || exit 1 cd "$storedir" || exit 1 [[ -d "$tmpdir" ]] || exit 1 lxc-usernsexec -m b:0:1000:1 -m b:100000:100000:1 -- rm -rf "$tmpdir" } trap cleanup EXIT set -e storedir="$(pwd)" # create tmpdir tmpdir="$(mktemp -d --tmpdir=.)" cd "$tmpdir" # create lowerdir for overlay mkdir -p lower/sub touch lower/lower.txt lower/sub/sub.txt cd .. chmod -R a+rwX "$tmpdir" # run a script in a user namepace lxc-usernsexec -m b:0:100000:65534 -- bash << EOF set -e cd "$tmpdir" # create tmpfs mkdir mnt_tmpfs mount -t tmpfs tmpfs mnt_tmpfs # create upperdir and workdir for overlay mkdir mnt_tmpfs/{upper,work} # mount overlay mkdir mnt_ovl mount -t overlay \ -o lowerdir=lower,upperdir=mnt_tmpfs/upper,workdir=mnt_tmpfs/work \ overlay mnt_ovl echo 'overlay directory listing' ls -RF mnt_ovl echo '' set -x rm mnt_ovl/lower.txt # always succeeds rm mnt_ovl/sub/sub.txt # fails with kernel 4.4+ set +x echo 'script completed without encountering a kernel bug' EOF To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1617388/+subscriptions -- Mailing list: https://launchpad.net/~kernel-packages Post to : kernel-packages@lists.launchpad.net Unsubscribe : https://launchpad.net/~kernel-packages More help : https://help.launchpad.net/ListHelp
