3436e1c735
Permit overlayfs mounts within user namespaces to allow utilisation of e.g.
unprivileged LXC overlay snapshots.
Except by the Ubuntu community [1], overlayfs mounts in user namespaces are
expected to be a security risk [2] and thus are not enabled on upstream
Linux kernels. For the non-Ubuntu users that have to stick to unprivileged
overlay-based LXCs, this meant to patch and compile the kernel manually.
Instead, adding the kernel tainting 'permit_mounts_in_userns' module
parameter allows a kind of a user-friendly way to enable the feature.
Testable with:
sudo modprobe overlay permit_mounts_in_userns=1
sudo sysctl -w kernel.unprivileged_userns_clone=1
mkdir -p lower upper work mnt
unshare --map-root-user --mount \
mount -t overlay none mnt \
-o lowerdir=lower,upperdir=upper,workdir=work
[1]: Ubuntu allows unprivileged mounting of overlay filesystem
https://lists.ubuntu.com/archives/kernel-team/2014-February/038091.html
[2]: User namespaces + overlayfs = root privileges
https://lwn.net/Articles/671641/
Signed-off-by: Nicolas Schier <nicolas@fjasle.eu>
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