libdm currently has a fairly substantial DoS bug that makes certain
operations fail on a libdm device if the device has active references
through mountpoints. This is a significant problem with the advent of
mount namespaces and MS_PRIVATE, and can cause certain --volume mounts
to cause libdm to no longer be able to remove containers:
% docker run -d --name testA busybox top
% docker run -d --name testB -v /var/lib/docker:/docker busybox top
% docker rm -f testA
[fails on libdm with dm_task_run errors.]
This also solves the problem of unprivileged users being able to DoS
docker by using unprivileged mount namespaces to preseve mounts that
Docker has dropped.
Signed-off-by: Aleksa Sarai <asarai@suse.de>
Upstream-commit: 92e45b81e0a8b68d9567a2068247460a1ba59600
Component: engine
87c0724076