Daan De Meyer
406f177501
This new setting allows unsharing the pid namespace in a unit. Because you have to fork to get a process into a pid namespace, we fork in systemd-executor to get into the new pid namespace. The parent then sends the pid of the child process back to the manager and exits while the child process continues on with the rest of exec_invoke() and then executes the actual payload. Communicating the child pid is done via a new pidref socket pair that is set up on manager startup. We unshare the PID namespace right before the mount namespace so we mount procfs correctly. Note PrivatePIDs=yes always implies MountAPIVFS=yes to mount procfs. When running unprivileged in a user session, user namespace is set up first to allow for PID namespace to be unshared. However, when running in privileged mode, we unshare the user namespace last to ensure the user namespace does not own the PID namespace and cannot break out of the sandbox. Note we disallow Type=forking services from using PrivatePIDs=yes since the init proess inside the PID namespace must not exit for other processes in the namespace to exist. Note Daan De Meyer did the original work for this commit with Ryan Wilson addressing follow-ups. Co-authored-by: Daan De Meyer <daan.j.demeyer@gmail.com>
System and Service Manager
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