Add a function to read a pidfile, this helps to avoid some duplication.

Signed-off-by: Paul Holzinger <pholzing@redhat.com>

We have little to no control over what happens tot he slirp4netns/pasta
process after we started it. It could crash or get killed then we end up
in state where we think networking works when it doesn't.

To fix this each time we access the rootless-netns we should also make
to program is still running, if it is not try to recover by starting it
again. This ensures that we are much more fault tolerant.

Signed-off-by: Paul Holzinger <pholzing@redhat.com>

The IsRootless() check is dangerous in a sense that it may not do what
you think it does. It also returns true even when podman is run as root
and not in the podman userns but as part of a different userns. Could be
a other container manager that configured the userns.

This results in us doing the rootless-netns logic even when we should
not need to. To fix this we now check for the
_CONTAINERS_USERNS_CONFIGURED env var to make sure we are not
re-exe'ed. This is what we actually care about.

This is a regression compared to podman 4.X, because the code was moved
into c/common the IsRootless() check was changed to the c/storage
version which has the userns special case.

Fixes podman-container-tools/podman#22218

Signed-off-by: Paul Holzinger <pholzing@redhat.com>

While this is a none issue normally because we run in a unprivileged
userns we cannot modify the host mounts in any way. However in case
where the rootless netns logic might be executed from a non userns
context we might change the mount tree if the mounts are shared which is
the systemd default. While this should never happen let's make sure we
never mess up the system by accident in case there are more bugs and
explicitly make our mount tree private.

Signed-off-by: Paul Holzinger <pholzing@redhat.com>

This here just logs unnecessary errors in case there is an error during
the Run() call (podman unshare --rootless-netns). runInner() will
already call cleanup on errors if it created a new netns so we only need
to cleanup when there is no error.

Signed-off-by: Paul Holzinger <pholzing@redhat.com>

This is good to prevent any leaks but more important here there is a
bug because we cache the last assigned ip. However when a network is
removed the recreated with a different LeaseRange that ip might be very
well outside the expected range and the logic seems to handle this
correctly. I could fix it there but deleting the full bucket seems best
as it avoid other issues and leaking the bucket forever.

Fixes podman-container-tools/podman#22034

Signed-off-by: Paul Holzinger <pholzing@redhat.com>