From e73d4829900c4ef47ffca4be306ef84b944aa9c2 Mon Sep 17 00:00:00 2001 From: Akihiro Suda Date: Thu, 15 Jul 2021 17:11:06 +0900 Subject: CNI-in-slirp4netns: fix bind-mount for /run/systemd/resolve/stub-resolv.conf Fix issue 10929 : `[Regression in 3.2.0] CNI-in-slirp4netns DNS gets broken when running a rootful container after running a rootless container` When /etc/resolv.conf on the host is a symlink to /run/systemd/resolve/stub-resolv.conf, we have to mount an empty filesystem on /run/systemd/resolve in the child namespace, so as to isolate the directory from the host mount namespace. Otherwise our bind-mount for /run/systemd/resolve/stub-resolv.conf is unmounted when systemd-resolved unlinks and recreates /run/systemd/resolve/stub-resolv.conf on the host. [NO TESTS NEEDED] Signed-off-by: Akihiro Suda --- libpod/networking_linux.go | 15 +++++++++++++++ 1 file changed, 15 insertions(+) diff --git a/libpod/networking_linux.go b/libpod/networking_linux.go index 48b0c495c..15639aac4 100644 --- a/libpod/networking_linux.go +++ b/libpod/networking_linux.go @@ -177,6 +177,21 @@ func (r *RootlessCNI) Do(toRun func() error) error { if err != nil { return err } + logrus.Debugf("The actual path of /etc/resolv.conf on the host is %q", resolvePath) + // When /etc/resolv.conf on the host is a symlink to /run/systemd/resolve/stub-resolv.conf, + // we have to mount an empty filesystem on /run/systemd/resolve in the child namespace, + // so as to isolate the directory from the host mount namespace. + // + // Otherwise our bind-mount for /run/systemd/resolve/stub-resolv.conf is unmounted + // when systemd-resolved unlinks and recreates /run/systemd/resolve/stub-resolv.conf on the host. + // see: https://github.com/containers/podman/issues/10929 + if strings.HasPrefix(resolvePath, "/run/systemd/resolve/") { + rsr := r.getPath("/run/systemd/resolve") + err = unix.Mount("", rsr, "tmpfs", unix.MS_NOEXEC|unix.MS_NOSUID|unix.MS_NODEV, "") + if err != nil { + return errors.Wrapf(err, "failed to mount tmpfs on %q for rootless cni", rsr) + } + } if strings.HasPrefix(resolvePath, "/run/") { resolvePath = r.getPath(resolvePath) err = os.MkdirAll(filepath.Dir(resolvePath), 0700) -- cgit v1.2.3-54-g00ecf