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CNI-in-slirp4netns: fix bind-mount for /run/systemd/resolve/stub-resolv.conf

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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 <akihiro.suda.cz@hco.ntt.co.jp>
This commit is contained in:
Akihiro Suda
2021-07-15 17:11:06 +09:00
parent 9d98f56a64
commit e73d482990
1 changed files with 15 additions and 0 deletions
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15
libpod/networking_linux.go
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@ -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)