rootless: Rearrange setup of rootless containers

In order to run Podman with VM-based runtimes unprivileged, the
network must be set up prior to the container creation. Therefore
this commit modifies Podman to run rootless containers by:
  1. create a network namespace
  2. pass the netns persistent mount path to the slirp4netns
     to create the tap inferface
  3. pass the netns path to the OCI spec, so the runtime can
     enter the netns

Closes #2897

Signed-off-by: Gabi Beyer <gabrielle.n.beyer@intel.com>

2 files changed, 28 insertions, 4 deletions

diff --git a/pkg/netns/netns_linux.go b/pkg/netns/netns_linux.go
index 1d6fb873c..18d638809 100644
--- a/pkg/netns/netns_linux.go
+++ b/pkg/netns/netns_linux.go
@@ -23,23 +23,42 @@ import (
 	"fmt"
 	"os"
 	"path"
+	"path/filepath"
 	"runtime"
 	"strings"
 	"sync"
 
 	"github.com/containernetworking/plugins/pkg/ns"
+	"github.com/containers/libpod/pkg/rootless"
+	"github.com/containers/libpod/pkg/util"
 	"github.com/sirupsen/logrus"
 	"golang.org/x/sys/unix"
 )
 
-const nsRunDir = "/var/run/netns"
+// get NSRunDir returns the dir of where to create the netNS. When running
+// rootless, it needs to be at a location writable by user.
+func getNSRunDir() (string, error) {
+	if rootless.IsRootless() {
+		rootlessDir, err := util.GetRuntimeDir()
+		if err != nil {
+			return "", err
+		}
+		return filepath.Join(rootlessDir, "netns"), nil
+	}
+	return "/var/run/netns", nil
+}
 
 // NewNS creates a new persistent (bind-mounted) network namespace and returns
 // an object representing that namespace, without switching to it.
 func NewNS() (ns.NetNS, error) {
 
+	nsRunDir, err := getNSRunDir()
+	if err != nil {
+		return nil, err
+	}
+
 	b := make([]byte, 16)
-	_, err := rand.Reader.Read(b)
+	_, err = rand.Reader.Read(b)
 	if err != nil {
 		return nil, fmt.Errorf("failed to generate random netns name: %v", err)
 	}
@@ -127,7 +146,7 @@ func NewNS() (ns.NetNS, error) {
 		// Put this thread back to the orig ns, since it might get reused (pre go1.10)
 		defer func() {
 			if err := origNS.Set(); err != nil {
-				logrus.Errorf("unable to set namespace: %q", err)
+				logrus.Warnf("unable to set namespace: %q", err)
 			}
 		}()
 
@@ -150,6 +169,11 @@ func NewNS() (ns.NetNS, error) {
 
 // UnmountNS unmounts the NS held by the netns object
 func UnmountNS(ns ns.NetNS) error {
+	nsRunDir, err := getNSRunDir()
+	if err != nil {
+		return err
+	}
+
 	nsPath := ns.Path()
 	// Only unmount if it's been bind-mounted (don't touch namespaces in /proc...)
 	if strings.HasPrefix(nsPath, nsRunDir) {
diff --git a/pkg/spec/createconfig.go b/pkg/spec/createconfig.go
index c17172016..7c3195be4 100644
--- a/pkg/spec/createconfig.go
+++ b/pkg/spec/createconfig.go
@@ -275,7 +275,7 @@ func (c *CreateConfig) getContainerCreateOptions(runtime *libpod.Runtime, pod *l
 		options = append(options, libpod.WithNetNSFrom(connectedCtr))
 	} else if !c.NetMode.IsHost() && !c.NetMode.IsNone() {
 		hasUserns := c.UsernsMode.IsContainer() || c.UsernsMode.IsNS() || len(c.IDMappings.UIDMap) > 0 || len(c.IDMappings.GIDMap) > 0
-		postConfigureNetNS := c.NetMode.IsSlirp4netns() || (hasUserns && !c.UsernsMode.IsHost())
+		postConfigureNetNS := hasUserns && !c.UsernsMode.IsHost()
 		options = append(options, libpod.WithNetNS(portBindings, postConfigureNetNS, string(c.NetMode), networks))
 	}