net: copy netconf files into container dir

The user might modify or delete the net config
files while the container is running. This will
mess up the plugins on the teardown path. Copying
them into a the container directory and using them
from there should guard against that. It also lays
the foundation for GC to process unremoved files.

networking/networking.go

@@ -16,6 +16,7 @@ package networking
 
 import (
 	"fmt"
+	"io"
 	"log"
 	"net"
 	"os"
@@ -171,18 +172,30 @@ func (n *Networking) EnterContNS() error {
 	return util.SetNS(n.contNS, syscall.CLONE_NEWNET)
 }
 
+func (e *containerEnv) netDir() string {
+	return filepath.Join(e.rktRoot, "net")
+}
+
 func (e *containerEnv) setupNets(netns string, nets []Net) ([]activeNet, error) {
-	var err error
+	err := os.MkdirAll(e.netDir(), 0755)
+	if err != nil {
+		return nil, err
+	}
 
 	active := []activeNet{}
 
 	for i, nt := range nets {
+		log.Printf("Setup: executing net-plugin %v", nt.Type)
+
 		an := activeNet{
 			Net:    nt,
 			ifName: fmt.Sprintf(ifnamePattern, i),
 		}
 
-		log.Printf("Setup: executing net-plugin %v", nt.Type)
+		if an.Filename, err = copyFileToDir(nt.Filename, e.netDir()); err != nil {
+			err = fmt.Errorf("error copying %q to %q: %v", nt.Filename, e.netDir(), err)
+			break
+		}
 
 		an.ip, err = e.netPluginAdd(&nt, netns, nt.args, an.ifName)
 		if err != nil {
@@ -206,10 +219,17 @@ func (e *containerEnv) teardownNets(netns string, nets []activeNet) {
 		nt := nets[i]
 
 		log.Printf("Teardown: executing net-plugin %v", nt.Type)
+
 		err := e.netPluginDel(&nt.Net, netns, nt.args, nt.ifName)
 		if err != nil {
 			log.Printf("Error deleting %q: %v", nt.Name, err)
 		}
+
+		// Delete the conf file to signal that the network was
+		// torn down (or at least attempted to)
+		if err = os.Remove(nt.Filename); err != nil {
+			log.Printf("Error deleting %q: %v", nt.Filename, err)
+		}
 	}
 }
 
@@ -285,3 +305,22 @@ func bindMountFile(src, dstDir, dstFile string) error {
 
 	return syscall.Mount(src, dst, "none", syscall.MS_BIND, "")
 }
+
+func copyFileToDir(src, dstdir string) (string, error) {
+	dst := filepath.Join(dstdir, filepath.Base(src))
+
+	s, err := os.Open(src)
+	if err != nil {
+		return "", err
+	}
+	defer s.Close()
+
+	d, err := os.Create(dst)
+	if err != nil {
+		return "", err
+	}
+	defer d.Close()
+
+	_, err = io.Copy(d, s)
+	return dst, err
+}