Add [simple] network support to 'runsc do'

Sandbox always runsc with IP 192.168.10.2 and the peer
network adds 1 to the address (192.168.10.3). Sandbox
IP can be changed using --ip flag.

Here a few examples:
  sudo runsc do curl www.google.com
  sudo runsc do --ip=10.10.10.2 bash -c "echo 123 | netcat -l -p 8080"

PiperOrigin-RevId: 246421277
Change-Id: I7b3dce4af46a57300350dab41cb27e04e4b6e9da

1 files changed, 154 insertions, 6 deletions

diff --git a/runsc/cmd/do.go b/runsc/cmd/do.go
index 67d415733..842fe2341 100644
--- a/runsc/cmd/do.go
+++ b/runsc/cmd/do.go
@@ -21,7 +21,10 @@ import (
 	"io/ioutil"
 	"math/rand"
 	"os"
+	"os/exec"
 	"path/filepath"
+	"strconv"
+	"strings"
 	"syscall"
 
 	"flag"
@@ -38,6 +41,7 @@ import (
 type Do struct {
 	root string
 	cwd  string
+	ip   string
 }
 
 // Name implements subcommands.Command.Name.
@@ -65,7 +69,8 @@ used for testing only.
 // SetFlags implements subcommands.Command.SetFlags.
 func (c *Do) SetFlags(f *flag.FlagSet) {
 	f.StringVar(&c.root, "root", "/", `path to the root directory, defaults to "/"`)
-	f.StringVar(&c.cwd, "cwd", ".", `path to the current directory, defaults to the current directory`)
+	f.StringVar(&c.cwd, "cwd", ".", "path to the current directory, defaults to the current directory")
+	f.StringVar(&c.ip, "ip", "192.168.10.2", "IPv4 address for the sandbox")
 }
 
 // Execute implements subcommands.Command.Execute.
@@ -112,6 +117,15 @@ func (c *Do) Execute(_ context.Context, f *flag.FlagSet, args ...interface{}) su
 
 	specutils.LogSpec(spec)
 
+	cid := fmt.Sprintf("runsc-%06d", rand.Int31n(1000000))
+	if conf.Network != boot.NetworkNone {
+		clean, err := c.setupNet(cid, spec)
+		if err != nil {
+			Fatalf("Error setting up network: %v", err)
+		}
+		defer clean()
+	}
+
 	out, err := json.Marshal(spec)
 	if err != nil {
 		Fatalf("Error to marshal spec: %v", err)
@@ -130,11 +144,7 @@ func (c *Do) Execute(_ context.Context, f *flag.FlagSet, args ...interface{}) su
 		Fatalf("Error write spec: %v", err)
 	}
 
-	// No network support yet.
-	conf.Network = boot.NetworkNone
-
-	id := fmt.Sprintf("runcs-do-%06d", rand.Int31n(1000000))
-	ws, err := container.Run(id, spec, conf, tmpDir, "", "", "")
+	ws, err := container.Run(cid, spec, conf, tmpDir, "", "", "")
 	if err != nil {
 		Fatalf("running container: %v", err)
 	}
@@ -155,3 +165,141 @@ func resolvePath(path string) (string, error) {
 	}
 	return path, nil
 }
+
+func (c *Do) setupNet(cid string, spec *specs.Spec) (func(), error) {
+	dev, err := defaultDevice()
+	if err != nil {
+		return nil, err
+	}
+	peerIP, err := calculatePeerIP(c.ip)
+	if err != nil {
+		return nil, err
+	}
+	veth, peer := deviceNames(cid)
+
+	cmds := []string{
+		fmt.Sprintf("ip link add %s type veth peer name %s", veth, peer),
+
+		// Setup device outside the namespace.
+		fmt.Sprintf("ip addr add %s/24 dev %s", peerIP, peer),
+		fmt.Sprintf("ip link set %s up", peer),
+
+		// Setup device inside the namespace.
+		fmt.Sprintf("ip netns add %s", cid),
+		fmt.Sprintf("ip link set %s netns %s", veth, cid),
+		fmt.Sprintf("ip netns exec %s ip addr add %s/24 dev %s", cid, c.ip, veth),
+		fmt.Sprintf("ip netns exec %s ip link set %s up", cid, veth),
+		fmt.Sprintf("ip netns exec %s ip link set lo up", cid),
+		fmt.Sprintf("ip netns exec %s ip route add default via %s", cid, peerIP),
+
+		// Enable network access.
+		"sysctl -w net.ipv4.ip_forward=1",
+		fmt.Sprintf("iptables -t nat -A POSTROUTING -s %s -o %s -j MASQUERADE", c.ip, dev),
+		fmt.Sprintf("iptables -A FORWARD -i %s -o %s -j ACCEPT", dev, peer),
+		fmt.Sprintf("iptables -A FORWARD -o %s -i %s -j ACCEPT", dev, peer),
+	}
+
+	for _, cmd := range cmds {
+		log.Debugf("Run %q", cmd)
+		args := strings.Split(cmd, " ")
+		c := exec.Command(args[0], args[1:]...)
+		if err := c.Run(); err != nil {
+			return nil, fmt.Errorf("failed to run %q: %v", cmd, err)
+		}
+	}
+
+	if err := makeFile("/etc/resolv.conf", "nameserver 8.8.8.8\n", spec); err != nil {
+		return nil, err
+	}
+	if err := makeFile("/etc/hostname", cid+"\n", spec); err != nil {
+		return nil, err
+	}
+	hosts := fmt.Sprintf("127.0.0.1\tlocalhost\n%s\t%s\n", c.ip, cid)
+	if err := makeFile("/etc/hosts", hosts, spec); err != nil {
+		return nil, err
+	}
+
+	if spec.Linux == nil {
+		spec.Linux = &specs.Linux{}
+	}
+	netns := specs.LinuxNamespace{
+		Type: specs.NetworkNamespace,
+		Path: filepath.Join("/var/run/netns", cid),
+	}
+	spec.Linux.Namespaces = append(spec.Linux.Namespaces, netns)
+
+	return func() { c.cleanNet(cid, dev) }, nil
+}
+
+func (c *Do) cleanNet(cid, dev string) {
+	veth, peer := deviceNames(cid)
+
+	cmds := []string{
+		fmt.Sprintf("ip link delete %s", peer),
+		fmt.Sprintf("ip netns delete %s", cid),
+
+		fmt.Sprintf("iptables -t nat -D POSTROUTING -s %s/24 -o %s -j MASQUERADE", c.ip, dev),
+		fmt.Sprintf("iptables -D FORWARD -i %s -o %s -j ACCEPT", dev, veth),
+		fmt.Sprintf("iptables -D FORWARD -o %s -i %s -j ACCEPT", dev, veth),
+	}
+
+	for _, cmd := range cmds {
+		log.Debugf("Run %q", cmd)
+		args := strings.Split(cmd, " ")
+		c := exec.Command(args[0], args[1:]...)
+		if err := c.Run(); err != nil {
+			log.Warningf("Failed to run %q: %v", cmd, err)
+		}
+	}
+}
+
+func deviceNames(cid string) (string, string) {
+	// Device name is limited to 15 letters.
+	return "ve-" + cid, "vp-" + cid
+
+}
+
+func defaultDevice() (string, error) {
+	out, err := exec.Command("ip", "route", "list", "default").CombinedOutput()
+	if err != nil {
+		return "", err
+	}
+	parts := strings.Split(string(out), " ")
+	if len(parts) < 5 {
+		return "", fmt.Errorf("malformed %q output: %q", "ip route list default", string(out))
+	}
+	return parts[4], nil
+}
+
+func makeFile(dest, content string, spec *specs.Spec) error {
+	tmpFile, err := ioutil.TempFile("", filepath.Base(dest))
+	if err != nil {
+		return err
+	}
+	if _, err := tmpFile.WriteString(content); err != nil {
+		return err
+	}
+	spec.Mounts = append(spec.Mounts, specs.Mount{
+		Source:      tmpFile.Name(),
+		Destination: dest,
+		Type:        "bind",
+		Options:     []string{"ro"},
+	})
+	return nil
+}
+
+func calculatePeerIP(ip string) (string, error) {
+	parts := strings.Split(ip, ".")
+	if len(parts) != 4 {
+		return "", fmt.Errorf("invalid IP format %q", ip)
+	}
+	n, err := strconv.Atoi(parts[3])
+	if err != nil {
+		return "", fmt.Errorf("invalid IP format %q: %v", ip, err)
+	}
+	n++
+	if n > 255 {
+		n = 1
+	}
+	return fmt.Sprintf("%s.%s.%s.%d", parts[0], parts[1], parts[2], n), nil
+}