oci: keep exposed ports busy and leak the fd into conmon

Bind all the specified TCP and UDP ports so that another process
cannot reuse them.  The fd of the listener is then leaked into conmon
so that the socket is kept busy until the container exits.

Closes: https://github.com/projectatomic/libpod/issues/210

Signed-off-by: Giuseppe Scrivano <gscrivan@redhat.com>

Closes: #1100
Approved by: mheon

1 files changed, 58 insertions, 0 deletions

diff --git a/libpod/oci.go b/libpod/oci.go
index 3eaf159e7..0483c0d53 100644
--- a/libpod/oci.go
+++ b/libpod/oci.go
@@ -5,6 +5,7 @@ import (
 	"encoding/json"
 	"fmt"
 	"io/ioutil"
+	"net"
 	"os"
 	"os/exec"
 	"path/filepath"
@@ -15,6 +16,7 @@ import (
 	"time"
 
 	"github.com/coreos/go-systemd/activation"
+	"github.com/cri-o/ocicni/pkg/ocicni"
 	spec "github.com/opencontainers/runtime-spec/specs-go"
 	"github.com/opencontainers/selinux/go-selinux"
 	"github.com/opencontainers/selinux/go-selinux/label"
@@ -177,6 +179,51 @@ func waitPidsStop(pids []int, timeout time.Duration) error {
 	}
 }
 
+func bindPorts(ports []ocicni.PortMapping) ([]*os.File, error) {
+	var files []*os.File
+	for _, i := range ports {
+		switch i.Protocol {
+		case "udp":
+			addr, err := net.ResolveUDPAddr("udp", fmt.Sprintf("%s:%d", i.HostIP, i.HostPort))
+			if err != nil {
+				return nil, errors.Wrapf(err, "cannot resolve the UDP address")
+			}
+
+			server, err := net.ListenUDP("udp", addr)
+			if err != nil {
+				return nil, errors.Wrapf(err, "cannot listen on the UDP port")
+			}
+			f, err := server.File()
+			if err != nil {
+				return nil, errors.Wrapf(err, "cannot get file for UDP socket")
+			}
+			files = append(files, f)
+			break
+
+		case "tcp":
+			addr, err := net.ResolveTCPAddr("tcp4", fmt.Sprintf("%s:%d", i.HostIP, i.HostPort))
+			if err != nil {
+				return nil, errors.Wrapf(err, "cannot resolve the TCP address")
+			}
+
+			server, err := net.ListenTCP("tcp4", addr)
+			if err != nil {
+				return nil, errors.Wrapf(err, "cannot listen on the TCP port")
+			}
+			f, err := server.File()
+			if err != nil {
+				return nil, errors.Wrapf(err, "cannot get file for TCP socket")
+			}
+			files = append(files, f)
+			break
+		default:
+			return nil, fmt.Errorf("unknown protocol %s", i.Protocol)
+
+		}
+	}
+	return files, nil
+}
+
 func (r *OCIRuntime) createOCIContainer(ctr *Container, cgroupParent string) (err error) {
 	var stderrBuf bytes.Buffer
 
@@ -259,6 +306,17 @@ func (r *OCIRuntime) createOCIContainer(ctr *Container, cgroupParent string) (er
 	cmd.Env = append(r.conmonEnv, fmt.Sprintf("_OCI_SYNCPIPE=%d", 3))
 	cmd.Env = append(cmd.Env, fmt.Sprintf("_OCI_STARTPIPE=%d", 4))
 	cmd.Env = append(cmd.Env, fmt.Sprintf("XDG_RUNTIME_DIR=%s", runtimeDir))
+
+	ports, err := bindPorts(ctr.config.PortMappings)
+	if err != nil {
+		return err
+	}
+
+	// Leak the port we bound in the conmon process.  These fd's won't be used
+	// by the container and conmon will keep the ports busy so that another
+	// process cannot use them.
+	cmd.ExtraFiles = append(cmd.ExtraFiles, ports...)
+
 	if notify, ok := os.LookupEnv("NOTIFY_SOCKET"); ok {
 		cmd.Env = append(cmd.Env, fmt.Sprintf("NOTIFY_SOCKET=%s", notify))
 	}