sd-notify: do not hang when NOTIFY_SOCKET is used with create

if NOTIFY_SOCKET is used, do not block the main runc process waiting
for events on the notify socket.  Bind mount the parent directory of
the notify socket, so that "start" can create the socket and it is
still accessible from the container.

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

notify_socket.go

@@ -7,11 +7,13 @@ import (
 	"fmt"
 	"net"
 	"os"
+	"path"
 	"path/filepath"
+	"strconv"
+	"time"
 
+	"github.com/opencontainers/runc/libcontainer"
 	"github.com/opencontainers/runtime-spec/specs-go"
-
-	"github.com/sirupsen/logrus"
 	"github.com/urfave/cli"
 )
 
@@ -27,12 +29,12 @@ func newNotifySocket(context *cli.Context, notifySocketHost string, id string) *
 	}
 
 	root := filepath.Join(context.GlobalString("root"), id)
-	path := filepath.Join(root, "notify.sock")
+	socketPath := filepath.Join(root, "notify", "notify.sock")
 
 	notifySocket := &notifySocket{
 		socket:     nil,
 		host:       notifySocketHost,
-		socketPath: path,
+		socketPath: socketPath,
 	}
 
 	return notifySocket
@@ -44,13 +46,19 @@ func (s *notifySocket) Close() error {
 
 // If systemd is supporting sd_notify protocol, this function will add support
 // for sd_notify protocol from within the container.
-func (s *notifySocket) setupSpec(context *cli.Context, spec *specs.Spec) {
-	mount := specs.Mount{Destination: s.host, Source: s.socketPath, Options: []string{"bind"}}
+func (s *notifySocket) setupSpec(context *cli.Context, spec *specs.Spec) error {
+	pathInContainer := filepath.Join("/run/notify", path.Base(s.socketPath))
+	mount := specs.Mount{
+		Destination: path.Dir(pathInContainer),
+		Source:      path.Dir(s.socketPath),
+		Options:     []string{"bind", "nosuid", "noexec", "nodev", "ro"},
+	}
 	spec.Mounts = append(spec.Mounts, mount)
-	spec.Process.Env = append(spec.Process.Env, fmt.Sprintf("NOTIFY_SOCKET=%s", s.host))
+	spec.Process.Env = append(spec.Process.Env, fmt.Sprintf("NOTIFY_SOCKET=%s", pathInContainer))
+	return nil
 }
 
-func (s *notifySocket) setupSocket() error {
+func (s *notifySocket) bindSocket() error {
 	addr := net.UnixAddr{
 		Name: s.socketPath,
 		Net:  "unixgram",
@@ -71,46 +79,92 @@ func (s *notifySocket) setupSocket() error {
 	return nil
 }
 
-// pid1 must be set only with -d, as it is used to set the new process as the main process
-// for the service in systemd
-func (s *notifySocket) run(pid1 int) {
-	buf := make([]byte, 512)
-	notifySocketHostAddr := net.UnixAddr{Name: s.host, Net: "unixgram"}
+func (s *notifySocket) setupSocketDirectory() error {
+	return os.Mkdir(path.Dir(s.socketPath), 0755)
+}
+
+func notifySocketStart(context *cli.Context, notifySocketHost, id string) (*notifySocket, error) {
+	notifySocket := newNotifySocket(context, notifySocketHost, id)
+	if notifySocket == nil {
+		return nil, nil
+	}
+
+	if err := notifySocket.bindSocket(); err != nil {
+		return nil, err
+	}
+	return notifySocket, nil
+}
+
+func (n *notifySocket) waitForContainer(container libcontainer.Container) error {
+	s, err := container.State()
+	if err != nil {
+		return err
+	}
+	return n.run(s.InitProcessPid)
+}
+
+func (n *notifySocket) run(pid1 int) error {
+	if n.socket == nil {
+		return nil
+	}
+	notifySocketHostAddr := net.UnixAddr{Name: n.host, Net: "unixgram"}
 	client, err := net.DialUnix("unixgram", nil, &notifySocketHostAddr)
 	if err != nil {
-		logrus.Error(err)
-		return
+		return err
 	}
-	for {
-		r, err := s.socket.Read(buf)
-		if err != nil {
-			break
-		}
-		var out bytes.Buffer
-		for _, line := range bytes.Split(buf[0:r], []byte{'\n'}) {
-			if bytes.HasPrefix(line, []byte("READY=")) {
-				_, err = out.Write(line)
-				if err != nil {
-					return
-				}
 
-				_, err = out.Write([]byte{'\n'})
-				if err != nil {
-					return
-				}
+	ticker := time.NewTicker(time.Millisecond * 100)
+	defer ticker.Stop()
 
-				_, err = client.Write(out.Bytes())
-				if err != nil {
-					return
-				}
-
-				// now we can inform systemd to use pid1 as the pid to monitor
-				if pid1 > 0 {
-					newPid := fmt.Sprintf("MAINPID=%d\n", pid1)
-					client.Write([]byte(newPid))
-				}
+	fileChan := make(chan []byte)
+	go func() {
+		for {
+			buf := make([]byte, 4096)
+			r, err := n.socket.Read(buf)
+			if err != nil {
 				return
 			}
+			got := buf[0:r]
+			// systemd-ready sends a single datagram with the state string as payload,
+			// so we don't need to worry about partial messages.
+			for _, line := range bytes.Split(got, []byte{'\n'}) {
+				if bytes.HasPrefix(got, []byte("READY=")) {
+					fileChan <- line
+					return
+				}
+			}
+
+		}
+	}()
+
+	for {
+		select {
+		case <-ticker.C:
+			_, err := os.Stat(filepath.Join("/proc", strconv.Itoa(pid1)))
+			if err != nil {
+				return nil
+			}
+		case b := <-fileChan:
+			var out bytes.Buffer
+			_, err = out.Write(b)
+			if err != nil {
+				return err
+			}
+
+			_, err = out.Write([]byte{'\n'})
+			if err != nil {
+				return err
+			}
+
+			_, err = client.Write(out.Bytes())
+			if err != nil {
+				return err
+			}
+
+			// now we can inform systemd to use pid1 as the pid to monitor
+			newPid := fmt.Sprintf("MAINPID=%d\n", pid1)
+			client.Write([]byte(newPid))
+			return nil
 		}
 	}
 }

signals.go

@@ -70,6 +70,7 @@ func (h *signalHandler) forward(process *libcontainer.Process, tty *tty, detach
 			h.notifySocket.run(pid1)
 			return 0, nil
 		}
+		h.notifySocket.run(os.Getpid())
 		go h.notifySocket.run(0)
 	}
 
@@ -97,9 +98,6 @@ func (h *signalHandler) forward(process *libcontainer.Process, tty *tty, detach
 					// status because we must ensure that any of the go specific process
 					// fun such as flushing pipes are complete before we return.
 					process.Wait()
-					if h.notifySocket != nil {
-						h.notifySocket.Close()
-					}
 					return e.status, nil
 				}
 			}

start.go

@@ -3,6 +3,7 @@ package main
 import (
 	"errors"
 	"fmt"
+	"os"
 
 	"github.com/opencontainers/runc/libcontainer"
 	"github.com/urfave/cli"
@@ -31,7 +32,17 @@ your host.`,
 		}
 		switch status {
 		case libcontainer.Created:
-			return container.Exec()
+			notifySocket, err := notifySocketStart(context, os.Getenv("NOTIFY_SOCKET"), container.ID())
+			if err != nil {
+				return err
+			}
+			if err := container.Exec(); err != nil {
+				return err
+			}
+			if notifySocket != nil {
+				return notifySocket.waitForContainer(container)
+			}
+			return nil
 		case libcontainer.Stopped:
 			return errors.New("cannot start a container that has stopped")
 		case libcontainer.Running:

utils_linux.go

@@ -408,7 +408,9 @@ func startContainer(context *cli.Context, spec *specs.Spec, action CtAct, criuOp
 
 	notifySocket := newNotifySocket(context, os.Getenv("NOTIFY_SOCKET"), id)
 	if notifySocket != nil {
-		notifySocket.setupSpec(context, spec)
+		if err := notifySocket.setupSpec(context, spec); err != nil {
+			return -1, err
+		}
 	}
 
 	container, err := createContainer(context, id, spec)
@@ -417,10 +419,16 @@ func startContainer(context *cli.Context, spec *specs.Spec, action CtAct, criuOp
 	}
 
 	if notifySocket != nil {
-		err := notifySocket.setupSocket()
+		err := notifySocket.setupSocketDirectory()
 		if err != nil {
 			return -1, err
 		}
+		if action == CT_ACT_RUN {
+			err := notifySocket.bindSocket()
+			if err != nil {
+				return -1, err
+			}
+		}
 	}
 
 	// Support on-demand socket activation by passing file descriptors into the container init process.