Add synchronization and closure to IO pipes in userns path

The execdriver pipes setup uses OS pipes with fds so that they can be
chown'ed to the remapped root user for proper access. Recent flakiness
in certain short-lived tests (usually via the "exec" path) reveals that
the copy routines are not completing before exit/tear-down.

This fix adds synchronization and proper closure such that these
routines exit successfully.

Docker-DCO-1.1-Signed-off-by: Phil Estes <estesp@linux.vnet.ibm.com> (github: estesp)

daemon/execdriver/native/driver.go

@@ -152,7 +152,9 @@ func (d *Driver) Run(c *execdriver.Command, pipes *execdriver.Pipes, hooks execd
 		User: c.ProcessConfig.User,
 	}
 
-	if err := setupPipes(container, &c.ProcessConfig, p, pipes); err != nil {
+	wg := sync.WaitGroup{}
+	writers, err := setupPipes(container, &c.ProcessConfig, p, pipes, &wg)
+	if err != nil {
 		return execdriver.ExitStatus{ExitCode: -1}, err
 	}
 
@@ -174,6 +176,10 @@ func (d *Driver) Run(c *execdriver.Command, pipes *execdriver.Pipes, hooks execd
 		return execdriver.ExitStatus{ExitCode: -1}, err
 	}
 
+	//close the write end of any opened pipes now that they are dup'ed into the container
+	for _, writer := range writers {
+		writer.Close()
+	}
 	// 'oom' is used to emit 'oom' events to the eventstream, 'oomKilled' is used
 	// to set the 'OOMKilled' flag in state
 	oom := notifyOnOOM(cont)
@@ -202,6 +208,9 @@ func (d *Driver) Run(c *execdriver.Command, pipes *execdriver.Pipes, hooks execd
 		}
 		ps = execErr.ProcessState
 	}
+	// wait for all IO goroutine copiers to finish
+	wg.Wait()
+
 	cont.Destroy()
 	destroyed = true
 	// oomKilled will have an oom event if any process within the container was
@@ -480,24 +489,26 @@ func (t *TtyConsole) Close() error {
 	return t.console.Close()
 }
 
-func setupPipes(container *configs.Config, processConfig *execdriver.ProcessConfig, p *libcontainer.Process, pipes *execdriver.Pipes) error {
+func setupPipes(container *configs.Config, processConfig *execdriver.ProcessConfig, p *libcontainer.Process, pipes *execdriver.Pipes, wg *sync.WaitGroup) ([]io.WriteCloser, error) {
+
+	writers := []io.WriteCloser{}
 
 	rootuid, err := container.HostUID()
 	if err != nil {
-		return err
+		return writers, err
 	}
 
 	if processConfig.Tty {
 		cons, err := p.NewConsole(rootuid)
 		if err != nil {
-			return err
+			return writers, err
 		}
 		term, err := NewTtyConsole(cons, pipes)
 		if err != nil {
-			return err
+			return writers, err
 		}
 		processConfig.Terminal = term
-		return nil
+		return writers, nil
 	}
 	// not a tty--set up stdio pipes
 	term := &execdriver.StdConsole{}
@@ -512,7 +523,7 @@ func setupPipes(container *configs.Config, processConfig *execdriver.ProcessConf
 
 		r, w, err := os.Pipe()
 		if err != nil {
-			return err
+			return writers, err
 		}
 		if pipes.Stdin != nil {
 			go func() {
@@ -521,23 +532,32 @@ func setupPipes(container *configs.Config, processConfig *execdriver.ProcessConf
 			}()
 			p.Stdin = r
 		}
-		return nil
+		return writers, nil
 	}
 
 	// if we have user namespaces enabled (rootuid != 0), we will set
 	// up os pipes for stderr, stdout, stdin so we can chown them to
 	// the proper ownership to allow for proper access to the underlying
 	// fds
-	var fds []int
+	var fds []uintptr
+
+	copyPipes := func(out io.Writer, in io.ReadCloser) {
+		defer wg.Done()
+		io.Copy(out, in)
+		in.Close()
+	}
 
 	//setup stdout
 	r, w, err := os.Pipe()
 	if err != nil {
-		return err
+		w.Close()
+		return writers, err
 	}
-	fds = append(fds, int(r.Fd()), int(w.Fd()))
+	writers = append(writers, w)
+	fds = append(fds, r.Fd(), w.Fd())
 	if pipes.Stdout != nil {
-		go io.Copy(pipes.Stdout, r)
+		wg.Add(1)
+		go copyPipes(pipes.Stdout, r)
 	}
 	term.Closers = append(term.Closers, r)
 	p.Stdout = w
@@ -545,11 +565,14 @@ func setupPipes(container *configs.Config, processConfig *execdriver.ProcessConf
 	//setup stderr
 	r, w, err = os.Pipe()
 	if err != nil {
-		return err
+		w.Close()
+		return writers, err
 	}
-	fds = append(fds, int(r.Fd()), int(w.Fd()))
+	writers = append(writers, w)
+	fds = append(fds, r.Fd(), w.Fd())
 	if pipes.Stderr != nil {
-		go io.Copy(pipes.Stderr, r)
+		wg.Add(1)
+		go copyPipes(pipes.Stderr, r)
 	}
 	term.Closers = append(term.Closers, r)
 	p.Stderr = w
@@ -557,9 +580,10 @@ func setupPipes(container *configs.Config, processConfig *execdriver.ProcessConf
 	//setup stdin
 	r, w, err = os.Pipe()
 	if err != nil {
-		return err
+		r.Close()
+		return writers, err
 	}
-	fds = append(fds, int(r.Fd()), int(w.Fd()))
+	fds = append(fds, r.Fd(), w.Fd())
 	if pipes.Stdin != nil {
 		go func() {
 			io.Copy(w, pipes.Stdin)
@@ -568,11 +592,11 @@ func setupPipes(container *configs.Config, processConfig *execdriver.ProcessConf
 		p.Stdin = r
 	}
 	for _, fd := range fds {
-		if err := syscall.Fchown(fd, rootuid, rootuid); err != nil {
-			return fmt.Errorf("Failed to chown pipes fd: %v", err)
+		if err := syscall.Fchown(int(fd), rootuid, rootuid); err != nil {
+			return writers, fmt.Errorf("Failed to chown pipes fd: %v", err)
 		}
 	}
-	return nil
+	return writers, nil
 }
 
 // SupportsHooks implements the execdriver Driver interface.

daemon/execdriver/native/exec.go

@@ -7,6 +7,7 @@ import (
 	"os"
 	"os/exec"
 	"strings"
+	"sync"
 	"syscall"
 
 	"github.com/docker/docker/daemon/execdriver"
@@ -52,13 +53,19 @@ func (d *Driver) Exec(c *execdriver.Command, processConfig *execdriver.ProcessCo
 	}
 
 	config := active.Config()
-	if err := setupPipes(&config, processConfig, p, pipes); err != nil {
+	wg := sync.WaitGroup{}
+	writers, err := setupPipes(&config, processConfig, p, pipes, &wg)
+	if err != nil {
 		return -1, err
 	}
 
 	if err := active.Start(p); err != nil {
 		return -1, err
 	}
+	//close the write end of any opened pipes now that they are dup'ed into the container
+	for _, writer := range writers {
+		writer.Close()
+	}
 
 	if hooks.Start != nil {
 		pid, err := p.Pid()
@@ -83,5 +90,7 @@ func (d *Driver) Exec(c *execdriver.Command, processConfig *execdriver.ProcessCo
 		}
 		ps = exitErr.ProcessState
 	}
+	// wait for all IO goroutine copiers to finish
+	wg.Wait()
 	return utils.ExitStatus(ps.Sys().(syscall.WaitStatus)), nil
 }