cio.copyIO: fix pipes potentially not being closed (Windows)

The defer functions were checking the local variable, and would therefore
not be executed, as the function returned if an error occurred.

Perhaps best illustrated when renaming the local variables;

    if fifos.Stdin != "" {
        l, err1 := winio.ListenPipe(fifos.Stdin, nil)
        if err1 != nil {
            return nil, errors.Wrapf(err1, "failed to create stdin pipe %s", fifos.Stdin)
        }
        defer func(l net.Listener) {
            if err1 != nil {
                l.Close()
            }
        }(l)
        // ...
    }

    if fifos.Stdout != "" {
        l, err2 := winio.ListenPipe(fifos.Stdout, nil)
        if err2 != nil {
            return nil, errors.Wrapf(err2, "failed to create stdout pipe %s", fifos.Stdout)
        }
        defer func(l net.Listener) {
            if err2 != nil {
                l.Close()
            }
        }(l)
        // ....
    }

This patch changes the function to use a named return variable, and to use
a single `defer()` that closes all pipes.

Signed-off-by: Sebastiaan van Stijn <github@gone.nl>

cio/io_windows.go

@@ -20,7 +20,6 @@ import (
 	"context"
 	"fmt"
 	"io"
-	"net"
 
 	winio "github.com/Microsoft/go-winio"
 	"github.com/containerd/containerd/log"
@@ -43,21 +42,28 @@ func NewFIFOSetInDir(_, id string, terminal bool) (*FIFOSet, error) {
 	}, nil), nil
 }
 
-func copyIO(fifos *FIFOSet, ioset *Streams) (*cio, error) {
+func copyIO(fifos *FIFOSet, ioset *Streams) (_ *cio, retErr error) {
 	var (
 		set []io.Closer
 	)
 
+	defer func() {
+		if retErr == nil {
+			return
+		}
+		for _, closer := range set {
+			if closer == nil {
+				continue
+			}
+			_ = closer.Close()
+		}
+	}()
+
 	if fifos.Stdin != "" {
 		l, err := winio.ListenPipe(fifos.Stdin, nil)
 		if err != nil {
 			return nil, errors.Wrapf(err, "failed to create stdin pipe %s", fifos.Stdin)
 		}
-		defer func(l net.Listener) {
-			if err != nil {
-				l.Close()
-			}
-		}(l)
 		set = append(set, l)
 
 		go func() {
@@ -81,11 +87,6 @@ func copyIO(fifos *FIFOSet, ioset *Streams) (*cio, error) {
 		if err != nil {
 			return nil, errors.Wrapf(err, "failed to create stdout pipe %s", fifos.Stdout)
 		}
-		defer func(l net.Listener) {
-			if err != nil {
-				l.Close()
-			}
-		}(l)
 		set = append(set, l)
 
 		go func() {
@@ -109,11 +110,6 @@ func copyIO(fifos *FIFOSet, ioset *Streams) (*cio, error) {
 		if err != nil {
 			return nil, errors.Wrapf(err, "failed to create stderr pipe %s", fifos.Stderr)
 		}
-		defer func(l net.Listener) {
-			if err != nil {
-				l.Close()
-			}
-		}(l)
 		set = append(set, l)
 
 		go func() {