rootlessport: fix potential hang

write to the error pipe only in case of an error.  Otherwise we may
end up in a race condition in the select statement below as the read
from errChan happens before initComplete and the function returns
immediately nil.

Closes: containers#5182

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

pkg/rootlessport/rootlessport_linux.go

@@ -122,6 +122,7 @@ func parent() error {
 			logrus.WithError(driverErr).Warn("parent driver exited")
 		}
 		errCh <- driverErr
+		close(errCh)
 	}()
 	opaque := driver.OpaqueForChild()
 	logrus.Infof("opaque=%+v", opaque)
@@ -142,7 +143,7 @@ func parent() error {
 	}()
 
 	// reexec the child process in the child netns
-	cmd := exec.Command(fmt.Sprintf("/proc/%d/exe", os.Getpid()))
+	cmd := exec.Command("/proc/self/exe")
 	cmd.Args = []string{reexecChildKey}
 	cmd.Stdin = childQuitR
 	cmd.Stdout = &logrusWriter{prefix: "child"}
@@ -164,12 +165,19 @@ func parent() error {
 
 	logrus.Info("waiting for initComplete")
 	// wait for the child to connect to the parent
-	select {
-	case <-initComplete:
-		logrus.Infof("initComplete is closed; parent and child established the communication channel")
-	case err := <-errCh:
-		return err
+outer:
+	for {
+		select {
+		case <-initComplete:
+			logrus.Infof("initComplete is closed; parent and child established the communication channel")
+			break outer
+		case err := <-errCh:
+			if err != nil {
+				return err
+			}
+		}
 	}
+
 	defer func() {
 		logrus.Info("stopping parent driver")
 		quit <- struct{}{}