Add timeout for session.Wait

session.Wait() can hand indefinitely, this adhoc solution pivots after
5 seconds of waiting time.

t.session is now also checked for nil, which led to panic in rare cases.

Signed-off-by: Paulo Gomes <paulo.gomes@weave.works>

pkg/git/libgit2/managed/ssh.go

@@ -53,6 +53,7 @@ import (
 	"net/url"
 	"runtime"
 	"strings"
+	"time"
 
 	"golang.org/x/crypto/ssh"
 
@@ -214,14 +215,40 @@ func (t *sshSmartSubtransport) Action(urlString string, action git2go.SmartServi
 }
 
 func (t *sshSmartSubtransport) Close() error {
+	var returnErr error
 	t.currentStream = nil
 	if t.client != nil {
-		t.stdin.Close()
-		t.session.Wait()
-		t.session.Close()
+		if err := t.stdin.Close(); err != nil {
+			returnErr = fmt.Errorf("cannot close stdin: %w", err)
+		}
 		t.client = nil
 	}
-	return nil
+	if t.session != nil {
+
+		// In some scenarios session.Wait() can hang indefinitely.
+		// Here we force a timeout to skip the wait and continue
+		// with closing the session.
+		done := make(chan error, 1)
+		go func() {
+			err := t.session.Wait()
+			done <- err
+		}()
+
+		select {
+		case doneErr := <-done:
+			if doneErr != nil {
+				returnErr = fmt.Errorf("cannot wait session: %w", doneErr)
+			}
+		case <-time.After(5 * time.Second):
+			returnErr = fmt.Errorf("timed out waiting for session.Wait()")
+		}
+
+		if err := t.session.Close(); err != nil {
+			returnErr = fmt.Errorf("cannot close session: %w", err)
+		}
+	}
+
+	return returnErr
 }
 
 func (t *sshSmartSubtransport) Free() {