fix(engine): allow limited recursion in templates

This is a backport for PR 7443.

Signed-off-by: Matthew Fisher <matt.fisher@microsoft.com>

pkg/engine/engine.go

@@ -32,6 +32,8 @@ import (
 	"k8s.io/helm/pkg/proto/hapi/chart"
 )
 
+const recursionMaxNums = 1000
+
 // Engine is an implementation of 'cmd/tiller/environment'.Engine that uses Go templates.
 type Engine struct {
 	// FuncMap contains the template functions that will be passed to each
@@ -145,21 +147,22 @@ func (e *Engine) alterFuncMap(t *template.Template, referenceTpls map[string]ren
 		funcMap[k] = v
 	}
 
-	includedNames := make([]string, 0)
+	includedNames := make(map[string]int)
 
 	// Add the 'include' function here so we can close over t.
 	funcMap["include"] = func(name string, data interface{}) (string, error) {
 		buf := bytes.NewBuffer(nil)
-		for _, n := range includedNames {
-			if n == name {
-				return "", errors.Wrapf(fmt.Errorf("unable to excute template"), "rendering template has a nested reference name: %s", name)
+		if v, ok := includedNames[name]; ok {
+			if v > recursionMaxNums {
+				return "", errors.Wrapf(fmt.Errorf("unable to execute template"), "rendering template has a nested reference name: %s", name)
 			}
+			includedNames[name]++
+		} else {
+			includedNames[name] = 1
 		}
-		includedNames = append(includedNames, name)
 		if err := t.ExecuteTemplate(buf, name, data); err != nil {
 			return "", err
 		}
-		includedNames = includedNames[:len(includedNames)-1]
 		return buf.String(), nil
 	}