html/template: avoid race when escaping updates template

Fixes #39807

Change-Id: Icf384f800e2541bc753507daa3a9bc7e5d1c3f79
Reviewed-on: https://go-review.googlesource.com/c/go/+/274450
Trust: Ian Lance Taylor <iant@golang.org>
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Roberto Clapis <roberto@golang.org>
Reviewed-by: Russ Cox <rsc@golang.org>

2 files changed, 147 insertions, 13 deletions

diff --git a/src/html/template/exec_test.go b/src/html/template/exec_test.go
index 232945a0bb..eb00824260 100644
--- a/src/html/template/exec_test.go
+++ b/src/html/template/exec_test.go
@@ -14,6 +14,7 @@ import (
 	"io"
 	"reflect"
 	"strings"
+	"sync"
 	"testing"
 	"text/template"
 )
@@ -1706,3 +1707,72 @@ func TestIssue31810(t *testing.T) {
 		t.Errorf("%s got %q, expected %q", textCall, b.String(), "result")
 	}
 }
+
+// Issue 39807. There was a race applying escapeTemplate.
+
+const raceText = `
+{{- define "jstempl" -}}
+var v = "v";
+{{- end -}}
+<script type="application/javascript">
+{{ template "jstempl" $ }}
+</script>
+`
+
+func TestEscapeRace(t *testing.T) {
+	tmpl := New("")
+	_, err := tmpl.New("templ.html").Parse(raceText)
+	if err != nil {
+		t.Fatal(err)
+	}
+	const count = 20
+	for i := 0; i < count; i++ {
+		_, err := tmpl.New(fmt.Sprintf("x%d.html", i)).Parse(`{{ template "templ.html" .}}`)
+		if err != nil {
+			t.Fatal(err)
+		}
+	}
+
+	var wg sync.WaitGroup
+	for i := 0; i < 10; i++ {
+		wg.Add(1)
+		go func() {
+			defer wg.Done()
+			for j := 0; j < count; j++ {
+				sub := tmpl.Lookup(fmt.Sprintf("x%d.html", j))
+				if err := sub.Execute(io.Discard, nil); err != nil {
+					t.Error(err)
+				}
+			}
+		}()
+	}
+	wg.Wait()
+}
+
+func TestRecursiveExecute(t *testing.T) {
+	tmpl := New("")
+
+	recur := func() (HTML, error) {
+		var sb strings.Builder
+		if err := tmpl.ExecuteTemplate(&sb, "subroutine", nil); err != nil {
+			t.Fatal(err)
+		}
+		return HTML(sb.String()), nil
+	}
+
+	m := FuncMap{
+		"recur": recur,
+	}
+
+	top, err := tmpl.New("x.html").Funcs(m).Parse(`{{recur}}`)
+	if err != nil {
+		t.Fatal(err)
+	}
+	_, err = tmpl.New("subroutine").Parse(`<a href="/x?p={{"'a<b'"}}">`)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if err := top.Execute(io.Discard, nil); err != nil {
+		t.Fatal(err)
+	}
+}
diff --git a/src/html/template/template.go b/src/html/template/template.go
index 69312d36fd..09d71d43e2 100644
--- a/src/html/template/template.go
+++ b/src/html/template/template.go
@@ -11,6 +11,7 @@ import (
 	"os"
 	"path"
 	"path/filepath"
+	"reflect"
 	"sync"
 	"text/template"
 	"text/template/parse"
@@ -26,7 +27,9 @@ type Template struct {
 	// template's in sync.
 	text *template.Template
 	// The underlying template's parse tree, updated to be HTML-safe.
-	Tree       *parse.Tree
+	Tree *parse.Tree
+	// The original functions, before wrapping.
+	funcMap    FuncMap
 	*nameSpace // common to all associated templates
 }
 
@@ -35,7 +38,7 @@ var escapeOK = fmt.Errorf("template escaped correctly")
 
 // nameSpace is the data structure shared by all templates in an association.
 type nameSpace struct {
-	mu      sync.Mutex
+	mu      sync.RWMutex
 	set     map[string]*Template
 	escaped bool
 	esc     escaper
@@ -45,8 +48,8 @@ type nameSpace struct {
 // itself.
 func (t *Template) Templates() []*Template {
 	ns := t.nameSpace
-	ns.mu.Lock()
-	defer ns.mu.Unlock()
+	ns.mu.RLock()
+	defer ns.mu.RUnlock()
 	// Return a slice so we don't expose the map.
 	m := make([]*Template, 0, len(ns.set))
 	for _, v := range ns.set {
@@ -84,8 +87,8 @@ func (t *Template) checkCanParse() error {
 	if t == nil {
 		return nil
 	}
-	t.nameSpace.mu.Lock()
-	defer t.nameSpace.mu.Unlock()
+	t.nameSpace.mu.RLock()
+	defer t.nameSpace.mu.RUnlock()
 	if t.nameSpace.escaped {
 		return fmt.Errorf("html/template: cannot Parse after Execute")
 	}
@@ -94,6 +97,16 @@ func (t *Template) checkCanParse() error {
 
 // escape escapes all associated templates.
 func (t *Template) escape() error {
+	t.nameSpace.mu.RLock()
+	escapeErr := t.escapeErr
+	t.nameSpace.mu.RUnlock()
+	if escapeErr != nil {
+		if escapeErr == escapeOK {
+			return nil
+		}
+		return escapeErr
+	}
+
 	t.nameSpace.mu.Lock()
 	defer t.nameSpace.mu.Unlock()
 	t.nameSpace.escaped = true
@@ -121,6 +134,8 @@ func (t *Template) Execute(wr io.Writer, data interface{}) error {
 	if err := t.escape(); err != nil {
 		return err
 	}
+	t.nameSpace.mu.RLock()
+	defer t.nameSpace.mu.RUnlock()
 	return t.text.Execute(wr, data)
 }
 
@@ -136,6 +151,8 @@ func (t *Template) ExecuteTemplate(wr io.Writer, name string, data interface{})
 	if err != nil {
 		return err
 	}
+	t.nameSpace.mu.RLock()
+	defer t.nameSpace.mu.RUnlock()
 	return tmpl.text.Execute(wr, data)
 }
 
@@ -143,13 +160,27 @@ func (t *Template) ExecuteTemplate(wr io.Writer, name string, data interface{})
 // is escaped, or returns an error if it cannot be. It returns the named
 // template.
 func (t *Template) lookupAndEscapeTemplate(name string) (tmpl *Template, err error) {
-	t.nameSpace.mu.Lock()
-	defer t.nameSpace.mu.Unlock()
-	t.nameSpace.escaped = true
+	t.nameSpace.mu.RLock()
 	tmpl = t.set[name]
+	var escapeErr error
+	if tmpl != nil {
+		escapeErr = tmpl.escapeErr
+	}
+	t.nameSpace.mu.RUnlock()
+
 	if tmpl == nil {
 		return nil, fmt.Errorf("html/template: %q is undefined", name)
 	}
+	if escapeErr != nil {
+		if escapeErr != escapeOK {
+			return nil, escapeErr
+		}
+		return tmpl, nil
+	}
+
+	t.nameSpace.mu.Lock()
+	defer t.nameSpace.mu.Unlock()
+	t.nameSpace.escaped = true
 	if tmpl.escapeErr != nil && tmpl.escapeErr != escapeOK {
 		return nil, tmpl.escapeErr
 	}
@@ -229,6 +260,7 @@ func (t *Template) AddParseTree(name string, tree *parse.Tree) (*Template, error
 		nil,
 		text,
 		text.Tree,
+		nil,
 		t.nameSpace,
 	}
 	t.set[name] = ret
@@ -259,8 +291,10 @@ func (t *Template) Clone() (*Template, error) {
 		nil,
 		textClone,
 		textClone.Tree,
+		t.funcMap,
 		ns,
 	}
+	ret.wrapFuncs()
 	ret.set[ret.Name()] = ret
 	for _, x := range textClone.Templates() {
 		name := x.Name()
@@ -269,12 +303,15 @@ func (t *Template) Clone() (*Template, error) {
 			return nil, fmt.Errorf("html/template: cannot Clone %q after it has executed", t.Name())
 		}
 		x.Tree = x.Tree.Copy()
-		ret.set[name] = &Template{
+		tc := &Template{
 			nil,
 			x,
 			x.Tree,
+			src.funcMap,
 			ret.nameSpace,
 		}
+		tc.wrapFuncs()
+		ret.set[name] = tc
 	}
 	// Return the template associated with the name of this template.
 	return ret.set[ret.Name()], nil
@@ -288,6 +325,7 @@ func New(name string) *Template {
 		nil,
 		template.New(name),
 		nil,
+		nil,
 		ns,
 	}
 	tmpl.set[name] = tmpl
@@ -313,6 +351,7 @@ func (t *Template) new(name string) *Template {
 		nil,
 		t.text.New(name),
 		nil,
+		nil,
 		t.nameSpace,
 	}
 	if existing, ok := tmpl.set[name]; ok {
@@ -343,10 +382,35 @@ type FuncMap map[string]interface{}
 // type. However, it is legal to overwrite elements of the map. The return
 // value is the template, so calls can be chained.
 func (t *Template) Funcs(funcMap FuncMap) *Template {
-	t.text.Funcs(template.FuncMap(funcMap))
+	t.funcMap = funcMap
+	t.wrapFuncs()
 	return t
 }
 
+// wrapFuncs records the functions with text/template. We wrap them to
+// unlock the nameSpace. See TestRecursiveExecute for a test case.
+func (t *Template) wrapFuncs() {
+	if len(t.funcMap) == 0 {
+		return
+	}
+	tfuncs := make(template.FuncMap, len(t.funcMap))
+	for name, fn := range t.funcMap {
+		fnv := reflect.ValueOf(fn)
+		wrapper := func(args []reflect.Value) []reflect.Value {
+			t.nameSpace.mu.RUnlock()
+			defer t.nameSpace.mu.RLock()
+			if fnv.Type().IsVariadic() {
+				return fnv.CallSlice(args)
+			} else {
+				return fnv.Call(args)
+			}
+		}
+		wrapped := reflect.MakeFunc(fnv.Type(), wrapper)
+		tfuncs[name] = wrapped.Interface()
+	}
+	t.text.Funcs(tfuncs)
+}
+
 // Delims sets the action delimiters to the specified strings, to be used in
 // subsequent calls to Parse, ParseFiles, or ParseGlob. Nested template
 // definitions will inherit the settings. An empty delimiter stands for the
@@ -360,8 +424,8 @@ func (t *Template) Delims(left, right string) *Template {
 // Lookup returns the template with the given name that is associated with t,
 // or nil if there is no such template.
 func (t *Template) Lookup(name string) *Template {
-	t.nameSpace.mu.Lock()
-	defer t.nameSpace.mu.Unlock()
+	t.nameSpace.mu.RLock()
+	defer t.nameSpace.mu.RUnlock()
 	return t.set[name]
 }