[FEAT] Enable ambiguous character detection in configured contexts

- The ambiguous character detection is an important security feature to
combat against sourcebase attacks (https://trojansource.codes/).
- However there are a few problems with the feature as it stands
today (i) it's apparantly an big performance hitter, it's twice as slow
as syntax highlighting (ii) it contains false positives, because it's
reporting valid problems but not valid within the context of a
programming language (ambiguous charachters in code comments being a
prime example) that can lead to security issues (iii) charachters from
certain languages always being marked as ambiguous. It's a lot of effort
to fix the aforementioned issues.
- Therefore, make it configurable in which context the ambiguous
character detection should be run, this avoids running detection in all
contexts such as file views, but still enable it in commits and pull
requests diffs where it matters the most. Ideally this also becomes an
per-repository setting, but the code architecture doesn't allow for a
clean implementation of that.
- Adds unit test.
- Adds integration tests to ensure that the contexts and instance-wide
is respected (and that ambigious charachter detection actually work in
different places).
- Ref: https://codeberg.org/forgejo/forgejo/pulls/2395#issuecomment-1575547
- Ref: https://codeberg.org/forgejo/forgejo/issues/564

modules/charset/escape.go

@@ -10,6 +10,7 @@ package charset
 import (
 	"html/template"
 	"io"
+	"slices"
 	"strings"
 
 	"code.gitea.io/gitea/modules/log"
@@ -20,16 +21,29 @@ import (
 // RuneNBSP is the codepoint for NBSP
 const RuneNBSP = 0xa0
 
+type escapeContext string
+
+// Keep this consistent with the documentation of [ui].SKIP_ESCAPE_CONTEXTS
+// Defines the different contexts that could be used to escape in.
+const (
+	// Wiki pages.
+	WikiContext escapeContext = "wiki"
+	// Rendered content (except markup), source code and blames.
+	FileviewContext escapeContext = "file-view"
+	// Commits or pull requet's diff.
+	DiffContext escapeContext = "diff"
+)
+
 // EscapeControlHTML escapes the unicode control sequences in a provided html document
-func EscapeControlHTML(html template.HTML, locale translation.Locale, allowed ...rune) (escaped *EscapeStatus, output template.HTML) {
+func EscapeControlHTML(html template.HTML, locale translation.Locale, context escapeContext, allowed ...rune) (escaped *EscapeStatus, output template.HTML) {
 	sb := &strings.Builder{}
-	escaped, _ = EscapeControlReader(strings.NewReader(string(html)), sb, locale, allowed...) // err has been handled in EscapeControlReader
+	escaped, _ = EscapeControlReader(strings.NewReader(string(html)), sb, locale, context, allowed...) // err has been handled in EscapeControlReader
 	return escaped, template.HTML(sb.String())
 }
 
 // EscapeControlReader escapes the unicode control sequences in a provided reader of HTML content and writer in a locale and returns the findings as an EscapeStatus
-func EscapeControlReader(reader io.Reader, writer io.Writer, locale translation.Locale, allowed ...rune) (escaped *EscapeStatus, err error) {
-	if !setting.UI.AmbiguousUnicodeDetection {
+func EscapeControlReader(reader io.Reader, writer io.Writer, locale translation.Locale, context escapeContext, allowed ...rune) (escaped *EscapeStatus, err error) {
+	if !setting.UI.AmbiguousUnicodeDetection || slices.Contains(setting.UI.SkipEscapeContexts, string(context)) {
 		_, err = io.Copy(writer, reader)
 		return &EscapeStatus{}, err
 	}

modules/charset/escape_test.go

@@ -4,6 +4,7 @@
 package charset
 
 import (
+	"html/template"
 	"strings"
 	"testing"
 
@@ -14,6 +15,8 @@ import (
 	"github.com/stretchr/testify/assert"
 )
 
+var testContext = escapeContext("test")
+
 type escapeControlTest struct {
 	name   string
 	text   string
@@ -159,7 +162,7 @@ func TestEscapeControlReader(t *testing.T) {
 	for _, tt := range tests {
 		t.Run(tt.name, func(t *testing.T) {
 			output := &strings.Builder{}
-			status, err := EscapeControlReader(strings.NewReader(tt.text), output, &translation.MockLocale{})
+			status, err := EscapeControlReader(strings.NewReader(tt.text), output, &translation.MockLocale{}, testContext)
 			assert.NoError(t, err)
 			assert.Equal(t, tt.status, *status)
 			assert.Equal(t, tt.result, output.String())
@@ -169,9 +172,22 @@ func TestEscapeControlReader(t *testing.T) {
 
 func TestSettingAmbiguousUnicodeDetection(t *testing.T) {
 	defer test.MockVariableValue(&setting.UI.AmbiguousUnicodeDetection, true)()
-	_, out := EscapeControlHTML("a test", &translation.MockLocale{})
+
+	_, out := EscapeControlHTML("a test", &translation.MockLocale{}, testContext)
 	assert.EqualValues(t, `a<span class="escaped-code-point" data-escaped="[U+00A0]"><span class="char"> </span></span>test`, out)
 	setting.UI.AmbiguousUnicodeDetection = false
-	_, out = EscapeControlHTML("a test", &translation.MockLocale{})
+	_, out = EscapeControlHTML("a test", &translation.MockLocale{}, testContext)
 	assert.EqualValues(t, `a test`, out)
 }
+
+func TestAmbiguousUnicodeDetectionContext(t *testing.T) {
+	defer test.MockVariableValue(&setting.UI.SkipEscapeContexts, []string{"test"})()
+
+	input := template.HTML("a test")
+
+	_, out := EscapeControlHTML(input, &translation.MockLocale{}, escapeContext("not-test"))
+	assert.EqualValues(t, `a<span class="escaped-code-point" data-escaped="[U+00A0]"><span class="char"> </span></span>test`, out)
+
+	_, out = EscapeControlHTML(input, &translation.MockLocale{}, testContext)
+	assert.EqualValues(t, input, out)
+}

modules/setting/ui.go

@@ -38,6 +38,7 @@ var UI = struct {
 	PreferredTimestampTense string
 
 	AmbiguousUnicodeDetection bool
+	SkipEscapeContexts        []string
 
 	Notification struct {
 		MinTimeout            time.Duration
@@ -89,6 +90,7 @@ var UI = struct {
 	PreferredTimestampTense: "mixed",
 
 	AmbiguousUnicodeDetection: true,
+	SkipEscapeContexts:        []string{},
 
 	Notification: struct {
 		MinTimeout            time.Duration

routers/web/repo/blame.go

@@ -279,7 +279,7 @@ func renderBlame(ctx *context.Context, blameParts []*git.BlamePart, commitNames
 				lexerName = lexerNameForLine
 			}
 
-			br.EscapeStatus, br.Code = charset.EscapeControlHTML(line, ctx.Locale)
+			br.EscapeStatus, br.Code = charset.EscapeControlHTML(line, ctx.Locale, charset.FileviewContext)
 			rows = append(rows, br)
 			escapeStatus = escapeStatus.Or(br.EscapeStatus)
 		}

routers/web/repo/setting/lfs.go

@@ -307,7 +307,7 @@ func LFSFileGet(ctx *context.Context) {
 
 		// Building code view blocks with line number on server side.
 		escapedContent := &bytes.Buffer{}
-		ctx.Data["EscapeStatus"], _ = charset.EscapeControlReader(rd, escapedContent, ctx.Locale)
+		ctx.Data["EscapeStatus"], _ = charset.EscapeControlReader(rd, escapedContent, ctx.Locale, charset.FileviewContext)
 
 		var output bytes.Buffer
 		lines := strings.Split(escapedContent.String(), "\n")

routers/web/repo/view.go

@@ -338,7 +338,7 @@ func renderReadmeFile(ctx *context.Context, subfolder string, readmeFile *git.Tr
 			log.Error("Read readme content failed: %v", err)
 		}
 		contentEscaped := template.HTMLEscapeString(util.UnsafeBytesToString(content))
-		ctx.Data["EscapeStatus"], ctx.Data["FileContent"] = charset.EscapeControlHTML(template.HTML(contentEscaped), ctx.Locale)
+		ctx.Data["EscapeStatus"], ctx.Data["FileContent"] = charset.EscapeControlHTML(template.HTML(contentEscaped), ctx.Locale, charset.FileviewContext)
 	}
 
 	if !fInfo.isLFSFile && ctx.Repo.CanEnableEditor(ctx, ctx.Doer) {
@@ -572,7 +572,7 @@ func renderFile(ctx *context.Context, entry *git.TreeEntry) {
 			status := &charset.EscapeStatus{}
 			statuses := make([]*charset.EscapeStatus, len(fileContent))
 			for i, line := range fileContent {
-				statuses[i], fileContent[i] = charset.EscapeControlHTML(line, ctx.Locale)
+				statuses[i], fileContent[i] = charset.EscapeControlHTML(line, ctx.Locale, charset.FileviewContext)
 				status = status.Or(statuses[i])
 			}
 			ctx.Data["EscapeStatus"] = status
@@ -678,7 +678,7 @@ func markupRender(ctx *context.Context, renderCtx *markup.RenderContext, input i
 	go func() {
 		sb := &strings.Builder{}
 		// We allow NBSP here this is rendered
-		escaped, _ = charset.EscapeControlReader(markupRd, sb, ctx.Locale, charset.RuneNBSP)
+		escaped, _ = charset.EscapeControlReader(markupRd, sb, ctx.Locale, charset.FileviewContext, charset.RuneNBSP)
 		output = template.HTML(sb.String())
 		close(done)
 	}()

routers/web/repo/wiki.go

@@ -254,7 +254,7 @@ func renderViewPage(ctx *context.Context) (*git.Repository, *git.TreeEntry) {
 		done := make(chan struct{})
 		go func() {
 			// We allow NBSP here this is rendered
-			escaped, _ = charset.EscapeControlReader(markupRd, buf, ctx.Locale, charset.RuneNBSP)
+			escaped, _ = charset.EscapeControlReader(markupRd, buf, ctx.Locale, charset.WikiContext, charset.RuneNBSP)
 			output = buf.String()
 			buf.Reset()
 			close(done)

services/gitdiff/gitdiff.go

@@ -284,14 +284,14 @@ type DiffInline struct {
 
 // DiffInlineWithUnicodeEscape makes a DiffInline with hidden unicode characters escaped
 func DiffInlineWithUnicodeEscape(s template.HTML, locale translation.Locale) DiffInline {
-	status, content := charset.EscapeControlHTML(s, locale)
+	status, content := charset.EscapeControlHTML(s, locale, charset.DiffContext)
 	return DiffInline{EscapeStatus: status, Content: content}
 }
 
 // DiffInlineWithHighlightCode makes a DiffInline with code highlight and hidden unicode characters escaped
 func DiffInlineWithHighlightCode(fileName, language, code string, locale translation.Locale) DiffInline {
 	highlighted, _ := highlight.Code(fileName, language, code)
-	status, content := charset.EscapeControlHTML(highlighted, locale)
+	status, content := charset.EscapeControlHTML(highlighted, locale, charset.DiffContext)
 	return DiffInline{EscapeStatus: status, Content: content}
 }
 

tests/integration/view_test.go

@@ -5,8 +5,16 @@ package integration
 
 import (
 	"net/http"
+	"net/url"
+	"strings"
 	"testing"
 
+	unit_model "code.gitea.io/gitea/models/unit"
+	"code.gitea.io/gitea/models/unittest"
+	user_model "code.gitea.io/gitea/models/user"
+	"code.gitea.io/gitea/modules/setting"
+	"code.gitea.io/gitea/modules/test"
+	files_service "code.gitea.io/gitea/services/repository/files"
 	"code.gitea.io/gitea/tests"
 
 	"github.com/stretchr/testify/assert"
@@ -25,3 +33,99 @@ func TestRenderFileSVGIsInImgTag(t *testing.T) {
 	assert.True(t, exists, "The SVG image should be in an <img> tag so that scripts in the SVG are not run")
 	assert.Equal(t, "/user2/repo2/raw/branch/master/line.svg", src)
 }
+
+func TestAmbiguousCharacterDetection(t *testing.T) {
+	onGiteaRun(t, func(t *testing.T, u *url.URL) {
+		user2 := unittest.AssertExistsAndLoadBean(t, &user_model.User{ID: 2})
+		session := loginUser(t, user2.Name)
+
+		// Prepare the environments. File view, commit view (diff), wiki page.
+		repo, commitID, f := CreateDeclarativeRepo(t, user2, "",
+			[]unit_model.Type{unit_model.TypeCode, unit_model.TypeWiki}, nil,
+			[]*files_service.ChangeRepoFile{
+				{
+					Operation:     "create",
+					TreePath:      "test.sh",
+					ContentReader: strings.NewReader("Hello there!\nline western"),
+				},
+			},
+		)
+		defer f()
+
+		req := NewRequestWithValues(t, "POST", repo.Link()+"/wiki?action=new", map[string]string{
+			"_csrf":   GetCSRF(t, session, repo.Link()+"/wiki?action=new"),
+			"title":   "Normal",
+			"content": "Hello – Hello",
+		})
+		session.MakeRequest(t, req, http.StatusSeeOther)
+
+		assertCase := func(t *testing.T, fileContext, commitContext, wikiContext bool) {
+			t.Helper()
+
+			t.Run("File context", func(t *testing.T) {
+				defer tests.PrintCurrentTest(t)()
+
+				req := NewRequest(t, "GET", repo.Link()+"/src/branch/main/test.sh")
+				resp := session.MakeRequest(t, req, http.StatusOK)
+
+				htmlDoc := NewHTMLParser(t, resp.Body)
+				htmlDoc.AssertElement(t, ".unicode-escape-prompt", fileContext)
+			})
+			t.Run("Commit context", func(t *testing.T) {
+				defer tests.PrintCurrentTest(t)()
+
+				req := NewRequest(t, "GET", repo.Link()+"/commit/"+commitID)
+				resp := session.MakeRequest(t, req, http.StatusOK)
+
+				htmlDoc := NewHTMLParser(t, resp.Body)
+				htmlDoc.AssertElement(t, ".lines-escape .toggle-escape-button", commitContext)
+			})
+			t.Run("Wiki context", func(t *testing.T) {
+				defer tests.PrintCurrentTest(t)()
+
+				req := NewRequest(t, "GET", repo.Link()+"/wiki/Normal")
+				resp := session.MakeRequest(t, req, http.StatusOK)
+
+				htmlDoc := NewHTMLParser(t, resp.Body)
+				htmlDoc.AssertElement(t, ".unicode-escape-prompt", wikiContext)
+			})
+		}
+
+		t.Run("Enabled all context", func(t *testing.T) {
+			defer test.MockVariableValue(&setting.UI.SkipEscapeContexts, []string{})()
+
+			assertCase(t, true, true, true)
+		})
+
+		t.Run("Enabled file context", func(t *testing.T) {
+			defer test.MockVariableValue(&setting.UI.SkipEscapeContexts, []string{"diff", "wiki"})()
+
+			assertCase(t, true, false, false)
+		})
+
+		t.Run("Enabled commit context", func(t *testing.T) {
+			defer test.MockVariableValue(&setting.UI.SkipEscapeContexts, []string{"file-view", "wiki"})()
+
+			assertCase(t, false, true, false)
+		})
+
+		t.Run("Enabled wiki context", func(t *testing.T) {
+			defer test.MockVariableValue(&setting.UI.SkipEscapeContexts, []string{"file-view", "diff"})()
+
+			assertCase(t, false, false, true)
+		})
+
+		t.Run("No context", func(t *testing.T) {
+			defer test.MockVariableValue(&setting.UI.SkipEscapeContexts, []string{"file-view", "wiki", "diff"})()
+
+			assertCase(t, false, false, false)
+		})
+
+		t.Run("Disabled detection", func(t *testing.T) {
+			defer test.MockVariableValue(&setting.UI.SkipEscapeContexts, []string{})()
+			defer test.MockVariableValue(&setting.UI.AmbiguousUnicodeDetection, false)()
+
+			assertCase(t, false, false, false)
+		})
+	})
+}