html: align in row insertion mode with spec

Update inRowIM to match the HTML specification. This fixes an issue
where a specific HTML document could cause the parser to enter an
infinite loop when trying to parse a </tbody> and implied </tr> next to
each other.

Fixes CVE-2025-58190
Fixes golang/go#70179

Change-Id: Idcb133c87c7d475cc8c7eb1f1550ea21d8bdddea
Reviewed-on: https://go-review.googlesource.com/c/net/+/709875
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Damien Neil <dneil@google.com>

Author: rolandshoemaker

html/parse.go

@@ -136,7 +136,7 @@ func (p *parser) indexOfElementInScope(s scope, matchTags ...a.Atom) int {
 					return -1
 				}
 			default:
-				panic("unreachable")
+				panic(fmt.Sprintf("html: internal error: indexOfElementInScope unknown scope: %d", s))
 			}
 		}
 		switch s {
@@ -179,7 +179,7 @@ func (p *parser) clearStackToContext(s scope) {
 				return
 			}
 		default:
-			panic("unreachable")
+			panic(fmt.Sprintf("html: internal error: clearStackToContext unknown scope: %d", s))
 		}
 	}
 }
@@ -1678,7 +1678,7 @@ func inTableBodyIM(p *parser) bool {
 	return inTableIM(p)
 }
 
-// Section 12.2.6.4.14.
+// Section 13.2.6.4.14.
 func inRowIM(p *parser) bool {
 	switch p.tok.Type {
 	case StartTagToken:
@@ -1690,7 +1690,9 @@ func inRowIM(p *parser) bool {
 			p.im = inCellIM
 			return true
 		case a.Caption, a.Col, a.Colgroup, a.Tbody, a.Tfoot, a.Thead, a.Tr:
-			if p.popUntil(tableScope, a.Tr) {
+			if p.elementInScope(tableScope, a.Tr) {
+				p.clearStackToContext(tableRowScope)
+				p.oe.pop()
 				p.im = inTableBodyIM
 				return false
 			}
@@ -1700,22 +1702,28 @@ func inRowIM(p *parser) bool {
 	case EndTagToken:
 		switch p.tok.DataAtom {
 		case a.Tr:
-			if p.popUntil(tableScope, a.Tr) {
+			if p.elementInScope(tableScope, a.Tr) {
+				p.clearStackToContext(tableRowScope)
+				p.oe.pop()
 				p.im = inTableBodyIM
 				return true
 			}
 			// Ignore the token.
 			return true
 		case a.Table:
-			if p.popUntil(tableScope, a.Tr) {
+			if p.elementInScope(tableScope, a.Tr) {
+				p.clearStackToContext(tableRowScope)
+				p.oe.pop()
 				p.im = inTableBodyIM
 				return false
 			}
 			// Ignore the token.
 			return true
 		case a.Tbody, a.Tfoot, a.Thead:
-			if p.elementInScope(tableScope, p.tok.DataAtom) {
-				p.parseImpliedToken(EndTagToken, a.Tr, a.Tr.String())
+			if p.elementInScope(tableScope, p.tok.DataAtom) && p.elementInScope(tableScope, a.Tr) {
+				p.clearStackToContext(tableRowScope)
+				p.oe.pop()
+				p.im = inTableBodyIM
 				return false
 			}
 			// Ignore the token.
@@ -2222,16 +2230,20 @@ func parseForeignContent(p *parser) bool {
 			p.acknowledgeSelfClosingTag()
 		}
 	case EndTagToken:
+		if strings.EqualFold(p.oe[len(p.oe)-1].Data, p.tok.Data) {
+			p.oe = p.oe[:len(p.oe)-1]
+			return true
+		}
 		for i := len(p.oe) - 1; i >= 0; i-- {
-			if p.oe[i].Namespace == "" {
-				return p.im(p)
-			}
 			if strings.EqualFold(p.oe[i].Data, p.tok.Data) {
 				p.oe = p.oe[:i]
+				return true
+			}
+			if i > 0 && p.oe[i-1].Namespace == "" {
 				break
 			}
 		}
-		return true
+		return p.im(p)
 	default:
 		// Ignore the token.
 	}

html/parse_test.go

@@ -251,31 +251,35 @@ func TestParser(t *testing.T) {
 			t.Fatal(err)
 		}
 		for _, tf := range testFiles {
-			f, err := os.Open(tf)
-			if err != nil {
-				t.Fatal(err)
-			}
-			defer f.Close()
-			r := bufio.NewReader(f)
-
-			for i := 0; ; i++ {
-				ta, err := readParseTest(r)
-				if err == io.EOF {
-					break
-				}
+			t.Run(tf, func(t *testing.T) {
+				f, err := os.Open(tf)
 				if err != nil {
 					t.Fatal(err)
 				}
-				if parseTestBlacklist[ta.text] {
-					continue
+				defer f.Close()
+				r := bufio.NewReader(f)
+
+				for i := 0; ; i++ {
+					ta, err := readParseTest(r)
+					if err == io.EOF {
+						break
+					}
+					if err != nil {
+						t.Fatal(err)
+					}
+					if parseTestBlacklist[ta.text] {
+						continue
+					}
+
+					t.Run(fmt.Sprint(i), func(t *testing.T) {
+						err = testParseCase(ta.text, ta.want, ta.context, ParseOptionEnableScripting(ta.scripting))
+
+						if err != nil {
+							t.Errorf("%s test #%d %q, %s", tf, i, ta.text, err)
+						}
+					})
 				}
-
-				err = testParseCase(ta.text, ta.want, ta.context, ParseOptionEnableScripting(ta.scripting))
-
-				if err != nil {
-					t.Errorf("%s test #%d %q, %s", tf, i, ta.text, err)
-				}
-			}
+			})
 		}
 	}
 }
@@ -506,3 +510,10 @@ func BenchmarkParser(b *testing.B) {
 		Parse(bytes.NewBuffer(buf))
 	}
 }
+
+func TestIssue70179(t *testing.T) {
+	_, err := Parse(strings.NewReader("<table><tbody><svg><td><desc><select></select></tbody>"))
+	if err != nil {
+		t.Fatalf("unexpected failure: %v", err)
+	}
+}