encoding/xml: check nil pointer in DecodeElement

Fixes #53350

Change-Id: Id5e1f4016db5f1d4349ee1a76a9dfe3aeae83cee
GitHub-Last-Rev: 45add12161
GitHub-Pull-Request: golang/go#53407
Reviewed-on: https://go-review.googlesource.com/c/go/+/412634
Auto-Submit: Ian Lance Taylor <iant@google.com>
Reviewed-by: Ian Lance Taylor <iant@google.com>
Run-TryBot: Ian Lance Taylor <iant@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Alex Rakoczy <alex@golang.org>

src/encoding/xml/read.go

@@ -148,6 +148,10 @@ func (d *Decoder) DecodeElement(v any, start *StartElement) error {
 	if val.Kind() != reflect.Pointer {
 		return errors.New("non-pointer passed to Unmarshal")
 	}
+
+	if val.IsNil() {
+		return errors.New("nil pointer passed to Unmarshal")
+	}
 	return d.unmarshal(val.Elem(), start)
 }
 

src/encoding/xml/read_test.go

@@ -1079,3 +1079,18 @@ func TestUnmarshalWhitespaceAttrs(t *testing.T) {
 		t.Fatalf("whitespace attrs: Unmarshal:\nhave: %#+v\nwant: %#+v", v, want)
 	}
 }
+
+// golang.org/issues/53350
+func TestUnmarshalIntoNil(t *testing.T) {
+	type T struct {
+		A int `xml:"A"`
+	}
+
+	var nilPointer *T
+	err := Unmarshal([]byte("<T><A>1</A></T>"), nilPointer)
+
+	if err == nil {
+		t.Fatalf("no error in unmarshalling")
+	}
+
+}