From d3d8852d8997a6429cbd498138908e537869a6ef Mon Sep 17 00:00:00 2001 From: Rob Pike Date: Sun, 24 Oct 2021 15:44:15 +1100 Subject: [PATCH] text/template: use reflect.Value.FieldByIndexErr to avoid a crash on a nil pointer as an embedded field. Fixes #48215 Change-Id: I214faa6e3cf08cdec1c01035e4bbca0900c6a408 Reviewed-on: https://go-review.googlesource.com/c/go/+/357963 Trust: Rob Pike Run-TryBot: Rob Pike TryBot-Result: Go Bot Reviewed-by: Ian Lance Taylor --- src/text/template/exec.go | 5 ++++- src/text/template/exec_test.go | 23 +++++++++++++++++++++++ 2 files changed, 27 insertions(+), 1 deletion(-) diff --git a/src/text/template/exec.go b/src/text/template/exec.go index 7e44497530..c42cbb2ad3 100644 --- a/src/text/template/exec.go +++ b/src/text/template/exec.go @@ -635,10 +635,13 @@ func (s *state) evalField(dot reflect.Value, fieldName string, node parse.Node, case reflect.Struct: tField, ok := receiver.Type().FieldByName(fieldName) if ok { - field := receiver.FieldByIndex(tField.Index) + field, err := receiver.FieldByIndexErr(tField.Index) if !tField.IsExported() { s.errorf("%s is an unexported field of struct type %s", fieldName, typ) } + if err != nil { + s.errorf("%v", err) + } // If it's a function, we must call it. if hasArgs { s.errorf("%s has arguments but cannot be invoked as function", fieldName) diff --git a/src/text/template/exec_test.go b/src/text/template/exec_test.go index 9c0772945e..3c40aa901e 100644 --- a/src/text/template/exec_test.go +++ b/src/text/template/exec_test.go @@ -1787,3 +1787,26 @@ func TestIssue39807(t *testing.T) { wg.Wait() } + +// Issue 48215: embedded nil pointer causes panic. +// Fixed by adding FieldByIndexErr to the reflect package. +func TestIssue48215(t *testing.T) { + type A struct { + S string + } + type B struct { + *A + } + tmpl, err := New("").Parse(`{{ .S }}`) + if err != nil { + t.Fatal(err) + } + err = tmpl.Execute(io.Discard, B{}) + // We expect an error, not a panic. + if err == nil { + t.Fatal("did not get error for nil embedded struct") + } + if !strings.Contains(err.Error(), "reflect: indirection through nil pointer to embedded struct field A") { + t.Fatal(err) + } +} -- 2.50.0