[release-branch.go1.20] cmd/compile: use absolute file name in isCgo check

For #23672
Updates #63211
Fixes #63213
Fixes CVE-2023-39323

Change-Id: I4586a69e1b2560036afec29d53e53cf25e6c7352
Reviewed-on: https://team-review.git.corp.google.com/c/golang/go-private/+/2032884
Reviewed-by: Matthew Dempsky <mdempsky@google.com>
Reviewed-by: Roland Shoemaker <bracewell@google.com>
(cherry picked from commit 9b19e751918dd218035811b1ef83a8c2693b864a)
Reviewed-on: https://team-review.git.corp.google.com/c/golang/go-private/+/2037629
Reviewed-by: Tatiana Bradley <tatianabradley@google.com>
Run-TryBot: Roland Shoemaker <bracewell@google.com>
Reviewed-by: Damien Neil <dneil@google.com>
Reviewed-on: https://go-review.googlesource.com/c/go/+/533195
Auto-Submit: Michael Pratt <mpratt@google.com>
Reviewed-by: Ian Lance Taylor <iant@google.com>
TryBot-Bypass: Michael Pratt <mpratt@google.com>
Reviewed-by: Than McIntosh <thanm@google.com>

misc/cgo/errors/errors_test.go

@@ -36,16 +36,23 @@ func check(t *testing.T, file string) {
 				continue
 			}
 
-			_, frag, ok := bytes.Cut(line, []byte("ERROR HERE: "))
+			if _, frag, ok := bytes.Cut(line, []byte("ERROR HERE: ")); ok {
-			if !ok {
+				re, err := regexp.Compile(fmt.Sprintf(":%d:.*%s", i+1, frag))
-				continue
+				if err != nil {
+					t.Errorf("Invalid regexp after `ERROR HERE: `: %#q", frag)
+					continue
+				}
+				errors = append(errors, re)
 			}
-			re, err := regexp.Compile(fmt.Sprintf(":%d:.*%s", i+1, frag))
+
-			if err != nil {
+			if _, frag, ok := bytes.Cut(line, []byte("ERROR MESSAGE: ")); ok {
-				t.Errorf("Invalid regexp after `ERROR HERE: `: %#q", frag)
+				re, err := regexp.Compile(string(frag))
-				continue
+				if err != nil {
+					t.Errorf("Invalid regexp after `ERROR MESSAGE: `: %#q", frag)
+					continue
+				}
+				errors = append(errors, re)
 			}
-			errors = append(errors, re)
 		}
 		if len(errors) == 0 {
 			t.Fatalf("cannot find ERROR HERE")
@@ -106,6 +113,7 @@ func TestReportsTypeErrors(t *testing.T) {
 	for _, file := range []string{
 		"err1.go",
 		"err2.go",
+		"err5.go",
 		"issue11097a.go",
 		"issue11097b.go",
 		"issue18452.go",

misc/cgo/errors/testdata/err5.go

@@ -0,0 +1,11 @@
+// Copyright 2023 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package main
+
+//line /tmp/_cgo_.go:1
+//go:cgo_dynamic_linker "/elf/interp"
+// ERROR MESSAGE: only allowed in cgo-generated code
+
+func main() {}

src/cmd/compile/internal/noder/noder.go

@@ -359,8 +359,14 @@ func (p *noder) pragma(pos syntax.Pos, blankLine bool, text string, old syntax.P
 // contain cgo directives, and for security reasons
 // (primarily misuse of linker flags), other files are not.
 // See golang.org/issue/23672.
+// Note that cmd/go ignores files whose names start with underscore,
+// so the only _cgo_ files we will see from cmd/go are generated by cgo.
+// It's easy to bypass this check by calling the compiler directly;
+// we only protect against uses by cmd/go.
 func isCgoGeneratedFile(pos syntax.Pos) bool {
-	return strings.HasPrefix(filepath.Base(trimFilename(pos.Base())), "_cgo_")
+	// We need the absolute file, independent of //line directives,
+	// so we call pos.Base().Pos().
+	return strings.HasPrefix(filepath.Base(trimFilename(pos.Base().Pos().Base())), "_cgo_")
 }
 
 // safeArg reports whether arg is a "safe" command-line argument,