tests: fsck: generate evil files with "\r" and "\n" on the fly

Because if we have them in git, we get this:

	$ go install github.com/rfjakob/gocryptfs/v2@latest
	go: downloading github.com/rfjakob/gocryptfs/v2 v2.5.2
	go: github.com/rfjakob/gocryptfs/v2@latest: create zip: tests/fsck/malleable_base64/27AG8t-XZH7G9ou2OSD_z
	g: malformed file path "tests/fsck/malleable_base64/27AG8t-XZH7G9ou2OSD_z\ng": invalid char '\n'
	g: malformed file path "tests/fsck/malleable_base64/27AG8t-XZH7G9ou2OSD_z\rg": invalid char '\r'

Fixes: #904
Relates-to: golang/go#28001

Author: rfjakob

tests/fsck/.gitignore

@@ -0,0 +1,7 @@
+# Cannot have these "evil" files in git because they break "go install"
+# https://github.com/golang/go/issues/28001
+#
+#	"malleable_base64/27AG8t-XZH7G9ou2OSD_z\ng"
+#	"malleable_base64/27AG8t-XZH7G9ou2OSD_z\rg"
+#
+malleable_base64/27AG8t-XZH7G9ou2OSD_z?g

tests/fsck/fsck_test.go

@@ -50,6 +50,17 @@ func TestBrokenFsV14(t *testing.T) {
 }
 
 func TestMalleableBase64(t *testing.T) {
+	// Evil filenames. Cannot have them in git, because if we do,
+	//  go install github.com/rfjakob/gocryptfs/v2@latest
+	// fails with
+	//  g: malformed file path "tests/fsck/malleable_base64/27AG8t-XZH7G9ou2OSD_z\rg": invalid char '\r'
+	//  g: malformed file path "tests/fsck/malleable_base64/27AG8t-XZH7G9ou2OSD_z\rg": invalid char '\r'
+	if err := os.WriteFile("malleable_base64/27AG8t-XZH7G9ou2OSD_z\ng", nil, 0644); err != nil {
+		t.Fatal(err)
+	}
+	if err := os.WriteFile("malleable_base64/27AG8t-XZH7G9ou2OSD_z\rg", nil, 0644); err != nil {
+		t.Fatal(err)
+	}
 	cmd := exec.Command(test_helpers.GocryptfsBinary, "-fsck", "-extpass", "echo test", "malleable_base64")
 	outBin, err := cmd.CombinedOutput()
 	out := string(outBin)