From d7a7823c41d8d0e90dee045b65151bfe5383b831 Mon Sep 17 00:00:00 2001
From: Eric Biggers <ebiggers@google.com>
Date: Tue, 1 Oct 2019 08:35:25 -0700
Subject: [PATCH] actions/config: ensure config file is created with mode 0644

If the user has set a restrictive umask, e.g. 0077, then
/etc/fscrypt.conf would be created without the world-readable bit set.
Fix it by overriding the umask when creating the file.

Resolves https://github.com/google/fscrypt/issues/151
---
 actions/config.go      |  4 ++-
 actions/config_test.go | 55 ++++++++++++++++++++++++++++++++++++++++++
 filesystem/path.go     | 10 ++++++++
 3 files changed, 68 insertions(+), 1 deletion(-)
 create mode 100644 actions/config_test.go

diff --git a/actions/config.go b/actions/config.go
index 386edc4a..7fdaf5b7 100644
--- a/actions/config.go
+++ b/actions/config.go
@@ -31,6 +31,7 @@ import (
 	"golang.org/x/sys/unix"
 
 	"github.com/google/fscrypt/crypto"
+	"github.com/google/fscrypt/filesystem"
 	"github.com/google/fscrypt/metadata"
 	"github.com/google/fscrypt/util"
 )
@@ -68,7 +69,8 @@ var (
 func CreateConfigFile(target time.Duration, useLegacy bool) error {
 	// Create the config file before computing the hashing costs, so we fail
 	// immediately if the program has insufficient permissions.
-	configFile, err := os.OpenFile(ConfigFileLocation, createFlags, configPermissions)
+	configFile, err := filesystem.OpenFileOverridingUmask(ConfigFileLocation,
+		createFlags, configPermissions)
 	switch {
 	case os.IsExist(err):
 		return ErrConfigFileExists
diff --git a/actions/config_test.go b/actions/config_test.go
new file mode 100644
index 00000000..037e4330
--- /dev/null
+++ b/actions/config_test.go
@@ -0,0 +1,55 @@
+/*
+ * config_test.go - tests for creating the config file
+ *
+ * Copyright 2019 Google LLC
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License"); you may not
+ * use this file except in compliance with the License. You may obtain a copy of
+ * the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+ * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
+ * License for the specific language governing permissions and limitations under
+ * the License.
+ */
+
+package actions
+
+import (
+	"io/ioutil"
+	"os"
+	"path/filepath"
+	"testing"
+	"time"
+
+	"golang.org/x/sys/unix"
+)
+
+// Test that the global config file is created with mode 0644, regardless of the
+// current umask.
+func TestConfigFileIsCreatedWithCorrectMode(t *testing.T) {
+	oldMask := unix.Umask(0)
+	defer unix.Umask(oldMask)
+	unix.Umask(0077)
+
+	tempDir, err := ioutil.TempDir("", "fscrypt")
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer os.RemoveAll(tempDir)
+	ConfigFileLocation = filepath.Join(tempDir, "test.conf")
+
+	if err = CreateConfigFile(time.Millisecond, false); err != nil {
+		t.Fatal(err)
+	}
+	fileInfo, err := os.Stat(ConfigFileLocation)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if fileInfo.Mode().Perm() != 0644 {
+		t.Error("Expected newly created config file to have mode 0644")
+	}
+}
diff --git a/filesystem/path.go b/filesystem/path.go
index 5fd3fdf2..cfc3dc0b 100644
--- a/filesystem/path.go
+++ b/filesystem/path.go
@@ -24,9 +24,19 @@ import (
 	"os"
 	"path/filepath"
 
+	"golang.org/x/sys/unix"
+
 	"github.com/pkg/errors"
 )
 
+// OpenFileOverridingUmask calls os.OpenFile but with the umask overridden so
+// that no permission bits are masked out if the file is created.
+func OpenFileOverridingUmask(name string, flag int, perm os.FileMode) (*os.File, error) {
+	oldMask := unix.Umask(0)
+	defer unix.Umask(oldMask)
+	return os.OpenFile(name, flag, perm)
+}
+
 // We only check the unix permissions and the sticky bit
 const permMask = os.ModeSticky | os.ModePerm