clientv3: Make saved snapshot readable by user only

Fixes #9976

clientv3/snapshot/v3_snapshot.go

@@ -102,7 +102,7 @@ func (s *v3Manager) Save(ctx context.Context, cfg clientv3.Config, dbPath string
 	defer os.RemoveAll(partpath)
 
 	var f *os.File
-	f, err = os.Create(partpath)
+	f, err = os.OpenFile(partpath, os.O_WRONLY|os.O_CREATE|os.O_TRUNC, fileutil.PrivateFileMode)
 	if err != nil {
 		return fmt.Errorf("could not open %s (%v)", partpath, err)
 	}

clientv3/snapshot/v3_snapshot_test.go

@@ -26,6 +26,7 @@ import (
 
 	"github.com/coreos/etcd/clientv3"
 	"github.com/coreos/etcd/embed"
+	"github.com/coreos/etcd/pkg/fileutil"
 	"github.com/coreos/etcd/pkg/testutil"
 
 	"go.uber.org/zap"
@@ -141,6 +142,25 @@ func TestSnapshotV3RestoreMulti(t *testing.T) {
 	}
 }
 
+// TestSnapshotFilePermissions ensures that the snapshot is saved with
+// the correct file permissions.
+func TestSnapshotFilePermissions(t *testing.T) {
+	expectedFileMode := os.FileMode(fileutil.PrivateFileMode)
+	kvs := []kv{{"foo1", "bar1"}, {"foo2", "bar2"}, {"foo3", "bar3"}}
+	dbPath := createSnapshotFile(t, kvs)
+	defer os.RemoveAll(dbPath)
+
+	dbInfo, err := os.Stat(dbPath)
+	if err != nil {
+		t.Fatalf("failed to get test snapshot file status: %v", err)
+	}
+	actualFileMode := dbInfo.Mode()
+
+	if expectedFileMode != actualFileMode {
+		t.Fatalf("expected test snapshot file mode %s, got %s:", expectedFileMode, actualFileMode)
+	}
+}
+
 type kv struct {
 	k, v string
 }