Add -acl flag to enable ACL enforcement

With test to verify that it actually works this
time: Run "make root_test".

Depends-on: https://github.com/rfjakob/gocryptfs/issues/536
Fixes: https://github.com/rfjakob/gocryptfs/issues/536

cli_args.go

@@ -30,7 +30,7 @@ type argContainer struct {
 	noprealloc, speed, hkdf, serialize_reads, forcedecode, hh, info,
 	sharedstorage, devrandom, fsck bool
 	// Mount options with opposites
-	dev, nodev, suid, nosuid, exec, noexec, rw, ro, kernel_cache bool
+	dev, nodev, suid, nosuid, exec, noexec, rw, ro, kernel_cache, acl bool
 	masterkey, mountpoint, cipherdir, cpuprofile,
 	memprofile, ko, ctlsock, fsname, force_owner, trace, fido2 string
 	// -extpass, -badname, -passfile can be passed multiple times
@@ -180,6 +180,7 @@ func parseCliOpts() (args argContainer) {
 	flagSet.BoolVar(&args.rw, "rw", false, "Mount the filesystem read-write")
 	flagSet.BoolVar(&args.ro, "ro", false, "Mount the filesystem read-only")
 	flagSet.BoolVar(&args.kernel_cache, "kernel_cache", false, "Enable the FUSE kernel_cache option")
+	flagSet.BoolVar(&args.acl, "acl", false, "Enforce ACLs")
 
 	flagSet.StringVar(&args.masterkey, "masterkey", "", "Mount with explicit master key")
 	flagSet.StringVar(&args.cpuprofile, "cpuprofile", "", "Write cpu profile to specified file")

mount.go

@@ -396,6 +396,9 @@ func initGoFuse(rootNode fs.InodeEmbedder, args *argContainer) *fuse.Server {
 		// Make the kernel check the file permissions for us
 		mOpts.Options = append(mOpts.Options, "default_permissions")
 	}
+	if args.acl {
+		mOpts.EnableAcl = true
+	}
 	if args.forcedecode {
 		tlog.Info.Printf(tlog.ColorYellow + "THE OPTION \"-forcedecode\" IS ACTIVE. GOCRYPTFS WILL RETURN CORRUPT DATA!" +
 			tlog.ColorReset)

tests/root_test/root_test.go

@@ -137,6 +137,7 @@ func writeTillFull(t *testing.T, path string) (int, syscall.Errno) {
 	return sz, 0
 }
 
+// TestDiskFull needs root permissions because it creates a loop disk
 func TestDiskFull(t *testing.T) {
 	if os.Getuid() != 0 {
 		t.Skip("must run as root")
@@ -229,3 +230,84 @@ func TestDiskFull(t *testing.T) {
 		t.Fail()
 	}
 }
+
+func TestAcl(t *testing.T) {
+	if os.Getuid() != 0 {
+		t.Skip("must run as root")
+	}
+	cDir := test_helpers.InitFS(t)
+	os.Chmod(cDir, 0755)
+	pDir := cDir + ".mnt"
+	test_helpers.MountOrFatal(t, cDir, pDir, "-allow_other", "-acl", "-extpass=echo test")
+	defer test_helpers.UnmountPanic(pDir)
+
+	f1 := pDir + "/f1"
+	if err := ioutil.WriteFile(f1, []byte("hello world\n"), 000); err != nil {
+		t.Fatal(err)
+	}
+
+	openUser1234 := func(rwMode int) error {
+		return asUser(1234, 1234, nil, func() error {
+			fd, err := syscall.Open(f1, rwMode, 0)
+			if err != nil {
+				return err
+			}
+			defer syscall.Close(fd)
+			buf := make([]byte, 100)
+			if rwMode == syscall.O_RDONLY || rwMode == syscall.O_RDWR {
+				_, err = syscall.Read(fd, buf)
+				if err != nil {
+					return err
+				}
+			}
+			if rwMode == syscall.O_WRONLY || rwMode == syscall.O_RDWR {
+				_, err = syscall.Write(fd, buf)
+				if err != nil {
+					return err
+				}
+			}
+			return err
+		})
+	}
+
+	dumpAcl := func() {
+		out, err := exec.Command("getfacl", f1).CombinedOutput()
+		if err != nil {
+			t.Fatal(err)
+		}
+		t.Log(string(out))
+	}
+
+	if err := openUser1234(syscall.O_RDONLY); err == nil {
+		t.Error("this should have failed")
+		dumpAcl()
+	}
+
+	// Allow read
+	out, err := exec.Command("setfacl", "-m", "u:1234:r", f1).CombinedOutput()
+	if err != nil {
+		t.Fatal(string(out))
+	}
+	if err := openUser1234(syscall.O_RDONLY); err != nil {
+		t.Errorf("O_RDONLY should have worked, but got error: %v", err)
+		dumpAcl()
+	}
+	if err := openUser1234(syscall.O_WRONLY); err == nil {
+		t.Error("O_WRONLY should have failed")
+		dumpAcl()
+	}
+
+	// Allow write
+	out, err = exec.Command("setfacl", "-m", "u:1234:w", f1).CombinedOutput()
+	if err != nil {
+		t.Fatal(string(out))
+	}
+	if err := openUser1234(syscall.O_WRONLY); err != nil {
+		t.Errorf("O_WRONLY should have worked, but got error: %v", err)
+		dumpAcl()
+	}
+	if err := openUser1234(syscall.O_RDONLY); err == nil {
+		t.Error("O_RDONLY should have failed")
+		dumpAcl()
+	}
+}