v2api: -sharestorage: disable hard link tracking & add tests

Hard link tracking was not correctly disabled
since the migration to the go-fuse v2 api.

Add a test to ensure it stays off.

Fixes https://github.com/rfjakob/gocryptfs/issues/525

internal/fusefrontend/args.go

@@ -46,4 +46,7 @@ type Args struct {
 	Suid bool
 	// Enable the FUSE kernel_cache option
 	KernelCache bool
+	// SharedStorage disables caching & hard link tracking,
+	// enabled via cli flag "-sharedstorage"
+	SharedStorage bool
 }

internal/fusefrontend/node_helpers.go

@@ -102,8 +102,9 @@ func (n *Node) prepareAtSyscall(child string) (dirfd int, cName string, errno sy
 // newChild attaches a new child inode to n.
 // The passed-in `st` will be modified to get a unique inode number.
 func (n *Node) newChild(ctx context.Context, st *syscall.Stat_t, out *fuse.EntryOut) *fs.Inode {
-	// Get unique inode number
 	rn := n.rootNode()
+	// Get stable inode number based on underlying (device,ino) pair
+	// (or set to zero in case of `-sharestorage`)
 	rn.inoMap.TranslateStat(st)
 	out.Attr.FromStat(st)
 	// Create child node

internal/fusefrontend/root_node.go

@@ -50,7 +50,7 @@ type RootNode struct {
 	IsIdle uint32
 	// inoMap translates inode numbers from different devices to unique inode
 	// numbers.
-	inoMap *inomap.InoMap
+	inoMap inomap.TranslateStater
 }
 
 func NewRootNode(args Args, c *contentenc.ContentEnc, n nametransform.NameTransformer) *RootNode {
@@ -60,12 +60,18 @@ func NewRootNode(args Args, c *contentenc.ContentEnc, n nametransform.NameTransf
 	if len(args.Exclude) > 0 {
 		tlog.Warn.Printf("Forward mode does not support -exclude")
 	}
-	return &RootNode{
+	rn := &RootNode{
 		args:          args,
 		nameTransform: n,
 		contentEnc:    c,
 		inoMap:        inomap.New(),
 	}
+	// In `-sharedstorage` mode we always set the inode number to zero.
+	// This makes go-fuse generate a new inode number for each lookup.
+	if args.SharedStorage {
+		rn.inoMap = &inomap.TranslateStatZero{}
+	}
+	return rn
 }
 
 // mangleOpenFlags is used by Create() and Open() to convert the open flags the user

internal/inomap/inomap.go

@@ -104,3 +104,14 @@ func (m *InoMap) TranslateStat(st *syscall.Stat_t) {
 	in := QInoFromStat(st)
 	st.Ino = m.Translate(in)
 }
+
+type TranslateStater interface {
+	TranslateStat(st *syscall.Stat_t)
+}
+
+// TranslateStatZero always sets st.Ino to zero. Used for `-sharedstorage`.
+type TranslateStatZero struct{}
+
+func (z TranslateStatZero) TranslateStat(st *syscall.Stat_t) {
+	st.Ino = 0
+}

mount.go

@@ -280,6 +280,7 @@ func initFuseFrontend(args *argContainer) (rootNode fs.InodeEmbedder, wipeKeys f
 		ExcludeFrom:     args.excludeFrom,
 		Suid:            args.suid,
 		KernelCache:     args.kernel_cache,
+		SharedStorage:   args.sharedstorage,
 	}
 	// confFile is nil when "-zerokey" or "-masterkey" was used
 	if confFile != nil {
@@ -349,7 +350,11 @@ func initGoFuse(rootNode fs.InodeEmbedder, args *argContainer) *fuse.Server {
 	if args.sharedstorage {
 		// sharedstorage mode sets all cache timeouts to zero so changes to the
 		// backing shared storage show up immediately.
-		fuseOpts = &fs.Options{}
+		// Hard links are disabled by using automatically incrementing
+		// inode numbers provided by go-fuse.
+		fuseOpts = &fs.Options{
+			FirstAutomaticIno: 1000,
+		}
 	} else {
 		fuseOpts = &fs.Options{
 			// These options are to be compatible with libfuse defaults,
@@ -421,7 +426,8 @@ func initGoFuse(rootNode fs.InodeEmbedder, args *argContainer) *fuse.Server {
 	} else if args.rw {
 		mOpts.Options = append(mOpts.Options, "rw")
 	}
-	// If both "nosuid" and "suid" were passed, the safer option wins.
+	// If both "nosuid" & "suid", "nodev" & "dev", etc were passed, the safer
+	// option wins.
 	if args.nosuid {
 		mOpts.Options = append(mOpts.Options, "nosuid")
 	} else if args.suid {

tests/cli/cli_test.go

@@ -822,3 +822,50 @@ func TestInitNotEmpty(t *testing.T) {
 		t.Fatalf("wrong exit code: have=%d, want=%d", exitCode, exitcodes.CipherDir)
 	}
 }
+
+// TestSharedstorage checks that `-sharedstorage` hands out arbitrary inode
+// numbers (no hard link tracking)
+func TestSharedstorage(t *testing.T) {
+	dir := test_helpers.InitFS(t)
+	mnt := dir + ".mnt"
+	err := os.Mkdir(mnt, 0700)
+	if err != nil {
+		t.Fatal(err)
+	}
+	test_helpers.MountOrFatal(t, dir, mnt, "-extpass=echo test", "-sharedstorage")
+	defer test_helpers.UnmountPanic(mnt)
+	foo1 := mnt + "/foo1"
+	foo2 := mnt + "/foo2"
+	if err := ioutil.WriteFile(foo1, nil, 0755); err != nil {
+		t.Fatal(err)
+	}
+	if err := os.Link(foo1, foo2); err != nil {
+		t.Fatal(err)
+	}
+	var st1, st2, st3 syscall.Stat_t
+	if err := syscall.Stat(foo1, &st1); err != nil {
+		t.Fatal(err)
+	}
+	// The link show show a new inode number
+	if err := syscall.Stat(foo2, &st2); err != nil {
+		t.Fatal(err)
+	}
+	// Stat()'ing again should give us again a new inode number
+	if err := syscall.Stat(foo2, &st3); err != nil {
+		t.Fatal(err)
+	}
+	if st1.Ino == st2.Ino || st2.Ino == st3.Ino || st1.Ino == st3.Ino {
+		t.Error(st1.Ino, st2.Ino, st3.Ino)
+	}
+	// Check that we we don't have stat caching. New length should show up
+	// on the hard link immediately.
+	if err := ioutil.WriteFile(foo1, []byte("xxxxxx"), 0755); err != nil {
+		t.Fatal(err)
+	}
+	if err := syscall.Stat(foo2, &st2); err != nil {
+		t.Fatal(err)
+	}
+	if st2.Size != 6 {
+		t.Fatal(st2.Size)
+	}
+}