Allow FSETXATTR/FGETXATTR host calls for Verity

These host calls are needed for Verity fs to generate/verify hashes.

PiperOrigin-RevId: 364598180

runsc/cmd/gofer.go

@@ -165,8 +165,8 @@ func (g *Gofer) Execute(_ context.Context, f *flag.FlagSet, args ...interface{})
 	// Start with root mount, then add any other additional mount as needed.
 	ats := make([]p9.Attacher, 0, len(spec.Mounts)+1)
 	ap, err := fsgofer.NewAttachPoint("/", fsgofer.Config{
-		ROMount:     spec.Root.Readonly || conf.Overlay,
-		EnableXattr: conf.Verity,
+		ROMount:           spec.Root.Readonly || conf.Overlay,
+		EnableVerityXattr: conf.Verity,
 	})
 	if err != nil {
 		Fatalf("creating attach point: %v", err)
@@ -178,9 +178,9 @@ func (g *Gofer) Execute(_ context.Context, f *flag.FlagSet, args ...interface{})
 	for _, m := range spec.Mounts {
 		if specutils.Is9PMount(m) {
 			cfg := fsgofer.Config{
-				ROMount:     isReadonlyMount(m.Options) || conf.Overlay,
-				HostUDS:     conf.FSGoferHostUDS,
-				EnableXattr: conf.Verity,
+				ROMount:           isReadonlyMount(m.Options) || conf.Overlay,
+				HostUDS:           conf.FSGoferHostUDS,
+				EnableVerityXattr: conf.Verity,
 			}
 			ap, err := fsgofer.NewAttachPoint(m.Destination, cfg)
 			if err != nil {
@@ -203,6 +203,10 @@ func (g *Gofer) Execute(_ context.Context, f *flag.FlagSet, args ...interface{})
 		filter.InstallUDSFilters()
 	}
 
+	if conf.Verity {
+		filter.InstallXattrFilters()
+	}
+
 	if err := filter.Install(); err != nil {
 		Fatalf("installing seccomp filters: %v", err)
 	}

runsc/fsgofer/filter/config.go

@@ -247,3 +247,8 @@ var udsSyscalls = seccomp.SyscallRules{
 		},
 	},
 }
+
+var xattrSyscalls = seccomp.SyscallRules{
+	unix.SYS_FGETXATTR: {},
+	unix.SYS_FSETXATTR: {},
+}

runsc/fsgofer/filter/filter.go

@@ -36,3 +36,9 @@ func InstallUDSFilters() {
 	// Add additional filters required for connecting to the host's sockets.
 	allowedSyscalls.Merge(udsSyscalls)
 }
+
+// InstallXattrFilters extends the allowed syscalls to include xattr calls that
+// are necessary for Verity enabled file systems.
+func InstallXattrFilters() {
+	allowedSyscalls.Merge(xattrSyscalls)
+}

runsc/fsgofer/fsgofer.go

@@ -48,6 +48,14 @@ const (
 	allowedOpenFlags = unix.O_TRUNC
 )
 
+// verityXattrs are the extended attributes used by verity file system.
+var verityXattrs = map[string]struct{}{
+	"user.merkle.offset":         struct{}{},
+	"user.merkle.size":           struct{}{},
+	"user.merkle.childrenOffset": struct{}{},
+	"user.merkle.childrenSize":   struct{}{},
+}
+
 // join is equivalent to path.Join() but skips path.Clean() which is expensive.
 func join(parent, child string) string {
 	if child == "." || child == ".." {
@@ -67,8 +75,9 @@ type Config struct {
 	// HostUDS signals whether the gofer can mount a host's UDS.
 	HostUDS bool
 
-	// enableXattr allows Get/SetXattr for the mounted file systems.
-	EnableXattr bool
+	// EnableVerityXattr allows access to extended attributes used by the
+	// verity file system.
+	EnableVerityXattr bool
 }
 
 type attachPoint struct {
@@ -799,7 +808,10 @@ func (l *localFile) SetAttr(valid p9.SetAttrMask, attr p9.SetAttr) error {
 }
 
 func (l *localFile) GetXattr(name string, size uint64) (string, error) {
-	if !l.attachPoint.conf.EnableXattr {
+	if !l.attachPoint.conf.EnableVerityXattr {
+		return "", unix.EOPNOTSUPP
+	}
+	if _, ok := verityXattrs[name]; !ok {
 		return "", unix.EOPNOTSUPP
 	}
 	buffer := make([]byte, size)
@@ -810,7 +822,10 @@ func (l *localFile) GetXattr(name string, size uint64) (string, error) {
 }
 
 func (l *localFile) SetXattr(name string, value string, flags uint32) error {
-	if !l.attachPoint.conf.EnableXattr {
+	if !l.attachPoint.conf.EnableVerityXattr {
+		return unix.EOPNOTSUPP
+	}
+	if _, ok := verityXattrs[name]; !ok {
 		return unix.EOPNOTSUPP
 	}
 	return unix.Fsetxattr(l.file.FD(), name, []byte(value), int(flags))

runsc/fsgofer/fsgofer_test.go

@@ -579,20 +579,24 @@ func SetGetXattr(l *localFile, name string, value string) error {
 	return nil
 }
 
-func TestSetGetXattr(t *testing.T) {
-	xattrConfs := []Config{{ROMount: false, EnableXattr: false}, {ROMount: false, EnableXattr: true}}
-	runCustom(t, []uint32{unix.S_IFREG}, xattrConfs, func(t *testing.T, s state) {
-		name := "user.test"
+func TestSetGetDisabledXattr(t *testing.T) {
+	runCustom(t, []uint32{unix.S_IFREG}, rwConfs, func(t *testing.T, s state) {
+		name := "user.merkle.offset"
 		value := "tmp"
 		err := SetGetXattr(s.file, name, value)
-		if s.conf.EnableXattr {
-			if err != nil {
-				t.Fatalf("%v: SetGetXattr failed, err: %v", s, err)
-			}
-		} else {
-			if err == nil {
-				t.Fatalf("%v: SetGetXattr should have failed", s)
-			}
+		if err == nil {
+			t.Fatalf("%v: SetGetXattr should have failed", s)
+		}
+	})
+}
+
+func TestSetGetXattr(t *testing.T) {
+	runCustom(t, []uint32{unix.S_IFREG}, []Config{{ROMount: false, EnableVerityXattr: true}}, func(t *testing.T, s state) {
+		name := "user.merkle.offset"
+		value := "tmp"
+		err := SetGetXattr(s.file, name, value)
+		if err != nil {
+			t.Fatalf("%v: SetGetXattr failed, err: %v", s, err)
 		}
 	})
 }