WIP work towards networking support

This supports networking restrictions
and is compatible with patch 11.

landlock/abi_versions.go

@@ -3,8 +3,9 @@ package landlock
 import ll "github.com/landlock-lsm/go-landlock/landlock/syscall"
 
 type abiInfo struct {
-	version           int
-	supportedAccessFS AccessFSSet
+	version            int
+	supportedAccessFS  AccessFSSet
+	supportedAccessNet AccessNetSet
 }
 
 var abiInfos = []abiInfo{
@@ -24,10 +25,18 @@ var abiInfos = []abiInfo{
 		version:           3,
 		supportedAccessFS: (1 << 15) - 1,
 	},
+	{
+		version:            4,
+		supportedAccessFS:  (1 << 15) - 1,
+		supportedAccessNet: (1 << 2) - 1,
+	},
 }
 
 func (a abiInfo) asConfig() Config {
-	return Config{handledAccessFS: a.supportedAccessFS}
+	return Config{
+		handledAccessFS:  a.supportedAccessFS,
+		handledAccessNet: a.supportedAccessNet,
+	}
 }
 
 // getSupportedABIVersion returns the kernel-supported ABI version.

landlock/abi_versions_test.go

@@ -13,7 +13,7 @@ func TestAbiVersionsIncrementing(t *testing.T) {
 }
 
 func TestSupportedAccessFS(t *testing.T) {
-	got := abiInfos[3].supportedAccessFS
+	got := abiInfos[4].supportedAccessFS
 	want := supportedAccessFS
 
 	if got != want {

landlock/accessnet.go

@@ -0,0 +1,35 @@
+package landlock
+
+// AccessNetSet is a set of Landlockable network access rights.
+type AccessNetSet uint64
+
+var accessNetNames = []string{
+	"bind_tcp",
+	"connect_tcp",
+}
+
+var supportedAccessNet = AccessNetSet((1 << len(accessNetNames)) - 1)
+
+func (a AccessNetSet) String() string {
+	return accessSetString(uint64(a), accessNetNames)
+}
+
+func (a AccessNetSet) isSubset(b AccessNetSet) bool {
+	return a&b == a
+}
+
+func (a AccessNetSet) intersect(b AccessNetSet) AccessNetSet {
+	return a & b
+}
+
+func (a AccessNetSet) union(b AccessNetSet) AccessNetSet {
+	return a | b
+}
+
+func (a AccessNetSet) isEmpty() bool {
+	return a == 0
+}
+
+func (a AccessNetSet) valid() bool {
+	return a.isSubset(supportedAccessNet)
+}

landlock/config.go

@@ -35,6 +35,8 @@ var (
 	V2 = abiInfos[2].asConfig()
 	// Landlock V3 support (V2 + file truncation)
 	V3 = abiInfos[3].asConfig()
+	// Landlock V4 support (V2 + networking)
+	V4 = abiInfos[4].asConfig()
 )
 
 // v0 denotes "no Landlock support". Only used internally.
@@ -44,8 +46,9 @@ var v0 = Config{}
 // landlockable operations to be restricted and the constraints on it
 // (e.g. best effort mode).
 type Config struct {
-	handledAccessFS AccessFSSet
-	bestEffort      bool
+	handledAccessFS  AccessFSSet
+	handledAccessNet AccessNetSet
+	bestEffort       bool
 }
 
 // NewConfig creates a new Landlock configuration with the given parameters.
@@ -64,15 +67,24 @@ func NewConfig(args ...interface{}) (*Config, error) {
 	// invalid Config values.
 	var c Config
 	for _, arg := range args {
-		if afs, ok := arg.(AccessFSSet); ok {
+		switch arg := arg.(type) {
+		case AccessFSSet:
 			if !c.handledAccessFS.isEmpty() {
 				return nil, errors.New("only one AccessFSSet may be provided")
 			}
-			if !afs.valid() {
+			if !arg.valid() {
 				return nil, errors.New("unsupported AccessFSSet value; upgrade go-landlock?")
 			}
-			c.handledAccessFS = afs
-		} else {
+			c.handledAccessFS = arg
+		case AccessNetSet:
+			if !c.handledAccessNet.isEmpty() {
+				return nil, errors.New("only one AccessNetSet may be provided")
+			}
+			if !arg.valid() {
+				return nil, errors.New("unsupported AccessNetSet value; upgrade go-landlock?")
+			}
+			c.handledAccessNet = arg
+		default:
 			return nil, fmt.Errorf("unknown argument %v; only AccessFSSet-type argument is supported", arg)
 		}
 	}
@@ -103,6 +115,11 @@ func (c Config) String() string {
 		fsDesc = "all"
 	}
 
+	var netDesc = c.handledAccessNet.String()
+	if abi.supportedAccessNet == c.handledAccessNet && c.handledAccessNet != 0 {
+		fsDesc = "all"
+	}
+
 	var bestEffort = ""
 	if c.bestEffort {
 		bestEffort = " (best effort)"
@@ -115,7 +132,7 @@ func (c Config) String() string {
 		version = fmt.Sprintf("V%v", abi.version)
 	}
 
-	return fmt.Sprintf("{Landlock %v; FS: %v%v}", version, fsDesc, bestEffort)
+	return fmt.Sprintf("{Landlock %v; FS: %v; Net: %v%v}", version, fsDesc, netDesc, bestEffort)
 }
 
 // BestEffort returns a config that will opportunistically enforce
@@ -222,6 +239,12 @@ func (c Config) BestEffort() Config {
 //
 // [Kernel Documentation about Access Rights]: https://www.kernel.org/doc/html/latest/userspace-api/landlock.html#access-rights
 func (c Config) RestrictPaths(rules ...Rule) error {
+	c.handledAccessNet = 0 // clear out everything but file system access
+	return restrict(c, rules...)
+}
+
+func (c Config) RestrictNet(rules ...Rule) error {
+	c.handledAccessFS = 0 // clear out everything but network access
 	return restrict(c, rules...)
 }
 
@@ -231,7 +254,8 @@ type PathOpt = Rule
 
 // compatibleWith is true if c is compatible to work at the given Landlock ABI level.
 func (c Config) compatibleWithABI(abi abiInfo) bool {
-	return c.handledAccessFS.isSubset(abi.supportedAccessFS)
+	return (c.handledAccessFS.isSubset(abi.supportedAccessFS) &&
+		c.handledAccessNet.isSubset(abi.supportedAccessNet))
 }
 
 // restrictTo returns a config that is a subset of c and which is compatible with the given ABI.

landlock/config_test.go

@@ -1,7 +1,6 @@
 package landlock
 
 import (
-	"fmt"
 	"testing"
 
 	ll "github.com/landlock-lsm/go-landlock/landlock/syscall"
@@ -13,24 +12,28 @@ func TestConfigString(t *testing.T) {
 		want string
 	}{
 		{
-			cfg:  Config{handledAccessFS: 0},
-			want: fmt.Sprintf("{Landlock V0; FS: %v}", AccessFSSet(0)),
+			cfg:  Config{handledAccessFS: 0, handledAccessNet: 0},
+			want: "{Landlock V0; FS: ∅; Net: ∅}",
 		},
 		{
 			cfg:  Config{handledAccessFS: ll.AccessFSWriteFile},
-			want: "{Landlock V1; FS: {write_file}}",
+			want: "{Landlock V1; FS: {write_file}; Net: ∅}",
+		},
+		{
+			cfg:  Config{handledAccessNet: ll.AccessNetBindTCP},
+			want: "{Landlock V4; FS: ∅; Net: {bind_tcp}}",
 		},
 		{
 			cfg:  V1,
-			want: "{Landlock V1; FS: all}",
+			want: "{Landlock V1; FS: all; Net: ∅}",
 		},
 		{
 			cfg:  V1.BestEffort(),
-			want: "{Landlock V1; FS: all (best effort)}",
+			want: "{Landlock V1; FS: all; Net: ∅ (best effort)}",
 		},
 		{
 			cfg:  Config{handledAccessFS: 1 << 63},
-			want: "{Landlock V???; FS: {1<<63}}",
+			want: "{Landlock V???; FS: {1<<63}; Net: ∅}",
 		},
 	} {
 		got := tc.cfg.String()

landlock/net_opt.go

@@ -0,0 +1,52 @@
+package landlock
+
+import (
+	"fmt"
+
+	ll "github.com/landlock-lsm/go-landlock/landlock/syscall"
+)
+
+type NetOpt struct {
+	access AccessNetSet
+	port   uint16
+}
+
+func DialTCP(port uint16) NetOpt {
+	return NetOpt{
+		access: ll.AccessNetConnectTCP,
+		port:   port,
+	}
+}
+
+// TODO: Should it be called ListenTCP? (In Go, the notions of
+// "binding" and "listening" are often conflated.)
+func BindTCP(port uint16) NetOpt {
+	return NetOpt{
+		access: ll.AccessNetBindTCP,
+		port:   port,
+	}
+}
+
+func (n NetOpt) String() string {
+	return fmt.Sprintf("ALLOW %v on TCP port %v", n.access, n.port)
+}
+
+func (n NetOpt) compatibleWithConfig(c Config) bool {
+	return n.access.isSubset(c.handledAccessNet)
+}
+
+func (n NetOpt) addToRuleset(rulesetFD int, c Config) error {
+	flags := 0
+	attr := &ll.NetServiceAttr{
+		AllowedAccess: uint64(n.access),
+		Port:          n.port,
+	}
+	return ll.LandlockAddNetServiceRule(rulesetFD, attr, flags)
+}
+
+func (n NetOpt) downgrade(c Config) (out Rule, ok bool) {
+	return NetOpt{
+		access: n.access.intersect(c.handledAccessNet),
+		port:   n.port,
+	}, true
+}

landlock/opt.go

@@ -12,7 +12,8 @@ type Rule interface {
 	//
 	// It establishes that:
 	//
-	//   - rule.accessFS ⊆ handledAccessFS
+	//   - rule.accessFS ⊆ handledAccessFS for PathOpts
+	//   - rule.accessNet ⊆ handledAccessNet for NetOpts
 	//
 	// If the rule is unsupportable under the given Config at
 	// all, ok is false. This happens when c represents a Landlock

landlock/restrict.go

@@ -50,12 +50,13 @@ func restrict(c Config, rules ...Rule) error {
 	// always implicit, even in Landlock V1. So enabling Landlock
 	// on a Landlock V1 kernel without any handled access rights
 	// will still forbid linking files between directories.
-	if c.handledAccessFS.isEmpty() {
+	if c.handledAccessFS.isEmpty() && c.handledAccessNet.isEmpty() {
 		return nil // Success: Nothing to restrict.
 	}
 
 	rulesetAttr := ll.RulesetAttr{
-		HandledAccessFS: uint64(c.handledAccessFS),
+		HandledAccessFS:  uint64(c.handledAccessFS),
+		HandledAccessNet: uint64(c.handledAccessNet),
 	}
 	fd, err := ll.LandlockCreateRuleset(&rulesetAttr, 0)
 	if err != nil {

landlock/restrict_downgrade_test.go

@@ -8,7 +8,7 @@ import (
 	ll "github.com/landlock-lsm/go-landlock/landlock/syscall"
 )
 
-func TestDowngrade(t *testing.T) {
+func TestDowngradeAccessFS(t *testing.T) {
 	for _, tc := range []struct {
 		Name string