7 files changed, 31 insertions, 15 deletions
diff --git a/pkg/tcpip/link/tun/tun_endpoint_refs.go b/pkg/tcpip/link/tun/tun_endpoint_refs.go
index e0595429c..7f80b1fa3 100644
--- a/pkg/tcpip/link/tun/tun_endpoint_refs.go
+++ b/pkg/tcpip/link/tun/tun_endpoint_refs.go
@@ -2,11 +2,11 @@ package tun
 
 import (
 	"fmt"
+	refs_vfs1 "gvisor.dev/gvisor/pkg/refs"
 	"runtime"
 	"sync/atomic"
 
 	"gvisor.dev/gvisor/pkg/log"
-	refs_vfs1 "gvisor.dev/gvisor/pkg/refs"
 )
 
 // ownerType is used to customize logging. Note that we use a pointer to T so
diff --git a/pkg/tcpip/network/arp/arp.go b/pkg/tcpip/network/arp/arp.go
index cbbe5b77f..7aaee08c4 100644
--- a/pkg/tcpip/network/arp/arp.go
+++ b/pkg/tcpip/network/arp/arp.go
@@ -217,12 +217,12 @@ func (*protocol) ResolveStaticAddress(addr tcpip.Address) (tcpip.LinkAddress, bo
 }
 
 // SetOption implements stack.NetworkProtocol.SetOption.
-func (*protocol) SetOption(option interface{}) *tcpip.Error {
+func (*protocol) SetOption(tcpip.SettableNetworkProtocolOption) *tcpip.Error {
 	return tcpip.ErrUnknownProtocolOption
 }
 
 // Option implements stack.NetworkProtocol.Option.
-func (*protocol) Option(option interface{}) *tcpip.Error {
+func (*protocol) Option(tcpip.GettableNetworkProtocolOption) *tcpip.Error {
 	return tcpip.ErrUnknownProtocolOption
 }
 
diff --git a/pkg/tcpip/network/ipv4/ipv4.go b/pkg/tcpip/network/ipv4/ipv4.go
index 55ca94268..fa4ae2012 100644
--- a/pkg/tcpip/network/ipv4/ipv4.go
+++ b/pkg/tcpip/network/ipv4/ipv4.go
@@ -486,10 +486,10 @@ func (*protocol) ParseAddresses(v buffer.View) (src, dst tcpip.Address) {
 }
 
 // SetOption implements NetworkProtocol.SetOption.
-func (p *protocol) SetOption(option interface{}) *tcpip.Error {
+func (p *protocol) SetOption(option tcpip.SettableNetworkProtocolOption) *tcpip.Error {
 	switch v := option.(type) {
-	case tcpip.DefaultTTLOption:
-		p.SetDefaultTTL(uint8(v))
+	case *tcpip.DefaultTTLOption:
+		p.SetDefaultTTL(uint8(*v))
 		return nil
 	default:
 		return tcpip.ErrUnknownProtocolOption
@@ -497,7 +497,7 @@ func (p *protocol) SetOption(option interface{}) *tcpip.Error {
 }
 
 // Option implements NetworkProtocol.Option.
-func (p *protocol) Option(option interface{}) *tcpip.Error {
+func (p *protocol) Option(option tcpip.GettableNetworkProtocolOption) *tcpip.Error {
 	switch v := option.(type) {
 	case *tcpip.DefaultTTLOption:
 		*v = tcpip.DefaultTTLOption(p.DefaultTTL())
diff --git a/pkg/tcpip/network/ipv6/ipv6.go b/pkg/tcpip/network/ipv6/ipv6.go
index 36fbbebf0..af3cd91c6 100644
--- a/pkg/tcpip/network/ipv6/ipv6.go
+++ b/pkg/tcpip/network/ipv6/ipv6.go
@@ -469,10 +469,10 @@ func (p *protocol) NewEndpoint(nicID tcpip.NICID, linkAddrCache stack.LinkAddres
 }
 
 // SetOption implements NetworkProtocol.SetOption.
-func (p *protocol) SetOption(option interface{}) *tcpip.Error {
+func (p *protocol) SetOption(option tcpip.SettableNetworkProtocolOption) *tcpip.Error {
 	switch v := option.(type) {
-	case tcpip.DefaultTTLOption:
-		p.SetDefaultTTL(uint8(v))
+	case *tcpip.DefaultTTLOption:
+		p.SetDefaultTTL(uint8(*v))
 		return nil
 	default:
 		return tcpip.ErrUnknownProtocolOption
@@ -480,7 +480,7 @@ func (p *protocol) SetOption(option interface{}) *tcpip.Error {
 }
 
 // Option implements NetworkProtocol.Option.
-func (p *protocol) Option(option interface{}) *tcpip.Error {
+func (p *protocol) Option(option tcpip.GettableNetworkProtocolOption) *tcpip.Error {
 	switch v := option.(type) {
 	case *tcpip.DefaultTTLOption:
 		*v = tcpip.DefaultTTLOption(p.DefaultTTL())
diff --git a/pkg/tcpip/stack/registration.go b/pkg/tcpip/stack/registration.go
index 21ac38583..2d88fa1f7 100644
--- a/pkg/tcpip/stack/registration.go
+++ b/pkg/tcpip/stack/registration.go
@@ -303,12 +303,12 @@ type NetworkProtocol interface {
 	// SetOption allows enabling/disabling protocol specific features.
 	// SetOption returns an error if the option is not supported or the
 	// provided option value is invalid.
-	SetOption(option interface{}) *tcpip.Error
+	SetOption(option tcpip.SettableNetworkProtocolOption) *tcpip.Error
 
 	// Option allows retrieving protocol specific option values.
 	// Option returns an error if the option is not supported or the
 	// provided option value is invalid.
-	Option(option interface{}) *tcpip.Error
+	Option(option tcpip.GettableNetworkProtocolOption) *tcpip.Error
 
 	// Close requests that any worker goroutines owned by the protocol
 	// stop.
diff --git a/pkg/tcpip/stack/stack.go b/pkg/tcpip/stack/stack.go
index 7f5ed9e83..c86ee1c13 100644
--- a/pkg/tcpip/stack/stack.go
+++ b/pkg/tcpip/stack/stack.go
@@ -785,7 +785,7 @@ func (s *Stack) UniqueID() uint64 {
 // options. This method returns an error if the protocol is not supported or
 // option is not supported by the protocol implementation or the provided value
 // is incorrect.
-func (s *Stack) SetNetworkProtocolOption(network tcpip.NetworkProtocolNumber, option interface{}) *tcpip.Error {
+func (s *Stack) SetNetworkProtocolOption(network tcpip.NetworkProtocolNumber, option tcpip.SettableNetworkProtocolOption) *tcpip.Error {
 	netProto, ok := s.networkProtocols[network]
 	if !ok {
 		return tcpip.ErrUnknownProtocol
@@ -802,7 +802,7 @@ func (s *Stack) SetNetworkProtocolOption(network tcpip.NetworkProtocolNumber, op
 // if err != nil {
 //   ...
 // }
-func (s *Stack) NetworkProtocolOption(network tcpip.NetworkProtocolNumber, option interface{}) *tcpip.Error {
+func (s *Stack) NetworkProtocolOption(network tcpip.NetworkProtocolNumber, option tcpip.GettableNetworkProtocolOption) *tcpip.Error {
 	netProto, ok := s.networkProtocols[network]
 	if !ok {
 		return tcpip.ErrUnknownProtocol
diff --git a/pkg/tcpip/tcpip.go b/pkg/tcpip/tcpip.go
index cd72d4f02..47a8d7c86 100644
--- a/pkg/tcpip/tcpip.go
+++ b/pkg/tcpip/tcpip.go
@@ -841,10 +841,26 @@ const (
 	PMTUDiscoveryProbe
 )
 
+// GettableNetworkProtocolOption is a marker interface for network protocol
+// options that may be queried.
+type GettableNetworkProtocolOption interface {
+	isGettableNetworkProtocolOption()
+}
+
+// SettableNetworkProtocolOption is a marker interface for network protocol
+// options that may be set.
+type SettableNetworkProtocolOption interface {
+	isSettableNetworkProtocolOption()
+}
+
 // DefaultTTLOption is used by stack.(*Stack).NetworkProtocolOption to specify
 // a default TTL.
 type DefaultTTLOption uint8
 
+func (*DefaultTTLOption) isGettableNetworkProtocolOption() {}
+
+func (*DefaultTTLOption) isSettableNetworkProtocolOption() {}
+
 // AvailableCongestionControlOption is used to query the supported congestion
 // control algorithms.
 type AvailableCongestionControlOption string