Improve type safety for socket options

The existing implementation for {G,S}etSockOpt take arguments of an
empty interface type which all types (implicitly) implement; any
type may be passed to the functions.

This change introduces marker interfaces for socket options that may be
set or queried which socket option types implement to ensure that invalid
types are caught at compile time. Different interfaces are used to allow
the compiler to enforce read-only or set-only socket options.

Fixes #3714.

RELNOTES: n/a
PiperOrigin-RevId: 328832161

1 files changed, 106 insertions, 21 deletions

diff --git a/pkg/tcpip/tcpip.go b/pkg/tcpip/tcpip.go
index cae943608..cd72d4f02 100644
--- a/pkg/tcpip/tcpip.go
+++ b/pkg/tcpip/tcpip.go
@@ -578,8 +578,8 @@ type Endpoint interface {
 	// if waiter.EventIn is set, the endpoint is immediately readable.
 	Readiness(mask waiter.EventMask) waiter.EventMask
 
-	// SetSockOpt sets a socket option. opt should be one of the *Option types.
-	SetSockOpt(opt interface{}) *Error
+	// SetSockOpt sets a socket option.
+	SetSockOpt(opt SettableSocketOption) *Error
 
 	// SetSockOptBool sets a socket option, for simple cases where a value
 	// has the bool type.
@@ -589,9 +589,8 @@ type Endpoint interface {
 	// has the int type.
 	SetSockOptInt(opt SockOptInt, v int) *Error
 
-	// GetSockOpt gets a socket option. opt should be a pointer to one of the
-	// *Option types.
-	GetSockOpt(opt interface{}) *Error
+	// GetSockOpt gets a socket option.
+	GetSockOpt(opt GettableSocketOption) *Error
 
 	// GetSockOptBool gets a socket option for simple cases where a return
 	// value has the bool type.
@@ -842,10 +841,37 @@ const (
 	PMTUDiscoveryProbe
 )
 
+// DefaultTTLOption is used by stack.(*Stack).NetworkProtocolOption to specify
+// a default TTL.
+type DefaultTTLOption uint8
+
+// AvailableCongestionControlOption is used to query the supported congestion
+// control algorithms.
+type AvailableCongestionControlOption string
+
+// ModerateReceiveBufferOption is used by buffer moderation.
+type ModerateReceiveBufferOption bool
+
+// GettableSocketOption is a marker interface for socket options that may be
+// queried.
+type GettableSocketOption interface {
+	isGettableSocketOption()
+}
+
+// SettableSocketOption is a marker interface for socket options that may be
+// configured.
+type SettableSocketOption interface {
+	isSettableSocketOption()
+}
+
 // BindToDeviceOption is used by SetSockOpt/GetSockOpt to specify that sockets
 // should bind only on a specific NIC.
 type BindToDeviceOption NICID
 
+func (*BindToDeviceOption) isGettableSocketOption() {}
+
+func (*BindToDeviceOption) isSettableSocketOption() {}
+
 // TCPInfoOption is used by GetSockOpt to expose TCP statistics.
 //
 // TODO(b/64800844): Add and populate stat fields.
@@ -854,68 +880,111 @@ type TCPInfoOption struct {
 	RTTVar time.Duration
 }
 
+func (*TCPInfoOption) isGettableSocketOption() {}
+
 // KeepaliveIdleOption is used by SetSockOpt/GetSockOpt to specify the time a
 // connection must remain idle before the first TCP keepalive packet is sent.
 // Once this time is reached, KeepaliveIntervalOption is used instead.
 type KeepaliveIdleOption time.Duration
 
+func (*KeepaliveIdleOption) isGettableSocketOption() {}
+
+func (*KeepaliveIdleOption) isSettableSocketOption() {}
+
 // KeepaliveIntervalOption is used by SetSockOpt/GetSockOpt to specify the
 // interval between sending TCP keepalive packets.
 type KeepaliveIntervalOption time.Duration
 
+func (*KeepaliveIntervalOption) isGettableSocketOption() {}
+
+func (*KeepaliveIntervalOption) isSettableSocketOption() {}
+
 // TCPUserTimeoutOption is used by SetSockOpt/GetSockOpt to specify a user
 // specified timeout for a given TCP connection.
 // See: RFC5482 for details.
 type TCPUserTimeoutOption time.Duration
 
+func (*TCPUserTimeoutOption) isGettableSocketOption() {}
+
+func (*TCPUserTimeoutOption) isSettableSocketOption() {}
+
 // CongestionControlOption is used by SetSockOpt/GetSockOpt to set/get
 // the current congestion control algorithm.
 type CongestionControlOption string
 
-// AvailableCongestionControlOption is used to query the supported congestion
-// control algorithms.
-type AvailableCongestionControlOption string
+func (*CongestionControlOption) isGettableSocketOption() {}
 
-// ModerateReceiveBufferOption is used by buffer moderation.
-type ModerateReceiveBufferOption bool
+func (*CongestionControlOption) isSettableSocketOption() {}
 
 // TCPLingerTimeoutOption is used by SetSockOpt/GetSockOpt to set/get the
 // maximum duration for which a socket lingers in the TCP_FIN_WAIT_2 state
 // before being marked closed.
 type TCPLingerTimeoutOption time.Duration
 
+func (*TCPLingerTimeoutOption) isGettableSocketOption() {}
+
+func (*TCPLingerTimeoutOption) isSettableSocketOption() {}
+
 // TCPTimeWaitTimeoutOption is used by SetSockOpt/GetSockOpt to set/get the
 // maximum duration for which a socket lingers in the TIME_WAIT state
 // before being marked closed.
 type TCPTimeWaitTimeoutOption time.Duration
 
+func (*TCPTimeWaitTimeoutOption) isGettableSocketOption() {}
+
+func (*TCPTimeWaitTimeoutOption) isSettableSocketOption() {}
+
 // TCPDeferAcceptOption is used by SetSockOpt/GetSockOpt to allow a
 // accept to return a completed connection only when there is data to be
 // read. This usually means the listening socket will drop the final ACK
 // for a handshake till the specified timeout until a segment with data arrives.
 type TCPDeferAcceptOption time.Duration
 
+func (*TCPDeferAcceptOption) isGettableSocketOption() {}
+
+func (*TCPDeferAcceptOption) isSettableSocketOption() {}
+
 // TCPMinRTOOption is use by SetSockOpt/GetSockOpt to allow overriding
 // default MinRTO used by the Stack.
 type TCPMinRTOOption time.Duration
 
+func (*TCPMinRTOOption) isGettableSocketOption() {}
+
+func (*TCPMinRTOOption) isSettableSocketOption() {}
+
 // TCPMaxRTOOption is use by SetSockOpt/GetSockOpt to allow overriding
 // default MaxRTO used by the Stack.
 type TCPMaxRTOOption time.Duration
 
+func (*TCPMaxRTOOption) isGettableSocketOption() {}
+
+func (*TCPMaxRTOOption) isSettableSocketOption() {}
+
 // TCPMaxRetriesOption is used by SetSockOpt/GetSockOpt to set/get the
 // maximum number of retransmits after which we time out the connection.
 type TCPMaxRetriesOption uint64
 
+func (*TCPMaxRetriesOption) isGettableSocketOption() {}
+
+func (*TCPMaxRetriesOption) isSettableSocketOption() {}
+
 // TCPSynRcvdCountThresholdOption is used by SetSockOpt/GetSockOpt to specify
 // the number of endpoints that can be in SYN-RCVD state before the stack
 // switches to using SYN cookies.
 type TCPSynRcvdCountThresholdOption uint64
 
+func (*TCPSynRcvdCountThresholdOption) isGettableSocketOption() {}
+
+func (*TCPSynRcvdCountThresholdOption) isSettableSocketOption() {}
+
 // TCPSynRetriesOption is used by SetSockOpt/GetSockOpt to specify stack-wide
 // default for number of times SYN is retransmitted before aborting a connect.
 type TCPSynRetriesOption uint8
 
+func (*TCPSynRetriesOption) isGettableSocketOption() {}
+
+func (*TCPSynRetriesOption) isSettableSocketOption() {}
+
 // MulticastInterfaceOption is used by SetSockOpt/GetSockOpt to specify a
 // default interface for multicast.
 type MulticastInterfaceOption struct {
@@ -923,45 +992,57 @@ type MulticastInterfaceOption struct {
 	InterfaceAddr Address
 }
 
-// MembershipOption is used by SetSockOpt/GetSockOpt as an argument to
-// AddMembershipOption and RemoveMembershipOption.
+func (*MulticastInterfaceOption) isGettableSocketOption() {}
+
+func (*MulticastInterfaceOption) isSettableSocketOption() {}
+
+// MembershipOption is used to identify a multicast membership on an interface.
 type MembershipOption struct {
 	NIC           NICID
 	InterfaceAddr Address
 	MulticastAddr Address
 }
 
-// AddMembershipOption is used by SetSockOpt/GetSockOpt to join a multicast
-// group identified by the given multicast address, on the interface matching
-// the given interface address.
+// AddMembershipOption identifies a multicast group to join on some interface.
 type AddMembershipOption MembershipOption
 
-// RemoveMembershipOption is used by SetSockOpt/GetSockOpt to leave a multicast
-// group identified by the given multicast address, on the interface matching
-// the given interface address.
+func (*AddMembershipOption) isSettableSocketOption() {}
+
+// RemoveMembershipOption identifies a multicast group to leave on some
+// interface.
 type RemoveMembershipOption MembershipOption
 
+func (*RemoveMembershipOption) isSettableSocketOption() {}
+
 // OutOfBandInlineOption is used by SetSockOpt/GetSockOpt to specify whether
 // TCP out-of-band data is delivered along with the normal in-band data.
 type OutOfBandInlineOption int
 
-// DefaultTTLOption is used by stack.(*Stack).NetworkProtocolOption to specify
-// a default TTL.
-type DefaultTTLOption uint8
+func (*OutOfBandInlineOption) isGettableSocketOption() {}
+
+func (*OutOfBandInlineOption) isSettableSocketOption() {}
 
 // SocketDetachFilterOption is used by SetSockOpt to detach a previously attached
 // classic BPF filter on a given endpoint.
 type SocketDetachFilterOption int
 
+func (*SocketDetachFilterOption) isSettableSocketOption() {}
+
 // OriginalDestinationOption is used to get the original destination address
 // and port of a redirected packet.
 type OriginalDestinationOption FullAddress
 
+func (*OriginalDestinationOption) isGettableSocketOption() {}
+
 // TCPTimeWaitReuseOption is used stack.(*Stack).TransportProtocolOption to
 // specify if the stack can reuse the port bound by an endpoint in TIME-WAIT for
 // new connections when it is safe from protocol viewpoint.
 type TCPTimeWaitReuseOption uint8
 
+func (*TCPTimeWaitReuseOption) isGettableSocketOption() {}
+
+func (*TCPTimeWaitReuseOption) isSettableSocketOption() {}
+
 const (
 	// TCPTimeWaitReuseDisabled indicates reuse of port bound by endponts in TIME-WAIT cannot
 	// be reused for new connections.
@@ -986,6 +1067,10 @@ type LingerOption struct {
 	Timeout time.Duration
 }
 
+func (*LingerOption) isGettableSocketOption() {}
+
+func (*LingerOption) isSettableSocketOption() {}
+
 // IPPacketInfo is the message structure for IP_PKTINFO.
 //
 // +stateify savable