Allow rebinding packet socket protocol

...to change the network protocol a packet socket may receive packets
from.

This CL is a portion of an originally larger CL that was split with
https://github.com/google/gvisor/commit/a8ad692fd36cbaf7f5a6b9af39d601053dbee338
being the dependent CL. That CL (accidentally) included the change in
the endpoint's `afterLoad` method to take the required lock when
accessing the endpoint's netProto field. That change should have been in
this CL.

The CL that made the change mentioned in the commit message is
cl/396946187.

PiperOrigin-RevId: 397412582

2 files changed, 11 insertions, 17 deletions

diff --git a/pkg/sentry/socket/netstack/netstack.go b/pkg/sentry/socket/netstack/netstack.go
index f79bda922..aa081e90d 100644
--- a/pkg/sentry/socket/netstack/netstack.go
+++ b/pkg/sentry/socket/netstack/netstack.go
@@ -672,13 +672,10 @@ func (s *socketOpsCommon) Bind(t *kernel.Task, sockaddr []byte) *syserr.Error {
 		}
 		a.UnmarshalBytes(sockaddr[:sockAddrLinkSize])
 
-		if a.Protocol != uint16(s.protocol) {
-			return syserr.ErrInvalidArgument
-		}
-
 		addr = tcpip.FullAddress{
 			NIC:  tcpip.NICID(a.InterfaceIndex),
 			Addr: tcpip.Address(a.HardwareAddr[:header.EthernetAddressSize]),
+			Port: socket.Ntohs(a.Protocol),
 		}
 	} else {
 		if s.minSockAddrLen() > len(sockaddr) {
diff --git a/pkg/tcpip/transport/packet/endpoint.go b/pkg/tcpip/transport/packet/endpoint.go
index 2c9786175..1f30e5adb 100644
--- a/pkg/tcpip/transport/packet/endpoint.go
+++ b/pkg/tcpip/transport/packet/endpoint.go
@@ -59,13 +59,11 @@ type packet struct {
 //
 // +stateify savable
 type endpoint struct {
-	stack.TransportEndpointInfo
 	tcpip.DefaultSocketOptionsHandler
 
 	// The following fields are initialized at creation time and are
 	// immutable.
 	stack       *stack.Stack `state:"manual"`
-	netProto    tcpip.NetworkProtocolNumber
 	waiterQueue *waiter.Queue
 	cooked      bool
 	ops         tcpip.SocketOptions
@@ -84,6 +82,8 @@ type endpoint struct {
 
 	mu sync.RWMutex `state:"nosave"`
 	// +checklocks:mu
+	netProto tcpip.NetworkProtocolNumber
+	// +checklocks:mu
 	closed bool
 	// +checklocks:mu
 	bound bool
@@ -98,10 +98,7 @@ type endpoint struct {
 // NewEndpoint returns a new packet endpoint.
 func NewEndpoint(s *stack.Stack, cooked bool, netProto tcpip.NetworkProtocolNumber, waiterQueue *waiter.Queue) (tcpip.Endpoint, tcpip.Error) {
 	ep := &endpoint{
-		stack: s,
-		TransportEndpointInfo: stack.TransportEndpointInfo{
-			NetProto: netProto,
-		},
+		stack:       s,
 		cooked:      cooked,
 		netProto:    netProto,
 		waiterQueue: waiterQueue,
@@ -214,13 +211,13 @@ func (ep *endpoint) Write(p tcpip.Payloader, opts tcpip.WriteOptions) (int64, tc
 	ep.mu.Lock()
 	closed := ep.closed
 	nicID := ep.boundNIC
+	proto := ep.netProto
 	ep.mu.Unlock()
 	if closed {
 		return 0, &tcpip.ErrClosedForSend{}
 	}
 
 	var remote tcpip.LinkAddress
-	proto := ep.netProto
 	if to := opts.To; to != nil {
 		remote = tcpip.LinkAddress(to.Addr)
 
@@ -296,7 +293,8 @@ func (ep *endpoint) Bind(addr tcpip.FullAddress) tcpip.Error {
 	ep.mu.Lock()
 	defer ep.mu.Unlock()
 
-	if ep.bound && ep.boundNIC == addr.NIC {
+	netProto := tcpip.NetworkProtocolNumber(addr.Port)
+	if ep.bound && ep.boundNIC == addr.NIC && ep.netProto == netProto {
 		// If the NIC being bound is the same then just return success.
 		return nil
 	}
@@ -306,12 +304,13 @@ func (ep *endpoint) Bind(addr tcpip.FullAddress) tcpip.Error {
 	ep.bound = false
 
 	// Bind endpoint to receive packets from specific interface.
-	if err := ep.stack.RegisterPacketEndpoint(addr.NIC, ep.netProto, ep); err != nil {
+	if err := ep.stack.RegisterPacketEndpoint(addr.NIC, netProto, ep); err != nil {
 		return err
 	}
 
 	ep.bound = true
 	ep.boundNIC = addr.NIC
+	ep.netProto = netProto
 
 	return nil
 }
@@ -473,10 +472,8 @@ func (*endpoint) State() uint32 {
 // Info returns a copy of the endpoint info.
 func (ep *endpoint) Info() tcpip.EndpointInfo {
 	ep.mu.RLock()
-	// Make a copy of the endpoint info.
-	ret := ep.TransportEndpointInfo
-	ep.mu.RUnlock()
-	return &ret
+	defer ep.mu.RUnlock()
+	return &stack.TransportEndpointInfo{NetProto: ep.netProto}
 }
 
 // Stats returns a pointer to the endpoint stats.