Add support for TIME_WAIT timeout.

This change adds explicit support for honoring the 2MSL timeout
for sockets in TIME_WAIT state. It also adds support for the
TCP_LINGER2 option that allows modification of the FIN_WAIT2
state timeout duration for a given socket.

It also adds an option to modify the Stack wide TIME_WAIT timeout
but this is only for testing. On Linux this is fixed at 60s.

Further, we also now correctly process RST's in CLOSE_WAIT and
close the socket similar to linux without moving it to error
state.

We also now handle SYN in ESTABLISHED state as per
RFC5961#section-4.1. Earlier we would just drop these SYNs.
Which can result in some tests that pass on linux to fail on
gVisor.

Netstack now honors TIME_WAIT correctly as well as handles the
following cases correctly.

- TCP RSTs in TIME_WAIT are ignored.
- A duplicate TCP FIN during TIME_WAIT extends the TIME_WAIT
  and a dup ACK is sent in response to the FIN as the dup FIN
  indicates potential loss of the original final ACK.
- An out of order segment during TIME_WAIT generates a dup ACK.
- A new SYN w/ a sequence number > the highest sequence number
  in the previous connection closes the TIME_WAIT early and
  opens a new connection.

Further to make the SYN case work correctly the ISN (Initial
Sequence Number) generation for Netstack has been updated to
be as per RFC. Its not a pure random number anymore and follows
the recommendation in https://tools.ietf.org/html/rfc6528#page-3.

The current hash used is not a cryptographically secure hash
function. A separate change will update the hash function used
to Siphash similar to what is used in Linux.

PiperOrigin-RevId: 279106406

2 files changed, 44 insertions, 9 deletions

diff --git a/pkg/tcpip/stack/stack.go b/pkg/tcpip/stack/stack.go
index 99809df75..2f8d8e822 100644
--- a/pkg/tcpip/stack/stack.go
+++ b/pkg/tcpip/stack/stack.go
@@ -402,11 +402,11 @@ type Stack struct {
 	// by the stack.
 	icmpRateLimiter *ICMPRateLimiter
 
-	// portSeed is a one-time random value initialized at stack startup
+	// seed is a one-time random value initialized at stack startup
 	// and is used to seed the TCP port picking on active connections
 	//
 	// TODO(gvisor.dev/issue/940): S/R this field.
-	portSeed uint32
+	seed uint32
 
 	// ndpConfigs is the default NDP configurations used by interfaces.
 	ndpConfigs NDPConfigurations
@@ -544,7 +544,7 @@ func New(opts Options) *Stack {
 		stats:                opts.Stats.FillIn(),
 		handleLocal:          opts.HandleLocal,
 		icmpRateLimiter:      NewICMPRateLimiter(),
-		portSeed:             generateRandUint32(),
+		seed:                 generateRandUint32(),
 		ndpConfigs:           opts.NDPConfigs,
 		autoGenIPv6LinkLocal: opts.AutoGenIPv6LinkLocal,
 		uniqueIDGenerator:    opts.UniqueID,
@@ -1186,6 +1186,12 @@ func (s *Stack) CompleteTransportEndpointCleanup(ep TransportEndpoint) {
 	s.mu.Unlock()
 }
 
+// FindTransportEndpoint finds an endpoint that most closely matches the provided
+// id. If no endpoint is found it returns nil.
+func (s *Stack) FindTransportEndpoint(netProto tcpip.NetworkProtocolNumber, transProto tcpip.TransportProtocolNumber, id TransportEndpointID, r *Route) TransportEndpoint {
+	return s.demux.findTransportEndpoint(netProto, transProto, id, r)
+}
+
 // RegisterRawTransportEndpoint registers the given endpoint with the stack
 // transport dispatcher. Received packets that match the provided transport
 // protocol will be delivered to the given endpoint.
@@ -1573,12 +1579,12 @@ func (s *Stack) HandleNDPRA(id tcpip.NICID, ip tcpip.Address, ra header.NDPRoute
 	return nil
 }
 
-// PortSeed returns a 32 bit value that can be used as a seed value for port
-// picking.
+// Seed returns a 32 bit value that can be used as a seed value for port
+// picking, ISN generation etc.
 //
 // NOTE: The seed is generated once during stack initialization only.
-func (s *Stack) PortSeed() uint32 {
-	return s.portSeed
+func (s *Stack) Seed() uint32 {
+	return s.seed
 }
 
 func generateRandUint32() uint32 {
diff --git a/pkg/tcpip/stack/transport_demuxer.go b/pkg/tcpip/stack/transport_demuxer.go
index 594570216..cb805522b 100644
--- a/pkg/tcpip/stack/transport_demuxer.go
+++ b/pkg/tcpip/stack/transport_demuxer.go
@@ -103,7 +103,6 @@ func (epsByNic *endpointsByNic) handlePacket(r *Route, id TransportEndpointID, p
 		epsByNic.mu.RUnlock() // Don't use defer for performance reasons.
 		return
 	}
-
 	// multiPortEndpoints are guaranteed to have at least one element.
 	selectEndpoint(id, mpep, epsByNic.seed).HandlePacket(r, id, pkt)
 	epsByNic.mu.RUnlock() // Don't use defer for performance reasons.
@@ -507,10 +506,40 @@ func (d *transportDemuxer) findAllEndpointsLocked(eps *transportEndpoints, id Tr
 	if ep, ok := eps.endpoints[nid]; ok {
 		matchedEPs = append(matchedEPs, ep)
 	}
-
 	return matchedEPs
 }
 
+// findTransportEndpoint find a single endpoint that most closely matches the provided id.
+func (d *transportDemuxer) findTransportEndpoint(netProto tcpip.NetworkProtocolNumber, transProto tcpip.TransportProtocolNumber, id TransportEndpointID, r *Route) TransportEndpoint {
+	eps, ok := d.protocol[protocolIDs{netProto, transProto}]
+	if !ok {
+		return nil
+	}
+	// Try to find the endpoint.
+	eps.mu.RLock()
+	epsByNic := d.findEndpointLocked(eps, id)
+	// Fail if we didn't find one.
+	if epsByNic == nil {
+		eps.mu.RUnlock()
+		return nil
+	}
+
+	epsByNic.mu.RLock()
+	eps.mu.RUnlock()
+
+	mpep, ok := epsByNic.endpoints[r.ref.nic.ID()]
+	if !ok {
+		if mpep, ok = epsByNic.endpoints[0]; !ok {
+			epsByNic.mu.RUnlock() // Don't use defer for performance reasons.
+			return nil
+		}
+	}
+
+	ep := selectEndpoint(id, mpep, epsByNic.seed)
+	epsByNic.mu.RUnlock()
+	return ep
+}
+
 // findEndpointLocked returns the endpoint that most closely matches the given
 // id.
 func (d *transportDemuxer) findEndpointLocked(eps *transportEndpoints, id TransportEndpointID) *endpointsByNic {