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

1 files changed, 13 insertions, 7 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 {