Track and export socket state.

This is necessary for implementing network diagnostic interfaces like
/proc/net/{tcp,udp,unix} and sock_diag(7).

For pass-through endpoints such as hostinet, we obtain the socket
state from the backend. For netstack, we add explicit tracking of TCP
states.

PiperOrigin-RevId: 251934850

1 files changed, 37 insertions, 0 deletions

diff --git a/pkg/tcpip/transport/tcp/rcv.go b/pkg/tcpip/transport/tcp/rcv.go
index b08a0e356..f02fa6105 100644
--- a/pkg/tcpip/transport/tcp/rcv.go
+++ b/pkg/tcpip/transport/tcp/rcv.go
@@ -134,6 +134,7 @@ func (r *receiver) consumeSegment(s *segment, segSeq seqnum.Value, segLen seqnum
 	// sequence numbers that have been consumed.
 	TrimSACKBlockList(&r.ep.sack, r.rcvNxt)
 
+	// Handle FIN or FIN-ACK.
 	if s.flagIsSet(header.TCPFlagFin) {
 		r.rcvNxt++
 
@@ -144,6 +145,25 @@ func (r *receiver) consumeSegment(s *segment, segSeq seqnum.Value, segLen seqnum
 		r.closed = true
 		r.ep.readyToRead(nil)
 
+		// We just received a FIN, our next state depends on whether we sent a
+		// FIN already or not.
+		r.ep.mu.Lock()
+		switch r.ep.state {
+		case StateEstablished:
+			r.ep.state = StateCloseWait
+		case StateFinWait1:
+			if s.flagIsSet(header.TCPFlagAck) {
+				// FIN-ACK, transition to TIME-WAIT.
+				r.ep.state = StateTimeWait
+			} else {
+				// Simultaneous close, expecting a final ACK.
+				r.ep.state = StateClosing
+			}
+		case StateFinWait2:
+			r.ep.state = StateTimeWait
+		}
+		r.ep.mu.Unlock()
+
 		// Flush out any pending segments, except the very first one if
 		// it happens to be the one we're handling now because the
 		// caller is using it.
@@ -156,6 +176,23 @@ func (r *receiver) consumeSegment(s *segment, segSeq seqnum.Value, segLen seqnum
 			r.pendingRcvdSegments[i].decRef()
 		}
 		r.pendingRcvdSegments = r.pendingRcvdSegments[:first]
+
+		return true
+	}
+
+	// Handle ACK (not FIN-ACK, which we handled above) during one of the
+	// shutdown states.
+	if s.flagIsSet(header.TCPFlagAck) {
+		r.ep.mu.Lock()
+		switch r.ep.state {
+		case StateFinWait1:
+			r.ep.state = StateFinWait2
+		case StateClosing:
+			r.ep.state = StateTimeWait
+		case StateLastAck:
+			r.ep.state = StateClose
+		}
+		r.ep.mu.Unlock()
 	}
 
 	return true