Support for connection tracking of TCP packets.

Connection tracking is used to track packets in prerouting and
output hooks of iptables. The NAT rules modify the tuples in
connections. The connection tracking code modifies the packets by
looking at the modified tuples.

5 files changed, 19 insertions, 25 deletions

diff --git a/pkg/tcpip/transport/tcp/BUILD b/pkg/tcpip/transport/tcp/BUILD
index f2aa69069..f38eb6833 100644
--- a/pkg/tcpip/transport/tcp/BUILD
+++ b/pkg/tcpip/transport/tcp/BUILD
@@ -115,7 +115,7 @@ go_test(
     size = "small",
     srcs = ["rcv_test.go"],
     deps = [
-        ":tcp",
+        "//pkg/tcpip/header",
         "//pkg/tcpip/seqnum",
     ],
 )
diff --git a/pkg/tcpip/transport/tcp/rcv.go b/pkg/tcpip/transport/tcp/rcv.go
index a4b73b588..6fe97fefd 100644
--- a/pkg/tcpip/transport/tcp/rcv.go
+++ b/pkg/tcpip/transport/tcp/rcv.go
@@ -70,24 +70,7 @@ func newReceiver(ep *endpoint, irs seqnum.Value, rcvWnd seqnum.Size, rcvWndScale
 // acceptable checks if the segment sequence number range is acceptable
 // according to the table on page 26 of RFC 793.
 func (r *receiver) acceptable(segSeq seqnum.Value, segLen seqnum.Size) bool {
-	return Acceptable(segSeq, segLen, r.rcvNxt, r.rcvAcc)
-}
-
-// Acceptable checks if a segment that starts at segSeq and has length segLen is
-// "acceptable" for arriving in a receive window that starts at rcvNxt and ends
-// before rcvAcc, according to the table on page 26 and 69 of RFC 793.
-func Acceptable(segSeq seqnum.Value, segLen seqnum.Size, rcvNxt, rcvAcc seqnum.Value) bool {
-	if rcvNxt == rcvAcc {
-		return segLen == 0 && segSeq == rcvNxt
-	}
-	if segLen == 0 {
-		// rcvWnd is incremented by 1 because that is Linux's behavior despite the
-		// RFC.
-		return segSeq.InRange(rcvNxt, rcvAcc.Add(1))
-	}
-	// Page 70 of RFC 793 allows packets that can be made "acceptable" by trimming
-	// the payload, so we'll accept any payload that overlaps the receieve window.
-	return rcvNxt.LessThan(segSeq.Add(segLen)) && segSeq.LessThan(rcvAcc)
+	return header.Acceptable(segSeq, segLen, r.rcvNxt, r.rcvAcc)
 }
 
 // getSendParams returns the parameters needed by the sender when building
diff --git a/pkg/tcpip/transport/tcp/rcv_test.go b/pkg/tcpip/transport/tcp/rcv_test.go
index dc02729ce..c9eeff935 100644
--- a/pkg/tcpip/transport/tcp/rcv_test.go
+++ b/pkg/tcpip/transport/tcp/rcv_test.go
@@ -17,8 +17,8 @@ package rcv_test
 import (
 	"testing"
 
+	"gvisor.dev/gvisor/pkg/tcpip/header"
 	"gvisor.dev/gvisor/pkg/tcpip/seqnum"
-	"gvisor.dev/gvisor/pkg/tcpip/transport/tcp"
 )
 
 func TestAcceptable(t *testing.T) {
@@ -67,8 +67,8 @@ func TestAcceptable(t *testing.T) {
 		{105, 2, 108, 108, false},
 		{105, 2, 109, 109, false},
 	} {
-		if got := tcp.Acceptable(tt.segSeq, tt.segLen, tt.rcvNxt, tt.rcvAcc); got != tt.want {
-			t.Errorf("tcp.Acceptable(%d, %d, %d, %d) = %t, want %t", tt.segSeq, tt.segLen, tt.rcvNxt, tt.rcvAcc, got, tt.want)
+		if got := header.Acceptable(tt.segSeq, tt.segLen, tt.rcvNxt, tt.rcvAcc); got != tt.want {
+			t.Errorf("header.Acceptable(%d, %d, %d, %d) = %t, want %t", tt.segSeq, tt.segLen, tt.rcvNxt, tt.rcvAcc, got, tt.want)
 		}
 	}
 }
diff --git a/pkg/tcpip/transport/tcpconntrack/BUILD b/pkg/tcpip/transport/tcpconntrack/BUILD
index 2025ff757..3ad6994a7 100644
--- a/pkg/tcpip/transport/tcpconntrack/BUILD
+++ b/pkg/tcpip/transport/tcpconntrack/BUILD
@@ -9,7 +9,6 @@ go_library(
     deps = [
         "//pkg/tcpip/header",
         "//pkg/tcpip/seqnum",
-        "//pkg/tcpip/transport/tcp",
     ],
 )
 
diff --git a/pkg/tcpip/transport/tcpconntrack/tcp_conntrack.go b/pkg/tcpip/transport/tcpconntrack/tcp_conntrack.go
index 30d05200f..12bc1b5b5 100644
--- a/pkg/tcpip/transport/tcpconntrack/tcp_conntrack.go
+++ b/pkg/tcpip/transport/tcpconntrack/tcp_conntrack.go
@@ -20,7 +20,6 @@ package tcpconntrack
 import (
 	"gvisor.dev/gvisor/pkg/tcpip/header"
 	"gvisor.dev/gvisor/pkg/tcpip/seqnum"
-	"gvisor.dev/gvisor/pkg/tcpip/transport/tcp"
 )
 
 // Result is returned when the state of a TCB is updated in response to an
@@ -312,7 +311,7 @@ type stream struct {
 // the window is zero, if it's a packet with no payload and sequence number
 // equal to una.
 func (s *stream) acceptable(segSeq seqnum.Value, segLen seqnum.Size) bool {
-	return tcp.Acceptable(segSeq, segLen, s.una, s.end)
+	return header.Acceptable(segSeq, segLen, s.una, s.end)
 }
 
 // closed determines if the stream has already been closed. This happens when
@@ -338,3 +337,16 @@ func logicalLen(tcp header.TCP) seqnum.Size {
 	}
 	return l
 }
+
+// IsEmpty returns true if tcb is not initialized.
+func (t *TCB) IsEmpty() bool {
+	if t.inbound != (stream{}) || t.outbound != (stream{}) {
+		return false
+	}
+
+	if t.firstFin != nil || t.state != ResultDrop {
+		return false
+	}
+
+	return true
+}