From b660f16d18827f0310594c80d9387de11430f15f Mon Sep 17 00:00:00 2001
From: Nayana Bidari <nybidari@google.com>
Date: Fri, 27 Mar 2020 12:18:45 -0700
Subject: 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.
---
 pkg/tcpip/transport/tcp/BUILD       |  2 +-
 pkg/tcpip/transport/tcp/rcv.go      | 19 +------------------
 pkg/tcpip/transport/tcp/rcv_test.go |  6 +++---
 3 files changed, 5 insertions(+), 22 deletions(-)

(limited to 'pkg/tcpip/transport/tcp')

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)
 		}
 	}
 }
-- 
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