netstack: use a proper network protocol to set gso.L3HdrLen

It is possible to create a listening socket which will accept
IPv4 and IPv6 connections. In this case, we set IPv6ProtocolNumber
for all accepted endpoints, even if they handle IPv4 connections.

This means that we can't use endpoint.netProto to set gso.L3HdrLen.

PiperOrigin-RevId: 244227948
Change-Id: I5e1863596cb9f3d216febacdb7dc75651882eef1

3 files changed, 22 insertions, 1 deletions

diff --git a/pkg/tcpip/transport/tcp/dual_stack_test.go b/pkg/tcpip/transport/tcp/dual_stack_test.go
index 52f20bef1..2886cc707 100644
--- a/pkg/tcpip/transport/tcp/dual_stack_test.go
+++ b/pkg/tcpip/transport/tcp/dual_stack_test.go
@@ -19,6 +19,7 @@ import (
 	"time"
 
 	"gvisor.googlesource.com/gvisor/pkg/tcpip"
+	"gvisor.googlesource.com/gvisor/pkg/tcpip/buffer"
 	"gvisor.googlesource.com/gvisor/pkg/tcpip/checker"
 	"gvisor.googlesource.com/gvisor/pkg/tcpip/header"
 	"gvisor.googlesource.com/gvisor/pkg/tcpip/network/ipv4"
@@ -330,6 +331,9 @@ func TestV6RefuseOnBoundToV4Mapped(t *testing.T) {
 }
 
 func testV4Accept(t *testing.T, c *context.Context) {
+	c.SetGSOEnabled(true)
+	defer c.SetGSOEnabled(false)
+
 	// Start listening.
 	if err := c.EP.Listen(10); err != nil {
 		t.Fatalf("Listen failed: %v", err)
@@ -406,6 +410,14 @@ func testV4Accept(t *testing.T, c *context.Context) {
 	if addr.Addr != context.TestAddr {
 		t.Fatalf("Unexpected remote address: got %v, want %v", addr.Addr, context.TestAddr)
 	}
+
+	data := "Don't panic"
+	nep.Write(tcpip.SlicePayload(buffer.NewViewFromBytes([]byte(data))), tcpip.WriteOptions{})
+	b = c.GetPacket()
+	tcp = header.TCP(header.IPv4(b).Payload())
+	if string(tcp.Payload()) != data {
+		t.Fatalf("Unexpected data: got %v, want %v", string(tcp.Payload()), data)
+	}
 }
 
 func TestV4AcceptOnV6(t *testing.T) {
diff --git a/pkg/tcpip/transport/tcp/endpoint.go b/pkg/tcpip/transport/tcp/endpoint.go
index b5d05af7d..c0b785431 100644
--- a/pkg/tcpip/transport/tcp/endpoint.go
+++ b/pkg/tcpip/transport/tcp/endpoint.go
@@ -1717,7 +1717,7 @@ func (e *endpoint) initGSO() {
 	}
 
 	gso := &stack.GSO{}
-	switch e.netProto {
+	switch e.route.NetProto {
 	case header.IPv4ProtocolNumber:
 		gso.Type = stack.GSOTCPv4
 		gso.L3HdrLen = header.IPv4MinimumSize
diff --git a/pkg/tcpip/transport/tcp/testing/context/context.go b/pkg/tcpip/transport/tcp/testing/context/context.go
index 8ac411b1d..6e2fed880 100644
--- a/pkg/tcpip/transport/tcp/testing/context/context.go
+++ b/pkg/tcpip/transport/tcp/testing/context/context.go
@@ -234,6 +234,10 @@ func (c *Context) GetPacket() []byte {
 		copy(b, p.Header)
 		copy(b[len(p.Header):], p.Payload)
 
+		if p.GSO != nil && p.GSO.L3HdrLen != header.IPv4MinimumSize {
+			c.t.Errorf("L3HdrLen %v (expected %v)", p.GSO.L3HdrLen, header.IPv4MinimumSize)
+		}
+
 		checker.IPv4(c.t, b, checker.SrcAddr(StackAddr), checker.DstAddr(TestAddr))
 		return b
 
@@ -956,3 +960,8 @@ func (c *Context) SACKEnabled() bool {
 	}
 	return bool(v)
 }
+
+// SetGSOEnabled enables or disables generic segmentation offload.
+func (c *Context) SetGSOEnabled(enable bool) {
+	c.linkEP.GSO = enable
+}