From 47d85257d3d015f0b9f7739c81af0ee9f510aaf5 Mon Sep 17 00:00:00 2001
From: Eyal Soha <eyalsoha@google.com>
Date: Fri, 17 Jan 2020 18:24:39 -0800
Subject: Filter out received packets with a local source IP address.

CERT Advisory CA-96.21 III. Solution advises that devices drop packets which
could not have correctly arrived on the wire, such as receiving a packet where
the source IP address is owned by the device that sent it.

Fixes #1507

PiperOrigin-RevId: 290378240
---
 pkg/tcpip/transport/udp/udp_test.go | 52 +++++++++++++++++++++++++++++++++++--
 1 file changed, 50 insertions(+), 2 deletions(-)

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

diff --git a/pkg/tcpip/transport/udp/udp_test.go b/pkg/tcpip/transport/udp/udp_test.go
index ee9d10555..51bb61167 100644
--- a/pkg/tcpip/transport/udp/udp_test.go
+++ b/pkg/tcpip/transport/udp/udp_test.go
@@ -274,11 +274,16 @@ type testContext struct {
 
 func newDualTestContext(t *testing.T, mtu uint32) *testContext {
 	t.Helper()
-
-	s := stack.New(stack.Options{
+	return newDualTestContextWithOptions(t, mtu, stack.Options{
 		NetworkProtocols:   []stack.NetworkProtocol{ipv4.NewProtocol(), ipv6.NewProtocol()},
 		TransportProtocols: []stack.TransportProtocol{udp.NewProtocol()},
 	})
+}
+
+func newDualTestContextWithOptions(t *testing.T, mtu uint32, options stack.Options) *testContext {
+	t.Helper()
+
+	s := stack.New(options)
 	ep := channel.New(256, mtu, "")
 	wep := stack.LinkEndpoint(ep)
 
@@ -763,6 +768,49 @@ func TestV6ReadOnV6(t *testing.T) {
 	testRead(c, unicastV6)
 }
 
+// TestV4ReadSelfSource checks that packets coming from a local IP address are
+// correctly dropped when handleLocal is true and not otherwise.
+func TestV4ReadSelfSource(t *testing.T) {
+	for _, tt := range []struct {
+		name              string
+		handleLocal       bool
+		wantErr           *tcpip.Error
+		wantInvalidSource uint64
+	}{
+		{"HandleLocal", false, nil, 0},
+		{"NoHandleLocal", true, tcpip.ErrWouldBlock, 1},
+	} {
+		t.Run(tt.name, func(t *testing.T) {
+			c := newDualTestContextWithOptions(t, defaultMTU, stack.Options{
+				NetworkProtocols:   []stack.NetworkProtocol{ipv4.NewProtocol(), ipv6.NewProtocol()},
+				TransportProtocols: []stack.TransportProtocol{udp.NewProtocol()},
+				HandleLocal:        tt.handleLocal,
+			})
+			defer c.cleanup()
+
+			c.createEndpointForFlow(unicastV4)
+
+			if err := c.ep.Bind(tcpip.FullAddress{Port: stackPort}); err != nil {
+				t.Fatalf("Bind failed: %s", err)
+			}
+
+			payload := newPayload()
+			h := unicastV4.header4Tuple(incoming)
+			h.srcAddr = h.dstAddr
+
+			c.injectV4Packet(payload, &h, true /* valid */)
+
+			if got := c.s.Stats().IP.InvalidSourceAddressesReceived.Value(); got != tt.wantInvalidSource {
+				t.Errorf("c.s.Stats().IP.InvalidSourceAddressesReceived got %d, want %d", got, tt.wantInvalidSource)
+			}
+
+			if _, _, err := c.ep.Read(nil); err != tt.wantErr {
+				t.Errorf("c.ep.Read() got error %v, want %v", err, tt.wantErr)
+			}
+		})
+	}
+}
+
 func TestV4ReadOnV4(t *testing.T) {
 	c := newDualTestContext(t, defaultMTU)
 	defer c.cleanup()
-- 
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