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

5 files changed, 95 insertions, 34 deletions

diff --git a/pkg/sentry/socket/netstack/netstack.go b/pkg/sentry/socket/netstack/netstack.go
index d2f7e987d..fec575357 100644
--- a/pkg/sentry/socket/netstack/netstack.go
+++ b/pkg/sentry/socket/netstack/netstack.go
@@ -138,13 +138,14 @@ var Metrics = tcpip.Stats{
 		},
 	},
 	IP: tcpip.IPStats{
-		PacketsReceived:            mustCreateMetric("/netstack/ip/packets_received", "Total number of IP packets received from the link layer in nic.DeliverNetworkPacket."),
-		InvalidAddressesReceived:   mustCreateMetric("/netstack/ip/invalid_addresses_received", "Total number of IP packets received with an unknown or invalid destination address."),
-		PacketsDelivered:           mustCreateMetric("/netstack/ip/packets_delivered", "Total number of incoming IP packets that are successfully delivered to the transport layer via HandlePacket."),
-		PacketsSent:                mustCreateMetric("/netstack/ip/packets_sent", "Total number of IP packets sent via WritePacket."),
-		OutgoingPacketErrors:       mustCreateMetric("/netstack/ip/outgoing_packet_errors", "Total number of IP packets which failed to write to a link-layer endpoint."),
-		MalformedPacketsReceived:   mustCreateMetric("/netstack/ip/malformed_packets_received", "Total number of IP packets which failed IP header validation checks."),
-		MalformedFragmentsReceived: mustCreateMetric("/netstack/ip/malformed_fragments_received", "Total number of IP fragments which failed IP fragment validation checks."),
+		PacketsReceived:                     mustCreateMetric("/netstack/ip/packets_received", "Total number of IP packets received from the link layer in nic.DeliverNetworkPacket."),
+		InvalidDestinationAddressesReceived: mustCreateMetric("/netstack/ip/invalid_addresses_received", "Total number of IP packets received with an unknown or invalid destination address."),
+		InvalidSourceAddressesReceived:      mustCreateMetric("/netstack/ip/invalid_source_addresses_received", "Total number of IP packets received with an unknown or invalid source address."),
+		PacketsDelivered:                    mustCreateMetric("/netstack/ip/packets_delivered", "Total number of incoming IP packets that are successfully delivered to the transport layer via HandlePacket."),
+		PacketsSent:                         mustCreateMetric("/netstack/ip/packets_sent", "Total number of IP packets sent via WritePacket."),
+		OutgoingPacketErrors:                mustCreateMetric("/netstack/ip/outgoing_packet_errors", "Total number of IP packets which failed to write to a link-layer endpoint."),
+		MalformedPacketsReceived:            mustCreateMetric("/netstack/ip/malformed_packets_received", "Total number of IP packets which failed IP header validation checks."),
+		MalformedFragmentsReceived:          mustCreateMetric("/netstack/ip/malformed_fragments_received", "Total number of IP fragments which failed IP fragment validation checks."),
 	},
 	TCP: tcpip.TCPStats{
 		ActiveConnectionOpenings:           mustCreateMetric("/netstack/tcp/active_connection_openings", "Number of connections opened successfully via Connect."),
diff --git a/pkg/sentry/socket/netstack/stack.go b/pkg/sentry/socket/netstack/stack.go
index a0db2d4fd..31ea66eca 100644
--- a/pkg/sentry/socket/netstack/stack.go
+++ b/pkg/sentry/socket/netstack/stack.go
@@ -148,25 +148,25 @@ func (s *Stack) Statistics(stat interface{}, arg string) error {
 	case *inet.StatSNMPIP:
 		ip := Metrics.IP
 		*stats = inet.StatSNMPIP{
-			0,                                   // TODO(gvisor.dev/issue/969): Support Ip/Forwarding.
-			0,                                   // TODO(gvisor.dev/issue/969): Support Ip/DefaultTTL.
-			ip.PacketsReceived.Value(),          // InReceives.
-			0,                                   // TODO(gvisor.dev/issue/969): Support Ip/InHdrErrors.
-			ip.InvalidAddressesReceived.Value(), // InAddrErrors.
-			0,                                   // TODO(gvisor.dev/issue/969): Support Ip/ForwDatagrams.
-			0,                                   // TODO(gvisor.dev/issue/969): Support Ip/InUnknownProtos.
-			0,                                   // TODO(gvisor.dev/issue/969): Support Ip/InDiscards.
-			ip.PacketsDelivered.Value(),         // InDelivers.
-			ip.PacketsSent.Value(),              // OutRequests.
-			ip.OutgoingPacketErrors.Value(),     // OutDiscards.
-			0,                                   // TODO(gvisor.dev/issue/969): Support Ip/OutNoRoutes.
-			0,                                   // TODO(gvisor.dev/issue/969): Support Ip/ReasmTimeout.
-			0,                                   // TODO(gvisor.dev/issue/969): Support Ip/ReasmReqds.
-			0,                                   // TODO(gvisor.dev/issue/969): Support Ip/ReasmOKs.
-			0,                                   // TODO(gvisor.dev/issue/969): Support Ip/ReasmFails.
-			0,                                   // TODO(gvisor.dev/issue/969): Support Ip/FragOKs.
-			0,                                   // TODO(gvisor.dev/issue/969): Support Ip/FragFails.
-			0,                                   // TODO(gvisor.dev/issue/969): Support Ip/FragCreates.
+			0,                          // TODO(gvisor.dev/issue/969): Support Ip/Forwarding.
+			0,                          // TODO(gvisor.dev/issue/969): Support Ip/DefaultTTL.
+			ip.PacketsReceived.Value(), // InReceives.
+			0,                          // TODO(gvisor.dev/issue/969): Support Ip/InHdrErrors.
+			ip.InvalidDestinationAddressesReceived.Value(), // InAddrErrors.
+			0,                               // TODO(gvisor.dev/issue/969): Support Ip/ForwDatagrams.
+			0,                               // TODO(gvisor.dev/issue/969): Support Ip/InUnknownProtos.
+			0,                               // TODO(gvisor.dev/issue/969): Support Ip/InDiscards.
+			ip.PacketsDelivered.Value(),     // InDelivers.
+			ip.PacketsSent.Value(),          // OutRequests.
+			ip.OutgoingPacketErrors.Value(), // OutDiscards.
+			0,                               // TODO(gvisor.dev/issue/969): Support Ip/OutNoRoutes.
+			0,                               // TODO(gvisor.dev/issue/969): Support Ip/ReasmTimeout.
+			0,                               // TODO(gvisor.dev/issue/969): Support Ip/ReasmReqds.
+			0,                               // TODO(gvisor.dev/issue/969): Support Ip/ReasmOKs.
+			0,                               // TODO(gvisor.dev/issue/969): Support Ip/ReasmFails.
+			0,                               // TODO(gvisor.dev/issue/969): Support Ip/FragOKs.
+			0,                               // TODO(gvisor.dev/issue/969): Support Ip/FragFails.
+			0,                               // TODO(gvisor.dev/issue/969): Support Ip/FragCreates.
 		}
 	case *inet.StatSNMPICMP:
 		in := Metrics.ICMP.V4PacketsReceived.ICMPv4PacketStats
diff --git a/pkg/tcpip/stack/nic.go b/pkg/tcpip/stack/nic.go
index 53abf29e5..4afe7b744 100644
--- a/pkg/tcpip/stack/nic.go
+++ b/pkg/tcpip/stack/nic.go
@@ -984,7 +984,7 @@ func handlePacket(protocol tcpip.NetworkProtocolNumber, dst, src tcpip.Address,
 
 // DeliverNetworkPacket finds the appropriate network protocol endpoint and
 // hands the packet over for further processing. This function is called when
-// the NIC receives a packet from the physical interface.
+// the NIC receives a packet from the link endpoint.
 // Note that the ownership of the slice backing vv is retained by the caller.
 // This rule applies only to the slice itself, not to the items of the slice;
 // the ownership of the items is not retained by the caller.
@@ -1029,6 +1029,14 @@ func (n *NIC) DeliverNetworkPacket(linkEP LinkEndpoint, remote, local tcpip.Link
 
 	src, dst := netProto.ParseAddresses(pkt.Data.First())
 
+	if n.stack.handleLocal && !n.isLoopback() && n.getRef(protocol, src) != nil {
+		// The source address is one of our own, so we never should have gotten a
+		// packet like this unless handleLocal is false. Loopback also calls this
+		// function even though the packets didn't come from the physical interface
+		// so don't drop those.
+		n.stack.stats.IP.InvalidSourceAddressesReceived.Increment()
+		return
+	}
 	if ref := n.getRef(protocol, dst); ref != nil {
 		handlePacket(protocol, dst, src, linkEP.LinkAddress(), remote, ref, pkt)
 		return
@@ -1041,7 +1049,7 @@ func (n *NIC) DeliverNetworkPacket(linkEP LinkEndpoint, remote, local tcpip.Link
 	if n.stack.Forwarding() {
 		r, err := n.stack.FindRoute(0, "", dst, protocol, false /* multicastLoop */)
 		if err != nil {
-			n.stack.stats.IP.InvalidAddressesReceived.Increment()
+			n.stack.stats.IP.InvalidDestinationAddressesReceived.Increment()
 			return
 		}
 		defer r.Release()
@@ -1079,7 +1087,7 @@ func (n *NIC) DeliverNetworkPacket(linkEP LinkEndpoint, remote, local tcpip.Link
 
 	// If a packet socket handled the packet, don't treat it as invalid.
 	if len(packetEPs) == 0 {
-		n.stack.stats.IP.InvalidAddressesReceived.Increment()
+		n.stack.stats.IP.InvalidDestinationAddressesReceived.Increment()
 	}
 }
 
diff --git a/pkg/tcpip/tcpip.go b/pkg/tcpip/tcpip.go
index b7813cbc0..6243762e3 100644
--- a/pkg/tcpip/tcpip.go
+++ b/pkg/tcpip/tcpip.go
@@ -903,9 +903,13 @@ type IPStats struct {
 	// link layer in nic.DeliverNetworkPacket.
 	PacketsReceived *StatCounter
 
-	// InvalidAddressesReceived is the total number of IP packets received
-	// with an unknown or invalid destination address.
-	InvalidAddressesReceived *StatCounter
+	// InvalidDestinationAddressesReceived is the total number of IP packets
+	// received with an unknown or invalid destination address.
+	InvalidDestinationAddressesReceived *StatCounter
+
+	// InvalidSourceAddressesReceived is the total number of IP packets received
+	// with a source address that should never have been received on the wire.
+	InvalidSourceAddressesReceived *StatCounter
 
 	// PacketsDelivered is the total number of incoming IP packets that
 	// are successfully delivered to the transport layer via HandlePacket.
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()