Support receiving broadcast IPv4 packets

Test: integration_test.TestIncomingSubnetBroadcast
PiperOrigin-RevId: 325135617

2 files changed, 49 insertions, 1 deletions

diff --git a/pkg/tcpip/stack/nic.go b/pkg/tcpip/stack/nic.go
index f21066fce..ae4d241de 100644
--- a/pkg/tcpip/stack/nic.go
+++ b/pkg/tcpip/stack/nic.go
@@ -609,6 +609,9 @@ func (n *NIC) findEndpoint(protocol tcpip.NetworkProtocolNumber, address tcpip.A
 // If none exists a temporary one may be created if we are in promiscuous mode
 // or spoofing. Promiscuous mode will only be checked if promiscuous is true.
 // Similarly, spoofing will only be checked if spoofing is true.
+//
+// If the address is the IPv4 broadcast address for an endpoint's network, that
+// endpoint will be returned.
 func (n *NIC) getRefOrCreateTemp(protocol tcpip.NetworkProtocolNumber, address tcpip.Address, peb PrimaryEndpointBehavior, tempRef getRefBehaviour) *referencedNetworkEndpoint {
 	n.mu.RLock()
 
@@ -633,6 +636,16 @@ func (n *NIC) getRefOrCreateTemp(protocol tcpip.NetworkProtocolNumber, address t
 		}
 	}
 
+	// Check if address is a broadcast address for the endpoint's network.
+	//
+	// Only IPv4 has a notion of broadcast addresses.
+	if protocol == header.IPv4ProtocolNumber {
+		if ref := n.getRefForBroadcastRLocked(address); ref != nil {
+			n.mu.RUnlock()
+			return ref
+		}
+	}
+
 	// A usable reference was not found, create a temporary one if requested by
 	// the caller or if the address is found in the NIC's subnets.
 	createTempEP := spoofingOrPromiscuous
@@ -670,8 +683,34 @@ func (n *NIC) getRefOrCreateTemp(protocol tcpip.NetworkProtocolNumber, address t
 	return ref
 }
 
+// getRefForBroadcastLocked returns an endpoint where address is the IPv4
+// broadcast address for the endpoint's network.
+//
+// n.mu MUST be read locked.
+func (n *NIC) getRefForBroadcastRLocked(address tcpip.Address) *referencedNetworkEndpoint {
+	for _, ref := range n.mu.endpoints {
+		// Only IPv4 has a notion of broadcast addresses.
+		if ref.protocol != header.IPv4ProtocolNumber {
+			continue
+		}
+
+		addr := ref.addrWithPrefix()
+		subnet := addr.Subnet()
+		if subnet.IsBroadcast(address) && ref.tryIncRef() {
+			return ref
+		}
+	}
+
+	return nil
+}
+
 /// getRefOrCreateTempLocked returns an existing endpoint for address or creates
 /// and returns a temporary endpoint.
+//
+// If the address is the IPv4 broadcast address for an endpoint's network, that
+// endpoint will be returned.
+//
+// n.mu must be write locked.
 func (n *NIC) getRefOrCreateTempLocked(protocol tcpip.NetworkProtocolNumber, address tcpip.Address, peb PrimaryEndpointBehavior) *referencedNetworkEndpoint {
 	if ref, ok := n.mu.endpoints[NetworkEndpointID{address}]; ok {
 		// No need to check the type as we are ok with expired endpoints at this
@@ -685,6 +724,15 @@ func (n *NIC) getRefOrCreateTempLocked(protocol tcpip.NetworkProtocolNumber, add
 		n.removeEndpointLocked(ref)
 	}
 
+	// Check if address is a broadcast address for an endpoint's network.
+	//
+	// Only IPv4 has a notion of broadcast addresses.
+	if protocol == header.IPv4ProtocolNumber {
+		if ref := n.getRefForBroadcastRLocked(address); ref != nil {
+			return ref
+		}
+	}
+
 	// Add a new temporary endpoint.
 	netProto, ok := n.stack.networkProtocols[protocol]
 	if !ok {
diff --git a/pkg/tcpip/stack/stack_test.go b/pkg/tcpip/stack/stack_test.go
index f22062889..63ddbc44e 100644
--- a/pkg/tcpip/stack/stack_test.go
+++ b/pkg/tcpip/stack/stack_test.go
@@ -1704,7 +1704,7 @@ func testNicForAddressRange(t *testing.T, nicID tcpip.NICID, s *stack.Stack, sub
 
 	// Trying the next address should always fail since it is outside the range.
 	if gotNicID := s.CheckLocalAddress(0, fakeNetNumber, tcpip.Address(addrBytes)); gotNicID != 0 {
-		t.Errorf("got CheckLocalAddress(0, %d, %s) = %d, want = %d", fakeNetNumber, tcpip.Address(addrBytes), gotNicID, 0)
+		t.Errorf("got CheckLocalAddress(0, %d, %s) = %d, want = 0", fakeNetNumber, tcpip.Address(addrBytes), gotNicID)
 	}
 }