Ensure that IP{V6}_RECVORIGDSTADDR yields the post-NAT address and port.

PiperOrigin-RevId: 352624174

3 files changed, 249 insertions, 26 deletions

diff --git a/test/iptables/BUILD b/test/iptables/BUILD
index 66453772a..ae4bba847 100644
--- a/test/iptables/BUILD
+++ b/test/iptables/BUILD
@@ -15,7 +15,9 @@ go_library(
     ],
     visibility = ["//test/iptables:__subpackages__"],
     deps = [
+        "//pkg/binary",
         "//pkg/test/testutil",
+        "//pkg/usermem",
     ],
 )
 
diff --git a/test/iptables/iptables_test.go b/test/iptables/iptables_test.go
index 4733146c0..9a4f60a9a 100644
--- a/test/iptables/iptables_test.go
+++ b/test/iptables/iptables_test.go
@@ -424,3 +424,11 @@ func TestNATPreOriginalDst(t *testing.T) {
 func TestNATOutOriginalDst(t *testing.T) {
 	singleTest(t, NATOutOriginalDst{})
 }
+
+func TestNATPreRECVORIGDSTADDR(t *testing.T) {
+	singleTest(t, NATPreRECVORIGDSTADDR{})
+}
+
+func TestNATOutRECVORIGDSTADDR(t *testing.T) {
+	singleTest(t, NATOutRECVORIGDSTADDR{})
+}
diff --git a/test/iptables/nat.go b/test/iptables/nat.go
index 495241482..c3874240f 100644
--- a/test/iptables/nat.go
+++ b/test/iptables/nat.go
@@ -20,6 +20,9 @@ import (
 	"fmt"
 	"net"
 	"syscall"
+
+	"gvisor.dev/gvisor/pkg/binary"
+	"gvisor.dev/gvisor/pkg/usermem"
 )
 
 const redirectPort = 42
@@ -43,6 +46,8 @@ func init() {
 	RegisterTestCase(NATLoopbackSkipsPrerouting{})
 	RegisterTestCase(NATPreOriginalDst{})
 	RegisterTestCase(NATOutOriginalDst{})
+	RegisterTestCase(NATPreRECVORIGDSTADDR{})
+	RegisterTestCase(NATOutRECVORIGDSTADDR{})
 }
 
 // NATPreRedirectUDPPort tests that packets are redirected to different port.
@@ -538,9 +543,9 @@ func (NATOutOriginalDst) LocalAction(ctx context.Context, ip net.IP, ipv6 bool)
 }
 
 func listenForRedirectedConn(ctx context.Context, ipv6 bool, originalDsts []net.IP) error {
-	// The net package doesn't give guarantee access to the connection's
+	// The net package doesn't give guaranteed access to the connection's
 	// underlying FD, and thus we cannot call getsockopt. We have to use
-	// traditional syscalls for SO_ORIGINAL_DST.
+	// traditional syscalls.
 
 	// Create the listening socket, bind, listen, and accept.
 	family := syscall.AF_INET
@@ -609,36 +614,14 @@ func listenForRedirectedConn(ctx context.Context, ipv6 bool, originalDsts []net.
 		if err != nil {
 			return err
 		}
-		// The original destination could be any of our IPs.
-		for _, dst := range originalDsts {
-			want := syscall.RawSockaddrInet6{
-				Family: syscall.AF_INET6,
-				Port:   htons(dropPort),
-			}
-			copy(want.Addr[:], dst.To16())
-			if got == want {
-				return nil
-			}
-		}
-		return fmt.Errorf("SO_ORIGINAL_DST returned %+v, but wanted one of %+v (note: port numbers are in network byte order)", got, originalDsts)
+		return addrMatches6(got, originalDsts, dropPort)
 	}
 
 	got, err := originalDestination4(connFD)
 	if err != nil {
 		return err
 	}
-	// The original destination could be any of our IPs.
-	for _, dst := range originalDsts {
-		want := syscall.RawSockaddrInet4{
-			Family: syscall.AF_INET,
-			Port:   htons(dropPort),
-		}
-		copy(want.Addr[:], dst.To4())
-		if got == want {
-			return nil
-		}
-	}
-	return fmt.Errorf("SO_ORIGINAL_DST returned %+v, but wanted one of %+v (note: port numbers are in network byte order)", got, originalDsts)
+	return addrMatches4(got, originalDsts, dropPort)
 }
 
 // loopbackTests runs an iptables rule and ensures that packets sent to
@@ -662,3 +645,233 @@ func loopbackTest(ctx context.Context, ipv6 bool, dest net.IP, args ...string) e
 		return err
 	}
 }
+
+// NATPreRECVORIGDSTADDR tests that IP{V6}_RECVORIGDSTADDR gets the post-NAT
+// address on the PREROUTING chain.
+type NATPreRECVORIGDSTADDR struct{ containerCase }
+
+// Name implements TestCase.Name.
+func (NATPreRECVORIGDSTADDR) Name() string {
+	return "NATPreRECVORIGDSTADDR"
+}
+
+// ContainerAction implements TestCase.ContainerAction.
+func (NATPreRECVORIGDSTADDR) ContainerAction(ctx context.Context, ip net.IP, ipv6 bool) error {
+	if err := natTable(ipv6, "-A", "PREROUTING", "-p", "udp", "-j", "REDIRECT", "--to-ports", fmt.Sprintf("%d", redirectPort)); err != nil {
+		return err
+	}
+
+	if err := recvWithRECVORIGDSTADDR(ctx, ipv6, nil, redirectPort); err != nil {
+		return err
+	}
+
+	return nil
+}
+
+// LocalAction implements TestCase.LocalAction.
+func (NATPreRECVORIGDSTADDR) LocalAction(ctx context.Context, ip net.IP, ipv6 bool) error {
+	return sendUDPLoop(ctx, ip, acceptPort)
+}
+
+// NATOutRECVORIGDSTADDR tests that IP{V6}_RECVORIGDSTADDR gets the post-NAT
+// address on the OUTPUT chain.
+type NATOutRECVORIGDSTADDR struct{ containerCase }
+
+// Name implements TestCase.Name.
+func (NATOutRECVORIGDSTADDR) Name() string {
+	return "NATOutRECVORIGDSTADDR"
+}
+
+// ContainerAction implements TestCase.ContainerAction.
+func (NATOutRECVORIGDSTADDR) ContainerAction(ctx context.Context, ip net.IP, ipv6 bool) error {
+	if err := natTable(ipv6, "-A", "OUTPUT", "-p", "udp", "-j", "REDIRECT", "--to-ports", fmt.Sprintf("%d", redirectPort)); err != nil {
+		return err
+	}
+
+	sendCh := make(chan error)
+	go func() {
+		// Packets will be sent to a non-container IP and redirected
+		// back to the container.
+		sendCh <- sendUDPLoop(ctx, ip, acceptPort)
+	}()
+
+	expectedIP := &net.IP{127, 0, 0, 1}
+	if ipv6 {
+		expectedIP = &net.IP{0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1}
+	}
+	if err := recvWithRECVORIGDSTADDR(ctx, ipv6, expectedIP, redirectPort); err != nil {
+		return err
+	}
+
+	select {
+	case err := <-sendCh:
+		return err
+	default:
+		return nil
+	}
+}
+
+// LocalAction implements TestCase.LocalAction.
+func (NATOutRECVORIGDSTADDR) LocalAction(ctx context.Context, ip net.IP, ipv6 bool) error {
+	// No-op.
+	return nil
+}
+
+func recvWithRECVORIGDSTADDR(ctx context.Context, ipv6 bool, expectedDst *net.IP, port uint16) error {
+	// The net package doesn't give guaranteed access to a connection's
+	// underlying FD, and thus we cannot call getsockopt. We have to use
+	// traditional syscalls for IP_RECVORIGDSTADDR.
+
+	// Create the listening socket.
+	var (
+		family                    = syscall.AF_INET
+		level                     = syscall.SOL_IP
+		option                    = syscall.IP_RECVORIGDSTADDR
+		bindAddr syscall.Sockaddr = &syscall.SockaddrInet4{
+			Port: int(port),
+			Addr: [4]byte{0, 0, 0, 0}, // INADDR_ANY
+		}
+	)
+	if ipv6 {
+		family = syscall.AF_INET6
+		level = syscall.SOL_IPV6
+		option = 74 // IPV6_RECVORIGDSTADDR, which is missing from the syscall package.
+		bindAddr = &syscall.SockaddrInet6{
+			Port: int(port),
+			Addr: [16]byte{0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0}, // in6addr_any
+		}
+	}
+	sockfd, err := syscall.Socket(family, syscall.SOCK_DGRAM, 0)
+	if err != nil {
+		return fmt.Errorf("failed Socket(%d, %d, 0): %w", family, syscall.SOCK_DGRAM, err)
+	}
+	defer syscall.Close(sockfd)
+
+	if err := syscall.Bind(sockfd, bindAddr); err != nil {
+		return fmt.Errorf("failed Bind(%d, %+v): %v", sockfd, bindAddr, err)
+	}
+
+	// Enable IP_RECVORIGDSTADDR.
+	if err := syscall.SetsockoptInt(sockfd, level, option, 1); err != nil {
+		return fmt.Errorf("failed SetsockoptByte(%d, %d, %d, 1): %v", sockfd, level, option, err)
+	}
+
+	addrCh := make(chan interface{})
+	errCh := make(chan error)
+	go func() {
+		var addr interface{}
+		var err error
+		if ipv6 {
+			addr, err = recvOrigDstAddr6(sockfd)
+		} else {
+			addr, err = recvOrigDstAddr4(sockfd)
+		}
+		if err != nil {
+			errCh <- err
+		} else {
+			addrCh <- addr
+		}
+	}()
+
+	// Wait to receive a packet.
+	var addr interface{}
+	select {
+	case <-ctx.Done():
+		return ctx.Err()
+	case err := <-errCh:
+		return err
+	case addr = <-addrCh:
+	}
+
+	// Get a list of local IPs to verify that the packet now appears to have
+	// been sent to us.
+	var localAddrs []net.IP
+	if expectedDst != nil {
+		localAddrs = []net.IP{*expectedDst}
+	} else {
+		localAddrs, err = getInterfaceAddrs(ipv6)
+		if err != nil {
+			return fmt.Errorf("failed to get local interfaces: %w", err)
+		}
+	}
+
+	// Verify that the address has the post-NAT port and address.
+	if ipv6 {
+		return addrMatches6(addr.(syscall.RawSockaddrInet6), localAddrs, redirectPort)
+	}
+	return addrMatches4(addr.(syscall.RawSockaddrInet4), localAddrs, redirectPort)
+}
+
+func recvOrigDstAddr4(sockfd int) (syscall.RawSockaddrInet4, error) {
+	buf, err := recvOrigDstAddr(sockfd, syscall.SOL_IP, syscall.SizeofSockaddrInet4)
+	if err != nil {
+		return syscall.RawSockaddrInet4{}, err
+	}
+	var addr syscall.RawSockaddrInet4
+	binary.Unmarshal(buf, usermem.ByteOrder, &addr)
+	return addr, nil
+}
+
+func recvOrigDstAddr6(sockfd int) (syscall.RawSockaddrInet6, error) {
+	buf, err := recvOrigDstAddr(sockfd, syscall.SOL_IP, syscall.SizeofSockaddrInet6)
+	if err != nil {
+		return syscall.RawSockaddrInet6{}, err
+	}
+	var addr syscall.RawSockaddrInet6
+	binary.Unmarshal(buf, usermem.ByteOrder, &addr)
+	return addr, nil
+}
+
+func recvOrigDstAddr(sockfd int, level uintptr, addrSize int) ([]byte, error) {
+	buf := make([]byte, 64)
+	oob := make([]byte, syscall.CmsgSpace(addrSize))
+	for {
+		_, oobn, _, _, err := syscall.Recvmsg(
+			sockfd,
+			buf, // Message buffer.
+			oob, // Out-of-band buffer.
+			0)   // Flags.
+		if errors.Is(err, syscall.EINTR) {
+			continue
+		}
+		if err != nil {
+			return nil, fmt.Errorf("failed when calling Recvmsg: %w", err)
+		}
+		oob = oob[:oobn]
+
+		// Parse out the control message.
+		msgs, err := syscall.ParseSocketControlMessage(oob)
+		if err != nil {
+			return nil, fmt.Errorf("failed to parse control message: %w", err)
+		}
+		return msgs[0].Data, nil
+	}
+}
+
+func addrMatches4(got syscall.RawSockaddrInet4, wantAddrs []net.IP, port uint16) error {
+	for _, wantAddr := range wantAddrs {
+		want := syscall.RawSockaddrInet4{
+			Family: syscall.AF_INET,
+			Port:   htons(port),
+		}
+		copy(want.Addr[:], wantAddr.To4())
+		if got == want {
+			return nil
+		}
+	}
+	return fmt.Errorf("got %+v, but wanted one of %+v (note: port numbers are in network byte order)", got, wantAddrs)
+}
+
+func addrMatches6(got syscall.RawSockaddrInet6, wantAddrs []net.IP, port uint16) error {
+	for _, wantAddr := range wantAddrs {
+		want := syscall.RawSockaddrInet6{
+			Family: syscall.AF_INET6,
+			Port:   htons(port),
+		}
+		copy(want.Addr[:], wantAddr.To16())
+		if got == want {
+			return nil
+		}
+	}
+	return fmt.Errorf("got %+v, but wanted one of %+v (note: port numbers are in network byte order)", got, wantAddrs)
+}