Enable IP_RECVTOS socket option for datagram sockets

Added the ability to get/set the IP_RECVTOS socket option on UDP endpoints. If
enabled, TOS from the incoming Network Header passed as ancillary data in the
ControlMessages.

Test:
* Added unit test to udp_test.go that tests getting/setting as well as
verifying that we receive expected TOS from incoming packet.
* Added a syscall test
PiperOrigin-RevId: 287029703

pkg/sentry/socket/netstack/netstack.go

@@ -1323,6 +1323,21 @@ func getSockOptIP(t *kernel.Task, ep commonEndpoint, name, outLen int, family in
 		}
 		return int32(v), nil
 
+	case linux.IP_RECVTOS:
+		if outLen < sizeOfInt32 {
+			return nil, syserr.ErrInvalidArgument
+		}
+
+		var v tcpip.ReceiveTOSOption
+		if err := ep.GetSockOpt(&v); err != nil {
+			return nil, syserr.TranslateNetstackError(err)
+		}
+
+		if v {
+			return int32(1), nil
+		}
+		return int32(0), nil
+
 	default:
 		emitUnimplementedEventIP(t, name)
 	}
@@ -1808,6 +1823,16 @@ func setSockOptIP(t *kernel.Task, ep commonEndpoint, name int, optVal []byte) *s
 		}
 		return syserr.TranslateNetstackError(ep.SetSockOpt(tcpip.IPv4TOSOption(v)))
 
+	case linux.IP_RECVTOS:
+		v, err := parseIntOrChar(optVal)
+		if err != nil {
+			return err
+		}
+
+		return syserr.TranslateNetstackError(ep.SetSockOpt(
+			tcpip.ReceiveTOSOption(v != 0),
+		))
+
 	case linux.IP_ADD_SOURCE_MEMBERSHIP,
 		linux.IP_BIND_ADDRESS_NO_PORT,
 		linux.IP_BLOCK_SOURCE,
@@ -1828,7 +1853,6 @@ func setSockOptIP(t *kernel.Task, ep commonEndpoint, name int, optVal []byte) *s
 		linux.IP_RECVFRAGSIZE,
 		linux.IP_RECVOPTS,
 		linux.IP_RECVORIGDSTADDR,
-		linux.IP_RECVTOS,
 		linux.IP_RECVTTL,
 		linux.IP_RETOPTS,
 		linux.IP_TRANSPARENT,
@@ -2139,6 +2163,21 @@ func (s *SocketOperations) fillCmsgInq(cmsg *socket.ControlMessages) {
 	cmsg.IP.Inq = int32(len(s.readView) + rcvBufUsed)
 }
 
+func (s *SocketOperations) fillCmsgTOS(cmsg *socket.ControlMessages) {
+	if s.skType != linux.SOCK_DGRAM {
+		return
+	}
+	var receiveTOS tcpip.ReceiveTOSOption
+	if err := s.Endpoint.GetSockOpt(&receiveTOS); err != nil {
+		return
+	}
+	if !receiveTOS {
+		return
+	}
+	cmsg.IP.HasTOS = s.readCM.HasTOS
+	cmsg.IP.TOS = s.readCM.TOS
+}
+
 // nonBlockingRead issues a non-blocking read.
 //
 // TODO(b/78348848): Support timestamps for stream sockets.
@@ -2244,6 +2283,7 @@ func (s *SocketOperations) nonBlockingRead(ctx context.Context, dst usermem.IOSe
 
 	cmsg := s.controlMessages()
 	s.fillCmsgInq(&cmsg)
+	s.fillCmsgTOS(&cmsg)
 	return n, flags, addr, addrLen, cmsg, syserr.FromError(err)
 }