Support firewall rules with hostnames.

Co-Authored-By: Mindy Preston <yomimono@users.noreply.github.com>
Co-Authored-By: Olle Jonsson <olle.jonsson@gmail.com>
Co-Authored-By: hannes <hannes@mehnert.org>
Co-Authored-By: cfcs <cfcs@users.noreply.github.com>

client_net.ml

@@ -59,7 +59,7 @@ let input_arp ~fixed_arp ~iface request =
       iface#writev `ARP (fun b -> Arp_packet.encode_into response b; Arp_packet.size)
 
 (** Handle an IPv4 packet from the client. *)
-let input_ipv4 get_ts cache ~iface ~router packet =
+let input_ipv4 get_ts cache ~iface ~router dns_client packet =
   let cache', r = Nat_packet.of_ipv4_packet !cache ~now:(get_ts ()) packet in
   cache := cache';
   match r with
@@ -70,7 +70,7 @@ let input_ipv4 get_ts cache ~iface ~router packet =
   | Ok (Some packet) ->
     let `IPv4 (ip, _) = packet in
     let src = ip.Ipv4_packet.src in
-    if src = iface#other_ip then Firewall.ipv4_from_client router ~src:iface packet
+    if src = iface#other_ip then Firewall.ipv4_from_client dns_client router ~src:iface packet
     else (
       Log.warn (fun f -> f "Incorrect source IP %a in IP packet from %a (dropping)"
                    Ipaddr.V4.pp src Ipaddr.V4.pp iface#other_ip);
@@ -78,7 +78,7 @@ let input_ipv4 get_ts cache ~iface ~router packet =
     )
 
 (** Connect to a new client's interface and listen for incoming frames and firewall rule changes. *)
-let add_vif get_ts { Dao.ClientVif.domid; device_id } ~client_ip ~router ~cleanup_tasks qubesDB =
+let add_vif get_ts { Dao.ClientVif.domid; device_id } dns_client ~client_ip ~router ~cleanup_tasks qubesDB =
   Netback.make ~domid ~device_id >>= fun backend ->
   Log.info (fun f -> f "Client %d (IP: %s) ready" domid (Ipaddr.V4.to_string client_ip));
   ClientEth.connect backend >>= fun eth ->
@@ -101,7 +101,7 @@ let add_vif get_ts { Dao.ClientVif.domid; device_id } ~client_ip ~router ~cleanu
                         (Ipaddr.V4.to_string client_ip)
                         Fmt.(list ~sep:(unit "@.") Pf_qubes.Parse_qubes.pp_rule) new_rules);
             (* empty NAT table if rules are updated: they might deny old connections *)
-            My_nat.remove_connections router.Router.nat client_ip;
+            My_nat.remove_connections router.Router.nat router.Router.ports client_ip;
           end);
           update new_db new_rules
         in
@@ -122,7 +122,7 @@ let add_vif get_ts { Dao.ClientVif.domid; device_id } ~client_ip ~router ~cleanu
           | Ok (eth, payload) ->
               match eth.Ethernet_packet.ethertype with
               | `ARP -> input_arp ~fixed_arp ~iface payload
-              | `IPv4 -> input_ipv4 get_ts fragment_cache ~iface ~router payload
+              | `IPv4 -> input_ipv4 get_ts fragment_cache ~iface ~router dns_client payload
               | `IPv6 -> Lwt.return_unit (* TODO: oh no! *)
         )
         >|= or_raise "Listen on client interface" Netback.pp_error)
@@ -132,13 +132,13 @@ let add_vif get_ts { Dao.ClientVif.domid; device_id } ~client_ip ~router ~cleanu
   Lwt.pick [ qubesdb_updater ; listener ]
 
 (** A new client VM has been found in XenStore. Find its interface and connect to it. *)
-let add_client get_ts ~router vif client_ip qubesDB =
+let add_client get_ts dns_client ~router vif client_ip qubesDB =
   let cleanup_tasks = Cleanup.create () in
   Log.info (fun f -> f "add client vif %a with IP %a"
                Dao.ClientVif.pp vif Ipaddr.V4.pp client_ip);
   Lwt.async (fun () ->
       Lwt.catch (fun () ->
-          add_vif get_ts vif ~client_ip ~router ~cleanup_tasks qubesDB
+          add_vif get_ts vif dns_client ~client_ip ~router ~cleanup_tasks qubesDB
         )
         (fun ex ->
            Log.warn (fun f -> f "Error with client %a: %s"
@@ -149,7 +149,7 @@ let add_client get_ts ~router vif client_ip qubesDB =
   cleanup_tasks
 
 (** Watch XenStore for notifications of new clients. *)
-let listen get_ts qubesDB router =
+let listen get_ts dns_client qubesDB router =
   Dao.watch_clients (fun new_set ->
     (* Check for removed clients *)
     !clients |> Dao.VifMap.iter (fun key cleanup ->
@@ -162,7 +162,7 @@ let listen get_ts qubesDB router =
     (* Check for added clients *)
     new_set |> Dao.VifMap.iter (fun key ip_addr ->
       if not (Dao.VifMap.mem key !clients) then (
-        let cleanup = add_client get_ts ~router key ip_addr qubesDB in
+        let cleanup = add_client get_ts dns_client ~router key ip_addr qubesDB in
         Log.debug (fun f -> f "client %a arrived" Dao.ClientVif.pp key);
         clients := !clients |> Dao.VifMap.add key cleanup
       )

client_net.mli

@@ -3,8 +3,10 @@
 
 (** Handling client VMs. *)
 
-val listen : (unit -> int64) -> Qubes.DB.t -> Router.t -> 'a Lwt.t
-(** [listen get_timestamp db router] is a thread that watches for clients being added to and
+val listen : (unit -> int64) ->
+  ([ `host ] Domain_name.t -> (int32 * Dns.Rr_map.Ipv4_set.t, [> `Msg of string ]) result Lwt.t) ->
+  Qubes.DB.t -> Router.t -> 'a Lwt.t
+(** [listen get_timestamp resolver db router] is a thread that watches for clients being added to and
     removed from XenStore. Clients are connected to the client network and
     packets are sent via [router]. We ensure the source IP address is correct
     before routing a packet. *)

config.ml

@@ -34,6 +34,7 @@ let main =
       package "mirage-nat" ~min:"2.2.1";
       package "mirage-logs";
       package "mirage-xen" ~min:"5.0.0";
+      package ~min:"4.5.0" "dns-client";
       package "pf-qubes";
     ]
     "Unikernel.Main" (random @-> mclock @-> job)

firewall.ml

@@ -45,8 +45,9 @@ let translate t packet =
 
 (* Add a NAT rule for the endpoints in this frame, via a random port on the firewall. *)
 let add_nat_and_forward_ipv4 t packet =
-  let xl_host = t.Router.uplink#my_ip in
-  My_nat.add_nat_rule_and_translate t.Router.nat ~xl_host `NAT packet >>= function
+  let open Router in
+  let xl_host = t.uplink#my_ip in
+  My_nat.add_nat_rule_and_translate t.nat t.ports ~xl_host `NAT packet >>= function
   | Ok packet -> forward_ipv4 t packet
   | Error e ->
     Log.warn (fun f -> f "Failed to add NAT rewrite rule: %s (%a)" e Nat_packet.pp packet);
@@ -54,11 +55,12 @@ let add_nat_and_forward_ipv4 t packet =
 
 (* Add a NAT rule to redirect this conversation to [host:port] instead of us. *)
 let nat_to t ~host ~port packet =
-  match Router.resolve t host with
+  let open Router in
+  match resolve t host with
   | Ipaddr.V6 _ -> Log.warn (fun f -> f "Cannot NAT with IPv6"); Lwt.return_unit
   | Ipaddr.V4 target ->
-    let xl_host = t.Router.uplink#my_ip in
-    My_nat.add_nat_rule_and_translate t.Router.nat ~xl_host (`Redirect (target, port)) packet >>= function
+    let xl_host = t.uplink#my_ip in
+    My_nat.add_nat_rule_and_translate t.nat t.ports ~xl_host (`Redirect (target, port)) packet >>= function
     | Ok packet -> forward_ipv4 t packet
     | Error e ->
       Log.warn (fun f -> f "Failed to add NAT redirect rule: %s (%a)" e Nat_packet.pp packet);
@@ -85,11 +87,11 @@ let handle_low_memory t =
   match Memory_pressure.status () with
   | `Memory_critical -> (* TODO: should happen before copying and async *)
       Log.warn (fun f -> f "Memory low - dropping packet and resetting NAT table");
-      My_nat.reset t.Router.nat >|= fun () ->
+      My_nat.reset t.Router.nat t.Router.ports >|= fun () ->
       `Memory_critical
   | `Ok -> Lwt.return `Ok
 
-let ipv4_from_client t ~src packet =
+let ipv4_from_client resolver t ~src packet =
   handle_low_memory t >>= function
   | `Memory_critical -> Lwt.return_unit
   | `Ok ->
@@ -102,7 +104,7 @@ let ipv4_from_client t ~src packet =
   let dst = Router.classify t (Ipaddr.V4 ip.Ipv4_packet.dst) in
   match of_mirage_nat_packet ~src:(`Client src) ~dst packet with
   | None -> Lwt.return_unit
-  | Some firewall_packet -> apply_rules t Rules.from_client ~dst firewall_packet
+  | Some firewall_packet -> apply_rules t (Rules.from_client resolver) ~dst firewall_packet
 
 let ipv4_from_netvm t packet =
   handle_low_memory t >>= function

firewall.mli

@@ -6,6 +6,8 @@
 val ipv4_from_netvm : Router.t -> Nat_packet.t -> unit Lwt.t
 (** Handle a packet from the outside world (this module will validate the source IP). *)
 
-val ipv4_from_client : Router.t -> src:Fw_utils.client_link -> Nat_packet.t -> unit Lwt.t
+(* TODO the function type is a workaround, rework the module dependencies / functors to get rid of it *)
+val ipv4_from_client : ([ `host ] Domain_name.t -> (int32 * Dns.Rr_map.Ipv4_set.t, [> `Msg of string ]) result Lwt.t) ->
+  Router.t -> src:Fw_utils.client_link -> Nat_packet.t -> unit Lwt.t
 (** Handle a packet from a client. Caller must check the source IP matches the client's
     before calling this. *)

my_dns.ml

@@ -0,0 +1,57 @@
+open Lwt.Infix
+
+module Transport (R : Mirage_random.S) (C : Mirage_clock.MCLOCK) = struct
+  type +'a io = 'a Lwt.t
+  type io_addr = Ipaddr.V4.t * int
+  type ns_addr = [ `TCP | `UDP ] * io_addr
+  type stack = Router.t * (src_port:int -> dst:Ipaddr.V4.t -> dst_port:int -> Cstruct.t -> (unit, [ `Msg of string ]) result Lwt.t) * (Udp_packet.t * Cstruct.t) Lwt_mvar.t
+
+  type t = {
+    nameserver : ns_addr ;
+    stack : stack ;
+    timeout_ns : int64 ;
+  }
+  type context = { t : t ; timeout_ns : int64 ref; mutable src_port : int }
+
+  let nameserver t = t.nameserver
+  let rng = R.generate ?g:None
+  let clock = C.elapsed_ns
+
+  let create ?(nameserver = `UDP, (Ipaddr.V4.of_string_exn "91.239.100.100", 53)) ~timeout stack =
+    { nameserver ; stack ; timeout_ns = timeout }
+
+  let with_timeout ctx f =
+    let timeout = OS.Time.sleep_ns !(ctx.timeout_ns) >|= fun () -> Error (`Msg "DNS request timeout") in
+    let start = clock () in
+    Lwt.pick [ f ; timeout ] >|= fun result ->
+    let stop = clock () in
+    ctx.timeout_ns := Int64.sub !(ctx.timeout_ns) (Int64.sub stop start);
+    result
+
+  let connect ?nameserver:_ (t : t) = Lwt.return (Ok { t ; timeout_ns = ref t.timeout_ns ; src_port = 0 })
+
+  let send (ctx : context) buf : (unit, [> `Msg of string ]) result Lwt.t =
+    let open Router in
+    let open My_nat in
+    let dst, dst_port = snd ctx.t.nameserver in
+    let router, send_udp, _ = ctx.t.stack in
+    let src_port = Ports.pick_free_port ~consult:router.ports.nat_udp router.ports.dns_udp in
+    ctx.src_port <- src_port;
+    with_timeout ctx (send_udp ~src_port ~dst ~dst_port buf >|= Rresult.R.open_error_msg)
+
+  let recv ctx =
+    let open Router in
+    let open My_nat in
+    let router, _, answers = ctx.t.stack in
+    with_timeout ctx
+      (Lwt_mvar.take answers >|= fun (_, dns_response) -> Ok dns_response) >|= fun result ->
+    router.ports.dns_udp := Ports.remove ctx.src_port !(router.ports.dns_udp);
+    result
+
+  let close _ = Lwt.return_unit
+
+  let bind = Lwt.bind
+
+  let lift = Lwt.return
+end
+

my_nat.ml

@@ -11,6 +11,20 @@ type action = [
   | `Redirect of Mirage_nat.endpoint
 ]
 
+type ports = {
+  nat_tcp : Ports.t ref;
+  nat_udp : Ports.t ref;
+  nat_icmp : Ports.t ref;
+  dns_udp : Ports.t ref;
+}
+
+let empty_ports () =
+  let nat_tcp = ref Ports.empty in
+  let nat_udp = ref Ports.empty in
+  let nat_icmp = ref Ports.empty in
+  let dns_udp = ref Ports.empty in
+  { nat_tcp ; nat_udp ; nat_icmp ; dns_udp }
+
 module Nat = Mirage_nat_lru
 
 type t = {
@@ -33,17 +47,23 @@ let translate t packet =
     None
   | Ok packet -> Some packet
 
-let random_user_port () =
-  1024 + Random.int (0xffff - 1024)
+let pick_free_port ~nat_ports ~dns_ports =
+  Ports.pick_free_port ~consult:dns_ports nat_ports
 
-let reset t =
+(* just clears the nat ports, dns ports stay as is *)
+let reset t ports =
+  ports.nat_tcp := Ports.empty;
+  ports.nat_udp := Ports.empty;
+  ports.nat_icmp := Ports.empty;
   Nat.reset t.table
 
-let remove_connections t ip =
-  let Mirage_nat.{ tcp ; udp } = Nat.remove_connections t.table ip in
-  ignore(tcp, udp)
+let remove_connections t ports ip =
+  let freed_ports = Nat.remove_connections t.table ip in
+  ports.nat_tcp := Ports.diff !(ports.nat_tcp) (Ports.of_list freed_ports.Mirage_nat.tcp);
+  ports.nat_udp := Ports.diff !(ports.nat_udp) (Ports.of_list freed_ports.Mirage_nat.udp);
+  ports.nat_icmp := Ports.diff !(ports.nat_icmp) (Ports.of_list freed_ports.Mirage_nat.icmp)
 
-let add_nat_rule_and_translate t ~xl_host action packet =
+let add_nat_rule_and_translate t ports ~xl_host action packet =
   let apply_action xl_port =
     Lwt.catch (fun () ->
         Nat.add t.table packet (xl_host, xl_port) action
@@ -54,19 +74,25 @@ let add_nat_rule_and_translate t ~xl_host action packet =
       )
   in
   let rec aux ~retries =
-    let xl_port = random_user_port () in
+    let nat_ports, dns_ports =
+      match packet with
+      | `IPv4 (_, `TCP _) -> ports.nat_tcp, ref Ports.empty
+      | `IPv4 (_, `UDP _) -> ports.nat_udp, ports.dns_udp
+      | `IPv4 (_, `ICMP _) -> ports.nat_icmp, ref Ports.empty
+    in
+    let xl_port = pick_free_port ~nat_ports ~dns_ports in
     apply_action xl_port >>= function
     | Error `Out_of_memory ->
       (* Because hash tables resize in big steps, this can happen even if we have a fair
          chunk of free memory. *)
       Log.warn (fun f -> f "Out_of_memory adding NAT rule. Dropping NAT table...");
-      reset t >>= fun () ->
+      reset t ports >>= fun () ->
       aux ~retries:(retries - 1)
     | Error `Overlap when retries < 0 -> Lwt.return (Error "Too many retries")
     | Error `Overlap ->
       if retries = 0 then (
         Log.warn (fun f -> f "Failed to find a free port; resetting NAT table");
-        reset t >>= fun () ->
+        reset t ports >>= fun () ->
         aux ~retries:(retries - 1)
       ) else (
         aux ~retries:(retries - 1)

my_nat.mli

@@ -3,6 +3,15 @@
 
 (* Abstract over NAT interface (todo: remove this) *)
 
+type ports = private {
+  nat_tcp : Ports.t ref;
+  nat_udp : Ports.t ref;
+  nat_icmp : Ports.t ref;
+  dns_udp : Ports.t ref;
+}
+
+val empty_ports : unit -> ports
+
 type t
 
 type action = [
@@ -11,8 +20,8 @@ type action = [
 ]
 
 val create : max_entries:int -> t Lwt.t
-val reset : t -> unit Lwt.t
-val remove_connections : t -> Ipaddr.V4.t -> unit
+val reset : t -> ports -> unit Lwt.t
+val remove_connections : t -> ports -> Ipaddr.V4.t -> unit
 val translate : t -> Nat_packet.t -> Nat_packet.t option Lwt.t
-val add_nat_rule_and_translate : t ->
+val add_nat_rule_and_translate : t -> ports ->
   xl_host:Ipaddr.V4.t -> action -> Nat_packet.t -> (Nat_packet.t, string) result Lwt.t

ports.ml

@@ -0,0 +1,16 @@
+module Set = Set.Make(struct
+  type t = int
+  let compare a b = compare a b
+end)
+
+include Set
+
+let rec pick_free_port ?(retries = 10) ~consult add_to =
+  let p = 1024 + Random.int (0xffff - 1024) in
+  if (mem p !consult || mem p !add_to) && retries <> 0
+  then pick_free_port ~retries:(retries - 1) ~consult add_to
+  else
+    begin
+      add_to := add p !add_to;
+      p
+    end

router.ml

@@ -9,10 +9,13 @@ type t = {
   client_eth : Client_eth.t;
   nat : My_nat.t;
   uplink : interface;
+  (* NOTE: do not try to make this pure, it relies on mvars / side effects *)
+  ports : My_nat.ports;
 }
 
 let create ~client_eth ~uplink ~nat =
-  { client_eth; nat; uplink }
+  let ports = My_nat.empty_ports () in
+  { client_eth; nat; uplink; ports }
 
 let target t buf =
   let dst_ip = buf.Ipv4_packet.dst in

router.mli

@@ -9,6 +9,7 @@ type t = private {
   client_eth : Client_eth.t;
   nat : My_nat.t;
   uplink : interface;
+  ports : My_nat.ports;
 }
 
 val create :

rules.ml

@@ -49,51 +49,60 @@ module Classifier = struct
       end
       | _, _ -> false
 
-  let matches_dest rule packet =
+  let matches_dest dns_client rule packet =
     let ip = packet.ipv4_header.Ipv4_packet.dst in
     match rule.Q.dst with
     | `any ->  Lwt.return @@ `Match rule
     | `hosts subnet ->
       Lwt.return @@ if (Ipaddr.Prefix.mem Ipaddr.(V4 ip) subnet) then `Match rule else `No_match
     | `dnsname name ->
-      Log.warn (fun f -> f "Resolving %a" Domain_name.pp name);
-      Lwt.return @@ `No_match
+      Log.debug (fun f -> f "Resolving %a" Domain_name.pp name);
+      dns_client name >|= function
+      | Ok (_ttl, found_ips) ->
+        if Dns.Rr_map.Ipv4_set.mem ip found_ips
+        then `Match rule
+        else `No_match
+      | Error (`Msg m) ->
+        Log.warn (fun f -> f "Ignoring rule %a, could not resolve" Q.pp_rule rule);
+        Log.debug (fun f -> f "%s" m);
+        `No_match
+      | Error _ -> assert false (* TODO: fix type of dns_client so that this case can go *)
 
 end
 
-let find_first_match packet acc rule =
+let find_first_match dns_client packet acc rule =
   match acc with
   | `No_match ->
     if Classifier.matches_proto rule packet
-    then Classifier.matches_dest rule packet
+    then Classifier.matches_dest dns_client rule packet
     else Lwt.return `No_match
   | q -> Lwt.return q
 
 (* Does the packet match our rules? *)
-let classify_client_packet (packet : ([`Client of Fw_utils.client_link], _) Packet.t)  =
+let classify_client_packet dns_client (packet : ([`Client of Fw_utils.client_link], _) Packet.t)  =
   let (`Client client_link) = packet.src in
   let rules = client_link#get_rules in
-  Lwt_list.fold_left_s (find_first_match packet) `No_match rules >|= function
+  Lwt_list.fold_left_s (find_first_match dns_client packet) `No_match rules >|= function
   | `No_match -> `Drop "No matching rule; assuming default drop"
   | `Match {Q.action = Q.Accept; _} -> `Accept
   | `Match ({Q.action = Q.Drop; _} as rule) ->
     `Drop (Format.asprintf "rule number %a explicitly drops this packet" Q.pp_rule rule)
 
-let translate_accepted_packets packet =
-  classify_client_packet packet >|= function
+let translate_accepted_packets dns_client packet =
+  classify_client_packet dns_client packet >|= function
   | `Accept -> `NAT
   | `Drop s -> `Drop s
 
 (** Packets from the private interface that don't match any NAT table entry are being checked against the fw rules here *)
-let from_client (packet : ([`Client of Fw_utils.client_link], _) Packet.t) : Packet.action Lwt.t =
+let from_client dns_client (packet : ([`Client of Fw_utils.client_link], _) Packet.t) : Packet.action Lwt.t =
   match packet with
   | { dst = `Firewall; transport_header = `UDP header; _ } ->
     if header.Udp_packet.dst_port = dns_port
     then Lwt.return @@ `NAT_to (`NetVM, dns_port)
     else Lwt.return @@ `Drop "packet addressed to client gateway"
-  | { dst = `External _ ; _ } | { dst = `NetVM; _ } -> translate_accepted_packets packet
+  | { dst = `External _ ; _ } | { dst = `NetVM; _ } -> translate_accepted_packets dns_client packet
   | { dst = `Firewall ; _ } -> Lwt.return @@ `Drop "packet addressed to firewall itself"
-  | { dst = `Client _ ; _ } -> classify_client_packet packet
+  | { dst = `Client _ ; _ } -> classify_client_packet dns_client packet
   | _ -> Lwt.return @@ `Drop "could not classify packet"
 
 (** Packets from the outside world that don't match any NAT table entry are being dropped by default *)

unikernel.ml

@@ -8,15 +8,18 @@ let src = Logs.Src.create "unikernel" ~doc:"Main unikernel code"
 module Log = (val Logs.src_log src : Logs.LOG)
 
 module Main (R : Mirage_random.S)(Clock : Mirage_clock.MCLOCK) = struct
+  module Uplink = Uplink.Make(R)(Clock)
+  module Dns_transport = My_dns.Transport(R)(Clock)
+  module Dns_client = Dns_client.Make(Dns_transport)
 
   (* Set up networking and listen for incoming packets. *)
-  let network uplink qubesDB router =
+  let network dns_client dns_responses uplink qubesDB router =
     (* Report success *)
     Dao.set_iptables_error qubesDB "" >>= fun () ->
     (* Handle packets from both networks *)
     Lwt.choose [
-      Client_net.listen Clock.elapsed_ns qubesDB router;
-      Uplink.listen uplink Clock.elapsed_ns router
+      Client_net.listen Clock.elapsed_ns dns_client qubesDB router;
+      Uplink.listen uplink Clock.elapsed_ns dns_responses router
     ]
 
   (* We don't use the GUI, but it's interesting to keep an eye on it.
@@ -76,7 +79,11 @@ module Main (R : Mirage_random.S)(Clock : Mirage_clock.MCLOCK) = struct
       ~nat
     in
 
-    let net_listener = network uplink qubesDB router in
+    let send_dns_query = Uplink.send_dns_client_query uplink in
+    let dns_mvar = Lwt_mvar.create_empty () in
+    let dns_client = Dns_client.create (router, send_dns_query, dns_mvar) in
+
+    let net_listener = network (Dns_client.getaddrinfo dns_client Dns.Rr_map.A) dns_mvar uplink qubesDB router in
 
     (* Report memory usage to XenStore *)
     Memory_pressure.init ();

uplink.ml

@@ -9,15 +9,20 @@ module Eth = Ethernet.Make(Netif)
 let src = Logs.Src.create "uplink" ~doc:"Network connection to NetVM"
 module Log = (val Logs.src_log src : Logs.LOG)
 
-module Arp = Arp.Make(Eth)(OS.Time)
+module Make (R:Mirage_random.S) (Clock : Mirage_clock.MCLOCK) = struct
+  module Arp = Arp.Make(Eth)(OS.Time)
+  module I = Static_ipv4.Make(R)(Clock)(Eth)(Arp)
+  module U = Udp.Make(I)(R)
 
-type t = {
-  net : Netif.t;
-  eth : Eth.t;
-  arp : Arp.t;
-  interface : interface;
-  mutable fragments : Fragments.Cache.t;
-}
+  type t = {
+    net : Netif.t;
+    eth : Eth.t;
+    arp : Arp.t;
+    interface : interface;
+    mutable fragments : Fragments.Cache.t;
+    ip : I.t;
+    udp: U.t;
+  }
 
 class netvm_iface eth mac ~my_ip ~other_ip : interface = object
   val queue = FrameQ.create (Ipaddr.V4.to_string other_ip)
@@ -31,10 +36,26 @@ class netvm_iface eth mac ~my_ip ~other_ip : interface = object
     )
 end
 
-let listen t get_ts router =
-  Netif.listen t.net ~header_size:Ethernet_wire.sizeof_ethernet (fun frame ->
-      (* Handle one Ethernet frame from NetVM *)
-      Eth.input t.eth
+  let send_dns_client_query t ~src_port ~dst ~dst_port buf =
+    U.write ~src_port ~dst ~dst_port t.udp buf >|= function
+    | Error s -> Log.err (fun f -> f "error sending udp packet: %a" U.pp_error s); Error (`Msg "failure")
+    | Ok () -> Ok ()
+
+  let listen t get_ts dns_responses router =
+    let handle_packet ip_header ip_packet =
+      let open Udp_packet in
+
+      Log.debug (fun f -> f "received ipv4 packet from %a on uplink" Ipaddr.V4.pp ip_header.Ipv4_packet.src);
+      match ip_packet with
+      | `UDP (header, packet) when Ports.mem header.dst_port !(router.Router.ports.My_nat.dns_udp) ->
+        Log.debug (fun f -> f "found a DNS packet whose dst_port (%d) was in the list of dns_client ports" header.dst_port);
+        Lwt_mvar.put dns_responses (header, packet)
+      | _ ->
+        Firewall.ipv4_from_netvm router (`IPv4 (ip_header, ip_packet))
+    in
+    Netif.listen t.net ~header_size:Ethernet_wire.sizeof_ethernet (fun frame ->
+        (* Handle one Ethernet frame from NetVM *)
+        Eth.input t.eth
         ~arpv4:(Arp.input t.arp)
         ~ipv4:(fun ip ->
             let cache, r =
@@ -42,30 +63,35 @@ let listen t get_ts router =
             in
             t.fragments <- cache;
             match r with
-            | Error e ->
-              Log.warn (fun f -> f "Ignored unknown IPv4 message from uplink: %a" Nat_packet.pp_error e);
-              Lwt.return_unit
-            | Ok None -> Lwt.return_unit
-            | Ok (Some packet) ->
-              Firewall.ipv4_from_netvm router packet
-          )
+              | Error e ->
+                Log.warn (fun f -> f "Ignored unknown IPv4 message from uplink: %a" Nat_packet.pp_error e);
+                Lwt.return ()
+              | Ok None -> Lwt.return_unit
+              | Ok (Some (`IPv4 (header, packet))) -> handle_packet header packet
+            )
         ~ipv6:(fun _ip -> Lwt.return_unit)
         frame
     ) >|= or_raise "Uplink listen loop" Netif.pp_error
 
+
 let interface t = t.interface
 
 let connect config =
-  let ip = config.Dao.uplink_our_ip in
+  let my_ip = config.Dao.uplink_our_ip in
+  let gateway = config.Dao.uplink_netvm_ip in
   Netif.connect "0" >>= fun net ->
   Eth.connect net >>= fun eth ->
   Arp.connect eth >>= fun arp ->
-  Arp.add_ip arp ip >>= fun () ->
+  Arp.add_ip arp my_ip >>= fun () ->
+  let network = Ipaddr.V4.Prefix.make 0 Ipaddr.V4.any in
+  I.connect ~ip:(network, my_ip) ~gateway eth arp >>= fun ip ->
+  U.connect ip >>= fun udp ->
   let netvm_mac =
-    Arp.query arp config.Dao.uplink_netvm_ip
+    Arp.query arp gateway
     >|= or_raise "Getting MAC of our NetVM" Arp.pp_error in
   let interface = new netvm_iface eth netvm_mac
-    ~my_ip:ip
+    ~my_ip
     ~other_ip:config.Dao.uplink_netvm_ip in
   let fragments = Fragments.Cache.empty (256 * 1024) in
-  Lwt.return { net; eth; arp; interface ; fragments }
+  Lwt.return { net; eth; arp; interface ; fragments ; ip ; udp }
+end

uplink.mli

@@ -5,13 +5,18 @@
 
 open Fw_utils
 
-type t
+[@@@ocaml.warning "-67"]
+module Make (R: Mirage_random.S)(Clock : Mirage_clock.MCLOCK) : sig
+  type t
 
-val connect : Dao.network_config -> t Lwt.t
-(** Connect to our NetVM (gateway). *)
+  val connect : Dao.network_config -> t Lwt.t
+  (** Connect to our NetVM (gateway). *)
 
-val interface : t -> interface
-(** The network interface to NetVM. *)
+  val interface : t -> interface
+  (** The network interface to NetVM. *)
 
-val listen : t -> (unit -> int64) -> Router.t -> unit Lwt.t
-(** Handle incoming frames from NetVM. *)
+  val listen : t -> (unit -> int64) -> (Udp_packet.t * Cstruct.t) Lwt_mvar.t -> Router.t -> unit Lwt.t
+  (** Handle incoming frames from NetVM. *)
+
+  val send_dns_client_query: t -> src_port:int-> dst:Ipaddr.V4.t -> dst_port:int -> Cstruct.t -> (unit, [`Msg of string]) result Lwt.t
+end