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(* Copyright (C) 2015, Thomas Leonard <thomas.leonard@unikernel.com>
See the README file for details. *)
open Fw_utils
open Packet
open Lwt.Infix
let src = Logs.Src.create "firewall" ~doc:"Packet handler"
module Log = (val Logs.src_log src : Logs.LOG)
(* Transmission *)
let transmit_ipv4 packet iface =
Lwt.catch
(fun () ->
let transport = Nat_packet.to_cstruct packet in
Lwt.catch
(fun () -> iface#writev Ethif_wire.IPv4 transport)
(fun ex ->
Log.warn (fun f -> f "Failed to write packet to %a: %s"
Ipaddr.V4.pp_hum iface#other_ip
(Printexc.to_string ex));
Lwt.return ()
)
)
(fun ex ->
Log.err (fun f -> f "Exception in transmit_ipv4: %s for:@.%a"
(Printexc.to_string ex)
Nat_packet.pp packet
);
Lwt.return ()
)
let forward_ipv4 t packet =
let `IPv4 (ip, _) = packet in
match Router.target t ip with
| Some iface -> transmit_ipv4 packet iface
| None -> return ()
(* Packet classification *)
let classify t packet =
let `IPv4 (ip, transport) = packet in
let proto =
match transport with
| `TCP ({Tcp.Tcp_packet.src_port; dst_port; _}, _) -> `TCP {sport = src_port; dport = dst_port}
| `UDP ({Udp_packet.src_port; dst_port; _}, _) -> `UDP {sport = src_port; dport = dst_port}
| `ICMP _ -> `ICMP
in
Some {
packet;
src = Router.classify t (Ipaddr.V4 ip.Ipv4_packet.src);
dst = Router.classify t (Ipaddr.V4 ip.Ipv4_packet.dst);
proto;
}
let pp_ports fmt {sport; dport} =
Format.fprintf fmt "sport=%d dport=%d" sport dport
let pp_host fmt = function
| `Client c -> Ipaddr.V4.pp_hum fmt (c#other_ip)
| `Unknown_client ip -> Format.fprintf fmt "unknown-client(%a)" Ipaddr.pp_hum ip
| `NetVM -> Format.pp_print_string fmt "net-vm"
| `External ip -> Format.fprintf fmt "external(%a)" Ipaddr.pp_hum ip
| `Firewall_uplink -> Format.pp_print_string fmt "firewall(uplink)"
| `Client_gateway -> Format.pp_print_string fmt "firewall(client-gw)"
let pp_proto fmt = function
| `UDP ports -> Format.fprintf fmt "UDP(%a)" pp_ports ports
| `TCP ports -> Format.fprintf fmt "TCP(%a)" pp_ports ports
| `ICMP -> Format.pp_print_string fmt "ICMP"
| `Unknown -> Format.pp_print_string fmt "UnknownProtocol"
let pp_packet fmt {src; dst; proto; packet = _} =
Format.fprintf fmt "[src=%a dst=%a proto=%a]"
pp_host src
pp_host dst
pp_proto proto
let pp_transport_headers f = function
| `ICMP (h, _) -> Icmpv4_packet.pp f h
| `TCP (h, _) -> Tcp.Tcp_packet.pp f h
| `UDP (h, _) -> Udp_packet.pp f h
let pp_header f = function
| `IPv4 (ip, transport) ->
Fmt.pf f "%a %a"
Ipv4_packet.pp ip
pp_transport_headers transport
(* NAT *)
let translate t packet =
My_nat.translate t.Router.nat 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
| Ok packet -> forward_ipv4 t packet
| Error e ->
Log.warn (fun f -> f "Failed to add NAT rewrite rule: %s (%a)" e pp_header packet);
Lwt.return ()
(* 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
| Ipaddr.V6 _ -> Log.warn (fun f -> f "Cannot NAT with IPv6"); Lwt.return ()
| 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
| Ok packet -> forward_ipv4 t packet
| Error e ->
Log.warn (fun f -> f "Failed to add NAT redirect rule: %s (%a)" e pp_header packet);
Lwt.return ()
(* Handle incoming packets *)
let apply_rules t rules info =
let packet = info.packet in
match rules info, info.dst with
| `Accept, `Client client_link -> transmit_ipv4 packet client_link
| `Accept, (`External _ | `NetVM) -> transmit_ipv4 packet t.Router.uplink
| `Accept, (`Firewall_uplink | `Client_gateway) ->
Log.warn (fun f -> f "Bad rule: firewall can't accept packets %a" pp_packet info);
return ()
| `NAT, _ -> add_nat_and_forward_ipv4 t packet
| `NAT_to (host, port), _ -> nat_to t packet ~host ~port
| `Drop reason, _ ->
Log.info (fun f -> f "Dropped packet (%s) %a" reason pp_packet info);
return ()
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 () ->
`Memory_critical
| `Ok -> Lwt.return `Ok
let ipv4_from_client t packet =
handle_low_memory t >>= function
| `Memory_critical -> return ()
| `Ok ->
(* Check for existing NAT entry for this packet *)
translate t packet >>= function
| Some frame -> forward_ipv4 t frame (* Some existing connection or redirect *)
| None ->
(* No existing NAT entry. Check the firewall rules. *)
match classify t packet with
| None -> return ()
| Some info -> apply_rules t Rules.from_client info
let ipv4_from_netvm t packet =
handle_low_memory t >>= function
| `Memory_critical -> return ()
| `Ok ->
match classify t packet with
| None -> return ()
| Some info ->
match info.src with
| `Client _ | `Firewall_uplink | `Client_gateway ->
Log.warn (fun f -> f "Frame from NetVM has internal source IP address! %a" pp_packet info);
return ()
| `External _ | `NetVM ->
translate t packet >>= function
| Some frame -> forward_ipv4 t frame
| None ->
apply_rules t Rules.from_netvm info