58 lines
2.3 KiB
OCaml
58 lines
2.3 KiB
OCaml
(* Copyright (C) 2015, Thomas Leonard <thomas.leonard@unikernel.com>
|
|
See the README file for details. *)
|
|
|
|
(** Perform NAT on the interface to our NetVM.
|
|
Based on https://github.com/yomimono/simple-nat *)
|
|
|
|
let src = Logs.Src.create "nat-rules" ~doc:"Firewall NAT rules"
|
|
module Log = (val Logs.src_log src : Logs.LOG)
|
|
|
|
let random_user_port () =
|
|
1024 + Random.int (0xffff - 1024)
|
|
|
|
(* Add a NAT rule for the endpoints in this frame, via a random port on [ip]. *)
|
|
let allow_nat_traffic table frame (ip : Ipaddr.t) =
|
|
let rec stubborn_insert port =
|
|
(* TODO: in the unlikely event that no port is available, this
|
|
function will never terminate (this is really a tcpip todo) *)
|
|
let open Nat_rewrite in
|
|
match make_nat_entry table frame ip port with
|
|
| Ok t ->
|
|
Log.info "added NAT entry: %s:%d -> firewall:%d -> %s:%d"
|
|
(fun f ->
|
|
match Nat_rewrite.layers frame with
|
|
| None -> assert false
|
|
| Some (_eth, ip, transport) ->
|
|
let src, dst = Nat_rewrite.addresses_of_ip ip in
|
|
let sport, dport = Nat_rewrite.ports_of_transport transport in
|
|
f (Ipaddr.to_string src) sport port (Ipaddr.to_string dst) dport
|
|
);
|
|
Some t
|
|
| Unparseable -> None
|
|
| Overlap -> stubborn_insert (random_user_port ())
|
|
in
|
|
(* TODO: connection tracking logic *)
|
|
stubborn_insert (random_user_port ())
|
|
|
|
(** Perform translation on [frame] and return translated packet.
|
|
Update NAT table for new outbound connections. *)
|
|
let nat translation_ip nat_table direction frame =
|
|
let rec retry () =
|
|
(* typical NAT logic: traffic from the internal "trusted" interface gets
|
|
new mappings by default; traffic from other interfaces gets dropped if
|
|
no mapping exists (which it doesn't, since we already checked) *)
|
|
let open Nat_rewrite in
|
|
match direction, Nat_rewrite.translate nat_table direction frame with
|
|
| _, Some f -> Some f
|
|
| Destination, None -> None (* nothing in the table, drop it *)
|
|
| Source, None ->
|
|
(* mutate nat_table to include entries for the frame *)
|
|
match allow_nat_traffic nat_table frame translation_ip with
|
|
| Some _t ->
|
|
(* try rewriting again; we should now have an entry for this packet *)
|
|
retry ()
|
|
| None ->
|
|
(* this frame is hopeless! *)
|
|
None in
|
|
retry ()
|