mirror of
https://github.com/mirage/qubes-mirage-firewall.git
synced 2024-12-29 00:56:13 -05:00
82 lines
2.4 KiB
OCaml
82 lines
2.4 KiB
OCaml
(* Copyright (C) 2015, Thomas Leonard <thomas.leonard@unikernel.com>
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See the README file for details. *)
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open Lwt.Infix
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let src = Logs.Src.create "my-nat" ~doc:"NAT shim"
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module Log = (val Logs.src_log src : Logs.LOG)
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type action = [
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| `NAT
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| `Redirect of Mirage_nat.endpoint
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]
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module Nat = Mirage_nat_lru
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type t = {
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table : Nat.t;
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get_time : unit -> Mirage_nat.time;
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}
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let create ~get_time ~max_entries =
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let tcp_size = 7 * max_entries / 8 in
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let udp_size = max_entries - tcp_size in
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Nat.empty ~tcp_size ~udp_size ~icmp_size:100 >|= fun table ->
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{ get_time; table }
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let translate t packet =
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Nat.translate t.table packet >|= function
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| Error (`Untranslated | `TTL_exceeded as e) ->
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Log.debug (fun f -> f "Failed to NAT %a: %a"
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Nat_packet.pp packet
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Mirage_nat.pp_error e
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);
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None
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| Ok packet -> Some packet
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let random_user_port () =
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1024 + Random.int (0xffff - 1024)
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let reset t =
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Nat.reset t.table
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let add_nat_rule_and_translate t ~xl_host action packet =
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let now = t.get_time () in
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let apply_action xl_port =
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Lwt.catch (fun () ->
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Nat.add t.table ~now packet (xl_host, xl_port) action
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)
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(function
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| Out_of_memory -> Lwt.return (Error `Out_of_memory)
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| x -> Lwt.fail x
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)
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in
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let rec aux ~retries =
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let xl_port = random_user_port () in
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apply_action xl_port >>= function
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| Error `Out_of_memory ->
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(* Because hash tables resize in big steps, this can happen even if we have a fair
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chunk of free memory. *)
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Log.warn (fun f -> f "Out_of_memory adding NAT rule. Dropping NAT table...");
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Nat.reset t.table >>= fun () ->
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aux ~retries:(retries - 1)
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| Error `Overlap when retries < 0 -> Lwt.return (Error "Too many retries")
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| Error `Overlap ->
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if retries = 0 then (
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Log.warn (fun f -> f "Failed to find a free port; resetting NAT table");
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Nat.reset t.table >>= fun () ->
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aux ~retries:(retries - 1)
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) else (
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aux ~retries:(retries - 1)
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)
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| Error `Cannot_NAT ->
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Lwt.return (Error "Cannot NAT this packet")
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| Ok () ->
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Log.debug (fun f -> f "Updated NAT table: %a" Nat.pp_summary t.table);
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translate t packet >|= function
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| None -> Error "No NAT entry, even after adding one!"
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| Some packet ->
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Ok packet
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in
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aux ~retries:100
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