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firewall: Improve the comments (documentation) (#21862)

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* Fix the FW names

FW_REFUSE was removed and nixos-fw-input was renamed to nixos-fw.

* Update the comment (documentation) at the top

Order the chains of the main table alphabetically (like in the rest of
the file) and add nixos-fw-rpfilter (from the raw table) and nixos-drop
(used while reloading the firewall).

* Refactor the module (mainly comments)

- Move some attributes to the top for better visibility (that should
  hopefully make it easier to read and understand this module without
  jumping around too much).
- Add some missing examples and improve some descriptions.
- Reorder the mkOption attributes for consistency.
- Wrap lines at 72 characters.
- Use two spaces between sentences.
This commit is contained in:
Michael Weiss 2017-01-18 17:18:11 +01:00 committed by Robin Gloster
parent f715d3fd2c
commit 460b43dbfe
1 changed files with 63 additions and 39 deletions
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102
nixos/modules/services/networking/firewall.nix
View file

@ -4,17 +4,29 @@
‘networking.firewall.extraCommands’. For modularity, the firewall
uses several chains:
- ‘nixos-fw-input’ is the main chain for input packet processing.
- ‘nixos-fw’ is the main chain for input packet processing.
- ‘nixos-fw-accept’ is called for accepted packets. If you want
additional logging, or want to reject certain packets anyway, you
can insert rules at the start of this chain.
- ‘nixos-fw-log-refuse’ and ‘nixos-fw-refuse’ are called for
refused packets. (The former jumps to the latter after logging
the packet.) If you want additional logging, or want to accept
certain packets anyway, you can insert rules at the start of
these chain.
this chain.
- ‘nixos-fw-accept’ is called for accepted packets. If you want
additional logging, or want to reject certain packets anyway, you
can insert rules at the start of this chain.
- ‘nixos-fw-rpfilter’ is used as the main chain in the raw table,
called from the built-in ‘PREROUTING’ chain. If the kernel
supports it and `cfg.checkReversePath` is set this chain will
perform a reverse path filter test.
- ‘nixos-drop’ is used while reloading the firewall in order to drop
all traffic. Since reloading isn't implemented in an atomic way
this'll prevent any traffic from leaking through while reloading
the firewall. However, if the reloading fails, the ‘firewall-stop’
script will be called which in return will effectively disable the
complete firewall (in the default configuration).
*/
@ -26,6 +38,11 @@ let
cfg = config.networking.firewall;
kernelPackages = config.boot.kernelPackages;
kernelHasRPFilter = kernelPackages.kernel.features.netfilterRPFilter or false;
kernelCanDisableHelpers = kernelPackages.kernel.features.canDisableNetfilterConntrackHelpers or false;
helpers =
''
# Helper command to manipulate both the IPv4 and IPv6 tables.
@ -49,7 +66,7 @@ let
# firewall would be atomic. Apparently that's possible
# with iptables-restore.
ip46tables -D INPUT -j nixos-fw 2> /dev/null || true
for chain in nixos-fw nixos-fw-accept nixos-fw-log-refuse nixos-fw-refuse FW_REFUSE; do
for chain in nixos-fw nixos-fw-accept nixos-fw-log-refuse nixos-fw-refuse; do
ip46tables -F "$chain" 2> /dev/null || true
ip46tables -X "$chain" 2> /dev/null || true
done
@ -231,11 +248,6 @@ let
fi
'';
kernelPackages = config.boot.kernelPackages;
kernelHasRPFilter = kernelPackages.kernel.features.netfilterRPFilter or false;
kernelCanDisableHelpers = kernelPackages.kernel.features.canDisableNetfilterConntrackHelpers or false;
in
{
@ -293,26 +305,30 @@ in
default = false;
description =
''
If set, forbidden packets are rejected rather than dropped
If set, refused packets are rejected rather than dropped
(ignored). This means that an ICMP "port unreachable" error
message is sent back to the client. Rejecting packets makes
message is sent back to the client (or a TCP RST packet in
case of an existing connection). Rejecting packets makes
port scanning somewhat easier.
'';
};
networking.firewall.trustedInterfaces = mkOption {
type = types.listOf types.str;
default = [ ];
example = [ "enp0s2" ];
description =
''
Traffic coming in from these interfaces will be accepted
unconditionally.
unconditionally. Traffic from the loopback (lo) interface
will always be accepted.
'';
};
networking.firewall.allowedTCPPorts = mkOption {
default = [];
example = [ 22 80 ];
type = types.listOf types.int;
default = [ ];
example = [ 22 80 ];
description =
''
List of TCP ports on which incoming connections are
@ -321,9 +337,9 @@ in
};
networking.firewall.allowedTCPPortRanges = mkOption {
default = [];
example = [ { from = 8999; to = 9003; } ];
type = types.listOf (types.attrsOf types.int);
default = [ ];
example = [ { from = 8999; to = 9003; } ];
description =
''
A range of TCP ports on which incoming connections are
@ -332,9 +348,9 @@ in
};
networking.firewall.allowedUDPPorts = mkOption {
default = [];
example = [ 53 ];
type = types.listOf types.int;
default = [ ];
example = [ 53 ];
description =
''
List of open UDP ports.
@ -342,9 +358,9 @@ in
};
networking.firewall.allowedUDPPortRanges = mkOption {
default = [];
example = [ { from = 60000; to = 61000; } ];
type = types.listOf (types.attrsOf types.int);
default = [ ];
example = [ { from = 60000; to = 61000; } ];
description =
''
Range of open UDP ports.
@ -352,8 +368,8 @@ in
};
networking.firewall.allowPing = mkOption {
default = true;
type = types.bool;
default = true;
description =
''
Whether to respond to incoming ICMPv4 echo requests
@ -364,36 +380,43 @@ in
};
networking.firewall.pingLimit = mkOption {
default = null;
type = types.nullOr (types.separatedString " ");
default = null;
example = "--limit 1/minute --limit-burst 5";
description =
''
If pings are allowed, this allows setting rate limits
on them. If non-null, this option should be in the form
of flags like "--limit 1/minute --limit-burst 5"
on them. If non-null, this option should be in the form of
flags like "--limit 1/minute --limit-burst 5"
'';
};
networking.firewall.checkReversePath = mkOption {
default = kernelHasRPFilter;
type = types.either types.bool (types.enum ["strict" "loose"]);
default = kernelHasRPFilter;
example = "loose";
description =
''
Performs a reverse path filter test on a packet.
If a reply to the packet would not be sent via the same interface
that the packet arrived on, it is refused.
Performs a reverse path filter test on a packet. If a reply
to the packet would not be sent via the same interface that
the packet arrived on, it is refused.
If using asymmetric routing or other complicated routing,
set this option to loose mode or disable it and setup your
own counter-measures.
If using asymmetric routing or other complicated routing, set
this option to loose mode or disable it and setup your own
counter-measures.
This option can be either true (or "strict"), "loose" (only
drop the packet if the source address is not reachable via any
interface) or false. Defaults to the value of
kernelHasRPFilter.
(needs kernel 3.3+)
'';
};
networking.firewall.logReversePathDrops = mkOption {
default = false;
type = types.bool;
default = false;
description =
''
Logs dropped packets failing the reverse path filter test if
@ -402,9 +425,9 @@ in
};
networking.firewall.connectionTrackingModules = mkOption {
type = types.listOf types.str;
default = [ "ftp" ];
example = [ "ftp" "irc" "sane" "sip" "tftp" "amanda" "h323" "netbios_sn" "pptp" "snmp" ];
type = types.listOf types.str;
description =
''
List of connection-tracking helpers that are auto-loaded.
@ -415,14 +438,14 @@ in
networking.firewall.autoLoadConntrackHelpers
Loading of helpers is recommended to be done through the new
CT target. More info:
CT target. More info:
https://home.regit.org/netfilter-en/secure-use-of-helpers/
'';
};
networking.firewall.autoLoadConntrackHelpers = mkOption {
default = true;
type = types.bool;
default = true;
description =
''
Whether to auto-load connection-tracking helpers.
@ -464,7 +487,8 @@ in
''
Additional shell commands executed as part of the firewall
shutdown script. These are executed just after the removal
of the nixos input rule, or if the service enters a failed state.
of the NixOS input rule, or if the service enters a failed
state.
'';
};
@ -502,7 +526,7 @@ in
path = [ pkgs.iptables ] ++ cfg.extraPackages;
# FIXME: this module may also try to load kernel modules, but
# containers don't have CAP_SYS_MODULE. So the host system had
# containers don't have CAP_SYS_MODULE. So the host system had
# better have all necessary modules already loaded.
unitConfig.ConditionCapability = "CAP_NET_ADMIN";
unitConfig.DefaultDependencies = false;