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|
{ flakeInputs, config, lib, pkgs, ... }:
with lib;
let
cfg = config.boot.initrd.network.ssh;
in
{
disabledModules = [ "system/boot/initrd-ssh.nix" ];
options.boot.initrd.network.ssh = {
enable = mkOption {
type = types.bool;
default = false;
description = lib.mdDoc ''
Start SSH service during initrd boot. It can be used to debug failing
boot on a remote server, enter pasphrase for an encrypted partition etc.
Service is killed when stage-1 boot is finished.
The sshd configuration is largely inherited from
{option}`services.openssh`.
'';
};
port = mkOption {
type = types.port;
default = 22;
description = lib.mdDoc ''
Port on which SSH initrd service should listen.
'';
};
shell = mkOption {
type = types.str;
default = "/bin/ash";
description = lib.mdDoc ''
Login shell of the remote user. Can be used to limit actions user can do.
'';
};
hostKeys = mkOption {
type = types.listOf (types.either types.str types.path);
default = [];
example = [
"/etc/secrets/initrd/ssh_host_rsa_key"
"/etc/secrets/initrd/ssh_host_ed25519_key"
];
description = lib.mdDoc ''
Specify SSH host keys to import into the initrd.
To generate keys, use
{manpage}`ssh-keygen(1)`
as root:
```
ssh-keygen -t rsa -N "" -f /etc/secrets/initrd/ssh_host_rsa_key
ssh-keygen -t ed25519 -N "" -f /etc/secrets/initrd/ssh_host_ed25519_key
```
::: {.warning}
Unless your bootloader supports initrd secrets, these keys
are stored insecurely in the global Nix store. Do NOT use
your regular SSH host private keys for this purpose or
you'll expose them to regular users!
Additionally, even if your initrd supports secrets, if
you're using initrd SSH to unlock an encrypted disk then
using your regular host keys exposes the private keys on
your unencrypted boot partition.
:::
'';
};
manageHostKeySecrets = mkEnableOption "automatically managing initrd secrets for configured hostkeys";
authorizedKeys = mkOption {
type = types.listOf types.str;
default = config.users.users.root.openssh.authorizedKeys.keys;
defaultText = literalExpression "config.users.users.root.openssh.authorizedKeys.keys";
description = lib.mdDoc ''
Authorized keys for the root user on initrd.
'';
};
extraConfig = mkOption {
type = types.lines;
default = "";
description = lib.mdDoc "Verbatim contents of {file}`sshd_config`.";
};
};
imports =
map (opt: mkRemovedOptionModule ([ "boot" "initrd" "network" "ssh" ] ++ [ opt ]) ''
The initrd SSH functionality now uses OpenSSH rather than Dropbear.
If you want to keep your existing initrd SSH host keys, convert them with
$ dropbearconvert dropbear openssh dropbear_host_$type_key ssh_host_$type_key
and then set options.boot.initrd.network.ssh.hostKeys.
'') [ "hostRSAKey" "hostDSSKey" "hostECDSAKey" ];
config = let
# Nix complains if you include a store hash in initrd path names, so
# as an awful hack we drop the first character of the hash.
initrdKeyPath = path: if isString path
then path
else let name = builtins.baseNameOf path; in
builtins.unsafeDiscardStringContext ("/etc/ssh/" +
substring 1 (stringLength name) name);
sshdCfg = config.services.openssh;
sshdConfig = ''
Port ${toString cfg.port}
PasswordAuthentication no
KbdInteractiveAuthentication no
${flip concatMapStrings cfg.hostKeys (path: ''
HostKey ${initrdKeyPath path}
'')}
KexAlgorithms ${concatStringsSep "," sshdCfg.settings.KexAlgorithms}
Ciphers ${concatStringsSep "," sshdCfg.settings.Ciphers}
MACs ${concatStringsSep "," sshdCfg.settings.Macs}
LogLevel ${sshdCfg.settings.LogLevel}
${if sshdCfg.settings.UseDns then ''
UseDNS yes
'' else ''
UseDNS no
''}
${cfg.extraConfig}
'';
in mkIf (config.boot.initrd.network.enable && cfg.enable) {
assertions = [
{
assertion = cfg.authorizedKeys != [];
message = "You should specify at least one authorized key for initrd SSH";
}
{
assertion = cfg.hostKeys != [];
message = ''
You must now pre-generate the host keys for initrd SSH.
See the boot.initrd.network.ssh.hostKeys documentation
for instructions.
'';
}
];
boot.initrd.extraUtilsCommands = ''
copy_bin_and_libs ${pkgs.openssh}/bin/sshd
cp -pv ${pkgs.glibc.out}/lib/libnss_files.so.* $out/lib
'';
boot.initrd.extraUtilsCommandsTest = ''
# sshd requires a host key to check config, so we pass in the test's
tmpkey="$(mktemp initrd-ssh-testkey.XXXXXXXXXX)"
cp ${escapeShellArg (flakeInputs.nixpkgs.outPath + "/nixos/tests/initrd-network-ssh/ssh_host_ed25519_key")} "$tmpkey"
# keys from Nix store are world-readable, which sshd doesn't like
chmod 600 "$tmpkey"
echo -n ${escapeShellArg sshdConfig} |
$out/bin/sshd -t -f /dev/stdin \
-h "$tmpkey"
rm "$tmpkey"
'';
boot.initrd.network.postCommands = ''
echo '${cfg.shell}' > /etc/shells
echo 'root:x:0:0:root:/root:${cfg.shell}' > /etc/passwd
echo 'sshd:x:1:1:sshd:/var/empty:/bin/nologin' >> /etc/passwd
echo 'passwd: files' > /etc/nsswitch.conf
mkdir -p /var/log /var/empty
touch /var/log/lastlog
mkdir -p /etc/ssh
echo -n ${escapeShellArg sshdConfig} > /etc/ssh/sshd_config
echo "export PATH=$PATH" >> /etc/profile
echo "export LD_LIBRARY_PATH=$LD_LIBRARY_PATH" >> /etc/profile
mkdir -p /root/.ssh
${concatStrings (map (key: ''
echo ${escapeShellArg key} >> /root/.ssh/authorized_keys
'') cfg.authorizedKeys)}
${flip concatMapStrings cfg.hostKeys (path: ''
# keys from Nix store are world-readable, which sshd doesn't like
chmod 0600 "${initrdKeyPath path}"
'')}
/bin/sshd -e
'';
boot.initrd.postMountCommands = ''
# Stop sshd cleanly before stage 2.
#
# If you want to keep it around to debug post-mount SSH issues,
# run `touch /.keep_sshd` (either from an SSH session or in
# another initrd hook like preDeviceCommands).
if ! [ -e /.keep_sshd ]; then
pkill -x sshd
fi
'';
boot.initrd.secrets = mkIf cfg.manageHostKeySecrets (listToAttrs
(map (path: nameValuePair (initrdKeyPath path) path) cfg.hostKeys));
};
}
|
