diff options
Diffstat (limited to 'nixos/modules/system/boot/initrd-ssh.nix')
| -rw-r--r-- | nixos/modules/system/boot/initrd-ssh.nix | 215 |
1 files changed, 215 insertions, 0 deletions
diff --git a/nixos/modules/system/boot/initrd-ssh.nix b/nixos/modules/system/boot/initrd-ssh.nix new file mode 100644 index 00000000000..0999142de86 --- /dev/null +++ b/nixos/modules/system/boot/initrd-ssh.nix @@ -0,0 +1,215 @@ +{ config, lib, pkgs, ... }: + +with lib; + +let + + cfg = config.boot.initrd.network.ssh; + +in + +{ + + options.boot.initrd.network.ssh = { + enable = mkOption { + type = types.bool; + default = false; + description = '' + 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</option>. + ''; + }; + + port = mkOption { + type = types.int; + default = 22; + description = '' + Port on which SSH initrd service should listen. + ''; + }; + + shell = mkOption { + type = types.str; + default = "/bin/ash"; + description = '' + 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 = '' + Specify SSH host keys to import into the initrd. + + To generate keys, use + <citerefentry><refentrytitle>ssh-keygen</refentrytitle><manvolnum>1</manvolnum></citerefentry>: + + <screen> + <prompt># </prompt>ssh-keygen -t rsa -N "" -f /etc/secrets/initrd/ssh_host_rsa_key + <prompt># </prompt>ssh-keygen -t ed25519 -N "" -f /etc/secrets/initrd/ssh_host_ed25519_key + </screen> + + <warning> + <para> + 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! + </para> + <para> + 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. + </para> + </warning> + ''; + }; + + 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 = '' + Authorized keys for the root user on initrd. + ''; + }; + + extraConfig = mkOption { + type = types.lines; + default = ""; + description = "Verbatim contents of <filename>sshd_config</filename>."; + }; + }; + + 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 + ChallengeResponseAuthentication no + + ${flip concatMapStrings cfg.hostKeys (path: '' + HostKey ${initrdKeyPath path} + '')} + + KexAlgorithms ${concatStringsSep "," sshdCfg.kexAlgorithms} + Ciphers ${concatStringsSep "," sshdCfg.ciphers} + MACs ${concatStringsSep "," sshdCfg.macs} + + LogLevel ${sshdCfg.logLevel} + + ${if sshdCfg.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 "${../../../tests/initrd-network-ssh/ssh_host_ed25519_key}" "$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 = listToAttrs + (map (path: nameValuePair (initrdKeyPath path) path) cfg.hostKeys); + }; + +} |