Merge pull request #30416 from symphorien/luksnokey

nixos/luksroot.nix: fallback to interactive password entry when no keyfile found

nixos/modules/system/boot/luksroot.nix

···
 let
   luks = config.boot.initrd.luks;
 
-  openCommand = name': { name, device, header, keyFile, keyFileSize, allowDiscards, yubikey, ... }: assert name' == name; ''
+  openCommand = name': { name, device, header, keyFile, keyFileSize, allowDiscards, yubikey, fallbackToPassword, ... }: assert name' == name; ''
 
     # Wait for a target (e.g. device, keyFile, header, ...) to appear.
     wait_target() {
···
     open_normally() {
         echo luksOpen ${device} ${name} ${optionalString allowDiscards "--allow-discards"} \
           ${optionalString (header != null) "--header=${header}"} \
-          ${optionalString (keyFile != null) "--key-file=${keyFile} ${optionalString (keyFileSize != null) "--keyfile-size=${toString keyFileSize}"}"} \
           > /.luksopen_args
+        ${optionalString (keyFile != null) ''
+        ${optionalString fallbackToPassword "if [ -e ${keyFile} ]; then"}
+            echo " --key-file=${keyFile} ${optionalString (keyFileSize != null) "--keyfile-size=${toString keyFileSize}"}" \
+              >> /.luksopen_args
+        ${optionalString fallbackToPassword ''
+        else
+            echo "keyfile ${keyFile} not found -- fallback to interactive unlocking"
+        fi
+        ''}
+        ''}
         cryptsetup-askpass
         rm /.luksopen_args
     }
···
               Whether to allow TRIM requests to the underlying device. This option
               has security implications; please read the LUKS documentation before
               activating it.
+            '';
+          };
+
+          fallbackToPassword = mkOption {
+            default = false;
+            type = types.bool;
+            description = ''
+              Whether to fallback to interactive passphrase prompt if the keyfile
+              cannot be found. This will prevent unattended boot should the keyfile
+              go missing.
             '';
           };