[PATCH] cryptodisk: allow the user to retry failed passphrases

[Forest]

Hi, folks.

I have long wished that GRUB would give me a chance to retry whenever I
make a typo in a LUKS passphrase, rather than immediately dumping me into
the rescue shell, so I finally took a crack at it myself.

Would this be a welcome addition?

The patch is a bit easier to read in a viewer that ignores whitespace,
since a good chunk of the changed lines are from reordering and indenting
existing code.


Signed-off-by: Forest <forestix@nom.one>
--- a/grub-core/disk/cryptodisk.c
+++ b/grub-core/disk/cryptodisk.c
@@ -1063,6 +1063,7 @@
   grub_cryptodisk_dev_t cr;
   struct cryptodisk_read_hook_ctx read_hook_data = {0};
   int askpass = 0;
+  int tries;
   char *part = NULL;
 
   dev = grub_cryptodisk_get_by_source_disk (source);
@@ -1114,33 +1115,48 @@
     if (!dev)
       continue;
 
-    if (!cargs->key_len)
+    if (cargs->key_len)
+      {
+       ret = cr->recover_key (source, dev, cargs);
+       if (ret != GRUB_ERR_NONE)
+         goto error;
+      }
+    else
       {
        /* Get the passphrase from the user, if no key data. */
        askpass = 1;
-       part = grub_partition_get_name (source->partition);
-       grub_printf_ (N_("Enter passphrase for %s%s%s (%s): "), source->name,
-                    source->partition != NULL ? "," : "",
-                    part != NULL ? part : N_("UNKNOWN"),
-                    dev->uuid);
-       grub_free (part);
-
        cargs->key_data = grub_malloc (GRUB_CRYPTODISK_MAX_PASSPHRASE);
        if (cargs->key_data == NULL)
          goto error_no_close;
 
-       if (!grub_password_get ((char *) cargs->key_data, 
GRUB_CRYPTODISK_MAX_PASSPHRASE))
+       for (tries = GRUB_CRYPTODISK_PASSPHRASE_TRIES; tries > 0; tries--)
          {
-           grub_error (GRUB_ERR_BAD_ARGUMENT, "passphrase not supplied");
-           goto error;
+           part = grub_partition_get_name (source->partition);
+           grub_printf_ (N_("Enter passphrase for %s%s%s (%s): "), 
source->name,
+                        source->partition != NULL ? "," : "",
+                        part != NULL ? part : N_("UNKNOWN"),
+                        dev->uuid);
+           grub_free (part);
+
+           if (!grub_password_get ((char *) cargs->key_data, 
GRUB_CRYPTODISK_MAX_PASSPHRASE))
+             {
+               grub_error (GRUB_ERR_BAD_ARGUMENT, "passphrase not supplied");
+               goto error;
+             }
+           cargs->key_len = grub_strlen ((char *) cargs->key_data);
+
+            ret = cr->recover_key (source, dev, cargs);
+           if (ret == GRUB_ERR_NONE)
+             break;
+           if (ret != GRUB_ERR_ACCESS_DENIED || tries == 1)
+             goto error;
+           grub_puts_ (N_("Invalid passphrase."));
+
+           /* Clear the last error to avoid recover_key() retry failure. */
+           grub_errno = GRUB_ERR_NONE;
          }
-       cargs->key_len = grub_strlen ((char *) cargs->key_data);
       }
 
-    ret = cr->recover_key (source, dev, cargs);
-    if (ret != GRUB_ERR_NONE)
-      goto error;
-
     ret = grub_cryptodisk_insert (dev, name, source);
     if (ret != GRUB_ERR_NONE)
       goto error;
--- a/include/grub/cryptodisk.h
+++ b/include/grub/cryptodisk.h
@@ -64,6 +64,9 @@
 
 #define GRUB_CRYPTODISK_MAX_KEYFILE_SIZE 8192
 
+/* Number of passphrase attempts the user is allowed. Must be > 0. */
+#define GRUB_CRYPTODISK_PASSPHRASE_TRIES 3
+
 struct grub_cryptodisk;
 
 typedef gcry_err_code_t