fallback: Use a dynamic buffer when list var names

Now that we are iterating over all EFI variables to look for duplicate
boot entries, we should use a dynamic buffer, so if the firmware tells
us the buffer is too small for the next variable name we can re-allocate
it to a big enough size.

Signed-off-by: João Paulo Rechi Vita <jprvita@endlessos.org>

fallback.c

@@ -415,9 +415,12 @@ find_boot_option(EFI_DEVICE_PATH *dp, EFI_DEVICE_PATH *fulldp,
  cursor += DevicePathSize(dp);
  StrCpy((CHAR16 *)cursor, arguments);
 
- CHAR16 varname[256];
  EFI_STATUS efi_status;
  EFI_GUID vendor_guid = NullGuid;
+ UINTN buffer_size = 256 * sizeof(CHAR16);
+ CHAR16 *varname = AllocateZeroPool(buffer_size);
+ if (!varname)
+ return EFI_OUT_OF_RESOURCES;
 
  UINTN max_candidate_size = calc_masked_boot_option_size(size);
  CHAR8 *candidate = AllocateZeroPool(max_candidate_size);
@@ -426,15 +429,24 @@ find_boot_option(EFI_DEVICE_PATH *dp, EFI_DEVICE_PATH *fulldp,
  return EFI_OUT_OF_RESOURCES;
  }
 
- varname[0] = 0;
  while (1) {
- UINTN varname_size = sizeof(varname);
+ UINTN varname_size = buffer_size;
  efi_status = gRT->GetNextVariableName(&varname_size, varname,
  &vendor_guid);
  if (EFI_ERROR(efi_status)) {
- if (efi_status == EFI_BUFFER_TOO_SMALL)
+ if (efi_status == EFI_BUFFER_TOO_SMALL) {
  VerbosePrint(L"Buffer too small for next var "
- L"name\n");
+ L"name, re-allocating it to be %d"
+ L" chars long and retrying\n",
+ varname_size);
+ varname = ReallocatePool(varname,
+ buffer_size,
+ varname_size);
+ if (!varname)
+ return EFI_OUT_OF_RESOURCES;
+ buffer_size = varname_size;
+ continue;
+ }
 
  if (efi_status == EFI_DEVICE_ERROR)
  VerbosePrint(L"The next variable name could "
@@ -487,6 +499,7 @@ find_boot_option(EFI_DEVICE_PATH *dp, EFI_DEVICE_PATH *fulldp,
  }
  FreePool(candidate);
  FreePool(data);
+ FreePool(varname);
  return efi_status;
 }