mok: delete the existing RT variables only when only_first=TRUE

For the firmware without the variable writing issues, MOK variables are
mirrored when only_first=TRUE. However, LibDeleteVariable() was called
in maybe_mirror_one_mok_variable() when only_first=FALSE, and this
could delete MOK variables that were just mirrored in the first round.

This bug was hidden since LibDeleteVariable() deletes BS+RT+NV variables
while we mirror MOK variables as BS+RT, and the firmware refused to
delete the mirrored MOK variable due to mismatching attributes. However,
some firmwares, such as VMWare, didn't enforce the attribute check and
just deleted the variables with matched name and GUID. In such system,
MokListRT was always removed before it reached OS.

Fixes: rhboot#386

Signed-off-by: Gary Lin <glin@suse.com>

mok.c

@@ -868,7 +868,7 @@ maybe_mirror_one_mok_variable(struct mok_state_variable *v,
  BOOLEAN present = FALSE;
 
  if (v->rtname) {
- if (!only_first && (v->flags & MOK_MIRROR_DELETE_FIRST)) {
+ if (only_first && (v->flags & MOK_MIRROR_DELETE_FIRST)) {
  dprint(L"deleting \"%s\"\n", v->rtname);
  efi_status = LibDeleteVariable(v->rtname, v->guid);
  dprint(L"LibDeleteVariable(\"%s\",...) => %r\n", v->rtname, efi_status);