efivars: only check for duplicates on the registered list

variable_is_present() accesses '__efivars' directly, but when called via
gsmi_init() Michel reports observing the following crash,

  BUG: unable to handle kernel NULL pointer dereference at (null)
  IP: variable_is_present+0x55/0x170
  Call Trace:
    register_efivars+0x106/0x370
    gsmi_init+0x2ad/0x3da
    do_one_initcall+0x3f/0x170

The reason for the crash is that '__efivars' hasn't been initialised nor
has it been registered with register_efivars() by the time the google
EFI SMI driver runs.  The gsmi code uses its own struct efivars, and
therefore, a different variable list.  Fix the above crash by passing
the registered struct efivars to variable_is_present(), so that we
traverse the correct list.

Reported-by: Michel Lespinasse <walken@google.com>
Tested-by: Michel Lespinasse <walken@google.com>
Cc: Mike Waychison <mikew@google.com>
Cc: Matthew Garrett <matthew.garrett@nebula.com>
Cc: Seiji Aguchi <seiji.aguchi@hds.com>
Signed-off-by: Matt Fleming <matt.fleming@intel.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 7 insertions, 5 deletions

diff --git a/drivers/firmware/efivars.c b/drivers/firmware/efivars.c
index 182ce9471175..f4baa11d3644 100644
--- a/drivers/firmware/efivars.c
+++ b/drivers/firmware/efivars.c
@@ -1628,10 +1628,11 @@ static ssize_t efivar_delete(struct file *filp, struct kobject *kobj,
         return count;
 }
 
-static bool variable_is_present(efi_char16_t *variable_name, efi_guid_t *vendor)
+static bool variable_is_present(struct efivars *efivars,
+                                efi_char16_t *variable_name,
+                                efi_guid_t *vendor)
 {
         struct efivar_entry *entry, *n;
-        struct efivars *efivars = &__efivars;
         unsigned long strsize1, strsize2;
         bool found = false;
 
@@ -1703,8 +1704,8 @@ static void efivar_update_sysfs_entries(struct work_struct *work)
                         if (status != EFI_SUCCESS) {
                                 break;
                         } else {
-                                if (!variable_is_present(variable_name,
-                                    &vendor)) {
+                                if (!variable_is_present(efivars,
+                                    variable_name, &vendor)) {
                                         found = true;
                                         break;
                                 }
@@ -2008,7 +2009,8 @@ int register_efivars(struct efivars *efivars,
                          * we'll ever see a different variable name,
                          * and may end up looping here forever.
                          */
-                        if (variable_is_present(variable_name, &vendor_guid)) {
+                        if (variable_is_present(efivars, variable_name,
+                                                &vendor_guid)) {
                                 dup_variable_bug(variable_name, &vendor_guid,
                                                  variable_name_size);
                                 status = EFI_NOT_FOUND;