efivars: only check for duplicates on the registered list [Linux 3.9]

This Linux kernel change "efivars: only check for duplicates on the registered list" is included in the Linux 3.9 release. This change is authored by Matt Fleming <matt.fleming [at] intel.com> on Fri Apr 26 10:10:55 2013 +0100. The commit for this change in Linux stable tree is f464246 (patch).

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:

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>

There are 12 lines of Linux source code added/deleted in this change. Code changes to Linux kernel are as follows.

 drivers/firmware/efivars.c | 12 +++++++-----
 1 file changed, 7 insertions(+), 5 deletions(-)

diff --git a/drivers/firmware/efivars.c b/drivers/firmware/efivars.c
index 182ce94..f4baa11 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) {
            } else {
-               if (!variable_is_present(variable_name,
-                   &vendor)) {
+               if (!variable_is_present(efivars,
+                   variable_name, &vendor)) {
                    found = true;
@@ -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,
                status = EFI_NOT_FOUND;

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