efivars: Check size of user object

Unbelieavably there are no checks to see whether the data structure
passed to 'new_var' and 'del_var' is the size that we expect. Let's add
some for better robustness.

Cc: Mike Waychison <mikew@google.com>
Signed-off-by: NMatt Fleming <matt.fleming@intel.com>

drivers/firmware/efi/efivars.c

@@ -347,6 +347,9 @@ static ssize_t efivar_create(struct file *filp, struct kobject *kobj,
 	if (!capable(CAP_SYS_ADMIN))
 		return -EACCES;
 
+	if (count != sizeof(*new_var))
+		return -EINVAL;
+
 	attributes = new_var->Attributes;
 	size = new_var->DataSize;
 	data = new_var->Data;
@@ -395,6 +398,9 @@ static ssize_t efivar_delete(struct file *filp, struct kobject *kobj,
 	if (!capable(CAP_SYS_ADMIN))
 		return -EACCES;
 
+	if (count != sizeof(*del_var))
+		return -EINVAL;
+
 	name = del_var->VariableName;
 	vendor = del_var->VendorGuid;