[PATCH 1/7][SRU][OEM-5.10] platform/x86: dell-wmi-sysman: Fix crash caused by calling kset_unregister twice

[AceLan Kao]

From: Hans de Goede <hdegoede at redhat.com>

BugLink: https://bugs.launchpad.net/bugs/1931509

On some system the WMI GUIDs used by dell-wmi-sysman are present but there
are no enum type attributes, this causes init_bios_attributes() to return
-ENODEV, after which sysman_init() does a "goto fail_create_group" and then
calls release_attributes_data().

release_attributes_data() calls kset_unregister(wmi_priv.main_dir_kset);
but before this commit it was missing a "wmi_priv.main_dir_kset = NULL;"
statement; and after calling release_attributes_data() the sysman_init()
error handling does this:

        if (wmi_priv.main_dir_kset) {
                kset_unregister(wmi_priv.main_dir_kset);
                wmi_priv.main_dir_kset = NULL;
        }

Which causes a second kset_unregister(wmi_priv.main_dir_kset), leading to
a double-free, which causes a crash.

Add the missing "wmi_priv.main_dir_kset = NULL;" statement to
release_attributes_data() to fix this double-free crash.

Fixes: e8a60aa7404b ("platform/x86: Introduce support for Systems Management Driver over WMI for Dell Systems")
Cc: Divya Bharathi <Divya_Bharathi at dell.com>
Cc: Mario Limonciello <mario.limonciello at dell.com>
Signed-off-by: Hans de Goede <hdegoede at redhat.com>
Link: https://lore.kernel.org/r/20210321115901.35072-2-hdegoede@redhat.com
(cherry picked from commit bdda39673fdef32631448dcb75df79aed9643b31)
Signed-off-by: Chia-Lin Kao (AceLan) <acelan.kao at canonical.com>
---
 drivers/platform/x86/dell/dell-wmi-sysman/sysman.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/drivers/platform/x86/dell/dell-wmi-sysman/sysman.c b/drivers/platform/x86/dell/dell-wmi-sysman/sysman.c
index cb81010ba1a21..c1997db74cca5 100644
--- a/drivers/platform/x86/dell/dell-wmi-sysman/sysman.c
+++ b/drivers/platform/x86/dell/dell-wmi-sysman/sysman.c
@@ -388,6 +388,7 @@ static void release_attributes_data(void)
 	if (wmi_priv.main_dir_kset) {
 		destroy_attribute_objs(wmi_priv.main_dir_kset);
 		kset_unregister(wmi_priv.main_dir_kset);
+		wmi_priv.main_dir_kset = NULL;
 	}
 	mutex_unlock(&wmi_priv.mutex);
 
-- 
2.25.1