[SRU][J/F][PATCH 1/1] sh: push-switch: Reorder cleanup operations to avoid use-after-free bug

[Bethany Jamison]

From: Duoming Zhou <duoming at zju.edu.cn>

The original code puts flush_work() before timer_shutdown_sync()
in switch_drv_remove(). Although we use flush_work() to stop
the worker, it could be rescheduled in switch_timer(). As a result,
a use-after-free bug can occur. The details are shown below:

      (cpu 0)                    |      (cpu 1)
switch_drv_remove()              |
 flush_work()                    |
  ...                            |  switch_timer // timer
                                 |   schedule_work(&psw->work)
 timer_shutdown_sync()           |
 ...                             |  switch_work_handler // worker
 kfree(psw) // free              |
                                 |   psw->state = 0 // use

This patch puts timer_shutdown_sync() before flush_work() to
mitigate the bugs. As a result, the worker and timer will be
stopped safely before the deallocate operations.

Fixes: 9f5e8eee5cfe ("sh: generic push-switch framework.")
Signed-off-by: Duoming Zhou <duoming at zju.edu.cn>
Reviewed-by: Geert Uytterhoeven <geert+renesas at glider.be>
Reviewed-by: John Paul Adrian Glaubitz <glaubitz at physik.fu-berlin.de>
Link: https://lore.kernel.org/r/20230802033737.9738-1-duoming@zju.edu.cn
Signed-off-by: John Paul Adrian Glaubitz <glaubitz at physik.fu-berlin.de>
(backported from commit 246f80a0b17f8f582b2c0996db02998239057c65)
[bjamison: made fix change manually as I can't modify the neighboring
line to fix the context conflict, I can't change del_timer_sync to
timer_shutdown_sync - 292a089d7 treewide: Convert del_timer*() to timer_shutdown*()]
CVE-2023-52629
Signed-off-by: Bethany Jamison <bethany.jamison at canonical.com>
---
 arch/sh/drivers/push-switch.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/sh/drivers/push-switch.c b/arch/sh/drivers/push-switch.c
index 2813140fd92bb..c3e8feedfe372 100644
--- a/arch/sh/drivers/push-switch.c
+++ b/arch/sh/drivers/push-switch.c
@@ -101,8 +101,8 @@ static int switch_drv_remove(struct platform_device *pdev)
 		device_remove_file(&pdev->dev, &dev_attr_switch);
 
 	platform_set_drvdata(pdev, NULL);
-	flush_work(&psw->work);
 	del_timer_sync(&psw->debounce);
+	flush_work(&psw->work);
 	free_irq(irq, pdev);
 
 	kfree(psw);
-- 
2.34.1