[PATCH 6.1.y] sh: push-switch: Reorder cleanup operations to avoid use-after-free bug

[Artem Dinaburg]

From: Duoming Zhou <duoming@xxxxxxxxxx>

[ Upstream commit 246f80a0b17f8f582b2c0996db02998239057c65 ]

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@xxxxxxxxxx>
Reviewed-by: Geert Uytterhoeven <geert+renesas@xxxxxxxxx>
Reviewed-by: John Paul Adrian Glaubitz <glaubitz@xxxxxxxxxxxxxxxxxxx>
Link: https://lore.kernel.org/r/20230802033737.9738-1-duoming@xxxxxxxxxx
Signed-off-by: John Paul Adrian Glaubitz <glaubitz@xxxxxxxxxxxxxxxxxxx>

[ Backport to 6.1.y: use timer_shutdown_sync(), already available here,
  so the timer cannot rearm before the queued work is flushed. ]
Assisted-by: LLM
Signed-off-by: Artem Dinaburg <artem@xxxxxxxxxxxxxxx>
---
Hi Greg, Sasha, and SH maintainers,

I am continuing with CVE backports still missing from 6.1.y.
This fix is inherited by v6.6 and every later mainline release, but 6.1.y
still has the affected code. The target-specific adjustment is described
in the bracketed note above.

Could you please queue it for 6.1.y?

Thanks,
Artem Dinaburg

CVE: CVE-2023-52629

Build validation: SH r7785rp_defconfig with CONFIG_PUSH_SWITCH=y and
CONFIG_WERROR=y built push-switch.o with no new warnings or errors.

AI assistance: An LLM helped find, adapt, and validate this
backport; I reviewed the patch and test output.

 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 2813140fd92bb2..6ecba5f521eb6c 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);
+	timer_shutdown_sync(&psw->debounce);
 	flush_work(&psw->work);
-	del_timer_sync(&psw->debounce);
 	free_irq(irq, pdev);
 
 	kfree(psw);
-- 
2.39.5