CVE-2023-52629

In the Linux kernel, the following vulnerability has been resolved:

sh: push-switch: Reorder cleanup operations to avoid use-after-free bug

The original code puts flushwork() before timershutdownsync() in switchdrvremove(). Although we use flushwork() 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)

switchdrvremove() | flushwork() | ... | switchtimer // timer | schedulework(&psw->work) timershutdownsync() | ... | switchwork_handler // worker kfree(psw) // free | | psw->state = 0 // use

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