fbdev: Fix invalid page access after closing deferred I/O devices

Vulnerability Description

In the Linux kernel, the following vulnerability has been resolved: fbdev: Fix invalid page access after closing deferred I/O devices When a fbdev with deferred I/O is once opened and closed, the dirty pages still remain queued in the pageref list, and eventually later those may be processed in the delayed work. This may lead to a corruption of pages, hitting an Oops. This patch makes sure to cancel the delayed work and clean up the pageref list at closing the device for addressing the bug. A part of the cleanup code is factored out as a new helper function that is called from the common fb_release().

References

• https://git.kernel.org/stable/c/87b9802ca824fcee7915e717e9a60471af62e8e9
• https://git.kernel.org/stable/c/f1d91f0e9d5a240a809698d7d9c5a538e7dcc149
• https://git.kernel.org/stable/c/3efc61d95259956db25347e2a9562c3e54546e20