fbdev: pxafb: Fix possible use after free in pxafb_task()

Vulnerability Description

In the Linux kernel, the following vulnerability has been resolved: fbdev: pxafb: Fix possible use after free in pxafb_task() In the pxafb_probe function, it calls the pxafb_init_fbinfo function, after which &fbi->task is associated with pxafb_task. Moreover, within this pxafb_init_fbinfo function, the pxafb_blank function within the &pxafb_ops struct is capable of scheduling work. If we remove the module which will call pxafb_remove to make cleanup, it will call unregister_framebuffer function which can call do_unregister_framebuffer to free fbi->fb through put_fb_info(fb_info), while the work mentioned above will be used. The sequence of operations that may lead to a UAF bug is as follows: CPU0 CPU1 | pxafb_task pxafb_remove | unregister_framebuffer(info) | do_unregister_framebuffer(fb_info) | put_fb_info(fb_info) | // free fbi->fb | set_ctrlr_state(fbi, state) | __pxafb_lcd_power(fbi, 0) | fbi->lcd_power(on, &fbi->fb.var) | //use fbi->fb Fix it by ensuring that the work is canceled before proceeding with the cleanup in pxafb_remove. Note that only root user can remove the driver at runtime.

References

• https://git.kernel.org/stable/c/e657fa2df4429f3805a9b3e47fb1a4a1b02a72bd
• https://git.kernel.org/stable/c/6d0a07f68b66269e167def6c0b90a219cd3e7473
• https://git.kernel.org/stable/c/e6897e299f57b103e999e62010b88e363b3eebae
• https://git.kernel.org/stable/c/4cda484e584be34d55ee17436ebf7ad11922b97a
• https://git.kernel.org/stable/c/3c0d416eb4bef705f699213cee94bf54b6acdacd
• https://git.kernel.org/stable/c/fdda354f60a576d52dcf90351254714681df4370
• https://git.kernel.org/stable/c/aaadc0cb05c999ccd8898a03298b7e5c31509b08
• https://git.kernel.org/stable/c/a3a855764dbacbdb1cc51e15dc588f2d21c93e0e
• https://git.kernel.org/stable/c/4a6921095eb04a900e0000da83d9475eb958e61e