4.19-stable review patch. If anyone has any objections, please let me know.
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From: Kaixin Wang kxwang23@m.fudan.edu.cn
[ Upstream commit 4a6921095eb04a900e0000da83d9475eb958e61e ]
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.
Signed-off-by: Kaixin Wang kxwang23@m.fudan.edu.cn Signed-off-by: Helge Deller deller@gmx.de Signed-off-by: Sasha Levin sashal@kernel.org --- drivers/video/fbdev/pxafb.c | 1 + 1 file changed, 1 insertion(+)
diff --git a/drivers/video/fbdev/pxafb.c b/drivers/video/fbdev/pxafb.c index 90dee3e6f8bc7..f76da5c6c6cd6 100644 --- a/drivers/video/fbdev/pxafb.c +++ b/drivers/video/fbdev/pxafb.c @@ -2437,6 +2437,7 @@ static int pxafb_remove(struct platform_device *dev) info = &fbi->fb;
pxafb_overlay_exit(fbi); + cancel_work_sync(&fbi->task); unregister_framebuffer(info);
pxafb_disable_controller(fbi);