[PATCH AUTOSEL 6.6 075/139] fbdev: pxafb: Fix possible use after free in pxafb_task()

Sasha Levin
2024-09-25T12:15:02Z

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 fa943612c4e2b..3a2427eb29f23 100644
--- a/drivers/video/fbdev/pxafb.c
+++ b/drivers/video/fbdev/pxafb.c
@@ -2403,6 +2403,7 @@ static void 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);
--
2.43.0