This is a note to let you know that I've just added the patch titled
fbdev: pxafb: Fix possible use after free in pxafb_task()
to the 4.19-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
fbdev-pxafb-fix-possible-use-after-free-in-pxafb_tas.patch
and it can be found in the queue-4.19 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
commit fdc42ed79c63f5c9ce4f18135fae9f7162d236a1
Author: Kaixin Wang <kxwang23@xxxxxxxxxxxxxx>
Date: Wed Sep 11 22:29:52 2024 +0800
fbdev: pxafb: Fix possible use after free in pxafb_task()
[ 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@xxxxxxxxxxxxxx>
Signed-off-by: Helge Deller <deller@xxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
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);
