[PATCH] usb: core: hcd: cancel giveback work synchronously on stop

[Igor Putko <igorpetindev@gmail.com>]

When an HCD is stopped/removed (either during module unload, driver
unbind, or an error path in probe), pending URBs are unlinked and
completed. However, for root hubs or HCDs with giveback done in BH
context, the work function usb_giveback_urb_bh() may still be executing
on another CPU after __usb_hcd_giveback_urb() finishes.

Since the caller may immediately free the struct usb_hcd via usb_put_hcd()
after usb_stop_hcd() or usb_remove_hcd(), the running worker accesses
the embedded giveback_urb_bh structure after it has been freed,
triggering a slab-use-after-free write detected by KASAN.

Ensure all giveback work is fully flushed and cancelled in usb_stop_hcd()
by calling cancel_work_sync() on both high and low priority BHs.

Fixes: 8fea0c8fda30 ("usb: core: hcd: Convert from tasklet to BH workqueue")
Reported-by: syzbot+a5b220cacb0618384d5a@syzkaller.appspotmail.com
Closes: https://syzkaller.appspotmail.com/bug?extid=a5b220cacb0618384d5a
Signed-off-by: Igor Putko <igorpetindev@gmail.com>
---
 drivers/usb/core/hcd.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/drivers/usb/core/hcd.c b/drivers/usb/core/hcd.c
index 8e8a5f59b319..0b7d30900f7a 100644
--- a/drivers/usb/core/hcd.c
+++ b/drivers/usb/core/hcd.c
@@ -2787,6 +2787,9 @@ static void usb_stop_hcd(struct usb_hcd *hcd)
 	/* In case the HCD restarted the timer, stop it again. */
 	clear_bit(HCD_FLAG_POLL_RH, &hcd->flags);
 	timer_delete_sync(&hcd->rh_timer);
+
+	cancel_work_sync(&hcd->high_prio_bh.bh);
+	cancel_work_sync(&hcd->low_prio_bh.bh);
 }
 
 /**
-- 
2.47.3