[PATCH] Bluetooth: hci_uart: fix UAF in hci_uart_tty_close()

[<w15303746062@163.com>]

From: Mingyu Wang <25181214217@stu.xidian.edu.cn>

A Use-After-Free (UAF) vulnerability and a subsequent General Protection
Fault (GPF) were observed in h5_recv() due to a race condition between
the initialization of the HCI UART line discipline and concurrent TTY
hangup via TIOCVHANGUP.

The issue arises because the workqueues (init_ready and write_work) are
only cancelled if the HCI_UART_PROTO_READY flag is set. However, during
the protocol initialization phase (HCI_UART_PROTO_INIT), the underlying
protocol (e.g., H5) may schedule work (such as sending sync/config
packets). If a hangup occurs before the setup completes and the READY
flag is set, hci_uart_tty_close() skips the cancel_work_sync() calls
and proceeds to free the `hu` struct.

When the delayed workqueue finally executes, it blindly dereferences
the freed `hu` struct, causing ODEBUG warnings and kernel panics.

Fix this by moving the cancel_work_sync() calls outside the
HCI_UART_PROTO_READY check, ensuring that any pending works are
unconditionally cancelled before the hci_uart structure is freed.

Signed-off-by: Mingyu Wang <25181214217@stu.xidian.edu.cn>
---
 drivers/bluetooth/hci_ldisc.c | 10 +++++++---
 1 file changed, 7 insertions(+), 3 deletions(-)

diff --git a/drivers/bluetooth/hci_ldisc.c b/drivers/bluetooth/hci_ldisc.c
index 275ea865bc29..566e1c525ee2 100644
--- a/drivers/bluetooth/hci_ldisc.c
+++ b/drivers/bluetooth/hci_ldisc.c
@@ -544,14 +544,18 @@ static void hci_uart_tty_close(struct tty_struct *tty)
 	if (hdev)
 		hci_uart_close(hdev);
 
+	/*
+	 * Always cancel workqueues unconditionally before freeing the hu
+	 * struct, as they might be active during the PROTO_INIT phase.
+	 */
+	cancel_work_sync(&hu->init_ready);
+	cancel_work_sync(&hu->write_work);
+
 	if (test_bit(HCI_UART_PROTO_READY, &hu->flags)) {
 		percpu_down_write(&hu->proto_lock);
 		clear_bit(HCI_UART_PROTO_READY, &hu->flags);
 		percpu_up_write(&hu->proto_lock);
 
-		cancel_work_sync(&hu->init_ready);
-		cancel_work_sync(&hu->write_work);
-
 		if (hdev) {
 			if (test_bit(HCI_UART_REGISTERED, &hu->flags))
 				hci_unregister_dev(hdev);
-- 
2.34.1