From: Mingyu Wang <25181214217@stu.xidian.edu.cn> Date: Mon, 18 May 2026 02:49:49 +0000 (+0800) Subject: Bluetooth: hci_uart: fix UAFs and race conditions in close and init paths X-Git-Url: http://git.ipfire.org/?a=commitdiff_plain;h=c1bb9336ae6b54a5f6a353c4bd4ed9a4307e429b;p=thirdparty%2Fkernel%2Flinux.git Bluetooth: hci_uart: fix UAFs and race conditions in close and init paths Vulnerabilities leading to Use-After-Free (UAF) and Null Pointer Dereference (NPD) conditions were observed in the lifecycle management of hci_uart. The primary issue arises because the workqueues (init_ready and write_work) are only flushed/cancelled if the HCI_UART_PROTO_READY flag is set during TTY close. If a hangup occurs before setup completes, hci_uart_tty_close() skips the teardown of these workqueues and proceeds to free the `hu` struct. When the scheduled work executes later, it blindly dereferences the freed `hu` struct. Furthermore, several data races and UAFs were identified in the teardown sequence: 1. Calling hci_uart_flush() from hci_uart_close() without effectively disabling write_work causes a race condition where both can concurrently double-free hu->tx_skb. This happens because protocol timers can concurrently invoke hci_uart_tx_wakeup() and requeue write_work. 2. Calling hci_free_dev(hdev) before hu->proto->close(hu) causes a UAF when vendor specific protocol close callbacks dereference hu->hdev. 3. In the initialization error paths, failing to take the proto_lock write lock before clearing PROTO_READY leads to races with active readers. Additionally, hci_uart_tty_receive() accesses hu->hdev outside the read lock, leading to UAFs if the initialization error path frees hdev concurrently. Fix these synchronization and lifecycle issues by: 1. Re-ordering hci_uart_tty_close() to clear HCI_UART_PROTO_READY first, followed immediately by a cancel_work_sync(&hu->write_work). Clearing the flag locks out concurrent protocol timers from successfully invoking hci_uart_tx_wakeup(), effectively rendering the cancellation permanent and preventing the tx_skb double-free. 2. Note: Clearing PROTO_READY early causes hci_uart_close() to skip hu->proto->flush(). This is perfectly safe in the tty_close path because hu->proto->close() executes shortly after, which intrinsically purges all protocol SKB queues and tears down the state. 3. Relocating hu->proto->close(hu) strictly prior to hci_free_dev(hdev) across all close and error paths to prevent vendor-level UAFs. 4. Moving the hdev->stat.byte_rx increment in hci_uart_tty_receive() inside the proto_lock read-side critical section to safely synchronize with device unregistration. 5. Adding cancel_work_sync(&hu->write_work) to hci_uart_close() to safely flush the workqueue before hci_uart_flush() is invoked via the HCI core. 6. Utilizing cancel_work_sync() instead of disable_work_sync() across all paths to prevent permanently breaking user-space retry capabilities. Fixes: 3b799254cf6f ("Bluetooth: hci_uart: Cancel init work before unregistering") Cc: stable@vger.kernel.org Signed-off-by: Mingyu Wang <25181214217@stu.xidian.edu.cn> Signed-off-by: Luiz Augusto von Dentz --- diff --git a/drivers/bluetooth/hci_ldisc.c b/drivers/bluetooth/hci_ldisc.c index 275ea865bc29..47f4902b40b4 100644 --- a/drivers/bluetooth/hci_ldisc.c +++ b/drivers/bluetooth/hci_ldisc.c @@ -194,7 +194,15 @@ void hci_uart_init_work(struct work_struct *work) err = hci_register_dev(hu->hdev); if (err < 0) { BT_ERR("Can't register HCI device"); + + percpu_down_write(&hu->proto_lock); clear_bit(HCI_UART_PROTO_READY, &hu->flags); + percpu_up_write(&hu->proto_lock); + + /* Safely cancel work after clearing flags */ + cancel_work_sync(&hu->write_work); + + /* Close protocol before freeing hdev */ hu->proto->close(hu); hdev = hu->hdev; hu->hdev = NULL; @@ -263,8 +271,12 @@ static int hci_uart_open(struct hci_dev *hdev) /* Close device */ static int hci_uart_close(struct hci_dev *hdev) { + struct hci_uart *hu = hci_get_drvdata(hdev); + BT_DBG("hdev %p", hdev); + cancel_work_sync(&hu->write_work); + hci_uart_flush(hdev); hdev->flush = NULL; return 0; @@ -531,6 +543,7 @@ static void hci_uart_tty_close(struct tty_struct *tty) { struct hci_uart *hu = tty->disc_data; struct hci_dev *hdev; + bool proto_ready; BT_DBG("tty %p", tty); @@ -540,24 +553,38 @@ static void hci_uart_tty_close(struct tty_struct *tty) if (!hu) return; - hdev = hu->hdev; - if (hdev) - hci_uart_close(hdev); + /* Wait for init_ready to finish to prevent registration races */ + cancel_work_sync(&hu->init_ready); - if (test_bit(HCI_UART_PROTO_READY, &hu->flags)) { + proto_ready = test_bit(HCI_UART_PROTO_READY, &hu->flags); + if (proto_ready) { 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); + /* + * Unconditionally cancel write_work AFTER clearing PROTO_READY. + * This ensures that concurrent protocol timers cannot requeue + * write_work via hci_uart_tx_wakeup(), permanently preventing + * double-free races and UAFs. + */ + cancel_work_sync(&hu->write_work); + + hdev = hu->hdev; + if (hdev) + hci_uart_close(hdev); /* proto->flush is safely skipped */ + if (proto_ready) { if (hdev) { if (test_bit(HCI_UART_REGISTERED, &hu->flags)) hci_unregister_dev(hdev); - hci_free_dev(hdev); } + /* Close protocol before freeing hdev (intrinsically purges queues) */ hu->proto->close(hu); + + if (hdev) + hci_free_dev(hdev); } clear_bit(HCI_UART_PROTO_SET, &hu->flags); @@ -625,11 +652,12 @@ static void hci_uart_tty_receive(struct tty_struct *tty, const u8 *data, * tty caller */ hu->proto->recv(hu, data, count); - percpu_up_read(&hu->proto_lock); if (hu->hdev) hu->hdev->stat.byte_rx += count; + percpu_up_read(&hu->proto_lock); + tty_unthrottle(tty); } @@ -695,6 +723,10 @@ static int hci_uart_register_dev(struct hci_uart *hu) percpu_down_write(&hu->proto_lock); clear_bit(HCI_UART_PROTO_INIT, &hu->flags); percpu_up_write(&hu->proto_lock); + /* Cancel work after clearing flags */ + cancel_work_sync(&hu->write_work); + + /* Close protocol before freeing hdev */ hu->proto->close(hu); hu->hdev = NULL; hci_free_dev(hdev);