In the Linux kernel, the following vulnerability has been resolved:
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.