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Before attempting to dequeue a Data Link protocol encapsulated message, check that the Data Link protocol is still bound to the HCI UART driver. This makes the code consistent with the usage of the other proto function pointers. Therefore, add a check for HCI_UART_PROTO_READY into hci_uart_dequeue() and return NULL if the Data Link protocol is not bound. This is needed for robustness as there is a scheduling race condition. hci_uart_write_work() is scheduled to run via work queue hu->write_work from hci_uart_tx_wakeup(). Therefore, there is a delay between scheduling hci_uart_write_work() to run and hci_uart_dequeue() running whereby the Data Link protocol layer could become unbound during the scheduling delay. In this case, without the check, the call to the unbound Data Link protocol layer dequeue function can crash. It is noted that hci_uart_tty_close() has a "cancel_work_sync(&hu->write_work)" statement but this only reduces the window of the race condition because it is possible for a new work-item to be added to work queue hu->write_work after the call to cancel_work_sync(). For example, Data Link layer retransmissions can be added to the work queue after the cancel_work_sync() has finished. Signed-off-by: Dean Jenkins <Dean_Jenkins@mentor.com> Signed-off-by: Marcel Holtmann <marcel@holtmann.org>
Linux kernel ============ This file was moved to Documentation/admin-guide/README.rst Please notice that there are several guides for kernel developers and users. These guides can be rendered in a number of formats, like HTML and PDF. In order to build the documentation, use ``make htmldocs`` or ``make pdfdocs``. There are various text files in the Documentation/ subdirectory, several of them using the Restructured Text markup notation. See Documentation/00-INDEX for a list of what is contained in each file. Please read the Documentation/process/changes.rst file, as it contains the requirements for building and running the kernel, and information about the problems which may result by upgrading your kernel.