From: Johan Hovold <johan@xxxxxxxxxx> commit 211cde4f5817dc88ef7f8f2fa286e57fbf14c8ee upstream. Commit 868f3ee6e452 ("serial: 8250: Add 8250 port clock update method") added a hack to support SoCs where the UART reference clock can change behind the back of the driver but failed to add the proper locking. First, make sure to take a reference to the tty struct to avoid dereferencing a NULL pointer if the clock change races with a hangup. Second, the termios semaphore must be held during the update to prevent a racing termios change. Fixes: 868f3ee6e452 ("serial: 8250: Add 8250 port clock update method") Fixes: c8dff3aa8241 ("serial: 8250: Skip uninitialized TTY port baud rate update") Cc: stable@xxxxxxxxxxxxxxx # 5.9 Cc: Serge Semin <Sergey.Semin@xxxxxxxxxxxxxxxxxxxx> Tested-by: Serge Semin <fancer.lancer@xxxxxxxxx> Reviewed-by: Serge Semin <fancer.lancer@xxxxxxxxx> Acked-by: Andy Shevchenko <andriy.shevchenko@xxxxxxxxxxxxxxx> Signed-off-by: Johan Hovold <johan@xxxxxxxxxx> Link: https://lore.kernel.org/r/20211015111422.1027-2-johan@xxxxxxxxxx Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- drivers/tty/serial/8250/8250_port.c | 21 +++++++++++++++++---- 1 file changed, 17 insertions(+), 4 deletions(-) --- a/drivers/tty/serial/8250/8250_port.c +++ b/drivers/tty/serial/8250/8250_port.c @@ -2675,21 +2675,32 @@ static unsigned int serial8250_get_baud_ void serial8250_update_uartclk(struct uart_port *port, unsigned int uartclk) { struct uart_8250_port *up = up_to_u8250p(port); + struct tty_port *tport = &port->state->port; unsigned int baud, quot, frac = 0; struct ktermios *termios; + struct tty_struct *tty; unsigned long flags; - mutex_lock(&port->state->port.mutex); + tty = tty_port_tty_get(tport); + if (!tty) { + mutex_lock(&tport->mutex); + port->uartclk = uartclk; + mutex_unlock(&tport->mutex); + return; + } + + down_write(&tty->termios_rwsem); + mutex_lock(&tport->mutex); if (port->uartclk == uartclk) goto out_lock; port->uartclk = uartclk; - if (!tty_port_initialized(&port->state->port)) + if (!tty_port_initialized(tport)) goto out_lock; - termios = &port->state->port.tty->termios; + termios = &tty->termios; baud = serial8250_get_baud_rate(port, termios, NULL); quot = serial8250_get_divisor(port, baud, &frac); @@ -2706,7 +2717,9 @@ void serial8250_update_uartclk(struct ua serial8250_rpm_put(up); out_lock: - mutex_unlock(&port->state->port.mutex); + mutex_unlock(&tport->mutex); + up_write(&tty->termios_rwsem); + tty_kref_put(tty); } EXPORT_SYMBOL_GPL(serial8250_update_uartclk);