Commit 211cde4f authored by Johan Hovold's avatar Johan Hovold Committed by Greg Kroah-Hartman
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serial: 8250: fix racy uartclk update 



Commit 868f3ee6 ("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: 868f3ee6 ("serial: 8250: Add 8250 port clock update method")
Fixes: c8dff3aa ("serial: 8250: Skip uninitialized TTY port baud rate update")
Cc: stable@vger.kernel.org      # 5.9
Cc: Serge Semin <Sergey.Semin@baikalelectronics.ru>
Tested-by: default avatarSerge Semin <fancer.lancer@gmail.com>
Reviewed-by: default avatarSerge Semin <fancer.lancer@gmail.com>
Acked-by: default avatarAndy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: default avatarJohan Hovold <johan@kernel.org>
Link: https://lore.kernel.org/r/20211015111422.1027-2-johan@kernel.org


Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent d1ec8a2e

drivers/tty/serial/8250/8250_port.c

+17 −4
Original line number Diff line number Diff line
@@ -2696,21 +2696,32 @@ static unsigned int serial8250_get_baud_rate(struct uart_port *port, 
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);
@@ -2727,7 +2738,9 @@ void serial8250_update_uartclk(struct uart_port *port, unsigned int uartclk) 
	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);