Donate to e Foundation | Murena handsets with /e/OS | Own a part of Murena! Learn more

Commit 2e758910 authored by Peter Hurley's avatar Peter Hurley Committed by Greg Kroah-Hartman
Browse files

serial: core: Flush ldisc after dropping port mutex in uart_close() 



The tty buffers (and any line discipline buffers) must be flushed after
the UART hardware has shutdown; otherwise, a racing open on the same
tty may receive data from the previous session, which is a security
hazard. However, holding the port mutex while flushing the line
discipline buffers creates a lock inversion if the set_termios()
handler takes the port mutex (as it does in the followup patch,
'serial: Fix locking for uart driver set_termios method'.

Flush the ldisc buffers after dropping the port mutex; the tty lock
is still held which prevents a concurrent open() from advancing while
flushing. Since no new rx data is possible after uart_shutdown() until
a new open reinitializes the port, the later flush has no impact on
what data is being discarded.

Signed-off-by: default avatarPeter Hurley <peter@hurleysoftware.com>
Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent 479e9b94

drivers/tty/serial/serial_core.c

+2 −3
Original line number Original line Diff line number Diff line
@@ -1361,9 +1361,6 @@ static void uart_close(struct tty_struct *tty, struct file *filp) 




	mutex_lock(&port->mutex);

	mutex_lock(&port->mutex);

	uart_shutdown(tty, state);

	uart_shutdown(tty, state);



	tty_ldisc_flush(tty);



	tty_port_tty_set(port, NULL);

	tty_port_tty_set(port, NULL);

	tty->closing = 0;

	tty->closing = 0;

	spin_lock_irqsave(&port->lock, flags);

	spin_lock_irqsave(&port->lock, flags);
@@ -1390,6 +1387,8 @@ static void uart_close(struct tty_struct *tty, struct file *filp) 
	wake_up_interruptible(&port->close_wait);

	wake_up_interruptible(&port->close_wait);





	mutex_unlock(&port->mutex);

	mutex_unlock(&port->mutex);



	tty_ldisc_flush(tty);

}

}





static void uart_wait_until_sent(struct tty_struct *tty, int timeout)

static void uart_wait_until_sent(struct tty_struct *tty, int timeout)