[PATCH v3 2/4] serial: fix ioctl hangup race

[Johan Hovold <johan@kernel.org>]

The tty ioctls can race with hangup and end up calling into a tty
driver for a device that is already gone or powered down.

Add the missing checks to make sure the port has not been hung up before
accessing the hardware to avoid issues like kernel panic due to
unclocked accesses.

Note that TIOCGSERIAL, TIOCGICOUNT do not access hardware and are
therefore not affected by the race.

Fixes: 04f378b198da ("tty: BKL pushdown")
Cc: stable@vger.kernel.org	# 2.6.26
Signed-off-by: Johan Hovold <johan@kernel.org>
---
 drivers/tty/serial/serial_core.c | 32 +++++++++++++++++++++++++-------
 1 file changed, 25 insertions(+), 7 deletions(-)

diff --git a/drivers/tty/serial/serial_core.c b/drivers/tty/serial/serial_core.c
index 1553bc6cbe7b..4213fa3dc988 100644
--- a/drivers/tty/serial/serial_core.c
+++ b/drivers/tty/serial/serial_core.c
@@ -896,7 +896,7 @@ static int uart_set_info(struct tty_struct *tty, struct tty_port *port,
 	upf_t old_flags, new_flags;
 	int retval;
 
-	if (!uport)
+	if (!uport || tty_io_error(tty))
 		return -EIO;
 
 	new_port = new_info->port;
@@ -1119,7 +1119,7 @@ static int uart_break_ctl(struct tty_struct *tty, int break_state)
 	guard(mutex)(&port->mutex);
 
 	uport = uart_port_check(state);
-	if (!uport)
+	if (!uport || tty_io_error(tty))
 		return -EIO;
 
 	if (uport->type != PORT_UNKNOWN && uport->ops->break_ctl)
@@ -1144,7 +1144,7 @@ static int uart_do_autoconfig(struct tty_struct *tty, struct uart_state *state)
 	 */
 	scoped_cond_guard(mutex_intr, return -ERESTARTSYS, &port->mutex) {
 		uport = uart_port_check(state);
-		if (!uport)
+		if (!uport || tty_io_error(tty))
 			return -EIO;
 
 		if (tty_port_users(port) != 1)
@@ -1199,7 +1199,7 @@ static void uart_enable_ms(struct uart_port *uport)
  * FIXME: This wants extracting into a common all driver implementation
  * of TIOCMWAIT using tty_port.
  */
-static int uart_wait_modem_status(struct uart_state *state, unsigned long arg)
+static int uart_wait_modem_status(struct tty_struct *tty, struct uart_state *state, unsigned long arg)
 {
 	struct uart_port *uport;
 	struct tty_port *port = &state->port;
@@ -1213,11 +1213,21 @@ static int uart_wait_modem_status(struct uart_state *state, unsigned long arg)
 	uport = uart_port_ref(state);
 	if (!uport)
 		return -EIO;
+
+	mutex_lock(&port->mutex);
+	if (tty_io_error(tty)) {
+		mutex_unlock(&port->mutex);
+		ret = -EIO;
+		goto out_deref;
+	}
+
 	uart_port_lock_irq(uport);
 	memcpy(&cprev, &uport->icount, sizeof(struct uart_icount));
 	uart_enable_ms(uport);
 	uart_port_unlock_irq(uport);
 
+	mutex_unlock(&port->mutex);
+
 	add_wait_queue(&port->delta_msr_wait, &wait);
 	for (;;) {
 		uart_port_lock_irq(uport);
@@ -1246,6 +1256,7 @@ static int uart_wait_modem_status(struct uart_state *state, unsigned long arg)
 	}
 	__set_current_state(TASK_RUNNING);
 	remove_wait_queue(&port->delta_msr_wait, &wait);
+out_deref:
 	uart_port_deref(uport);
 
 	return ret;
@@ -1568,7 +1579,7 @@ uart_ioctl(struct tty_struct *tty, unsigned int cmd, unsigned long arg)
 
 	/* This should only be used when the hardware is present. */
 	if (cmd == TIOCMIWAIT)
-		return uart_wait_modem_status(state, arg);
+		return uart_wait_modem_status(tty, state, arg);
 
 	/* rs485_config requires more locking than others */
 	if (cmd == TIOCSRS485)
@@ -1647,7 +1658,7 @@ static void uart_set_termios(struct tty_struct *tty,
 	guard(mutex)(&state->port.mutex);
 
 	uport = uart_port_check(state);
-	if (!uport)
+	if (!uport || tty_io_error(tty))
 		return;
 
 	/*
@@ -1799,7 +1810,14 @@ static void uart_wait_until_sent(struct tty_struct *tty, int timeout)
 	 * 'timeout' / 'expire' give us the maximum amount of time
 	 * we wait.
 	 */
-	while (!port->ops->tx_empty(port)) {
+	for (;;) {
+		mutex_lock(&state->port.mutex);
+		if (tty_io_error(tty) || port->ops->tx_empty(port)) {
+			mutex_unlock(&state->port.mutex);
+			break;
+		}
+		mutex_unlock(&state->port.mutex);
+
 		msleep_interruptible(jiffies_to_msecs(char_time));
 		if (signal_pending(current))
 			break;
-- 
2.55.0