serial_core: Fix race in uart_handle_dcd_change
If a serial driver is called post hangup with a second DCD event then we
will attempt to get the ldisc of NULL. Check we have a tty before trying to
do anything with it.
This is still only safe within the uart layer if the caller holds the
relevant uart locks. We could do with a version where the tty is passed for
more general use.
Signed-off-by: Alan Cox <alan@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
diff --git a/drivers/tty/serial/serial_core.c b/drivers/tty/serial/serial_core.c
index 046279c..78036c5 100644
--- a/drivers/tty/serial/serial_core.c
+++ b/drivers/tty/serial/serial_core.c
@@ -2501,9 +2501,12 @@
{
struct uart_state *state = uport->state;
struct tty_port *port = &state->port;
- struct tty_ldisc *ld = tty_ldisc_ref(port->tty);
+ struct tty_ldisc *ld = NULL;
struct pps_event_time ts;
+ struct tty_struct *tty = port->tty;
+ if (tty)
+ ld = tty_ldisc_ref(tty);
if (ld && ld->ops->dcd_change)
pps_get_ts(&ts);
@@ -2516,12 +2519,12 @@
if (port->flags & ASYNC_CHECK_CD) {
if (status)
wake_up_interruptible(&port->open_wait);
- else if (port->tty)
- tty_hangup(port->tty);
+ else if (tty)
+ tty_hangup(tty);
}
if (ld && ld->ops->dcd_change)
- ld->ops->dcd_change(port->tty, status, &ts);
+ ld->ops->dcd_change(tty, status, &ts);
if (ld)
tty_ldisc_deref(ld);
}