From: Alan Cox <alan@linux.intel.com>
Date: Wed, 19 Sep 2012 14:35:46 +0000 (+0100)
Subject: serial_core: Fix race in uart_handle_dcd_change
X-Git-Tag: v5.15~21594^2~28
X-Git-Url: https://git.proxmox.com/?a=commitdiff_plain;h=43eca0aef73cc6f0d37ad139f1cbb810e62e409d;p=mirror_ubuntu-kernels.git

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 046279ce3e8d..78036c510ccc 100644
--- a/drivers/tty/serial/serial_core.c
+++ b/drivers/tty/serial/serial_core.c
@@ -2501,9 +2501,12 @@ void uart_handle_dcd_change(struct uart_port *uport, unsigned int status)
 {
 	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 @@ void uart_handle_dcd_change(struct uart_port *uport, unsigned int status)
 	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);
 }