From: Norm Murray <nmurray@redhat.com>
Subject: [PATCH RHEL5.1 BZ238394] panic in check_modem_status on 8250
Date: Mon, 30 Apr 2007 15:42:09 +1000
Bugzilla: 238394
Message-Id: <1177911729.31878.11.camel@strange.brisbane.redhat.com>
Changelog: [serial] panic in check_modem_status on 8250


Fujitsu is encountering a panic in check_modem_status with the 8250
serial device where there's a possible NULL pointer dereference in
check_modem_status if called before uart_open(). 

Upstream discussion at:
http://www.ussg.iu.edu/hypermail/linux/kernel/0704.2/0331.html

The attached was committed in 2.6.21 and the only difference is line
numbers for the backport to RHEL 5.

BZ238394, IT119124



--- linux-2.6.18.x86_64/drivers/serial/8250.c.orig	2007-04-30 15:06:16.000000000 +1000
+++ linux-2.6.18.x86_64/drivers/serial/8250.c	2007-04-30 15:15:27.000000000 +1000
@@ -1292,7 +1292,8 @@ static unsigned int check_modem_status(s
 {
 	unsigned int status = serial_in(up, UART_MSR);
 
-	if (status & UART_MSR_ANY_DELTA && up->ier & UART_IER_MSI) {
+	if (status & UART_MSR_ANY_DELTA && up->ier & UART_IER_MSI &&
+	    up->port.info != NULL) {
 		if (status & UART_MSR_TERI)
 			up->port.icount.rng++;
 		if (status & UART_MSR_DDSR)