[PATCH] pSeries hvsi char driver null pointer deref

[linas@austin.ibm.com (Linas Vepstas)]

Andrew, 
Please apply.

Under certain rare circumstances, it appears that there can be
be a NULL-pointer deref when a user fiddles with terminal
emeulation programs while outpu is being sent to the console.
This patch checks for and avoids a NULL-pointer deref.

Signed-off-by: Hollis Blanchard <hollisbl@austin.ibm.com>
Signed-off-by: Linas Vepstas <linas@austin.ibm.com>

----
 drivers/char/hvsi.c |    3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

Index: linux-2.6.18-rc3-git1/drivers/char/hvsi.c
===================================================================
--- linux-2.6.18-rc3-git1.orig/drivers/char/hvsi.c	2006-08-03 14:50:00.000000000 -0500
+++ linux-2.6.18-rc3-git1/drivers/char/hvsi.c	2006-08-03 14:51:46.000000000 -0500
@@ -311,7 +311,8 @@ static void hvsi_recv_control(struct hvs
 				/* CD went away; no more connection */
 				pr_debug("hvsi%i: CD dropped\n", hp->index);
 				hp->mctrl &= TIOCM_CD;
-				if (!(hp->tty->flags & CLOCAL))
+				/* If userland hasn't done an open(2) yet, hp->tty is NULL. */
+				if (hp->tty && !(hp->tty->flags & CLOCAL))
 					*to_hangup = hp->tty;
 			}
 			break;