[PATCH 5/5] tty: n_gsm: Fixed NULL ptr OOPs in tty_write_room()

[Russ Gorby <russ.gorby@intel.com>]

We saw a case where gsmld_output was called after the MUX
was shutdown. In this case gsm->tty was null so tty_write_room(NULL)
was called which resulted in an exception.

checked for gsm->tty == NULL in gsmld_output()

Signed-off-by: Russ Gorby <russ.gorby@intel.com>
---
 drivers/tty/n_gsm.c |    2 ++
 1 files changed, 2 insertions(+), 0 deletions(-)

diff --git a/drivers/tty/n_gsm.c b/drivers/tty/n_gsm.c
index 22c844d..2908199 100644
--- a/drivers/tty/n_gsm.c
+++ b/drivers/tty/n_gsm.c
@@ -2168,6 +2168,8 @@ EXPORT_SYMBOL_GPL(gsm_alloc_mux);
 
 static int gsmld_output(struct gsm_mux *gsm, u8 *data, int len)
 {
+	if (!gsm->tty)
+		return -ENXIO;
 	if (tty_write_room(gsm->tty) < len) {
 		set_bit(TTY_DO_WRITE_WAKEUP, &gsm->tty->flags);
 		return -ENOSPC;
-- 
1.7.0.4