[PATCH] tty: Add missing lock in n_tty_write()

[Joerg Roedel <joro@8bytes.org>]

The call of the tty->ops->write callback is protected by
output_lock in all other places I looked at. So it seems the
lock in this code-branch is missing, so take the output_lock
there too.

Cc: stable@vger.kernel.org
Signed-off-by: Joerg Roedel <joro@8bytes.org>
---
 drivers/tty/n_tty.c |    5 +++++
 1 file changed, 5 insertions(+)

diff --git a/drivers/tty/n_tty.c b/drivers/tty/n_tty.c
index d655416..ffb94a4 100644
--- a/drivers/tty/n_tty.c
+++ b/drivers/tty/n_tty.c
@@ -2058,10 +2058,14 @@ static ssize_t n_tty_write(struct tty_struct *tty, struct file *file,
 			if (tty->ops->flush_chars)
 				tty->ops->flush_chars(tty);
 		} else {
+			struct n_tty_data *l = tty->disc_data;
+
+			mutex_lock(&l->output_lock);
 			while (nr > 0) {
 				c = tty->ops->write(tty, b, nr);
 				if (c < 0) {
 					retval = c;
+					mutex_unlock(&l->output_lock);
 					goto break_out;
 				}
 				if (!c)
@@ -2069,6 +2073,7 @@ static ssize_t n_tty_write(struct tty_struct *tty, struct file *file,
 				b += c;
 				nr -= c;
 			}
+			mutex_unlock(&l->output_lock);
 		}
 		if (!nr)
 			break;
-- 
1.7.9.5