linux-kernel - [PATCH 3/3] tty: Prevent tty teardown during tty_write

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Message-Id: <1444523324-9884-3-git-send-email-peter@hurleysoftware.com>
Date:	Sat, 10 Oct 2015 20:28:44 -0400
From:	Peter Hurley <peter@...leysoftware.com>
To:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:	Jiri Slaby <jslaby@...e.cz>, linux-kernel@...r.kernel.org,
	Peter Hurley <peter@...leysoftware.com>
Subject: [PATCH 3/3] tty: Prevent tty teardown during tty_write_message()

tty_write_message() allows the caller to directly write to a specific
tty. Since the line discipline is bypassed for the direct write,
nothing prevents the tty from being torn down after the tty count is
checked.

Hold the tty lock for the duration of the direct write.

Signed-off-by: Peter Hurley <peter@...leysoftware.com>
---
 drivers/tty/tty_io.c | 6 ++----
 1 file changed, 2 insertions(+), 4 deletions(-)

diff --git a/drivers/tty/tty_io.c b/drivers/tty/tty_io.c
index bf404cd..4530993 100644
--- a/drivers/tty/tty_io.c
+++ b/drivers/tty/tty_io.c
@@ -1200,11 +1200,9 @@ void tty_write_message(struct tty_struct *tty, char *msg)
 	if (tty) {
 		mutex_lock(&tty->atomic_write_lock);
 		tty_lock(tty);
-		if (tty->ops->write && tty->count > 0) {
-			tty_unlock(tty);
+		if (tty->ops->write && tty->count > 0)
 			tty->ops->write(tty, msg, strlen(msg));
-		} else
-			tty_unlock(tty);
+		tty_unlock(tty);
 		tty_write_unlock(tty);
 	}
 	return;
-- 
2.6.1

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