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From:   Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To:     linux-kernel@vger.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        stable@vger.kernel.org, Tyrel Datwyler <tyreld@linux.ibm.com>,
        Sasha Levin <sashal@kernel.org>
Subject: [PATCH 4.9 037/139] tty: hvcs: Dont NULL tty->driver_data until hvcs_cleanup()
Date:   Tue, 27 Oct 2020 14:48:51 +0100
Message-Id: <20201027134903.902337999@linuxfoundation.org>
In-Reply-To: <20201027134902.130312227@linuxfoundation.org>
References: <20201027134902.130312227@linuxfoundation.org>
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From: Tyrel Datwyler <tyreld@linux.ibm.com>

[ Upstream commit 63ffcbdad738e3d1c857027789a2273df3337624 ]

The code currently NULLs tty->driver_data in hvcs_close() with the
intent of informing the next call to hvcs_open() that device needs to be
reconfigured. However, when hvcs_cleanup() is called we copy hvcsd from
tty->driver_data which was previoulsy NULLed by hvcs_close() and our
call to tty_port_put(&hvcsd->port) doesn't actually do anything since
&hvcsd->port ends up translating to NULL by chance. This has the side
effect that when hvcs_remove() is called we have one too many port
references preventing hvcs_destuct_port() from ever being called. This
also prevents us from reusing the /dev/hvcsX node in a future
hvcs_probe() and we can eventually run out of /dev/hvcsX devices.

Fix this by waiting to NULL tty->driver_data in hvcs_cleanup().

Fixes: 27bf7c43a19c ("TTY: hvcs, add tty install")
Signed-off-by: Tyrel Datwyler <tyreld@linux.ibm.com>
Link: https://lore.kernel.org/r/20200820234643.70412-1-tyreld@linux.ibm.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 drivers/tty/hvc/hvcs.c | 14 +++++++-------
 1 file changed, 7 insertions(+), 7 deletions(-)

diff --git a/drivers/tty/hvc/hvcs.c b/drivers/tty/hvc/hvcs.c
index 3c4d7c2b4ade8..de05196738da5 100644
--- a/drivers/tty/hvc/hvcs.c
+++ b/drivers/tty/hvc/hvcs.c
@@ -1232,13 +1232,6 @@ static void hvcs_close(struct tty_struct *tty, struct file *filp)
 
 		tty_wait_until_sent(tty, HVCS_CLOSE_WAIT);
 
-		/*
-		 * This line is important because it tells hvcs_open that this
-		 * device needs to be re-configured the next time hvcs_open is
-		 * called.
-		 */
-		tty->driver_data = NULL;
-
 		free_irq(irq, hvcsd);
 		return;
 	} else if (hvcsd->port.count < 0) {
@@ -1254,6 +1247,13 @@ static void hvcs_cleanup(struct tty_struct * tty)
 {
 	struct hvcs_struct *hvcsd = tty->driver_data;
 
+	/*
+	 * This line is important because it tells hvcs_open that this
+	 * device needs to be re-configured the next time hvcs_open is
+	 * called.
+	 */
+	tty->driver_data = NULL;
+
 	tty_port_put(&hvcsd->port);
 }
 
-- 
2.25.1