[PATCH 1/1] TTY: fix PTY hangup vs close race

[Jiri Slaby]

Commit d3bda5298 (TTY: get rid of BTM around devpts_*) moved
devpts_pty_kill out of BTM, but the BTM was not protecting only
devpts_pty_kill, but also tty->link. Hence move the function back at
this late stage until this gets resolved properly some time later.

I was confused by tty_vhangup(tty->link) outside BTM. But inside of
tty_vhangup, there is a check for tty == NULL. But we cannot add such
a check here. We have to have the tty and free the devpts node...

Signed-off-by: Jiri Slaby <jslaby@xxxxxxx>
Reported-by: Sasha Levin <levinsasha928@xxxxxxxxx>
---
 drivers/tty/pty.c |    3 ++-
 1 files changed, 2 insertions(+), 1 deletions(-)

diff --git a/drivers/tty/pty.c b/drivers/tty/pty.c
index fa1bd2e..95037aa 100644
--- a/drivers/tty/pty.c
+++ b/drivers/tty/pty.c
@@ -54,8 +54,9 @@ static void pty_close(struct tty_struct *tty, struct file *filp)
 	wake_up_interruptible(&tty->link->write_wait);
 	if (tty->driver->subtype == PTY_TYPE_MASTER) {
 		set_bit(TTY_OTHER_CLOSED, &tty->flags);
-		tty_unlock();
+		/* BTM protects tty->link here */
 		devpts_pty_kill(tty->link);
+		tty_unlock();
 		tty_vhangup(tty->link);
 		tty_lock();
 	}
-- 
1.7.9


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