Re: [PATCH 1/4] tty: Drop tty->count on tty_reopen() failure

On Wed, 2018-08-29 at 16:38 +0200, Jiri Slaby wrote:

On 08/29/2018, 04:23 AM, Dmitry Safonov wrote:

quoted

In case of tty_ldisc_reinit() failure, tty->count should be
decremented
back, otherwise we will never release_tty().
Never seen it in the real life, but it seems not really hard to
hit.

I did see it. And this fixes it.

Thanks, I'll add your tested-by, if I'll have to resend.

quoted

Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Jiri Slaby <redacted>
Cc: stable@vger.kernel.org
Signed-off-by: Dmitry Safonov <redacted>
---
 drivers/tty/tty_io.c | 11 ++++++++---
 1 file changed, 8 insertions(+), 3 deletions(-)

diff --git a/drivers/tty/tty_io.c b/drivers/tty/tty_io.c
index 32bc3e3fe4d3..5e5da9acaf0a 100644
--- a/drivers/tty/tty_io.c
+++ b/drivers/tty/tty_io.c

@@ -1255,6 +1255,7 @@ static void tty_driver_remove_tty(struct

tty_driver *driver, struct tty_struct *
 static int tty_reopen(struct tty_struct *tty)
 {
 	struct tty_driver *driver = tty->driver;
+	int retval;
 
 	if (driver->type == TTY_DRIVER_TYPE_PTY &&
 	    driver->subtype == PTY_TYPE_MASTER)

@@ -1268,10 +1269,14 @@ static int tty_reopen(struct tty_struct

*tty)
 
 	tty->count++;
 
-	if (!tty->ldisc)
-		return tty_ldisc_reinit(tty, tty->termios.c_line);
+	if (tty->ldisc)
+		return 0;
 
-	return 0;
+	retval = tty_ldisc_reinit(tty, tty->termios.c_line);
+	if (retval)
+		tty->count--;

I would just do:
  if (!retval)
    tty->count++;
here. Nobody from ldiscs should rely on tty->count.

I thought about that and probably should have described in commit
message why I haven't done that: I prefer to keep it as was as I did Cc
stable tree - to keep the chance of regression to minimum.

I agree that your way is cleaner, but probably it may be done as
cleanup on top for linux-next..

-- 
Thanks,
             Dmitry