4.20-stable review patch. If anyone has any objections, please let me know.
------------------
From: Dmitry Safonov dima@arista.com
commit d3736d82e8169768218ee0ef68718875918091a0 upstream.
Try to get reference for ldisc during tty_reopen(). If ldisc present, we don't need to do tty_ldisc_reinit() and lock the write side for line discipline semaphore. Effectively, it optimizes fast-path for tty_reopen(), but more importantly it won't interrupt ongoing IO on the tty as no ldisc change is needed. Fixes user-visible issue when tty_reopen() interrupted login process for user with a long password, observed and reported by Lukas.
Fixes: c96cf923a98d ("tty: Don't block on IO when ldisc change is pending") Fixes: 83d817f41070 ("tty: Hold tty_ldisc_lock() during tty_reopen()") Cc: Jiri Slaby jslaby@suse.com Reported-by: Lukas F. Hartmann lukas@mntmn.com Tested-by: Lukas F. Hartmann lukas@mntmn.com Cc: stable stable@vger.kernel.org Signed-off-by: Dmitry Safonov dima@arista.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- drivers/tty/tty_io.c | 22 ++++++++++++++-------- 1 file changed, 14 insertions(+), 8 deletions(-)
--- a/drivers/tty/tty_io.c +++ b/drivers/tty/tty_io.c @@ -1256,7 +1256,8 @@ static void tty_driver_remove_tty(struct static int tty_reopen(struct tty_struct *tty) { struct tty_driver *driver = tty->driver; - int retval; + struct tty_ldisc *ld; + int retval = 0;
if (driver->type == TTY_DRIVER_TYPE_PTY && driver->subtype == PTY_TYPE_MASTER) @@ -1268,13 +1269,18 @@ static int tty_reopen(struct tty_struct if (test_bit(TTY_EXCLUSIVE, &tty->flags) && !capable(CAP_SYS_ADMIN)) return -EBUSY;
- retval = tty_ldisc_lock(tty, 5 * HZ); - if (retval) - return retval; - - if (!tty->ldisc) - retval = tty_ldisc_reinit(tty, tty->termios.c_line); - tty_ldisc_unlock(tty); + ld = tty_ldisc_ref_wait(tty); + if (ld) { + tty_ldisc_deref(ld); + } else { + retval = tty_ldisc_lock(tty, 5 * HZ); + if (retval) + return retval; + + if (!tty->ldisc) + retval = tty_ldisc_reinit(tty, tty->termios.c_line); + tty_ldisc_unlock(tty); + }
if (retval == 0) tty->count++;