4.9-stable review patch. If anyone has any objections, please let me know.
------------------ From: Dmitry Vyukov <[email protected]> [ Upstream commit a4a3e061149f09c075f108b6f1cf04d9739a6bc2 ] tty_ldisc_ref_wait() checks tty->ldisc under tty->ldisc_sem. But if ldisc==NULL it releases them sem and reloads tty->ldisc without holding the sem. This is wrong and can lead to returning non-NULL ldisc without protection. Don't reload tty->ldisc second time. Signed-off-by: Dmitry Vyukov <[email protected]> Cc: [email protected] Cc: [email protected] Cc: Greg Kroah-Hartman <[email protected]> Cc: Jiri Slaby <[email protected]> Cc: Peter Hurley <[email protected]> Cc: One Thousand Gnomes <[email protected]> Signed-off-by: Greg Kroah-Hartman <[email protected]> Signed-off-by: Sasha Levin <[email protected]> Signed-off-by: Greg Kroah-Hartman <[email protected]> --- drivers/tty/tty_ldisc.c | 7 +++++-- 1 file changed, 5 insertions(+), 2 deletions(-) --- a/drivers/tty/tty_ldisc.c +++ b/drivers/tty/tty_ldisc.c @@ -271,10 +271,13 @@ const struct file_operations tty_ldiscs_ struct tty_ldisc *tty_ldisc_ref_wait(struct tty_struct *tty) { + struct tty_ldisc *ld; + ldsem_down_read(&tty->ldisc_sem, MAX_SCHEDULE_TIMEOUT); - if (!tty->ldisc) + ld = tty->ldisc; + if (!ld) ldsem_up_read(&tty->ldisc_sem); - return tty->ldisc; + return ld; } EXPORT_SYMBOL_GPL(tty_ldisc_ref_wait);
