From: Dmitry Vyukov dvyukov@google.com
[ 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 dvyukov@google.com Cc: syzkaller@googlegroups.com Cc: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman gregkh@linuxfoundation.org Cc: Jiri Slaby jslaby@suse.com Cc: Peter Hurley peter@hurleysoftware.com Cc: One Thousand Gnomes gnomes@lxorguk.ukuu.org.uk Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org Signed-off-by: Sasha Levin alexander.levin@verizon.com --- drivers/tty/tty_ldisc.c | 7 +++++-- 1 file changed, 5 insertions(+), 2 deletions(-)
diff --git a/drivers/tty/tty_ldisc.c b/drivers/tty/tty_ldisc.c index c3956ca022e4..b0500a0a87b8 100644 --- a/drivers/tty/tty_ldisc.c +++ b/drivers/tty/tty_ldisc.c @@ -271,10 +271,13 @@ const struct file_operations tty_ldiscs_proc_fops = {
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);