From ee0c1a65cf95230d5eb3d9de94fd2ead9a428c67 Mon Sep 17 00:00:00 2001 From: Peter Hurley Date: Wed, 11 Nov 2015 08:03:54 -0500 Subject: [PATCH] tty: Fix tty_send_xchar() lock order inversion The correct lock order is atomic_write_lock => termios_rwsem, as established by tty_write() => n_tty_write(). Fixes: c274f6ef1c666 ("tty: Hold termios_rwsem for tcflow(TCIxxx)") Reported-and-Tested-by: Dmitry Vyukov Cc: # v3.18+ Signed-off-by: Peter Hurley Signed-off-by: Greg Kroah-Hartman --- drivers/tty/tty_io.c | 4 ++++ drivers/tty/tty_ioctl.c | 4 ---- 2 files changed, 4 insertions(+), 4 deletions(-) diff --git a/drivers/tty/tty_io.c b/drivers/tty/tty_io.c index 0c41dbcb90b8..bcc8e1e8bb72 100644 --- a/drivers/tty/tty_io.c +++ b/drivers/tty/tty_io.c @@ -1282,18 +1282,22 @@ int tty_send_xchar(struct tty_struct *tty, char ch) int was_stopped = tty->stopped; if (tty->ops->send_xchar) { + down_read(&tty->termios_rwsem); tty->ops->send_xchar(tty, ch); + up_read(&tty->termios_rwsem); return 0; } if (tty_write_lock(tty, 0) < 0) return -ERESTARTSYS; + down_read(&tty->termios_rwsem); if (was_stopped) start_tty(tty); tty->ops->write(tty, &ch, 1); if (was_stopped) stop_tty(tty); + up_read(&tty->termios_rwsem); tty_write_unlock(tty); return 0; } diff --git a/drivers/tty/tty_ioctl.c b/drivers/tty/tty_ioctl.c index 9c5aebfe7053..1445dd39aa62 100644 --- a/drivers/tty/tty_ioctl.c +++ b/drivers/tty/tty_ioctl.c @@ -1147,16 +1147,12 @@ int n_tty_ioctl_helper(struct tty_struct *tty, struct file *file, spin_unlock_irq(&tty->flow_lock); break; case TCIOFF: - down_read(&tty->termios_rwsem); if (STOP_CHAR(tty) != __DISABLED_CHAR) retval = tty_send_xchar(tty, STOP_CHAR(tty)); - up_read(&tty->termios_rwsem); break; case TCION: - down_read(&tty->termios_rwsem); if (START_CHAR(tty) != __DISABLED_CHAR) retval = tty_send_xchar(tty, START_CHAR(tty)); - up_read(&tty->termios_rwsem); break; default: return -EINVAL; -- 2.25.1