From 710dbb61210c0546cd1bfd9ebd0ad29207202d26 Mon Sep 17 00:00:00 2001 From: Peter Hurley Date: Sun, 10 Jan 2016 22:40:55 -0800 Subject: [PATCH] tty: Fix unsafe ldisc reference via ioctl(TIOCGETD) commit 5c17c861a357e9458001f021a7afa7aab9937439 upstream. ioctl(TIOCGETD) retrieves the line discipline id directly from the ldisc because the line discipline id (c_line) in termios is untrustworthy; userspace may have set termios via ioctl(TCSETS*) without actually changing the line discipline via ioctl(TIOCSETD). However, directly accessing the current ldisc via tty->ldisc is unsafe; the ldisc ptr dereferenced may be stale if the line discipline is changing via ioctl(TIOCSETD) or hangup. Wait for the line discipline reference (just like read() or write()) to retrieve the "current" line discipline id. Signed-off-by: Peter Hurley Signed-off-by: Greg Kroah-Hartman Signed-off-by: Ben Hutchings --- drivers/tty/tty_io.c | 24 +++++++++++++++++++++++- 1 file changed, 23 insertions(+), 1 deletion(-) diff --git a/drivers/tty/tty_io.c b/drivers/tty/tty_io.c index 6ab03229c837..1f9ee25b635e 100644 --- a/drivers/tty/tty_io.c +++ b/drivers/tty/tty_io.c @@ -2474,6 +2474,28 @@ static int tiocsetd(struct tty_struct *tty, int __user *p) return ret; } +/** + * tiocgetd - get line discipline + * @tty: tty device + * @p: pointer to user data + * + * Retrieves the line discipline id directly from the ldisc. + * + * Locking: waits for ldisc reference (in case the line discipline + * is changing or the tty is being hungup) + */ + +static int tiocgetd(struct tty_struct *tty, int __user *p) +{ + struct tty_ldisc *ld; + int ret; + + ld = tty_ldisc_ref_wait(tty); + ret = put_user(ld->ops->num, p); + tty_ldisc_deref(ld); + return ret; +} + /** * send_break - performed time break * @tty: device to break on @@ -2684,7 +2706,7 @@ long tty_ioctl(struct file *file, unsigned int cmd, unsigned long arg) case TIOCGSID: return tiocgsid(tty, real_tty, p); case TIOCGETD: - return put_user(tty->ldisc->ops->num, (int __user *)p); + return tiocgetd(tty, p); case TIOCSETD: return tiocsetd(tty, p); case TIOCVHANGUP: -- 2.39.2