[PATCHv2 3/4] tty/lockdep: Add ldisc_sem asserts

Dmitry Safonov
2018-09-03T16:53:09Z

Make sure under CONFIG_LOCKDEP that each change to line discipline
is done with held write semaphor.
Otherwise potential reader will have a good time dereferencing
incomplete/uninitialized ldisc.

Exception here is tty_ldisc_open(), as it's called without ldisc_sem
locked by tty_init_dev() for the tty->link.

Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Jiri Slaby <jslaby@suse.com>
Signed-off-by: Dmitry Safonov <dima@arista.com>
---
drivers/tty/tty_ldisc.c | 5 +++++
1 file changed, 5 insertions(+)

diff --git a/drivers/tty/tty_ldisc.c b/drivers/tty/tty_ldisc.c
index fc4c97cae01e..202cb645582f 100644
--- a/drivers/tty/tty_ldisc.c
+++ b/drivers/tty/tty_ldisc.c
@@ -471,6 +471,7 @@ static int tty_ldisc_open(struct tty_struct *tty, struct tty_ldisc *ld)

static void tty_ldisc_close(struct tty_struct *tty, struct tty_ldisc *ld)
{
+ lockdep_assert_held(&tty->ldisc_sem);
WARN_ON(!test_bit(TTY_LDISC_OPEN, &tty->flags));
clear_bit(TTY_LDISC_OPEN, &tty->flags);
if (ld->ops->close)
@@ -492,6 +493,7 @@ static int tty_ldisc_failto(struct tty_struct *tty, int ld)
struct tty_ldisc *disc = tty_ldisc_get(tty, ld);
int r;

+ lockdep_assert_held(&tty->ldisc_sem);
if (IS_ERR(disc))
return PTR_ERR(disc);
tty->ldisc = disc;
@@ -615,6 +617,7 @@ EXPORT_SYMBOL_GPL(tty_set_ldisc);
*/
static void tty_ldisc_kill(struct tty_struct *tty)
{
+ lockdep_assert_held(&tty->ldisc_sem);
if (!tty->ldisc)
return;
/*
@@ -662,6 +665,7 @@ int tty_ldisc_reinit(struct tty_struct *tty, int disc)
struct tty_ldisc *ld;
int retval;

+ lockdep_assert_held(&tty->ldisc_sem);
ld = tty_ldisc_get(tty, disc);
if (IS_ERR(ld)) {
BUG_ON(disc == N_TTY);
@@ -825,6 +829,7 @@ int tty_ldisc_init(struct tty_struct *tty)
*/
void tty_ldisc_deinit(struct tty_struct *tty)
{
+ /* no ldisc_sem, tty is being destroyed */
if (tty->ldisc)
tty_ldisc_put(tty->ldisc);
tty->ldisc = NULL;
--
2.13.6