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.
An exception here is tty_ldisc_open(), as it's called without ldisc_sem
locked by tty_init_dev() => tty_ldisc_setup() for the tty->link.
It seem valid as tty_init_dev() will call tty_driver_install_tty()
which will find ops->install(). Install will establish tty->link in
pty_common_install(), just after allocation of slave tty with
alloc_tty_struct(). So, no one should have a reference to slave pty yet.
Cc: Greg Kroah-Hartman <gre...@linuxfoundation.org>
Cc: Jiri Slaby <jsl...@suse.com>
Cc: Peter Zijlstra <pet...@infradead.org>
Signed-off-by: Dmitry Safonov <d...@arista.com>
---
drivers/tty/tty_ldisc.c | 9 +++++++++
1 file changed, 9 insertions(+)
diff --git a/drivers/tty/tty_ldisc.c b/drivers/tty/tty_ldisc.c
index fc4c97cae01e..bc0171f984a1 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_exclusive(&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_exclusive(&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_exclusive(&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_exclusive(&tty->ldisc_sem);
ld = tty_ldisc_get(tty, disc);
if (IS_ERR(ld)) {
BUG_ON(disc == N_TTY);
@@ -760,6 +764,10 @@ int tty_ldisc_setup(struct tty_struct *tty, struct
tty_struct *o_tty)
return retval;
if (o_tty) {
+ /*
+ * Called without o_tty->ldisc_sem held, as o_tty has been
+ * just allocated and no one has a reference to it.
+ */
retval = tty_ldisc_open(o_tty, o_tty->ldisc);
if (retval) {
tty_ldisc_close(tty, tty->ldisc);
@@ -825,6 +833,7 @@ 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
