lkml.org 
[lkml]   [2018]   [Nov]   [1]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
Patch in this message
/
From
Subject[PATCHv6 6/7] tty/ldsem: Add lockdep asserts for ldisc_sem
Date
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 <gregkh@linuxfoundation.org>
Cc: Jiri Slaby <jslaby@suse.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Dmitry Safonov <dima@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 9434d20cf3ca..45eda69b150c 100644
--- a/drivers/tty/tty_ldisc.c
+++ b/drivers/tty/tty_ldisc.c
@@ -478,6 +478,7 @@ 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)
@@ -499,6 +500,7 @@ 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;
@@ -622,6 +624,7 @@ 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;
/*
@@ -669,6 +672,7 @@ 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);
@@ -767,6 +771,10 @@ 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);
@@ -832,6 +840,7 @@ 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;
--
2.19.1
\
 
 \ /
  Last update: 2018-11-01 01:26    [W:0.152 / U:4.788 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site