From: Dmitry Vyukov <dvyukov@google.com>
To: gregkh@linuxfoundation.org, peter@hurleysoftware.com,
jslaby@suse.com, linux-kernel@vger.kernel.org
Cc: jslaby@suse.cz, andreyknvl@google.com, kcc@google.com,
glider@google.com, Dmitry Vyukov <dvyukov@google.com>
Subject: [PATCH] tty: fix data race in flush_to_ldisc
Date: Wed, 2 Sep 2015 19:53:42 +0200 [thread overview]
Message-ID: <1441216422-47412-1-git-send-email-dvyukov@google.com> (raw)
In-Reply-To: <55E715B2.1060304@hurleysoftware.com>
The data race is found with KernelThreadSanitizer (on rev 21bdb584af8c):
ThreadSanitizer: data-race in release_tty
Write of size 8 by thread T325 (K2579):
release_tty+0xf3/0x1c0 drivers/tty/tty_io.c:1688
tty_release+0x698/0x7c0 drivers/tty/tty_io.c:1920
__fput+0x15f/0x310 fs/file_table.c:207
____fput+0x1d/0x30 fs/file_table.c:243
task_work_run+0x115/0x130 kernel/task_work.c:123
do_notify_resume+0x73/0x80
tracehook_notify_resume include/linux/tracehook.h:190
do_notify_resume+0x73/0x80 arch/x86/kernel/signal.c:757
int_signal+0x12/0x17 arch/x86/entry/entry_64.S:326
Previous read of size 8 by thread T19 (K16):
flush_to_ldisc+0x29/0x300 drivers/tty/tty_buffer.c:472
process_one_work+0x47e/0x930 kernel/workqueue.c:2036
worker_thread+0xb0/0x900 kernel/workqueue.c:2170
kthread+0x150/0x170 kernel/kthread.c:207
flush_to_ldisc reads port->itty and checks that it is not NULL,
concurrently release_tty sets port->itty to NULL. It is possible
that flush_to_ldisc loads port->itty once, ensures that it is
not NULL, but then reloads it again and uses. The second load
can already return NULL, which will cause a crash.
Use READ_ONCE/WRITE_ONCE to read/update port->itty.
Signed-off-by: Dmitry Vyukov <dvyukov@google.com>
---
drivers/tty/tty_buffer.c | 2 +-
drivers/tty/tty_io.c | 2 +-
2 files changed, 2 insertions(+), 2 deletions(-)
diff --git a/drivers/tty/tty_buffer.c b/drivers/tty/tty_buffer.c
index 4cf263d..1f1031d 100644
--- a/drivers/tty/tty_buffer.c
+++ b/drivers/tty/tty_buffer.c
@@ -469,7 +469,7 @@ static void flush_to_ldisc(struct work_struct *work)
struct tty_struct *tty;
struct tty_ldisc *disc;
- tty = port->itty;
+ tty = READ_ONCE(port->itty);
if (tty == NULL)
return;
diff --git a/drivers/tty/tty_io.c b/drivers/tty/tty_io.c
index 57fc6ee..aad47df 100644
--- a/drivers/tty/tty_io.c
+++ b/drivers/tty/tty_io.c
@@ -1685,7 +1685,7 @@ static void release_tty(struct tty_struct *tty, int idx)
tty_driver_remove_tty(tty->driver, tty);
tty->port->itty = NULL;
if (tty->link)
- tty->link->port->itty = NULL;
+ WRITE_ONCE(tty->link->port->itty, NULL);
cancel_work_sync(&tty->port->buf.work);
tty_kref_put(tty->link);
--
2.5.0.457.gab17608
next prev parent reply other threads:[~2015-09-02 17:53 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-09-01 20:11 [PATCH] tty: fix data race in flush_to_ldisc Dmitry Vyukov
2015-09-02 14:18 ` Peter Hurley
2015-09-02 14:41 ` Dmitry Vyukov
2015-09-02 15:28 ` Peter Hurley
2015-09-02 17:53 ` Dmitry Vyukov [this message]
2015-09-03 0:50 ` Peter Hurley
2015-09-04 19:28 ` Dmitry Vyukov
2015-09-16 2:54 ` Peter Hurley
2015-09-17 11:42 ` Dmitry Vyukov
2015-09-02 17:55 ` Dmitry Vyukov
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