From: Peter Hurley <peter@hurleysoftware.com>
Date: Fri, 5 Feb 2016 18:49:36 +0000 (-0800)
Subject: tty: Drop krefs for interrupted tty lock
X-Git-Url: http://drtracing.org/?a=commitdiff_plain;h=e9036d066236;p=deliverable%2Flinux.git

tty: Drop krefs for interrupted tty lock

When the tty lock is interrupted on attempted re-open, 2 tty krefs
are still held. Drop extra kref before returning failure from
tty_lock_interruptible(), and drop lookup kref before returning
failure from tty_open().

Fixes: 0bfd464d3fdd ("tty: Wait interruptibly for tty lock on reopen")
Reported-by: Dmitry Vyukov <dvyukov@google.com>
Signed-off-by: Peter Hurley <peter@hurleysoftware.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---

diff --git a/drivers/tty/tty_io.c b/drivers/tty/tty_io.c
index 5cec01c75691..a7eacef1bd22 100644
--- a/drivers/tty/tty_io.c
+++ b/drivers/tty/tty_io.c
@@ -2066,13 +2066,12 @@ retry_open:
 		if (tty) {
 			mutex_unlock(&tty_mutex);
 			retval = tty_lock_interruptible(tty);
+			tty_kref_put(tty);  /* drop kref from tty_driver_lookup_tty() */
 			if (retval) {
 				if (retval == -EINTR)
 					retval = -ERESTARTSYS;
 				goto err_unref;
 			}
-			/* safe to drop the kref from tty_driver_lookup_tty() */
-			tty_kref_put(tty);
 			retval = tty_reopen(tty);
 			if (retval < 0) {
 				tty_unlock(tty);
diff --git a/drivers/tty/tty_mutex.c b/drivers/tty/tty_mutex.c
index d2f3c4cd697f..dfa9ec03fa8e 100644
--- a/drivers/tty/tty_mutex.c
+++ b/drivers/tty/tty_mutex.c
@@ -21,10 +21,15 @@ EXPORT_SYMBOL(tty_lock);
 
 int tty_lock_interruptible(struct tty_struct *tty)
 {
+	int ret;
+
 	if (WARN(tty->magic != TTY_MAGIC, "L Bad %p\n", tty))
 		return -EIO;
 	tty_kref_get(tty);
-	return mutex_lock_interruptible(&tty->legacy_mutex);
+	ret = mutex_lock_interruptible(&tty->legacy_mutex);
+	if (ret)
+		tty_kref_put(tty);
+	return ret;
 }
 
 void __lockfunc tty_unlock(struct tty_struct *tty)