linux-kernel - [PATCH] tty: don't leak cdev in tty_cdev

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Message-Id: <1441631317-6238-1-git-send-email-chianglungyu@gmail.com>
Date:	Mon,  7 Sep 2015 13:08:37 +0000
From:	Leon Yu <chianglungyu@...il.com>
To:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Jiri Slaby <jslaby@...e.com>, linux-kernel@...r.kernel.org,
	linux-serial@...r.kernel.org
Cc:	Leon Yu <chianglungyu@...il.com>, Richard Watts <rrw@...esim.co.uk>
Subject: [PATCH] tty: don't leak cdev in tty_cdev_add()

Commit a3a10ce3429e ("Avoid usb reset crashes by making tty_io cdevs truly
dynamic") which mixes using cdev_alloc() and cdev_init() is problematic.
Subsequent call to cdev_init() after cdev_alloc() sets kobj release method
from cdev_dynamic_release() to cdev_default_release() and thus makes it
impossible to free allocated cdev.

This patch also consolidates error path of cdev_add() as cdev can also leak
here if things went wrong.

Signed-off-by: Leon Yu <chianglungyu@...il.com>
Fixes: a3a10ce3429e ("Avoid usb reset crashes by making tty_io cdevs truly dynamic")
---
 drivers/tty/tty_io.c | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/drivers/tty/tty_io.c b/drivers/tty/tty_io.c
index 02785d8..17b0272 100644
--- a/drivers/tty/tty_io.c
+++ b/drivers/tty/tty_io.c
@@ -3151,13 +3151,18 @@ struct class *tty_class;
 static int tty_cdev_add(struct tty_driver *driver, dev_t dev,
 		unsigned int index, unsigned int count)
 {
+	int err;
+
 	/* init here, since reused cdevs cause crashes */
 	driver->cdevs[index] = cdev_alloc();
 	if (!driver->cdevs[index])
 		return -ENOMEM;
-	cdev_init(driver->cdevs[index], &tty_fops);
+	driver->cdevs[index]->ops = &tty_fops;
 	driver->cdevs[index]->owner = driver->owner;
-	return cdev_add(driver->cdevs[index], dev, count);
+	err = cdev_add(driver->cdevs[index], dev, count);
+	if (err)
+		kobject_put(&driver->cdevs[index]->kobj);
+	return err;
 }
 
 /**
-- 
2.5.1

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