linux-kernel - Re: BUG: KASAN: i2c dev use after free

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Message-ID: <20190304153714.GD13452@kadam>
Date:   Mon, 4 Mar 2019 18:37:14 +0300
From:   Dan Carpenter <dan.carpenter@...cle.com>
To:     Anders Roxell <anders.roxell@...aro.org>
Cc:     erico.nunes@...acom.ind.br, wsa@...-dreams.de,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: BUG: KASAN: i2c dev use after free

I wasn't trying to fix anything so complicated as this, it was a
more obvious use after free.  It does feel intuitively that we should
call device_destroy() before the cdev_del() so that it's in the reverse
order from how it was allocated but I don't see any reason to think
that will make a difference.

---
 drivers/i2c/i2c-dev.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/i2c/i2c-dev.c b/drivers/i2c/i2c-dev.c
index 3f7b9af11137..7e85e2cf26c1 100644
--- a/drivers/i2c/i2c-dev.c
+++ b/drivers/i2c/i2c-dev.c
@@ -687,9 +687,9 @@ static int i2cdev_detach_adapter(struct device *dev, void *dummy)
 	if (!i2c_dev) /* attach_adapter must have failed */
 		return 0;
 
+	device_destroy(i2c_dev_class, MKDEV(I2C_MAJOR, adap->nr));
 	cdev_del(&i2c_dev->cdev);
 	put_i2c_dev(i2c_dev);
-	device_destroy(i2c_dev_class, MKDEV(I2C_MAJOR, adap->nr));
 
 	pr_debug("i2c-dev: adapter [%s] unregistered\n", adap->name);
 	return 0;
-- 
2.17.1