linux-kernel - [PATCH] char: pcmcia: scr24x_cs: Fix use-after-free in scr24x

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Date:   Thu, 15 Sep 2022 22:00:06 -0700
From:   Hyunwoo Kim <imv4bel@...il.com>
To:     lkundrak@...sk, arnd@...db.de, gregkh@...uxfoundation.org
Cc:     linux-kernel@...r.kernel.org, imv4bel@...il.com
Subject: [PATCH] char: pcmcia: scr24x_cs: Fix use-after-free in scr24x_fops

A race condition may occur if the user physically removes the
pcmcia device while calling open() for this char device node.

This is a race condition between the scr24x_open() function and
the scr24x_remove() function, which may eventually result in UAF.

So, add a mutex to the scr24x_open() and scr24x_remove() functions
to avoid race contidion of krefs.

Signed-off-by: Hyunwoo Kim <imv4bel@...il.com>
---
 drivers/char/pcmcia/scr24x_cs.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/drivers/char/pcmcia/scr24x_cs.c b/drivers/char/pcmcia/scr24x_cs.c
index 1bdce08fae3d..319e8d79048e 100644
--- a/drivers/char/pcmcia/scr24x_cs.c
+++ b/drivers/char/pcmcia/scr24x_cs.c
@@ -76,8 +76,10 @@ static int scr24x_open(struct inode *inode, struct file *filp)
 	struct scr24x_dev *dev = container_of(inode->i_cdev,
 				struct scr24x_dev, c_dev);
 
+	mutex_lock(&dev->lock);
 	kref_get(&dev->refcnt);
 	filp->private_data = dev;
+	mutex_unlock(&dev->lock);
 
 	return stream_open(inode, filp);
 }
@@ -298,9 +300,10 @@ static void scr24x_remove(struct pcmcia_device *link)
 	cdev_del(&dev->c_dev);
 	clear_bit(dev->devno, scr24x_minors);
 	dev->dev = NULL;
-	mutex_unlock(&dev->lock);
 
 	kref_put(&dev->refcnt, scr24x_delete);
+
+	mutex_unlock(&dev->lock);
 }
 
 static const struct pcmcia_device_id scr24x_ids[] = {
-- 
2.25.1