[PATCH v2] char: pcmcia: scr24x_cs: Fix use-after-free in scr24x_fops

[Hyunwoo Kim <imv4bel@gmail.com>]

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@gmail.com>
---
 drivers/char/pcmcia/scr24x_cs.c | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/drivers/char/pcmcia/scr24x_cs.c b/drivers/char/pcmcia/scr24x_cs.c
index 1bdce08fae3d..f630da554cc4 100644
--- a/drivers/char/pcmcia/scr24x_cs.c
+++ b/drivers/char/pcmcia/scr24x_cs.c
@@ -39,10 +39,12 @@ struct scr24x_dev {
 	struct mutex lock;
 	struct kref refcnt;
 	u8 __iomem *regs;
+	int removed;
 };
 
 #define SCR24X_DEVS 8
 static DECLARE_BITMAP(scr24x_minors, SCR24X_DEVS);
+static DEFINE_MUTEX(remove_mutex);
 
 static struct class *scr24x_class;
 static dev_t scr24x_devt;
@@ -76,8 +78,15 @@ 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(&remove_mutex);
+	if (dev->removed == 1) {
+		mutex_unlock(&remove_mutex);
+		return -ENODEV;
+	}
+
 	kref_get(&dev->refcnt);
 	filp->private_data = dev;
+	mutex_unlock(&remove_mutex);
 
 	return stream_open(inode, filp);
 }
@@ -292,6 +301,7 @@ static void scr24x_remove(struct pcmcia_device *link)
 {
 	struct scr24x_dev *dev = (struct scr24x_dev *)link->priv;
 
+	mutex_lock(&remove_mutex);
 	device_destroy(scr24x_class, MKDEV(MAJOR(scr24x_devt), dev->devno));
 	mutex_lock(&dev->lock);
 	pcmcia_disable_device(link);
@@ -301,6 +311,8 @@ static void scr24x_remove(struct pcmcia_device *link)
 	mutex_unlock(&dev->lock);
 
 	kref_put(&dev->refcnt, scr24x_delete);
+	dev->removed = 1;
+	mutex_unlock(&remove_mutex);
 }
 
 static const struct pcmcia_device_id scr24x_ids[] = {
-- 
2.25.1