Patch "USB: chaoskey: fail open after removal" has been added to the 5.15-stable tree

[Sasha Levin <sashal@xxxxxxxxxx>]

This is a note to let you know that I've just added the patch titled

    USB: chaoskey: fail open after removal

to the 5.15-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     usb-chaoskey-fail-open-after-removal.patch
and it can be found in the queue-5.15 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.



commit 910285eab11db5823127b94bdaf790b5cd05e25c
Author: Oliver Neukum <oneukum@xxxxxxxx>
Date:   Wed Oct 2 15:21:41 2024 +0200

    USB: chaoskey: fail open after removal
    
    [ Upstream commit 422dc0a4d12d0b80dd3aab3fe5943f665ba8f041 ]
    
    chaoskey_open() takes the lock only to increase the
    counter of openings. That means that the mutual exclusion
    with chaoskey_disconnect() cannot prevent an increase
    of the counter and chaoskey_open() returning a success.
    
    If that race is hit, chaoskey_disconnect() will happily
    free all resources associated with the device after
    it has dropped the lock, as it has read the counter
    as zero.
    
    To prevent this race chaoskey_open() has to check
    the presence of the device under the lock.
    However, the current per device lock cannot be used,
    because it is a part of the data structure to be
    freed. Hence an additional global mutex is needed.
    The issue is as old as the driver.
    
    Signed-off-by: Oliver Neukum <oneukum@xxxxxxxx>
    Reported-by: syzbot+422188bce66e76020e55@xxxxxxxxxxxxxxxxxxxxxxxxx
    Closes: https://syzkaller.appspot.com/bug?extid=422188bce66e76020e55
    Fixes: 66e3e591891da ("usb: Add driver for Altus Metrum ChaosKey device (v2)")
    Rule: add
    Link: https://lore.kernel.org/stable/20241002132201.552578-1-oneukum%40suse.com
    Link: https://lore.kernel.org/r/20241002132201.552578-1-oneukum@xxxxxxxx
    Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
    Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>

diff --git a/drivers/usb/misc/chaoskey.c b/drivers/usb/misc/chaoskey.c
index 87067c3d6109b..32fa7fd50c380 100644
--- a/drivers/usb/misc/chaoskey.c
+++ b/drivers/usb/misc/chaoskey.c
@@ -27,6 +27,8 @@ static struct usb_class_driver chaoskey_class;
 static int chaoskey_rng_read(struct hwrng *rng, void *data,
 			     size_t max, bool wait);
 
+static DEFINE_MUTEX(chaoskey_list_lock);
+
 #define usb_dbg(usb_if, format, arg...) \
 	dev_dbg(&(usb_if)->dev, format, ## arg)
 
@@ -231,6 +233,7 @@ static void chaoskey_disconnect(struct usb_interface *interface)
 	if (dev->hwrng_registered)
 		hwrng_unregister(&dev->hwrng);
 
+	mutex_lock(&chaoskey_list_lock);
 	usb_deregister_dev(interface, &chaoskey_class);
 
 	usb_set_intfdata(interface, NULL);
@@ -245,6 +248,7 @@ static void chaoskey_disconnect(struct usb_interface *interface)
 	} else
 		mutex_unlock(&dev->lock);
 
+	mutex_unlock(&chaoskey_list_lock);
 	usb_dbg(interface, "disconnect done");
 }
 
@@ -252,6 +256,7 @@ static int chaoskey_open(struct inode *inode, struct file *file)
 {
 	struct chaoskey *dev;
 	struct usb_interface *interface;
+	int rv = 0;
 
 	/* get the interface from minor number and driver information */
 	interface = usb_find_interface(&chaoskey_driver, iminor(inode));
@@ -267,18 +272,23 @@ static int chaoskey_open(struct inode *inode, struct file *file)
 	}
 
 	file->private_data = dev;
+	mutex_lock(&chaoskey_list_lock);
 	mutex_lock(&dev->lock);
-	++dev->open;
+	if (dev->present)
+		++dev->open;
+	else
+		rv = -ENODEV;
 	mutex_unlock(&dev->lock);
+	mutex_unlock(&chaoskey_list_lock);
 
-	usb_dbg(interface, "open success");
-	return 0;
+	return rv;
 }
 
 static int chaoskey_release(struct inode *inode, struct file *file)
 {
 	struct chaoskey *dev = file->private_data;
 	struct usb_interface *interface;
+	int rv = 0;
 
 	if (dev == NULL)
 		return -ENODEV;
@@ -287,14 +297,15 @@ static int chaoskey_release(struct inode *inode, struct file *file)
 
 	usb_dbg(interface, "release");
 
+	mutex_lock(&chaoskey_list_lock);
 	mutex_lock(&dev->lock);
 
 	usb_dbg(interface, "open count at release is %d", dev->open);
 
 	if (dev->open <= 0) {
 		usb_dbg(interface, "invalid open count (%d)", dev->open);
-		mutex_unlock(&dev->lock);
-		return -ENODEV;
+		rv = -ENODEV;
+		goto bail;
 	}
 
 	--dev->open;
@@ -303,13 +314,15 @@ static int chaoskey_release(struct inode *inode, struct file *file)
 		if (dev->open == 0) {
 			mutex_unlock(&dev->lock);
 			chaoskey_free(dev);
-		} else
-			mutex_unlock(&dev->lock);
-	} else
-		mutex_unlock(&dev->lock);
-
+			goto destruction;
+		}
+	}
+bail:
+	mutex_unlock(&dev->lock);
+destruction:
+	mutex_lock(&chaoskey_list_lock);
 	usb_dbg(interface, "release success");
-	return 0;
+	return rv;
 }
 
 static void chaos_read_callback(struct urb *urb)