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USB: legousbtower: fix use-after-free on disconnect race

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mutex_unlock() may access the mutex structure after releasing the lock
and therefore cannot be used to manage lifetime of objects directly
(unlike spinlocks and refcounts). [1][2]

Use a kref to release the driver data to avoid use-after-free in
mutex_unlock() when release() races with disconnect().

[1] a51749ab34 ("locking/mutex: Document that mutex_unlock() is
                   non-atomic")
[2] 2b9d9e0a9b ("locking/mutex: Clarify that mutex_unlock(), and most
                   other sleeping locks, can still use the lock object
                   after it's unlocked")

Fixes: 18bcbcfe9c ("USB: misc: legousbtower: semaphore to mutex")
Cc: stable <stable@kernel.org>
Cc: Daniel Walker <dwalker@mvista.com>
Signed-off-by: Johan Hovold <johan@kernel.org>
Link: https://patch.msgid.link/20260622152612.116422-5-johan@kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Johan Hovold
2026-06-22 17:26:12 +02:00
committed by Greg Kroah-Hartman
parent 19bdfc7b3c
commit 62fc8eb1b1
1 changed files with 19 additions and 18 deletions
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37
drivers/usb/misc/legousbtower.c
View File

@@ -185,6 +185,7 @@ MODULE_DEVICE_TABLE(usb, tower_table);
/* Structure to hold all of our device specific stuff */
struct lego_usb_tower {
struct kref kref;
struct mutex lock; /* locks this structure */
struct usb_device *udev; /* save off the usb device pointer */
unsigned char minor; /* the starting minor number for this device */
@@ -220,7 +221,6 @@ struct lego_usb_tower {
/* local function prototypes */
static ssize_t tower_read(struct file *file, char __user *buffer, size_t count, loff_t *ppos);
static ssize_t tower_write(struct file *file, const char __user *buffer, size_t count, loff_t *ppos);
static inline void tower_delete(struct lego_usb_tower *dev);
static int tower_open(struct inode *inode, struct file *file);
static int tower_release(struct inode *inode, struct file *file);
static __poll_t tower_poll(struct file *file, poll_table *wait);
@@ -286,8 +286,10 @@ static inline void lego_usb_tower_debug_data(struct device *dev,
/*
* tower_delete
*/
static inline void tower_delete(struct lego_usb_tower *dev)
static inline void tower_delete(struct kref *kref)
{
struct lego_usb_tower *dev = container_of(kref, struct lego_usb_tower, kref);
/* free data structures */
usb_free_urb(dev->interrupt_in_urb);
usb_free_urb(dev->interrupt_out_urb);
@@ -381,6 +383,8 @@ static int tower_open(struct inode *inode, struct file *file)
dev->open_count = 1;
kref_get(&dev->kref);
unlock_exit:
mutex_unlock(&dev->lock);
@@ -404,14 +408,8 @@ static int tower_release(struct inode *inode, struct file *file)
mutex_lock(&dev->lock);
if (dev->disconnected) {
/* the device was unplugged before the file was released */
/* unlock here as tower_delete frees dev */
mutex_unlock(&dev->lock);
tower_delete(dev);
goto exit;
}
if (dev->disconnected)
goto out_unlock;
/* wait until write transfer is finished */
if (dev->interrupt_out_busy) {
@@ -425,7 +423,9 @@ static int tower_release(struct inode *inode, struct file *file)
dev->open_count = 0;
out_unlock:
mutex_unlock(&dev->lock);
kref_put(&dev->kref, tower_delete);
exit:
return retval;
}
@@ -752,6 +752,7 @@ static int tower_probe(struct usb_interface *interface, const struct usb_device_
if (!dev)
goto exit;
kref_init(&dev->kref);
mutex_init(&dev->lock);
dev->udev = usb_get_dev(udev);
spin_lock_init(&dev->read_buffer_lock);
@@ -828,7 +829,7 @@ static int tower_probe(struct usb_interface *interface, const struct usb_device_
return retval;
error:
tower_delete(dev);
kref_put(&dev->kref, tower_delete);
return retval;
}
@@ -856,18 +857,18 @@ static void tower_disconnect(struct usb_interface *interface)
mutex_lock(&dev->lock);
/* if the device is not opened, then we clean up right now */
if (!dev->open_count) {
mutex_unlock(&dev->lock);
tower_delete(dev);
} else {
dev->disconnected = 1;
dev->disconnected = 1;
if (dev->open_count) {
/* wake up pollers */
wake_up_interruptible_all(&dev->read_wait);
wake_up_interruptible_all(&dev->write_wait);
mutex_unlock(&dev->lock);
}
mutex_unlock(&dev->lock);
kref_put(&dev->kref, tower_delete);
dev_info(&interface->dev, "LEGO USB Tower #%d now disconnected\n",
(minor - LEGO_USB_TOWER_MINOR_BASE));
}