[PATCH 4.19 05/81] USB: yurex: fix NULL-derefs on disconnect

[Greg Kroah-Hartman]

From: Johan Hovold <jo...@kernel.org>

commit aafb00a977cf7d81821f7c9d12e04c558c22dc3c upstream.

The driver was using its struct usb_interface pointer as an inverted
disconnected flag, but was setting it to NULL without making sure all
code paths that used it were done with it.

Before commit ef61eb43ada6 ("USB: yurex: Fix protection fault after
device removal") this included the interrupt-in completion handler, but
there are further accesses in dev_err and dev_dbg statements in
yurex_write() and the driver-data destructor (sic!).

Fix this by unconditionally stopping also the control URB at disconnect
and by using a dedicated disconnected flag.

Note that we need to take a reference to the struct usb_interface to
avoid a use-after-free in the destructor whenever the device was
disconnected while the character device was still open.

Fixes: aadd6472d904 ("USB: yurex.c: remove dbg() usage")
Fixes: 45714104b9e8 ("USB: yurex.c: remove err() usage")
Cc: stable <sta...@vger.kernel.org>     # 3.5: ef61eb43ada6
Signed-off-by: Johan Hovold <jo...@kernel.org>
Link: https://lore.kernel.org/r/20191009153848.8664-6-jo...@kernel.org
Signed-off-by: Greg Kroah-Hartman <gre...@linuxfoundation.org>

---
 drivers/usb/misc/yurex.c |   11 +++++++----
 1 file changed, 7 insertions(+), 4 deletions(-)

--- a/drivers/usb/misc/yurex.c
+++ b/drivers/usb/misc/yurex.c
@@ -60,6 +60,7 @@ struct usb_yurex {
 
        struct kref             kref;
        struct mutex            io_mutex;
+       unsigned long           disconnected:1;
        struct fasync_struct    *async_queue;
        wait_queue_head_t       waitq;
 
@@ -107,6 +108,7 @@ static void yurex_delete(struct kref *kr
                                dev->int_buffer, dev->urb->transfer_dma);
                usb_free_urb(dev->urb);
        }
+       usb_put_intf(dev->interface);
        usb_put_dev(dev->udev);
        kfree(dev);
 }
@@ -205,7 +207,7 @@ static int yurex_probe(struct usb_interf
        init_waitqueue_head(&dev->waitq);
 
        dev->udev = usb_get_dev(interface_to_usbdev(interface));
-       dev->interface = interface;
+       dev->interface = usb_get_intf(interface);
 
        /* set up the endpoint information */
        iface_desc = interface->cur_altsetting;
@@ -316,8 +318,9 @@ static void yurex_disconnect(struct usb_
 
        /* prevent more I/O from starting */
        usb_poison_urb(dev->urb);
+       usb_poison_urb(dev->cntl_urb);
        mutex_lock(&dev->io_mutex);
-       dev->interface = NULL;
+       dev->disconnected = 1;
        mutex_unlock(&dev->io_mutex);
 
        /* wakeup waiters */
@@ -405,7 +408,7 @@ static ssize_t yurex_read(struct file *f
        dev = file->private_data;
 
        mutex_lock(&dev->io_mutex);
-       if (!dev->interface) {          /* already disconnected */
+       if (dev->disconnected) {                /* already disconnected */
                mutex_unlock(&dev->io_mutex);
                return -ENODEV;
        }
@@ -440,7 +443,7 @@ static ssize_t yurex_write(struct file *
                goto error;
 
        mutex_lock(&dev->io_mutex);
-       if (!dev->interface) {          /* already disconnected */
+       if (dev->disconnected) {                /* already disconnected */
                mutex_unlock(&dev->io_mutex);
                retval = -ENODEV;
                goto error;