[PATCH 1/3] USB: usb-skeleton: fix NULL-deref on disconnect

[Johan Hovold]

The driver was using its struct usb_interface pointer as an inverted
disconnected flag and was setting it to NULL before making sure all
completion handlers had run. This could lead to NULL-pointer
dereferences in the dev_err() statements in the completion handlers
which relies on said pointer.

Fix this by using a dedicated disconnected flag.

Note that this is also addresses a NULL-pointer dereference at release()
and a struct usb_interface reference leak introduced by a recent runtime
PM fix, which depends on and should have been submitted together with
this patch.

Fixes: 4212cd74ca6f ("USB: usb-skeleton.c: remove err() usage")
Fixes: 5c290a5e42c3 ("USB: usb-skeleton: fix runtime PM after driver unbind")
Cc: stable <sta...@vger.kernel.org>
Signed-off-by: Johan Hovold <jo...@kernel.org>
---
 drivers/usb/usb-skeleton.c | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/drivers/usb/usb-skeleton.c b/drivers/usb/usb-skeleton.c
index 8001d6384c73..c2843fcfa52d 100644
--- a/drivers/usb/usb-skeleton.c
+++ b/drivers/usb/usb-skeleton.c
@@ -61,6 +61,7 @@ struct usb_skel {
        spinlock_t              err_lock;               /* lock for errors */
        struct kref             kref;
        struct mutex            io_mutex;               /* synchronize I/O with 
disconnect */
+       unsigned long           disconnected:1;
        wait_queue_head_t       bulk_in_wait;           /* to wait for an 
ongoing read */
 };
 #define to_skel_dev(d) container_of(d, struct usb_skel, kref)
@@ -238,7 +239,7 @@ static ssize_t skel_read(struct file *file, char *buffer, 
size_t count,
        if (rv < 0)
                return rv;
 
-       if (!dev->interface) {          /* disconnect() was called */
+       if (dev->disconnected) {                /* disconnect() was called */
                rv = -ENODEV;
                goto exit;
        }
@@ -420,7 +421,7 @@ static ssize_t skel_write(struct file *file, const char 
*user_buffer,
 
        /* this lock makes sure we don't submit URBs to gone devices */
        mutex_lock(&dev->io_mutex);
-       if (!dev->interface) {          /* disconnect() was called */
+       if (dev->disconnected) {                /* disconnect() was called */
                mutex_unlock(&dev->io_mutex);
                retval = -ENODEV;
                goto error;
@@ -571,7 +572,7 @@ static void skel_disconnect(struct usb_interface *interface)
 
        /* prevent more I/O from starting */
        mutex_lock(&dev->io_mutex);
-       dev->interface = NULL;
+       dev->disconnected = 1;
        mutex_unlock(&dev->io_mutex);
 
        usb_kill_anchored_urbs(&dev->submitted);
-- 
2.23.0