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    Subject[PATCH 4.19 07/81] USB: usb-skeleton: fix NULL-deref on disconnect
    Date
    From: Johan Hovold <johan@kernel.org>

    commit bed5ef230943863b9abf5eae226a20fad9a8ff71 upstream.

    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 <stable@vger.kernel.org>
    Signed-off-by: Johan Hovold <johan@kernel.org>
    Link: https://lore.kernel.org/r/20191009170944.30057-2-johan@kernel.org
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

    ---
    drivers/usb/usb-skeleton.c | 7 ++++---
    1 file changed, 4 insertions(+), 3 deletions(-)

    --- a/drivers/usb/usb-skeleton.c
    +++ b/drivers/usb/usb-skeleton.c
    @@ -59,6 +59,7 @@ 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)
    @@ -236,7 +237,7 @@ static ssize_t skel_read(struct file *fi
    if (rv < 0)
    return rv;

    - if (!dev->interface) { /* disconnect() was called */
    + if (dev->disconnected) { /* disconnect() was called */
    rv = -ENODEV;
    goto exit;
    }
    @@ -418,7 +419,7 @@ static ssize_t skel_write(struct file *f

    /* 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;
    @@ -569,7 +570,7 @@ static void skel_disconnect(struct usb_i

    /* 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);

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