On Sun, 2 Jun 2019, Christian Lamparter wrote:
> This patch follows Alan Stern's recent patch:
> "p54: Fix race between disconnect and firmware loading"
>
> that overhauled carl9170 buggy firmware loading and driver
> unbinding procedures.
>
> Since the carl9170 code was adapted from p54 it uses the
> same functions and is likely to have the same problem, but
> it's just that the syzbot hasn't reproduce them (yet).
>
> a summary from the changes (copied from the p54 patch):
> * Call usb_driver_release_interface() rather than
> device_release_driver().
>
> * Lock udev (the interface's parent) before unbinding the
> driver instead of locking udev->parent.
>
> * During the firmware loading process, take a reference
> to the USB interface instead of the USB device.
>
> * Don't take an unnecessary reference to the device during
> probe (and then don't drop it during disconnect).
>
> and
>
> * Make sure to prevent use-after-free bugs by explicitly
> setting the driver context to NULL after signaling the
> completion.
>
> Cc: <sta...@vger.kernel.org>
> Cc: Alan Stern <st...@rowland.harvard.edu>
> Signed-off-by: Christian Lamparter <chunk...@gmail.com>
This basically looks right. However...
> ---
> drivers/net/wireless/ath/carl9170/usb.c | 26 ++++++++++++-------------
> 1 file changed, 12 insertions(+), 14 deletions(-)
>
> diff --git a/drivers/net/wireless/ath/carl9170/usb.c
> b/drivers/net/wireless/ath/carl9170/usb.c
> index e7c3f3b8457d..297a7b877d31 100644
> --- a/drivers/net/wireless/ath/carl9170/usb.c
> +++ b/drivers/net/wireless/ath/carl9170/usb.c
> @@ -128,6 +128,8 @@ static const struct usb_device_id carl9170_usb_ids[] = {
> };
> MODULE_DEVICE_TABLE(usb, carl9170_usb_ids);
>
> +static struct usb_driver carl9170_driver;
> +
> static void carl9170_usb_submit_data_urb(struct ar9170 *ar)
> {
> struct urb *urb;
> @@ -966,7 +968,7 @@ static int carl9170_usb_init_device(struct ar9170 *ar)
>
> static void carl9170_usb_firmware_failed(struct ar9170 *ar)
> {
> - struct device *parent = ar->udev->dev.parent;
> + struct usb_interface *intf = ar->intf;
> struct usb_device *udev;
It looks a little strange to initialize intf in the definition but to
initialize udev afterward. Nothing wrong with it, just odd.
>
> /*
> @@ -978,16 +980,15 @@ static void carl9170_usb_firmware_failed(struct ar9170
> *ar)
> udev = ar->udev;
>
> complete(&ar->fw_load_wait);
> + /* at this point 'ar' could be already freed. Don't use it anymore */
> + ar = NULL;
>
> /* unbind anything failed */
> - if (parent)
> - device_lock(parent);
> -
> - device_release_driver(&udev->dev);
> - if (parent)
> - device_unlock(parent);
> + usb_lock_device(udev);
> + usb_driver_release_interface(&carl9170_driver, intf);
> + usb_unlock_device(udev);
>
> - usb_put_dev(udev);
> + usb_put_intf(intf);
> }
>
> static void carl9170_usb_firmware_finish(struct ar9170 *ar)
> @@ -1009,7 +1010,7 @@ static void carl9170_usb_firmware_finish(struct ar9170
> *ar)
> goto err_unrx;
>
> complete(&ar->fw_load_wait);
> - usb_put_dev(ar->udev);
> + usb_put_intf(ar->intf);
But this could be a problem. As soon as the complete() call runs, ar
might be deallocated. The code should copy ar->intf before calling
complete().
Alan Stern
> return;
>
> err_unrx:
> @@ -1052,7 +1053,6 @@ static int carl9170_usb_probe(struct usb_interface
> *intf,
> return PTR_ERR(ar);
>
> udev = interface_to_usbdev(intf);
> - usb_get_dev(udev);
> ar->udev = udev;
> ar->intf = intf;
> ar->features = id->driver_info;
> @@ -1094,15 +1094,14 @@ static int carl9170_usb_probe(struct usb_interface
> *intf,
> atomic_set(&ar->rx_anch_urbs, 0);
> atomic_set(&ar->rx_pool_urbs, 0);
>
> - usb_get_dev(ar->udev);
> + usb_get_intf(intf);
>
> carl9170_set_state(ar, CARL9170_STOPPED);
>
> err = request_firmware_nowait(THIS_MODULE, 1, CARL9170FW_NAME,
> &ar->udev->dev, GFP_KERNEL, ar, carl9170_usb_firmware_step2);
> if (err) {
> - usb_put_dev(udev);
> - usb_put_dev(udev);
> + usb_put_intf(intf);
> carl9170_free(ar);
> }
> return err;
> @@ -1131,7 +1130,6 @@ static void carl9170_usb_disconnect(struct
> usb_interface *intf)
>
> carl9170_release_firmware(ar);
> carl9170_free(ar);
> - usb_put_dev(udev);
> }
>
> #ifdef CONFIG_PM
>
