Re: [PATCH v2] usb: raw-gadget: fix double-free race during UDC unbind and rebind

[Andrey Konovalov]

On Sat, Oct 24, 2026 at 9:08 PM Igor Putko <igorpetindev@xxxxxxxxx> wrote:
>
> raw-gadget defers endpoint disabling, request freeing, and descriptor
> cleanup to dev_free(). However, dev_free() is only called after
> dev->count drops to zero in raw_release(), which happens after
> usb_gadget_unregister_driver() has already returned.
>
> Once usb_gadget_unregister_driver() finishes, the UDC can be immediately
> rebound by another raw_gadget instance. If that new instance enables an
> endpoint, it assigns its newly allocated descriptor to ep->ep->desc on
> the shared UDC endpoint. When dev_free() from the old instance runs
> concurrently, it calls usb_ep_disable() and frees dev->eps[i].ep->desc,
> which now belongs to the new instance. The new instance's usb_ep_enable()
> subsequently fails with -ESHUTDOWN, and its error path frees the descriptor
> again, causing a KASAN double-free.
>
> Tear down active endpoints and requests synchronously in gadget_unbind()
> before the UDC can be bound again. Keep the descriptor pointer inside
> struct raw_ep and clear ep->ep->desc on error and disable paths so no
> dangling pointers are left on the UDC endpoints.
>
> Reported-by: syzbot+b7534c9b380f81a3b4be@xxxxxxxxxxxxxxxxxxxxxxxxx
> Closes: https://syzkaller.appspot.com/bug?extid=b7534c9b380f81a3b4be

Please also ask syzbot to test your patch - it has a reproducer for this issue.

> Fixes: f2c2e717642c ("usb: gadget: add raw-gadget interface")
> Signed-off-by: Igor Putko <igorpetindev@xxxxxxxxx>
> ---
> v1 -> v2:
> - Keep ep0 request handling in dev_free() to avoid any lock recursion.
> - Synchronously disable and clean up active endpoints in gadget_unbind()
>   to prevent use after UDC unbind.
> - Update endpoint cleanup in dev_free() to free raw_ep->desc.
> ---
> ---
>  drivers/usb/gadget/legacy/raw_gadget.c | 30 ++++++++++++++++++++++----
>  1 file changed, 26 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/usb/gadget/legacy/raw_gadget.c b/drivers/usb/gadget/legacy/raw_gadget.c
> index 4febf8dac7ca..a6b42679acc7 100644
> --- a/drivers/usb/gadget/legacy/raw_gadget.c
> +++ b/drivers/usb/gadget/legacy/raw_gadget.c
> @@ -141,6 +141,7 @@ struct raw_ep {
>         enum ep_state           state;
>         struct usb_ep           *ep;
>         u8                      addr;
> +       struct usb_endpoint_descriptor *desc;

Why do we need this extra field? Why is ep->desc not enough?

>         struct usb_request      *req;
>         bool                    urb_queued;
>         bool                    disabling;
> @@ -223,7 +224,9 @@ static void dev_free(struct kref *kref)
>                         continue;
>                 usb_ep_disable(dev->eps[i].ep);
>                 usb_ep_free_request(dev->eps[i].ep, dev->eps[i].req);
> -               kfree(dev->eps[i].ep->desc);
> +               kfree(dev->eps[i].desc);
> +               dev->eps[i].desc = NULL;
> +               dev->eps[i].ep->desc = NULL;
>                 dev->eps[i].state = STATE_EP_DISABLED;
>         }
>         kfree(dev);
> @@ -328,6 +331,20 @@ static int gadget_bind(struct usb_gadget *gadget,
>  static void gadget_unbind(struct usb_gadget *gadget)
>  {
>         struct raw_dev *dev = get_gadget_data(gadget);
> +       int i;
> +
> +       if (dev) {
> +               for (i = 0; i < dev->eps_num; i++) {
> +                       if (dev->eps[i].state == STATE_EP_DISABLED)
> +                               continue;
> +                       usb_ep_disable(dev->eps[i].ep);
> +                       usb_ep_free_request(dev->eps[i].ep, dev->eps[i].req);
> +                       kfree(dev->eps[i].desc);
> +                       dev->eps[i].desc = NULL;
> +                       dev->eps[i].ep->desc = NULL;
> +                       dev->eps[i].state = STATE_EP_DISABLED;
> +               }
> +       }

Any of the other things dev_free() does need to be repeated here too?

Also, if we release/free all these things here during unbind, do we
still need to do the same during dev_free()?

>
>         set_gadget_data(gadget, NULL);
>         /* Matches kref_get() in gadget_bind(). */
> @@ -886,6 +903,7 @@ static int raw_ioctl_ep_enable(struct raw_dev *dev, unsigned long value)
>                 if (ret < 0) {
>                         dev_err(&dev->gadget->dev,
>                                 "fail, usb_ep_enable returned %d\n", ret);
> +                       ep->ep->desc = NULL;
>                         goto out_free;
>                 }
>                 ep->req = usb_ep_alloc_request(ep->ep, GFP_ATOMIC);
> @@ -893,10 +911,12 @@ static int raw_ioctl_ep_enable(struct raw_dev *dev, unsigned long value)
>                         dev_err(&dev->gadget->dev,
>                                 "fail, usb_ep_alloc_request failed\n");
>                         usb_ep_disable(ep->ep);
> +                       ep->ep->desc = NULL;

usb_ep_disable() should already do this for UDC drivers that care
about value of ep->desc for disabled endpoints.

>                         ret = -ENOMEM;
>                         goto out_free;
>                 }
>                 ep->state = STATE_EP_ENABLED;
> +               ep->desc = desc;
>                 ep->ep->driver_data = ep;
>                 ret = i;
>                 goto out_unlock;
> @@ -962,7 +982,9 @@ static int raw_ioctl_ep_disable(struct raw_dev *dev, unsigned long value)
>
>         spin_lock_irqsave(&dev->lock, flags);
>         usb_ep_free_request(dev->eps[i].ep, dev->eps[i].req);
> -       kfree(dev->eps[i].ep->desc);
> +       kfree(dev->eps[i].desc);
> +       dev->eps[i].desc = NULL;
> +       dev->eps[i].ep->desc = NULL;
>         dev->eps[i].state = STATE_EP_DISABLED;
>         dev->eps[i].disabling = false;
>
> @@ -1010,7 +1032,7 @@ static int raw_ioctl_ep_set_clear_halt_wedge(struct raw_dev *dev,
>                 ret = -EINVAL;
>                 goto out_unlock;
>         }
> -       if (usb_endpoint_xfer_isoc(dev->eps[i].ep->desc)) {
> +       if (usb_endpoint_xfer_isoc(dev->eps[i].desc)) {
>                 dev_dbg(&dev->gadget->dev,
>                                 "fail, can't halt/wedge ISO endpoint\n");
>                 ret = -EINVAL;
> @@ -1096,7 +1118,7 @@ static int raw_process_ep_io(struct raw_dev *dev, struct usb_raw_ep_io *io,
>                 ret = -EBUSY;
>                 goto out_unlock;
>         }
> -       if (in != usb_endpoint_dir_in(ep->ep->desc)) {
> +       if (in != usb_endpoint_dir_in(ep->desc)) {
>                 dev_dbg(&dev->gadget->dev, "fail, wrong direction\n");
>                 ret = -EINVAL;
>                 goto out_unlock;
> --
> 2.47.3
>