linux-kernel - Re: [PATCH v1] usb: dwc3: gadget: fix gadget workqueue use-after-free

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Message-ID: <20250131234407.fyv4iu5yadp5xeg2@synopsys.com>
Date: Fri, 31 Jan 2025 23:44:17 +0000
From: Thinh Nguyen <Thinh.Nguyen@...opsys.com>
To: Roy Luo <royluo@...gle.com>, Alan Stern <stern@...land.harvard.edu>
CC: Thinh Nguyen <Thinh.Nguyen@...opsys.com>,
        "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
        "linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "andre.draszik@...aro.org" <andre.draszik@...aro.org>
Subject: Re: [PATCH v1] usb: dwc3: gadget: fix gadget workqueue use-after-free

Cc Alan

On Fri, Jan 31, 2025, Roy Luo wrote:
> On Mon, Jan 27, 2025 at 5:44 PM Thinh Nguyen <Thinh.Nguyen@...opsys.com> wrote:
> >
> > On Wed, Jan 22, 2025, Roy Luo wrote:
> > > `dwc3_gadget_soft_disconnect` function, called as part of
> >
> > The dwc3_gadget_soft_disconnect() isn't directly part of
> > device_del(&gadget->dev). It should be part of disconnect.
> >
> > Can you provide the full sequence of events so I can have more context?
> > The handling of the flushing of gadget->work should not be part of the
> > dwc3.
> 
> 
> Yes, it's a part of disconnect, and disconnect is a part of gadget unbind.
> Let me try my best to explain. Here's the call stack for usb_del_gadget:
> -> usb_del_gadget
>     -> flush_work(&gadget->work)
>     -> device_del
>         -> bus_remove_device
>         -> device_release_driver
>         -> gadget_unbind_driver
>         -> usb_gadget_disconnect_locked
>         -> dwc3_gadget_pullup
>         -> dwc3_gadget_soft_disconnect
>         -> usb_gadget_set_state
>         -> schedule_work(&gadget->work)
> 
> Then when usb_put_gadget is called, gadget could be freed before
> gadget->work is executed.
> -> usb_put_gadget
> -> put_device
> -> kobject_put
> -> device_release
> -> dwc_gadget_release
> -> kfree(gadget)
> 

Thanks for the details!

The UDC core is initiating and handling the gadget->work, so the
flushing of the gadget->work should also be handled there.

Since the usb_gadget_disconnect_locked() may trigger a state change work
on unbind, the flushing of the gadget->work should to be moved to
gadget_unbind_driver() instead:

diff --git a/drivers/usb/gadget/udc/core.c b/drivers/usb/gadget/udc/core.c
index f8c1ef465e45..9e4abd6e40f8 100644
--- a/drivers/usb/gadget/udc/core.c
+++ b/drivers/usb/gadget/udc/core.c
@@ -1568,7 +1568,6 @@ void usb_del_gadget(struct usb_gadget *gadget)
 
        kobject_uevent(&udc->dev.kobj, KOBJ_REMOVE);
        sysfs_remove_link(&udc->dev.kobj, "gadget");
-       flush_work(&gadget->work);
        device_del(&gadget->dev);
        ida_free(&gadget_id_numbers, gadget->id_number);
        cancel_work_sync(&udc->vbus_work);
@@ -1694,6 +1693,8 @@ static void gadget_unbind_driver(struct device *dev)
                synchronize_irq(gadget->irq);
        mutex_unlock(&udc->connect_lock);
 
+       flush_work(&gadget->work);
+
        udc->driver->unbind(gadget);
 
        mutex_lock(&udc->connect_lock);


BR,
Thinh