Re: [PATCH v2] usb: dwc3: gadget: Free gadget structure only after freeing endpoints

From: Felipe Balbi <balbi@kernel.org>
To: Jack Pham <jackp@codeaurora.org>,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: linux-usb@vger.kernel.org, linux-arm-msm@vger.kernel.org,
	Peter Chen <peter.chen@nxp.com>,
	Sandeep Maheswaram <sanm@codeaurora.org>,
	Wesley Cheng <wcheng@codeaurora.org>,
	Elliot Berman <eberman@codeaurora.org>,
	Prasad Sodagudi <psodagud@codeaurora.org>,
	Jack Pham <jackp@codeaurora.org>
Subject: Re: [PATCH v2] usb: dwc3: gadget: Free gadget structure only after freeing endpoints
Date: Mon, 10 May 2021 15:12:12 +0300	[thread overview]
Message-ID: <878s4mhjoj.fsf@kernel.org> (raw)
In-Reply-To: <20210501093558.7375-1-jackp@codeaurora.org>

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Hi,

Jack Pham <jackp@codeaurora.org> writes:

> As part of commit e81a7018d93a ("usb: dwc3: allocate gadget structure
> dynamically") the dwc3_gadget_release() was added which will free
> the dwc->gadget structure upon the device's removal when
> usb_del_gadget_udc() is called in dwc3_gadget_exit().
>
> However, simply freeing the gadget results a dangling pointer
> situation: the endpoints created in dwc3_gadget_init_endpoints()
> have their dep->endpoint.ep_list members chained off the list_head
> anchored at dwc->gadget->ep_list.  Thus when dwc->gadget is freed,
> the first dwc3_ep in the list now has a dangling prev pointer and
> likewise for the next pointer of the dwc3_ep at the tail of the list.
> The dwc3_gadget_free_endpoints() that follows will result in a
> use-after-free when it calls list_del().
>
> This was caught by enabling KASAN and performing a driver unbind.
> The recent commit 568262bf5492 ("usb: dwc3: core: Add shutdown
> callback for dwc3") also exposes this as a panic during shutdown.
>
> There are a few possibilities to fix this.  One could be to perform
> a list_del() of the gadget->ep_list itself which removes it from
> the rest of the dwc3_ep chain.
>
> Another approach is what this patch does, by splitting up the
> usb_del_gadget_udc() call into its separate "del" and "put"
> components.  This allows dwc3_gadget_free_endpoints() to be
> called before the gadget is finally freed with usb_put_gadget().
>
> Fixes: e81a7018d93a ("usb: dwc3: allocate gadget structure dynamically")
> Signed-off-by: Jack Pham <jackp@codeaurora.org>
> ---
> v2: Fix silly typo: usb_del_gadget_put -> usb_put_gadget (brain fart
> when manually recomposing the patch)

I thought I had acked this one already, looks like I missed it:

Acked-by: Felipe Balbi <balbi@kernel.org>

-- 
balbi

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