linux-kernel - Re: [PATCH] usb: mtu3: Fix possible use-before-initialization bug

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Message-ID: <20230705080625.02b2bac5@bootlin.com>
Date:   Wed, 5 Jul 2023 08:06:25 +0200
From:   Herve Codina <herve.codina@...tlin.com>
To:     Yu Hao <yhao016@....edu>
Cc:     chunfeng.yun@...iatek.com, gregkh@...uxfoundation.org,
        linux-usb@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-mediatek@...ts.infradead.org,
        linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] usb: mtu3: Fix possible use-before-initialization bug

Hi Yu,

On Tue, 4 Jul 2023 16:25:50 -0700
Yu Hao <yhao016@....edu> wrote:

> The struct usb_ctrlrequest setup should be initialized in the function
> ep0_read_setup(mtu, &setup). However, inside that function,
> the variable count could be 0 and the struct usb_ctrlrequest setup
> is not initialized. But there is a read for setup.bRequestType.
> 
> Signed-off-by: Yu Hao <yhao016@....edu>
> ---
>  drivers/usb/mtu3/mtu3_gadget_ep0.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/usb/mtu3/mtu3_gadget_ep0.c
> b/drivers/usb/mtu3/mtu3_gadget_ep0.c
> index e4fd1bb14a55..67034fa515d0 100644
> --- a/drivers/usb/mtu3/mtu3_gadget_ep0.c
> +++ b/drivers/usb/mtu3/mtu3_gadget_ep0.c
> @@ -638,7 +638,7 @@ static int ep0_handle_setup(struct mtu3 *mtu)
>  __releases(mtu->lock)
>  __acquires(mtu->lock)
>  {
> -   struct usb_ctrlrequest setup;
> +   struct usb_ctrlrequest setup = {};
>     struct mtu3_request *mreq;
>     int handled = 0;
> 

Looks strange to me because, if ep0_read_setup() cannot read the setup data
why don't we simply abort the operation ?

With setup = {}, the following test is true:
  if ((setup.bRequestType & USB_TYPE_MASK) == USB_TYPE_STANDARD)
	handled = handle_standard_request(mtu, &setup);

handle_standard_request() is called and supposes an USB_REQ_GET_STATUS
(0x00) request:
   case USB_REQ_GET_STATUS:
	handled = ep0_get_status(mtu, setup);
	break;

Then ep0_get_status() supposes USB_RECIP_DEVICE (0x00) and performs some
operation sending the data related to the GET_STATUS.

All of these are not correct as the setup data that triggered this sequence
was never received.
Aborting the operation if ep0_read_setup() cannot read the setup data seems
better to me.

Best regards,
Hervé

-- 
Hervé Codina, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com