linux-kernel - Re: [PATCH v3 4/6] staging: r8188eu: add error handling of rtw

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Date:   Wed, 25 Aug 2021 06:35:08 +0200
From:   "Fabio M. De Francesco" <fmdefrancesco@...il.com>
To:     Larry.Finger@...inger.net, phil@...lpotter.co.uk,
        gregkh@...uxfoundation.org, straube.linux@...il.com,
        Pavel Skripkin <paskripkin@...il.com>
Cc:     linux-staging@...ts.linux.dev, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 4/6] staging: r8188eu: add error handling of rtw_read16

On Tuesday, August 24, 2021 9:27:35 AM CEST Pavel Skripkin wrote:
> _rtw_read16 function can fail in case of usb transfer failure. But
> previous function prototype wasn't designed to return an error to
> caller. It can cause a lot uninit value bugs all across the driver code,
> since rtw_read16() returns local stack variable to caller.
> 
> Fix it by changing the prototype of this function. Now it returns an
> int: 0 on success, negative error value on failure and callers should pass
> the pointer to storage location for register value.
> 
> Signed-off-by: Pavel Skripkin <paskripkin@...il.com>
> 
> [...]
>
> -static u16 usb_read16(struct intf_hdl *pintfhdl, u32 addr)
> +static int usb_read16(struct intf_hdl *pintfhdl, u32 addr, u16 *data)
>  {
>  	u8 requesttype;
>  	u16 wvalue;
>  	u16 len;
> -	__le32 data;
> +	int res;
> +	__le32 tmp;
> +
> +	if (WARN_ON(unlikely(!data)))
> +		return -EINVAL;
>  
>  	requesttype = 0x01;/* read_in */
>  	wvalue = (u16)(addr & 0x0000ffff);
>  	len = 2;
> -	usbctrl_vendorreq(pintfhdl, wvalue, &data, len, requesttype);
> +	res = usbctrl_vendorreq(pintfhdl, wvalue, &tmp, len, requesttype);
> +	if (res < 0) {
> +		dev_err(dvobj_to_dev(pintfhdl->pintf_dev), "Failed to read 16 bytes: %d\n", res);
> +		return res;
> +	} else if (res != len) {

Dear Pavel,

Please note that if and when my patch "Use usb_control_msg_recv / send () in 
usbctrl_vendorreq ()" will be merged, "if (res! = len)" will always evaluate 'true' 
and usb_read16 () will always return -EIO even if usbctrl_vendorreq () succeeds.

> +		dev_err(dvobj_to_dev(pintfhdl->pintf_dev),
> +			"Failed to read 16 bytes, could read only %d bytes\n", res);
> +		return -EIO;
> +	}
>  
> -	return (u16)(le32_to_cpu(data) & 0xffff);
> +	*data = le32_to_cpu(tmp) & 0xffff;
> +
> +	return 0;
>  }

[...]

Regards,

Fabio