linux-kernel - Re: [PATCH v2] USB: core: devio: Restructured proc

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Date:   Sun, 12 Aug 2018 18:46:34 -0400 (EDT)
From:   Alan Stern <stern@...land.harvard.edu>
To:     Tom Todd <thomas.m.a.todd@...il.com>
cc:     gregkh@...uxfoundation.org, <joe@...ches.com>,
        <dan.carpenter@...cle.com>, <arvind.yadav.cs@...il.com>,
        <linux-usb@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2] USB: core: devio: Restructured proc_ioctl for
 readability

On Sun, 12 Aug 2018, Tom Todd wrote:

> On, Sun, 12 Aug 2018 11:34:59 -0700 Joe Perches wrote:
> >On Sun, 2018-08-12 at 19:06 +0100, Tom Todd wrote:
> >> Fixed a code styling issue
> >while it's OK to fix style only issues, it's much better
> >to reorganize the code for reader clarity.
> 
> Ok, thank you, I've taken your suggestions and created the a new version
> 
> Restructured method proc_ioctl for readability and fixed code style
> errors.
> 
> Signed-off-by: Tom Todd <thomas.m.a.todd@...il.com>

"Style fixes" that introduce bugs are quite annoying...

> ---
>  drivers/usb/core/devio.c | 67 ++++++++++++++++++++++------------------
>  1 file changed, 37 insertions(+), 30 deletions(-)
> 
> diff --git a/drivers/usb/core/devio.c b/drivers/usb/core/devio.c
> index 476dcc5f2da3..740e60e086e2 100644
> --- a/drivers/usb/core/devio.c
> +++ b/drivers/usb/core/devio.c
> @@ -2117,46 +2117,52 @@ static int proc_ioctl(struct usb_dev_state *ps, struct usbdevfs_ioctl *ctl)
>  	/* alloc buffer */
>  	size = _IOC_SIZE(ctl->ioctl_code);
>  	if (size > 0) {
> -		buf = kmalloc(size, GFP_KERNEL);
> -		if (buf == NULL)
> -			return -ENOMEM;
> -		if ((_IOC_DIR(ctl->ioctl_code) & _IOC_WRITE)) {
> -			if (copy_from_user(buf, ctl->data, size)) {
> -				kfree(buf);
> +		if (_IOC_DIR(ctl->ioctl_code) & _IOC_WRITE) {
> +			buf = memdup_user(ctl->data, size);
> +			if (!buf)
>  				return -EFAULT;
> -			}
>  		} else {
> -			memset(buf, 0, size);
> +			buf = kmalloc(size, GFP_KERNEL);
> +			if (!buf)
> +				return -ENOMEM;

Where do the contents of buf get set to 0 now?

>  		}
>  	}
>  
>  	if (!connected(ps)) {
> -		kfree(buf);
> -		return -ENODEV;
> +		retval = -ENODEV;
> +		goto exit;
>  	}
>  
> -	if (ps->dev->state != USB_STATE_CONFIGURED)
> +	if (ps->dev->state != USB_STATE_CONFIGURED) {
>  		retval = -EHOSTUNREACH;
> -	else if (!(intf = usb_ifnum_to_if(ps->dev, ctl->ifno)))
> +		goto exit;
> +	}
> +
> +	intf = usb_ifnum_to_if(ps->dev, ctl->ifno);
> +	if (!intf) {
>  		retval = -EINVAL;
> -	else switch (ctl->ioctl_code) {
> +		goto exit;
> +	}
>  
> +	switch (ctl->ioctl_code) {
>  	/* disconnect kernel driver from interface */
>  	case USBDEVFS_DISCONNECT:
> -		if (intf->dev.driver) {
> -			driver = to_usb_driver(intf->dev.driver);
> -			dev_dbg(&intf->dev, "disconnect by usbfs\n");
> -			usb_driver_release_interface(driver, intf);
> -		} else
> +		if (!intf->dev.driver) {
>  			retval = -ENODATA;
> +			goto exit;
> +		}
> +		driver = to_usb_driver(intf->dev.driver);
> +		dev_dbg(&intf->dev, "disconnect by usbfs\n");
> +		usb_driver_release_interface(driver, intf);
>  		break;
>  
>  	/* let kernel drivers try to (re)bind to the interface */
>  	case USBDEVFS_CONNECT:
> -		if (!intf->dev.driver)
> -			retval = device_attach(&intf->dev);
> -		else
> +		if (!intf->dev.driver) {

Now !intf->dev.driver generates an error instead of working?

>  			retval = -EBUSY;
> +			goto exit;
> +		}
> +		retval = device_attach(&intf->dev);
>  		break;
>  
>  	/* talk directly to the interface's driver */
> @@ -2165,20 +2171,21 @@ static int proc_ioctl(struct usb_dev_state *ps, struct usbdevfs_ioctl *ctl)
>  			driver = to_usb_driver(intf->dev.driver);
>  		if (driver == NULL || driver->unlocked_ioctl == NULL) {
>  			retval = -ENOTTY;
> -		} else {
> -			retval = driver->unlocked_ioctl(intf, ctl->ioctl_code, buf);
> -			if (retval == -ENOIOCTLCMD)
> -				retval = -ENOTTY;
> +			goto exit;
>  		}
> +		retval = driver->unlocked_ioctl(intf, ctl->ioctl_code, buf);
> +		if (retval == -ENOIOCTLCMD) {
> +			retval = -ENOTTY;
> +			goto exit;
> +		}
> +		break;
>  	}
>  
>  	/* cleanup and return */
> -	if (retval >= 0
> -			&& (_IOC_DIR(ctl->ioctl_code) & _IOC_READ) != 0
> -			&& size > 0
> -			&& copy_to_user(ctl->data, buf, size) != 0)
> +	if (retval >= 0 && (_IOC_DIR(ctl->ioctl_code) & _IOC_READ) != 0 &&
> +		size > 0 && copy_to_user(ctl->data, buf, size) != 0)
>  		retval = -EFAULT;

Isn't the style in this file to indent continuation lines by two tab
stops?

> -
> +exit:
>  	kfree(buf);
>  	return retval;
>  }

Alan Stern