linux-kernel - RE: [PATCH V3 04/12] misc: xilinx_sdfec: Add open, close and ioctl

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Message-ID: <BL0PR02MB5681F4C4AF4786AC6241DDA1CB350@BL0PR02MB5681.namprd02.prod.outlook.com>
Date:   Fri, 3 May 2019 16:44:57 +0000
From:   Dragan Cvetic <draganc@...inx.com>
To:     Greg KH <gregkh@...uxfoundation.org>
CC:     "arnd@...db.de" <arnd@...db.de>, Michal Simek <michals@...inx.com>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "robh+dt@...nel.org" <robh+dt@...nel.org>,
        "mark.rutland@....com" <mark.rutland@....com>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Derek Kiernan <dkiernan@...inx.com>
Subject: RE: [PATCH V3 04/12] misc: xilinx_sdfec: Add open, close and ioctl

Hi Greg,

Please find inline comments below.

Regards
Dragan

> -----Original Message-----
> From: Greg KH [mailto:gregkh@...uxfoundation.org]
> Sent: Thursday 2 May 2019 18:23
> To: Dragan Cvetic <draganc@...inx.com>
> Cc: arnd@...db.de; Michal Simek <michals@...inx.com>; linux-arm-kernel@...ts.infradead.org; robh+dt@...nel.org;
> mark.rutland@....com; devicetree@...r.kernel.org; linux-kernel@...r.kernel.org; Derek Kiernan <dkiernan@...inx.com>
> Subject: Re: [PATCH V3 04/12] misc: xilinx_sdfec: Add open, close and ioctl
> 
> On Sat, Apr 27, 2019 at 11:04:58PM +0100, Dragan Cvetic wrote:
> > +static int xsdfec_dev_open(struct inode *iptr, struct file *fptr)
> > +{
> > +	struct xsdfec_dev *xsdfec;
> > +
> > +	xsdfec = container_of(iptr->i_cdev, struct xsdfec_dev, xsdfec_cdev);
> > +
> > +	if (!atomic_dec_and_test(&xsdfec->open_count)) {
> 
> Why do you care about this?
> 
> And do you really think it matters?  What are you trying to protect from
> here?

There is a request to increase the driver security. 
It is acceptable for us for now, even with non-perfections (will not be protected if opened twice with dup() or fork()).
This is covered in the documentation.
> 
> > +		atomic_inc(&xsdfec->open_count);
> > +		return -EBUSY;
> > +	}
> > +
> > +	fptr->private_data = xsdfec;
> > +	return 0;
> > +}
> > +
> > +static int xsdfec_dev_release(struct inode *iptr, struct file *fptr)
> > +{
> > +	struct xsdfec_dev *xsdfec;
> > +
> > +	xsdfec = container_of(iptr->i_cdev, struct xsdfec_dev, xsdfec_cdev);
> > +
> > +	atomic_inc(&xsdfec->open_count);
> 
> You increment a number when the device is closed?
> 
> You are trying to make it hard to maintain this code over time :)
> 
> 
> > +	return 0;
> > +}
> > +
> > +static long xsdfec_dev_ioctl(struct file *fptr, unsigned int cmd,
> > +			     unsigned long data)
> > +{
> > +	struct xsdfec_dev *xsdfec = fptr->private_data;
> > +	void __user *arg = NULL;
> > +	int rval = -EINVAL;
> > +	int err = 0;
> > +
> > +	if (!xsdfec)
> > +		return rval;
> > +
> > +	if (_IOC_TYPE(cmd) != XSDFEC_MAGIC)
> > +		return -ENOTTY;
> > +
> > +	/* check if ioctl argument is present and valid */
> > +	if (_IOC_DIR(cmd) != _IOC_NONE) {
> > +		arg = (void __user *)data;
> > +		if (!arg) {
> > +			dev_err(xsdfec->dev,
> > +				"xilinx sdfec ioctl argument is NULL Pointer");
> 
> You just created a way for userspace to spam the kernel log, please do
> not do that :(

Will be removed.

> 
> 
> 
> > +			return rval;
> > +		}
> > +	}
> > +
> > +	if (err) {
> > +		dev_err(xsdfec->dev, "Invalid xilinx sdfec ioctl argument");
> > +		return -EFAULT;
> 
> Wrong error, you did not have a memory fault.

Absolutely useless code. Will be removed. Thanks.

> 
> Again, you just created a way to spam the kernel log by a user :(
> 
> thanks,
> 
> greg k-h