linux-kernel - Re: [PATCH] I2C driver of Topcliff PCH

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Date:	Tue, 20 Jul 2010 11:29:52 +0200
From:	Arnd Bergmann <arnd@...db.de>
To:	"Masayuki Ohtake" <masa-korg@....okisemi.com>
Cc:	andrew.chih.howe.khor@...el.com, joel.clark@...el.com,
	"Wang, Yong Y" <yong.y.wang@...el.com>, qi.wang@...el.com,
	"LKML" <linux-kernel@...r.kernel.org>, linux-i2c@...r.kernel.org,
	"Ben Dooks \(embedded platforms\)" <ben-linux@...ff.org>,
	"Jean Delvare \(PC drivers, core\)" <khali@...ux-fr.org>
Subject: Re: [PATCH] I2C driver of Topcliff PCH

On Tuesday 20 July 2010, Masayuki Ohtake wrote:
> > > @@ -147,6 +148,11 @@ static ssize_t i2cdev_read(struct file *file, char __user *buf, size_t count,
> > >  if (tmp == NULL)
> > >  return -ENOMEM;
> > >
> > > + if (copy_from_user(tmp, buf, count)) {
> > > + kfree(tmp);
> > > + return -EFAULT;
> > > + }
> > > +
> > >  pr_debug("i2c-dev: i2c-%d reading %zu bytes.\n",
> > >  iminor(file->f_path.dentry->d_inode), count);
> >
> >
> > A read function should not do copy_from_user, only copy_to_user.
> > If you are worried about returning invalid data from kernel space,
> > better use kzalloc instead of kmalloc to get the buffer.
> 
> Our I2C HW has special mode.
> To control the mode, our i2c driver has copy_from_user.

That is a highly unusual interface and I would definitely not recommend doing
this. Please use an ioctl operation for anything that has both input and output
data.

	Arnd
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