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Date: Thu, 15 Jun 2017 07:24:37 +0200
From: Greg KH <gregkh@linuxfoundation.org>
To: "Edward A. James" <eajames@us.ibm.com>
Cc: linux-kernel@vger.kernel.org, bradleyb@fuzziesquirrel.com,
        jk@ozlabs.org, cbostic@linux.vnet.ibm.com, joel@jms.id.au,
        andrew@aj.id.au
Subject: Re: [PATCH linux] drivers/fsi: Add SBEFIFO FSI client device driver
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On Wed, Jun 14, 2017 at 02:47:27PM -0500, Edward A. James wrote:
> +static ssize_t sbefifo_read(struct file *file, char __user *buf,
> +		size_t len, loff_t *offset)
> +{
> +	struct sbefifo_client *client = file->private_data;
> +
> +	WARN_ON(*offset);

Huh?  Why?

> +	if (!access_ok(VERIFY_WRITE, buf, len))
> +		return -EFAULT;

What does this check?  You should never need to call access_ok in any
driver, copy_from/to_user handles that all for you just fine.

thanks,

greg k-h