linux-kernel - RE: [PATCH 4/7] staging: comedi: don't allow read() on async command set up for "write"

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Date:	Thu, 30 Oct 2014 18:05:40 +0000
From:	Hartley Sweeten <HartleyS@...ionengravers.com>
To:	Ian Abbott <abbotti@....co.uk>,
	"driverdev-devel@...uxdriverproject.org" 
	<driverdev-devel@...uxdriverproject.org>
CC:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH 4/7] staging: comedi: don't allow read() on async
 command set up for "write"

On Thursday, October 30, 2014 5:42 AM, Ian Abbott wrote:
> If a Comedi asynchronous command has been set up for data transfer in
> the "write" direction on the current "read" subdevice (for those
> subdevices that support both directions), don't allow the "read" file
> operation as that would mess with the data in the comedi data buffer
> that is read by the low-level comedi hardware driver.
>
> Signed-off-by: Ian Abbott <abbotti@....co.uk>
> ---
>  drivers/staging/comedi/comedi_fops.c | 8 ++++++++
>  1 file changed, 8 insertions(+)
>
> diff --git a/drivers/staging/comedi/comedi_fops.c b/drivers/staging/comedi/comedi_fops.c
> index fef68da..6805ec9 100644
> --- a/drivers/staging/comedi/comedi_fops.c
> +++ b/drivers/staging/comedi/comedi_fops.c
> @@ -2210,6 +2210,10 @@ static ssize_t comedi_read(struct file *file, char __user *buf, size_t nbytes,
>  		retval = -EACCES;
>  		goto out;
>  	}
> +	if (async->cmd.flags & CMDF_WRITE) {
> +		retval = -EINVAL;
> +		goto out;
> +	}
>  
>  	add_wait_queue(&async->wait_head, &wait);
>  	while (nbytes > 0 && !retval) {
> @@ -2249,6 +2253,10 @@ static ssize_t comedi_read(struct file *file, char __user *buf, size_t nbytes,
>  				retval = -EACCES;
>  				break;
>  			}
> +			if (async->cmd.flags & CMDF_WRITE) {
> +				retval = -EINVAL;
> +				break;
> +			}

Is this second test really needed in the while() loop?

For that matter, are the s->busy tests needed in the while() loop?

>  			continue;
 >		}
 >		m = copy_to_user(buf, async->prealloc_buf +

Regards,
Hartley

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