Re: [PATCH 1/7] staging: comedi: comedi_compat32.c: fix COMEDI_CMD copy back

[Ian Abbott <abbotti@mev.co.uk>]

On 27/01/15 15:50, Ian Abbott wrote:
> `do_cmd_ioctl()` in "comedi_fops.c" handles the `COMEDI_CMD` ioctl.
> This returns `-EAGAIN` if it has copied a modified `struct comedi_cmd`
> back to user-space.  (This occurs when the low-level Comedi driver's
> `do_cmdtest()` handler returns non-zero to indicate a problem with the
> contents of the `struct comedi_cmd`, or when the `struct comedi_cmd` has
> the `CMDF_BOGUS` flag set.)
>
> `compat_cmd()` in "comedi_compat32.c" handles the 32-bit compatible
> version of the `COMEDI_CMD` ioctl.  Currently, it never copies a 32-bit
> compatible version of `struct comedi_cmd` back to user-space, which is
> at odds with the way the regular `COMEDI_CMD` ioctl is handled.  To fix
> it, change `compat_cmd()` to copy a 32-bit compatible version of the
> `struct comedi_cmd` back to user-space when the main ioctl handler
> returns `-EAGAIN`.
>
> Signed-off-by: Ian Abbott <abbotti@mev.co.uk>
> Cc: <stable@vger.kernel.org>
> ---
>   drivers/staging/comedi/comedi_compat32.c | 13 +++++++++++--
>   1 file changed, 11 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/staging/comedi/comedi_compat32.c b/drivers/staging/comedi/comedi_compat32.c
> index 5a4c74f..2440c60 100644
> --- a/drivers/staging/comedi/comedi_compat32.c
> +++ b/drivers/staging/comedi/comedi_compat32.c
> @@ -262,7 +262,8 @@ static int compat_cmd(struct file *file, unsigned long arg)
>   {
>   	struct comedi_cmd __user *cmd;
>   	struct comedi32_cmd_struct __user *cmd32;
> -	int rc;
> +	long rc;
> +	int err;

Gah!  That change in type of the 'rc' variable resulted from me changing 
the order of the patches in the series.  It still works, but looks a bit 
out of place.  Should I post an updated version without this niggle?

>
>   	cmd32 = compat_ptr(arg);
>   	cmd = compat_alloc_user_space(sizeof(*cmd));
> @@ -271,7 +272,15 @@ static int compat_cmd(struct file *file, unsigned long arg)
>   	if (rc)
>   		return rc;
>
> -	return translated_ioctl(file, COMEDI_CMD, (unsigned long)cmd);
> +	rc = translated_ioctl(file, COMEDI_CMD, (unsigned long)cmd);
> +	if (rc == -EAGAIN) {
> +		/* Special case: copy cmd back to user. */
> +		err = put_compat_cmd(cmd32, cmd);
> +		if (err)
> +			rc = err;
> +	}
> +
> +	return rc;
>   }
>
>   /* Handle 32-bit COMEDI_CMDTEST ioctl. */
>


-- 
-=( Ian Abbott @ MEV Ltd.    E-mail: <abbotti@mev.co.uk> )=-
-=(                          Web: http://www.mev.co.uk/  )=-