Re: [PATCH] char: ppdev: check if ioctl argument is present and valid

[Arnd Bergmann]

On Thu, Oct 8, 2020 at 8:27 PM Harshal Chaudhari
<harshalchau04@xxxxxxxxx> wrote:
>
> Checking the argument passed to the ioctl is valid
> or not. if not then return -EINVAL.
>
> Signed-off-by: Harshal Chaudhari <harshalchau04@xxxxxxxxx>
> ---
>  drivers/char/ppdev.c | 12 +++++++++++-
>  1 file changed, 11 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/char/ppdev.c b/drivers/char/ppdev.c
> index 38b46c7d1737..001392980202 100644
> --- a/drivers/char/ppdev.c
> +++ b/drivers/char/ppdev.c
> @@ -354,7 +354,7 @@ static int pp_do_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
>         unsigned int minor = iminor(file_inode(file));
>         struct pp_struct *pp = file->private_data;
>         struct parport *port;
> -       void __user *argp = (void __user *)arg;
> +       void __user *argp = NULL;
>         struct ieee1284_info *info;
>         unsigned char reg;
>         unsigned char mask;

Assigning to NULL serves no purpose here.

> @@ -364,6 +364,16 @@ static int pp_do_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
>         struct timespec64 ts;
>         int ret;
>
> +       if (_IOC_TYPE(cmd) != PP_IOCTL)
> +               return -ENOTTY;

This looks correct but is normally done as a "default" case

> +       /* check if ioctl argument is present and valid */
> +       if (_IOC_DIR(cmd) != _IOC_NONE) {
> +               argp = (void __user *)arg;
> +               if (!argp)
> +                       return -EINVAL;
> +       }

This is a change in behavior, it changes the return code from the correct
-EFAULT to an unusual -EINVAL for the special case that the pointer
is NULL compared to other invalid pointers.

      Arnd