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

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Message-ID: <CAK8P3a0y5MjP7AXOpmqc7xpGFCSvTGWHPT_eev5OpJJGVcRVdA@mail.gmail.com>
Date:   Sat, 24 Oct 2020 21:21:11 +0200
From:   Arnd Bergmann <arnd@...nel.org>
To:     harshal chaudhari <harshalchau04@...il.com>
Cc:     David Laight <David.Laight@...lab.com>,
        Greg KH <gregkh@...uxfoundation.org>,
        Sudip Mukherjee <sudipm.mukherjee@...il.com>,
        linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] char: ppdev: check if ioctl argument is present and valid

On Sat, Oct 24, 2020 at 5:54 PM harshal chaudhari
<harshalchau04@...il.com> wrote:
> On Tue, Oct 13, 2020 at 4:42 PM David Laight <David.Laight@...lab.com> wrote:

> So I am a little bit confused about this check whether it's required or not
> Please could you point me in the right direction?
>
> In any case, thanks for your help ...
>
> Here is a driver source located in: linux/drivers/misc/xilinx_sdfec.c
>
> static long xsdfec_dev_ioctl(struct file *fptr, unsigned int cmd,
> unsigned long data)
> {
> struct xsdfec_dev *xsdfec;
> void __user *arg = NULL;
> int rval = -EINVAL;
>
> if (_IOC_TYPE(cmd) != XSDFEC_MAGIC)
>                return -ENOTTY;
>
> /* check if ioctl argument is present and valid */
> if (_IOC_DIR(cmd) != _IOC_NONE)
> {
>         arg = (void __user *)data;
>         if (!arg)
>                    return rval;
> }
>

All of this can be removed, and replaced with unconditional

     void __user *arg = (void __user *)data;
     int rval;

with an "rval = -ENOTTY" added in the 'default' case. This will
make it behave more like other drivers, returning -ENOTTY for
any unknown ioctl command, and returning -EFAULT for all
invalid pointers, including NULL.

xsdfec_dev_compat_ioctl() can removed as well, with the file operations
changed to an unconditional (removing the #ifdef)

      .compat_ioctl = compat_ptr_ioctl(),

This will not affect behavior, it's just another simplification.


          Arnd