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

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Message-ID: <CAFEvwukbxCY4wffd_1jLo+vjfXfBC4sFDpJ1vY4wfT+=yFA--w@mail.gmail.com>
Date:   Tue, 13 Oct 2020 14:31:21 +0530
From:   harshal chaudhari <harshalchau04@...il.com>
To:     Sudip Mukherjee <sudipm.mukherjee@...il.com>,
        Greg KH <gregkh@...uxfoundation.org>
Cc:     linux-kernel <linux-kernel@...r.kernel.org>,
        Arnd Bergmann <arnd@...db.de>
Subject: Re: [PATCH] char: ppdev: check if ioctl argument is present and valid

On Sat, Oct 10, 2020 at 2:41 PM Sudip Mukherjee
<sudipm.mukherjee@...il.com> wrote:
>
> On Sat, Oct 10, 2020 at 1:08 AM Sudip Mukherjee
> <sudipm.mukherjee@...il.com> wrote:
> >
> > On Fri, Oct 9, 2020 at 5:57 AM Greg KH <gregkh@...uxfoundation.org> wrote:
> > >
> > > On Thu, Oct 08, 2020 at 11:57:13PM +0530, Harshal Chaudhari wrote:
> > > > Checking the argument passed to the ioctl is valid
> > > > or not. if not then return -EINVAL.
> > >
> > > Along the the comments that Arnd made, this is not the correct value to
> > > be returning from an ioctl when you don't pass in the correct command.

Thanks Greg for the comment. i am checking with value
-EFAULT now, i will get back to you with changes as consideration
of Arnd comments.

> > > And it doesn't match what your patch says, please be consistent.

I just want to perform the Argument check here only.  back then i
was trying with access_ok() as well, but access_ok() return success
even if i passed a NULL pointer. so that's why i removed it from here.

> > > And do you have this device to be able to test your changes?

Yes I have a device and I tested these changes with the few ioctls.

> > I will test this tomorrow. But from an initial look, its going to
> > break ppdev. There are few ioctls which don't need any arguments.
>
> No, sorry. I missed the check for _IOC_NONE.
> Tested on a desktop which has a parallel port with a very basic test
> code of open->claim->write->release->close and it still works.

Thanks a lot Sudip for your time.

> --
> Regards
> Sudip