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

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Date:   Tue, 13 Oct 2020 11:12:54 +0000
From:   David Laight <David.Laight@...LAB.COM>
To:     'harshal chaudhari' <harshalchau04@...il.com>,
        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

From: harshal chaudhari
> Sent: 13 October 2020 10:01
> 
> 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.

Why bother.
You have to check the copy_from_user() whatever else you might have
checked earlied.
So why optimise for the error case that never happens.

	David

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