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

[David Laight]

From: harshal chaudhari
> Sent: 13 October 2020 10:01
> 
> On Sat, Oct 10, 2020 at 2:41 PM Sudip Mukherjee
> <sudipm.mukherjee@xxxxxxxxx> wrote:
> >
> > On Sat, Oct 10, 2020 at 1:08 AM Sudip Mukherjee
> > <sudipm.mukherjee@xxxxxxxxx> wrote:
> > >
> > > On Fri, Oct 9, 2020 at 5:57 AM Greg KH <gregkh@xxxxxxxxxxxxxxxxxxx> 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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