netdev - Re: [PATCH] ppp: remove the PPPIOCDETACH ioctl

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Date:   Wed, 23 May 2018 14:17:09 -0700
From:   Eric Biggers <ebiggers3@...il.com>
To:     David Miller <davem@...emloft.net>
Cc:     g.nault@...halink.fr, linux-ppp@...r.kernel.org, paulus@...ba.org,
        netdev@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        linux-kernel@...r.kernel.org, syzkaller-bugs@...glegroups.com,
        ebiggers@...gle.com
Subject: Re: [PATCH] ppp: remove the PPPIOCDETACH ioctl

On Wed, May 23, 2018 at 11:56:36AM -0400, David Miller wrote:
> From: Guillaume Nault <g.nault@...halink.fr>
> Date: Wed, 23 May 2018 15:57:08 +0200
> 
> > I'd rather add
> > +	if (cmd == PPPIOCDETACH) {
> > +		err = -EINVAL;
> > +		goto out;
> > +	}
> > 
> > Making PPPIOCDETACH unknown to ppp_generic means that the ioctl would
> > be handled by the underlying channel when pf->kind == CHANNEL (see the
> > chan->ops->ioctl() call further down). That shouldn't be a problem per
> > se, but even though PPPIOCDETACH is unsupported, I feel that it should
> > remain a ppp_generic thing. I don't really want its value to be reused
> > for other purposes in the future or have different behaviour depending
> > on the underlying channel.
> > 
> > Also PPPIOCDETACH can already fail with -EINVAL. Therefore, if ever
> > there really were programs out there using this call, they'd already
> > have to handle this case. Unconditionally returning -EINVAL would
> > further minimise possibilities for breakage.
> 
> I agree.

Okay, I'll do that and leave the ioctl number reserved.
I will add a pr_warn_once() too.

Thanks,

- Eric