From mboxrd@z Thu Jan  1 00:00:00 1970
From: David Miller <davem@davemloft.net>
Date: Wed, 23 May 2018 15:56:36 +0000
Subject: Re: [PATCH] ppp: remove the PPPIOCDETACH ioctl
Message-Id: <20180523.115636.2241611659399097483.davem@davemloft.net>
List-Id: <linux-ppp.vger.kernel.org>
References: <20180523032958.GE658@sol.localdomain>
        <20180523035952.25768-1-ebiggers3@gmail.com>
        <20180523135708.GB1569@alphalink.fr>
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To: g.nault@alphalink.fr
Cc: ebiggers3@gmail.com, linux-ppp@vger.kernel.org, paulus@samba.org, netdev@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, syzkaller-bugs@googlegroups.com, ebiggers@google.com

From: Guillaume Nault <g.nault@alphalink.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.