netdev - Re: [PATCH net-next] ipv6: allow userspace to add IFA_F

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Message-Id: <20180226.105711.81890471902412308.davem@davemloft.net>
Date:   Mon, 26 Feb 2018 10:57:11 -0500 (EST)
From:   David Miller <davem@...emloft.net>
To:     sd@...asysnail.net
Cc:     dsahern@...il.com, netdev@...r.kernel.org
Subject: Re: [PATCH net-next] ipv6: allow userspace to add IFA_F_OPTIMISTIC
 addresses

From: Sabrina Dubroca <sd@...asysnail.net>
Date: Mon, 26 Feb 2018 16:41:32 +0100

> What are you concerned about, if we let userspace set this flag?

I am concerned that the kernel is no longer in charge of making sure
that all of the RFC rules are met in this area.

Userland is now repsonsible for implementing correct behavior when it
takes over this task, and therefore the kernel has no say in the
matter of proper ipv6 neighbor discovery and addrconf behavior.

Unlike with things like DHCP, addrconf et al. in ipv6 are
fundamentally defined aspects of the protocol suite.

This division of responsibility means that we will also run into
situations where who (kernel or user) must take care of X or Y might
be ambiguous or hard to pin down in certain circumstances.

I really don't like this situation where a fundamental protocol is
conditionally the responsibility of the kernel, it's really bad design
decision overall.