netdev - Re: net: do not allow changing SO_REUSEADDR/SO

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Date:   Fri, 8 Jun 2018 03:07:30 -0700
From:   Maciej Żenczykowski <zenczykowski@...il.com>
To:     Andrei Vagin <avagin@...tuozzo.com>
Cc:     "David S . Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Linux NetDev <netdev@...r.kernel.org>
Subject: Re: net: do not allow changing SO_REUSEADDR/SO_REUSEPORT on bound sockets

I think we probably need to make sk->sk_reuse back into a boolean.
(ie. eliminate SK_FORCE_REUSE)

Then add a new tcp/udp sk->ignore_bind_conflicts boolean setting...
(ie. not just for tcp, but sol_socket)  [or perhaps SO_REPAIR,
sk->repair or something]

What I'm not certain of is exactly what sorts of conflicts it should ignore...
all?  probably not, still seems utterly wrong to allow creation of 2 connected
tcp sockets with identical 5-tuples.

Would it only ignore conflicts against other i_b_c sockets?
ie. set it on all sockets as we're repairing, then clear it on them
all once we're done?

and ignore all the fast caching when checking conflicts for an i_b_c socket?

For CRIU is it safe to assume we're restoring an entire namespace into
a new namespace?

Could we perhaps instead allow a new namespace to ignore bind conflicts until
we flip it into enforcing mode?