netdev - Re: [PATCH] Revert "net: do not allow changing SO_REUSEADDR/SO

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Date:   Tue, 12 Jun 2018 14:40:25 -0700
From:   Maciej Żenczykowski <maze@...gle.com>
To:     David Miller <davem@...emloft.net>
Cc:     bart.vanassche@....com, Linux NetDev <netdev@...r.kernel.org>,
        Eric Dumazet <edumazet@...gle.com>
Subject: Re: [PATCH] Revert "net: do not allow changing SO_REUSEADDR/SO_REUSEPORT
 on bound sockets"

Any ideas about how to fix the core issue of tb->fast* being
effectively invalid?

ie. currently any reader of tb->fastreuse(port) which isn't simply
testing for it being >= 0 is basically a bug (-1 is the empty tb case,
so that AFAICT keeps on working).

For example sk_reuseport_match(tb, sk) can both fail to match when it
should, and can match when it shouldn't...

(at a quick glance, all the readers, and thus bugs are constrained to
the inet_csk_get_port() function)

Do we just delete that entire 'tb->fast*' optimization?  It would
certainly make the code much simpler...

Do we put special case per-family/protocol code (ie. presumably
another indirect call) to fix up tb->fast in the
setsockopt(SOREUSEADDR/PORT) codepath?

Something else?

(btw. I'm not certain if both 0->1 and 1->0 transitions on a bound
socket are equally buggy, I think one is more dangerous then the
other)