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

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Date:   Mon, 04 Jun 2018 17:14:55 -0400 (EDT)
From:   David Miller <davem@...emloft.net>
To:     zenczykowski@...il.com
Cc:     maze@...gle.com, edumazet@...gle.com, netdev@...r.kernel.org
Subject: Re: [PATCH] net: do not allow changing SO_REUSEADDR/SO_REUSEPORT
 on bound sockets

From: "Maciej Żenczykowski" <zenczykowski@...il.com>
Date: Sun,  3 Jun 2018 10:47:05 -0700

> From: Maciej Żenczykowski <maze@...gle.com>
> 
> It is not safe to do so because such sockets are already in the
> hash tables and changing these options can result in invalidating
> the tb->fastreuse(port) caching.
> 
> This can have later far reaching consequences wrt. bind conflict checks
> which rely on these caches (for optimization purposes).
> 
> Not to mention that you can currently end up with two identical
> non-reuseport listening sockets bound to the same local ip:port
> by clearing reuseport on them after they've already both been bound.
> 
> There is unfortunately no EISBOUND error or anything similar,
> and EISCONN seems to be misleading for a bound-but-not-connected
> socket, so use EUCLEAN 'Structure needs cleaning' which AFAICT
> is the closest you can get to meaning 'socket in bad state'.
> (although perhaps EINVAL wouldn't be a bad choice either?)
> 
> This does unfortunately run the risk of breaking buggy
> userspace programs...
> 
> Signed-off-by: Maciej Żenczykowski <maze@...gle.com>
> Change-Id: I77c2b3429b2fdf42671eee0fa7a8ba721c94963b

Applied and queued up for -stable.