linux-kernel - Re: SO_REUSEADDR not allowing server and client to use same port

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Date:	Thu, 28 Feb 2008 21:41:47 +0100
From:	Willy Tarreau <w@....eu>
To:	Alan Cox <alan@...rguk.ukuu.org.uk>
Cc:	Nebojsa Miljanovic <neb@...atel-lucent.com>,
	linux-kernel@...r.kernel.org,
	"Kittlitz, Edward (Ned)" <nkittlitz@...atel-lucent.com>,
	asweeney@...atel-lucent.com,
	"Polhemus, William (Bart)" <bpolhemus@...atel-lucent.com>
Subject: Re: SO_REUSEADDR not allowing server and client to use same port

On Thu, Feb 28, 2008 at 08:19:26PM +0000, Alan Cox wrote:
> > Currently, Linux does not allow reuse of same local port for both TCP server and
> > TCP client. I understand that there may be a need to prevent two servers from
> 
> Think about what happens for simultaneous connect (that obscure little
> corner of the tcp/ip spec). Now think about what it means for security.
>
> ALan

exactly. That's why I think that requiring the server to explicitly allow
socket reuse is mandatory. On another side of the problem, I really think
that we should make the simultaneous connect configurable. I've been patching
all of my own 2.4 kernels for a while to add a config option to turn it off
because there is a real security issue with this on. At least for mainline,
it should be a sysctl. No stateful firewall I know supports the feature, so
legitimate uses of this feature are likely very very small.

Willy
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