netdev - Re: Add a SOCK_DESTROY operation to close sockets from userspace

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Message-ID: <CALx6S379hXL=QEBF-HmOvPr3K55tS87HV=wKOySro1A0ogmWcQ@mail.gmail.com>
Date:	Thu, 19 Nov 2015 09:38:37 -0800
From:	Tom Herbert <tom@...bertland.com>
To:	Hannes Frederic Sowa <hannes@...essinduktion.org>
Cc:	Eric Dumazet <eric.dumazet@...il.com>,
	David Miller <davem@...emloft.net>, zenczykowski@...il.com,
	Lorenzo Colitti <lorenzo@...gle.com>,
	Stephen Hemminger <stephen@...workplumber.org>,
	Linux Kernel Network Developers <netdev@...r.kernel.org>,
	Eric Dumazet <edumazet@...gle.com>, Erik Kline <ek@...gle.com>,
	Dmitry Torokhov <dtor@...gle.com>
Subject: Re: Add a SOCK_DESTROY operation to close sockets from userspace

> I actually don't have an issue with killing from user space that much. I
> still recommend (and actually have started to look at it today) to add a
> new substate for TCP TIMEWAIT and don't have any issue if we block the
> socket for 60 seconds and send RSTs to all incoming data. This way we
> can solve the problem Florian indicated as well as this problem. Users
> can happily kill TCP connections then.
>
Neither do I have a problem with killing connections from userspace,
but we do have to acknowledge that this is a powerful and invasive
mechanism. I suggest:

1) We need transparency. If a third party kills a TCP connection then
the application should be informed of specifically that. This seems
easy enough to just pick an appropriate error number as I suggested.
2) We need constraints. This feature seems to be specific to a very
narrow use case. It is not at all clear to me if there are any
legitimate uses cases beyond Android, enabling this by default in the
stack creates a non-zero amount of risk and liability for abuse. It
seems like this should be an opt-in sort of feature, with a kernel
CONFIG or maybe opt-in per socket.

Tom

> Bye,
> Hannes
>
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