Re: [msysGit] [PATCH/RFC 06/11] run-command: add kill_async() and is_async_alive()

From: Johannes Sixt <j6t@kdbg.org>
Date: Dec 2, 2009, 19:27 UTC
Message-ID: <200912022027.23344.j6t@kdbg.org>
In-Reply-To: <40aa078e0912020757i3b63ef6eh71c3d4d99047f1f2@mail.gmail.com>

On Mittwoch, 2. Dezember 2009, Erik Faye-Lund wrote:

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> On Fri, Nov 27, 2009 at 8:59 PM, Johannes Sixt <j6t@kdbg.org> wrote:
> > "relatively small chance of stuff blowing up"? The docs of
> > TerminateThread: "... the kernel32 state for the thread's process could
> > be inconsistent." That's scary if we are talking about a process that
> > should run for days or weeks without interruption.
>
> I think there's a misunderstanding here. I thought your suggestion was
> to simply call die(), which would take down the main process. After
> reading this explanation, I think you're talking about giving an error
> and rejecting the connection instead. Which makes more sense than to
> risk crashing the main-process, indeed.

Just rejecting a connection is certainly the simplest do to keep the daemon process alive. But the server can be DoS-ed from a single source IP.

Currently git-daemon can only be DDoS-ed because there is a maximum number of connections, which are not closed if all of them originate from different IPs.

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> > Case 2 could be achieved by using setsockopt() with SO_RCVTIMEO and
> > SO_SNDTIMEO and a tiny timeout. But notice that we would set a timeout in
> > one thread while another thread is waiting in ReadFile() or WriteFile().
> > Would that work?
>
> I think it should work fine, but I won't give you a guarantee ;)
> Perhaps we should have a configurable global max timeout, and just set
> that on all sockets? Or does this open for DDOS attacks?

I'm sure that there is a global timeout already, but it is in the order of minutes, which is too long. Here I mean it to be set to zero or one milli-second so that the connection closes right away - as if the process on the server side had been killed.

Hm - perhaps it is possible to really *close* the socket while some other thread waits in ReadFile() or WriteFile()?

-- Hannes