netdev - Re: [PATCH 8/8] x25: use limited socket backlog

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Date:	Thu, 4 Mar 2010 09:44:49 +1100
From:	andrew hendry <andrew.hendry@...il.com>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	"Zhu, Yi" <yi.zhu@...el.com>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: Re: [PATCH 8/8] x25: use limited socket backlog

Thinking like someone trying to break it, it may be possible for X25
to flood backlog.
With specific environments, enough circuits XoT/XoE may be able to.
Also tun + TUNSETLINK and some userspace code it might be possible. A
limit should be set just in case, and to cover X25 normal use it
doesn't need to be very big. 256 seems reasonable to start.
I'll look at setting up a fast virtual x.25 environment to test its
backlog behavior.

I think resolve issue for common protocols first, I don't know if
X25=m would be used widely.

Andrew.

On Thu, Mar 4, 2010 at 1:33 AM, Eric Dumazet <eric.dumazet@...il.com> wrote:
> Le mercredi 03 mars 2010 à 22:00 +0800, Zhu, Yi a écrit :
>> andrew hendry <andrew.hendry@...il.com> wrote:
>>
>> > Will wait for the next spin and in the meantime think if there is way
>> > to test it. x25 with no loopback and being so slow probably cant generate the same
>> > as your UDP case.
>>
>> I didn't find a way to drop the packet correctly. So I didn't change any behavior in
>> this patch. Nor did I do in the second spin. It will be fine if you also think x25 doesn't
>> need to limit its backlog size.
>
> So are we sure we cant flood X25 backlog, using X25 over IP ?
>
> You discovered a _fatal_ flaw in backlog processing, we should close all
> holes, not only UDP case. You can be sure many bad guys will inspect all
> possibilities to bring down Linux hosts.
>
> If you feel uncomfortable with a small limit, just stick a big one, like
> 256 packets, and you are 100% sure you wont break a protocol. If this
> limit happens to be too small, we can change it later.
>
> (No need to count bytes, since truesize includes kernel overhead, and
> this overhead depends on 32/64 wide of host and kernel versions)
>
>
>
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