netdev - Re: Unix Socket buffer attribution

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Date:	Wed, 23 Jan 2013 08:56:28 -0800
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Yannick Koehler <yannick@...hler.name>
Cc:	Cong Wang <xiyou.wangcong@...il.com>, netdev@...r.kernel.org
Subject: Re: Unix Socket buffer attribution

On Wed, 2013-01-23 at 11:36 -0500, Yannick Koehler wrote:
> > So what prevents a malicious program to DOS the machine ?
> 
> The recv queue (checked with recvq_full()) and receiving's socket
> rcvbuf (check added in my patch).
> 

Nope. The limit is given in number of messages, and its the socket
backlog. Many machines setup a somaxconn = 1024 limit in order
to reasonably listen for TCP connections.

> Actually the current situation can easily lead to a DOS situation.  I
> simply have to write one application that connect to a unix socket
> domain and have it send me data for which I never call recvfrom() and
> voilà, all other consumer of this unix socket application will no more
> be able to communicate with this application once it maxed out it's
> sndbuf, default is 128k I believe.

A single message can consume ~128k.

If we allow 1024 messages being sent, we consume 128 Mbytes per evil
socket.

Enough to kill many linux based devices.

You'll have to add proper limits (SO_RCVBUF), accounting the truesize of
all accumulated messages.



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