netdev - Re: [PATCH] tun: orphan an skb on tx

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Message-ID: <20100414005822.GD18044@gondor.apana.org.au>
Date:	Wed, 14 Apr 2010 08:58:22 +0800
From:	Herbert Xu <herbert@...dor.apana.org.au>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	"Michael S. Tsirkin" <mst@...hat.com>,
	Jan Kiszka <jan.kiszka@...mens.com>,
	"David S. Miller" <davem@...emloft.net>,
	Paul Moore <paul.moore@...com>,
	David Woodhouse <David.Woodhouse@...el.com>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	qemu-devel <qemu-devel@...gnu.org>
Subject: Re: [PATCH] tun: orphan an skb on tx

On Tue, Apr 13, 2010 at 08:31:03PM +0200, Eric Dumazet wrote:
>
> Herbert Acked your patch, so I guess its OK, but I think it can be
> dangerous.

The tun socket accounting was never designed to stop it from
flooding another tun interface.  It's there to stop it from
transmitting above a destination interface TX bandwidth and
cause unnecessary packet drops.  It also limits the total amount
of kernel memory that can be pinned down by a single tun interface.

In this case, all we're doing is shifting the accounting from the
"hardware" queue to the qdisc queue.

So your ability to flood a tun interface is essentially unchanged.

BTW we do the same thing in a number of hardware drivers, as well
as virtio-net.

Cheers,
-- 
Visit Openswan at http://www.openswan.org/
Email: Herbert Xu ~{PmV>HI~} <herbert@...dor.apana.org.au>
Home Page: http://gondor.apana.org.au/~herbert/
PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt
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