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

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Message-ID: <20100413151238.GA13153@gondor.apana.org.au>
Date:	Tue, 13 Apr 2010 23:12:38 +0800
From:	Herbert Xu <herbert@...dor.apana.org.au>
To:	"Michael S. Tsirkin" <mst@...hat.com>
Cc:	"David S. Miller" <davem@...emloft.net>,
	Paul Moore <paul.moore@...com>,
	David Woodhouse <David.Woodhouse@...el.com>,
	netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
	Jan Kiszka <jan.kiszka@...mens.com>,
	qemu-devel <qemu-devel@...gnu.org>
Subject: Re: [PATCH] tun: orphan an skb on tx

On Tue, Apr 13, 2010 at 05:59:44PM +0300, Michael S. Tsirkin wrote:
> The following situation was observed in the field:
> tap1 sends packets, tap2 does not consume them, as a result
> tap1 can not be closed. This happens because
> tun/tap devices can hang on to skbs undefinitely.
> 
> As noted by Herbert, possible solutions include a timeout followed by a
> copy/change of ownership of the skb, or always copying/changing
> ownership if we're going into a hostile device.
> 
> This patch implements the second approach.
> 
> Note: one issue still remaining is that since skbs
> keep reference to tun socket and tun socket has a
> reference to tun device, we won't flush backlog,
> instead simply waiting for all skbs to get transmitted.
> At least this is not user-triggerable, and
> this was not reported in practice, my assumption is
> other devices besides tap complete an skb
> within finite time after it has been queued.
> 
> A possible solution for the second issue
> would not to have socket reference the device,
> instead, implement dev->destructor for tun, and
> wait for all skbs to complete there, but this
> needs some thought, probably too risky for 2.6.34.
> 
> Signed-off-by: Michael S. Tsirkin <mst@...hat.com>
> Tested-by: Yan Vugenfirer <yvugenfi@...hat.com>

Acked-by: Herbert Xu <herbert@...dor.apana.org.au>

Thanks,
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Email: Herbert Xu ~{PmV>HI~} <herbert@...dor.apana.org.au>
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