From e17f49e28a1686f3d21ee3e0f62a802f97bac386 Mon Sep 17 00:00:00 2001
From: Michael S. Tsirkin <mst@redhat.com>
Date: Tue, 13 Apr 2010 04:59:44 +0000
Subject: tun: orphan an skb on tx


From: Michael S. Tsirkin <mst@redhat.com>

[ Upstream commit 0110d6f22f392f976e84ab49da1b42f85b64a3c5 ]

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@redhat.com>
Tested-by: Yan Vugenfirer <yvugenfi@redhat.com>
Acked-by: Herbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
---
 drivers/net/tun.c |    4 ++++
 1 file changed, 4 insertions(+)

--- a/drivers/net/tun.c
+++ b/drivers/net/tun.c
@@ -380,6 +380,10 @@ static netdev_tx_t tun_net_xmit(struct s
 		}
 	}
 
+	/* Orphan the skb - required as we might hang on to it
+	 * for indefinite time. */
+	skb_orphan(skb);
+
 	/* Enqueue packet */
 	skb_queue_tail(&tun->socket.sk->sk_receive_queue, skb);
 	dev->trans_start = jiffies;