Re: [PATCH net] tun: fix premature POLLOUT notification on tun devices

[David Miller]

From: Hannes Frederic Sowa 
Date: Mon, 13 Mar 2017 00:00:26 +0100

> aszlig observed failing ssh tunnels (-w) during initialization since
> commit cc9da6cc4f56e0 ("ipv6: addrconf: use stable address generator for
> ARPHRD_NONE"). We already had reports that the mentioned commit breaks
> Juniper VPN connections. I can't clearly say that the Juniper VPN client
> has the same problem, but it is worth a try to hint to this patch.
> 
> Because of the early generation of link local addresses, the kernel now
> can start asking for routers on the local subnet much earlier than usual.
> Those router solicitation packets arrive inside the ssh channels and
> should be transmitted to the tun fd before the configuration scripts
> might have upped the interface and made it ready for transmission.
> 
> ssh polls on the interface and receives back a POLL_OUT. It tries to send
> the earily router solicitation packet to the tun interface.  Unfortunately
> it hasn't been up'ed yet by config scripts, thus failing with -EIO. ssh
> doesn't retry again and considers the tun interface broken forever.
> 
> Link: https://bugzilla.kernel.org/show_bug.cgi?id=121131
> Fixes: cc9da6cc4f56 ("ipv6: addrconf: use stable address generator for 
> ARPHRD_NONE")
> Cc: Bjørn Mork 
> Reported-by: Valdis Kletnieks 
> Cc: Valdis Kletnieks 
> Reported-by: Jonas Lippuner 
> Cc: Jonas Lippuner 
> Reported-by: aszlig 
> Cc: aszlig 
> Signed-off-by: Hannes Frederic Sowa 

Applied and queued up for -stable.

[PATCH net] tun: fix premature POLLOUT notification on tun devices

[Hannes Frederic Sowa]

aszlig observed failing ssh tunnels (-w) during initialization since
commit cc9da6cc4f56e0 ("ipv6: addrconf: use stable address generator for
ARPHRD_NONE"). We already had reports that the mentioned commit breaks
Juniper VPN connections. I can't clearly say that the Juniper VPN client
has the same problem, but it is worth a try to hint to this patch.

Because of the early generation of link local addresses, the kernel now
can start asking for routers on the local subnet much earlier than usual.
Those router solicitation packets arrive inside the ssh channels and
should be transmitted to the tun fd before the configuration scripts
might have upped the interface and made it ready for transmission.

ssh polls on the interface and receives back a POLL_OUT. It tries to send
the earily router solicitation packet to the tun interface.  Unfortunately
it hasn't been up'ed yet by config scripts, thus failing with -EIO. ssh
doesn't retry again and considers the tun interface broken forever.

Link: https://bugzilla.kernel.org/show_bug.cgi?id=121131
Fixes: cc9da6cc4f56 ("ipv6: addrconf: use stable address generator for 
ARPHRD_NONE")
Cc: Bjørn Mork 
Reported-by: Valdis Kletnieks 
Cc: Valdis Kletnieks 
Reported-by: Jonas Lippuner 
Cc: Jonas Lippuner 
Reported-by: aszlig 
Cc: aszlig 
Signed-off-by: Hannes Frederic Sowa 
---
 drivers/net/tun.c | 18 +++---
 1 file changed, 15 insertions(+), 3 deletions(-)

diff --git a/drivers/net/tun.c b/drivers/net/tun.c
index f58b7d850114b0..34cc3c590aa5c5 100644
--- a/drivers/net/tun.c
+++ b/drivers/net/tun.c
@@ -822,7 +822,18 @@ static void tun_net_uninit(struct net_device *dev)
 /* Net device open. */
 static int tun_net_open(struct net_device *dev)
 {
+   struct tun_struct *tun = netdev_priv(dev);
+   int i;
+
netif_tx_start_all_queues(dev);
+
+   for (i = 0; i < tun->numqueues; i++) {
+   struct tun_file *tfile;
+
+   tfile = rtnl_dereference(tun->tfiles[i]);
+   tfile->socket.sk->sk_write_space(tfile->socket.sk);
+   }
+
return 0;
 }
 
@@ -1103,9 +1114,10 @@ static unsigned int tun_chr_poll(struct file *file, 
poll_table *wait)
if (!skb_array_empty(>tx_array))
mask |= POLLIN | POLLRDNORM;
 
-   if (sock_writeable(sk) ||
-   (!test_and_set_bit(SOCKWQ_ASYNC_NOSPACE, >sk_socket->flags) &&
-sock_writeable(sk)))
+   if (tun->dev->flags & IFF_UP &&
+   (sock_writeable(sk) ||
+(!test_and_set_bit(SOCKWQ_ASYNC_NOSPACE, >sk_socket->flags) &&
+ sock_writeable(sk
mask |= POLLOUT | POLLWRNORM;
 
if (tun->dev->reg_state != NETREG_REGISTERED)
-- 
2.9.3