Re: [PATCH net-next] net: ipv4: set orig_oif based on fib result for local traffic

[David Miller]

From: David Ahern 
Date: Thu, 10 Aug 2017 13:49:10 -0700

> Attempts to connect to a local address with a socket bound
> to a device with the local address hangs if there is no listener:
> 
>   $ ip addr sh dev eth1
>   3: eth1:  mtu 1500 qdisc mq state UP group 
> default qlen 1000
> link/ether 02:e0:f9:1c:00:37 brd ff:ff:ff:ff:ff:ff
> inet 10.100.1.4/24 scope global eth1
>valid_lft forever preferred_lft forever
> inet6 2001:db8:1::4/120 scope global
>valid_lft forever preferred_lft forever
> inet6 fe80::e0:f9ff:fe1c:37/64 scope link
>valid_lft forever preferred_lft forever
> 
>   $ vrf-test -I eth1 -r 10.100.1.4
>   
> 
> (don't let the command name fool you; vrf-test works without vrfs.)
> 
> The problem is that the original intended device, eth1 in this case, is
> lost when the tcp reset is sent, so the socket lookup does not find a
> match for the reset and the connect attempt hangs. Fix by adjusting
> orig_oif for local traffic to the device from the fib lookup result.
> 
> With this patch you get the more user friendly:
>   $ vrf-test -I eth1 -r 10.100.1.4
>   connect failed: 111: Connection refused
> 
> orig_oif is saved to the newly created rtable as rt_iif and when set
> it is used as the dif for socket lookups. It is set based on flowi4_oif
> passed in to ip_route_output_key_hash_rcu and will be set to either
> the loopback device, an l3mdev device, nothing (flowi4_oif = 0 which
> is the case in the example above) or a netdev index depending on the
> lookup path. In each case, resetting orig_oif to the device in the fib
> result for the RTN_LOCAL case allows the actual device to be preserved
> as the skb tx and rx is done over the loopback or VRF device.
> 
> Signed-off-by: David Ahern 
> ---
> As far as I can tell the current behavior goes back to the 2.6 days
> at least. Not sure it is worth adding to stable branches.

Applied, thanks David.

[PATCH net-next] net: ipv4: set orig_oif based on fib result for local traffic

[David Ahern]

Attempts to connect to a local address with a socket bound
to a device with the local address hangs if there is no listener:

  $ ip addr sh dev eth1
  3: eth1:  mtu 1500 qdisc mq state UP group 
default qlen 1000
link/ether 02:e0:f9:1c:00:37 brd ff:ff:ff:ff:ff:ff
inet 10.100.1.4/24 scope global eth1
   valid_lft forever preferred_lft forever
inet6 2001:db8:1::4/120 scope global
   valid_lft forever preferred_lft forever
inet6 fe80::e0:f9ff:fe1c:37/64 scope link
   valid_lft forever preferred_lft forever

  $ vrf-test -I eth1 -r 10.100.1.4
  

(don't let the command name fool you; vrf-test works without vrfs.)

The problem is that the original intended device, eth1 in this case, is
lost when the tcp reset is sent, so the socket lookup does not find a
match for the reset and the connect attempt hangs. Fix by adjusting
orig_oif for local traffic to the device from the fib lookup result.

With this patch you get the more user friendly:
  $ vrf-test -I eth1 -r 10.100.1.4
  connect failed: 111: Connection refused

orig_oif is saved to the newly created rtable as rt_iif and when set
it is used as the dif for socket lookups. It is set based on flowi4_oif
passed in to ip_route_output_key_hash_rcu and will be set to either
the loopback device, an l3mdev device, nothing (flowi4_oif = 0 which
is the case in the example above) or a netdev index depending on the
lookup path. In each case, resetting orig_oif to the device in the fib
result for the RTN_LOCAL case allows the actual device to be preserved
as the skb tx and rx is done over the loopback or VRF device.

Signed-off-by: David Ahern 
---
As far as I can tell the current behavior goes back to the 2.6 days
at least. Not sure it is worth adding to stable branches.

 net/ipv4/route.c | 6 ++
 1 file changed, 6 insertions(+)

diff --git a/net/ipv4/route.c b/net/ipv4/route.c
index 2ef46294475f..aae8f681ce1b 100644
--- a/net/ipv4/route.c
+++ b/net/ipv4/route.c
@@ -2439,6 +2439,12 @@ struct rtable *ip_route_output_key_hash_rcu(struct net 
*net, struct flowi4 *fl4,
/* L3 master device is the loopback for that domain */
dev_out = l3mdev_master_dev_rcu(FIB_RES_DEV(*res)) ? :
net->loopback_dev;
+
+   /* make sure orig_oif points to fib result device even
+* though packet rx/tx happens over loopback or l3mdev
+*/
+   orig_oif = FIB_RES_OIF(*res);
+
fl4->flowi4_oif = dev_out->ifindex;
flags |= RTCF_LOCAL;
goto make_route;
-- 
2.1.4