[PATCH 3.19.y-ckt 131/146] net: core: Correct an over-stringent device loop detection.

[Kamal Mostafa]

3.19.8-ckt2 -stable review patch.  If anyone has any objections, please let me know.

------------------

From: Vlad Yasevich <vyasevich at gmail.com>

[ Upstream commit d66bf7dd27573ee5ea90484899ee952c19ccb194 ]

The code in __netdev_upper_dev_link() has an over-stringent
loop detection logic that actually prevents valid configurations
from working correctly.

In particular, the logic returns an error if an upper device
is already in the list of all upper devices for a given dev.
This particular check seems to be a overzealous as it disallows
perfectly valid configurations.  For example:
  # ip l a link eth0 name eth0.10 type vlan id 10
  # ip l a dev br0 typ bridge
  # ip l s eth0.10 master br0
  # ip l s eth0 master br0  <--- Will fail

If you switch the last two commands (add eth0 first), then both
will succeed.  If after that, you remove eth0 and try to re-add
it, it will fail!

It appears to be enough to simply check adj_list to keeps things
safe.

I've tried stacking multiple devices multiple times in all different
combinations, and either rx_handler registration prevented the stacking
of the device linking cought the error.

Signed-off-by: Vladislav Yasevich <vyasevic at redhat.com>
Acked-by: Jiri Pirko <jiri at resnulli.us>
Acked-by: Veaceslav Falico <vfalico at gmail.com>
Signed-off-by: David S. Miller <davem at davemloft.net>
Signed-off-by: Kamal Mostafa <kamal at canonical.com>
---
 net/core/dev.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/core/dev.c b/net/core/dev.c
index 5dd905c..307e744f 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -5131,7 +5131,7 @@ static int __netdev_upper_dev_link(struct net_device *dev,
 	if (__netdev_find_adj(upper_dev, dev, &upper_dev->all_adj_list.upper))
 		return -EBUSY;
 
-	if (__netdev_find_adj(dev, upper_dev, &dev->all_adj_list.upper))
+	if (__netdev_find_adj(dev, upper_dev, &dev->adj_list.upper))
 		return -EEXIST;
 
 	if (master && netdev_master_upper_dev_get(dev))
-- 
1.9.1