net: core: Correct an over-stringent device loop detection.

commit d66bf7dd27573ee5ea90484899ee952c19ccb194 upstream.

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@redhat.com>
Acked-by: Jiri Pirko <jiri@resnulli.us>
Acked-by: Veaceslav Falico <vfalico@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Luis Henriques <luis.henriques@canonical.com>

diff --git a/net/core/dev.c b/net/core/dev.c
index 9742052fb55e5032a5192e95ce593cef4ad46427..afa766c453e005d62479615643cbf280199ce455 100644 (file)
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -4997,7 +4997,7 @@ 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))