[PATCH] net_namespace: fixed net_device reference leak

During namespace cleanup, if ‘dst’ subsystem is holding
a reference to the loopback interface in the namespace, it does not get
released. This is because in the case where the net_device held by 'dst'
is same as the namespace's loopback net_device, current code first
does a ’dev_hold’ on the same device followed by a ‘dev_put’ on the
same device resulting in a no-op.

This change fixes this leak by assigning the initial namespace’s loopback
device to the ‘dst’’ before releasing the reference to the network device
being unregistered.

Additional reference: https://github.com/docker/docker/issues/5618

Signed-off-by: Jojy G Varghese <redacted>
---
 net/core/dst.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/core/dst.c b/net/core/dst.c
index a1656e3..a18e8ea 100644
--- a/net/core/dst.c
+++ b/net/core/dst.c

@@ -433,7 +433,7 @@ static void dst_ifdown(struct dst_entry *dst,

struct net_device *dev,
                dst->input = dst_discard;
                dst->output = dst_discard_out;
        } else {
-               dst->dev = dev_net(dst->dev)->loopback_dev;
+               dst->dev = init_net.loopback_dev;
                dev_hold(dst->dev);
                dev_put(dev);
        }
-- 
1.8.3.1