netns: don't allocate an id for dead netns

First, let's explain the problem.
Suppose you have an ipip interface that stands in the netns foo and its link
part in the netns bar (so the netns bar has an nsid into the netns foo).
Now, you remove the netns bar:
 - the bar nsid into the netns foo is removed
 - the netns exit method of ipip is called, thus our ipip iface is removed:
   => a netlink message is built in the netns foo to advertise this deletion
   => this netlink message requests an nsid for bar, thus a new nsid is
      allocated for bar and never removed.

This patch adds a check in peernet2id() so that an id cannot be allocated for
a netns which is currently destroyed.

Signed-off-by: Nicolas Dichtel <nicolas.dichtel@6wind.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/net/core/net_namespace.c b/net/core/net_namespace.c
index cb5290b8c428c5c348b25d842ab9cf3797b70eba..70d3450588b2c73cbb4a3027f7f92e0c285b90d7 100644 (file)
--- a/net/core/net_namespace.c
+++ b/net/core/net_namespace.c
@@ -198,8 +198,10 @@ static int __peernet2id(struct net *net, struct net *peer, bool alloc)
  */
 int peernet2id(struct net *net, struct net *peer)
 {
-       int id = __peernet2id(net, peer, true);
+       bool alloc = atomic_read(&peer->count) == 0 ? false : true;
+       int id;
 
+       id = __peernet2id(net, peer, alloc);
        return id >= 0 ? id : NETNSA_NSID_NOT_ASSIGNED;
 }
 EXPORT_SYMBOL(peernet2id);