[PATCH 4.4 02/28] net: check dead netns for peernet2id_alloc()

From: Greg Kroah-Hartman
Date: Fri Dec 09 2016 - 11:19:54 EST

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


From: WANG Cong <xiyou.wangcong@xxxxxxxxx>

[ Upstream commit cfc44a4d147ea605d66ccb917cc24467d15ff867 ]

Andrei reports we still allocate netns ID from idr after we destroy
it in cleanup_net().

list_for_each_entry_reverse(ops, &pernet_list, list)
ops_exit_list(ops, &net_exit_list);
-> rollback_registered_many()
-> rtmsg_ifinfo_build_skb()
-> rtnl_fill_ifinfo()
-> peernet2id_alloc()

After that point we should not even access net->netns_ids, we
should check the death of the current netns as early as we can in

For net-next we can consider to avoid sending rtmsg totally,
it is a good optimization for netns teardown path.

Fixes: 0c7aecd4bde4 ("netns: add rtnl cmd to add and get peer netns ids")
Reported-by: Andrei Vagin <avagin@xxxxxxxxx>
Cc: Nicolas Dichtel <nicolas.dichtel@xxxxxxxxx>
Signed-off-by: Cong Wang <xiyou.wangcong@xxxxxxxxx>
Acked-by: Andrei Vagin <avagin@xxxxxxxxxx>
Signed-off-by: Nicolas Dichtel <nicolas.dichtel@xxxxxxxxx>
Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
net/core/net_namespace.c | 2 ++
1 file changed, 2 insertions(+)

--- a/net/core/net_namespace.c
+++ b/net/core/net_namespace.c
@@ -217,6 +217,8 @@ int peernet2id_alloc(struct net *net, st
bool alloc;
int id;

+ if (atomic_read(&net->count) == 0)
spin_lock_irqsave(&net->nsid_lock, flags);
alloc = atomic_read(&peer->count) == 0 ? false : true;
id = __peernet2id_alloc(net, peer, &alloc);