peernet2id_alloc() is racy without rtnl_lock() as atomic_read(&peer->count) under net->nsid_lock does not guarantee, peer is alive:
rcu_read_lock() peernet2id_alloc() .. spin_lock_bh(&net->nsid_lock) .. atomic_read(&peer->count) == 1 .. .. put_net() .. cleanup_net() .. for_each_net(tmp) .. spin_lock_bh(&tmp->nsid_lock) .. __peernet2id(tmp, net) == -1 .. .. .. .. __peernet2id_alloc(alloc == true) .. .. .. rcu_read_unlock() .. .. synchronize_rcu() .. kmem_cache_free(net) After the above situation, net::netns_id contains id pointing to freed memory, and any other dereferencing by the id will operate with this freed memory. Currently, peernet2id_alloc() is used under rtnl_lock() everywhere except ovs_vport_cmd_fill_info(), and this race can't occur. But peernet2id_alloc() is generic interface, and better we fix it before someone really starts use it in wrong context. Signed-off-by: Kirill Tkhai <ktk...@virtuozzo.com> --- net/core/net_namespace.c | 23 +++++++++++++++++++---- 1 file changed, 19 insertions(+), 4 deletions(-) diff --git a/net/core/net_namespace.c b/net/core/net_namespace.c index 60a71be75aea..6a4eab438221 100644 --- a/net/core/net_namespace.c +++ b/net/core/net_namespace.c @@ -221,17 +221,32 @@ static void rtnl_net_notifyid(struct net *net, int cmd, int id); */ int peernet2id_alloc(struct net *net, struct net *peer) { - bool alloc; + bool alloc = false, alive = false; int id; - if (atomic_read(&net->count) == 0) - return NETNSA_NSID_NOT_ASSIGNED; spin_lock_bh(&net->nsid_lock); - alloc = atomic_read(&peer->count) == 0 ? false : true; + /* Spinlock guarantees we never hash a peer to net->netns_ids + * after idr_destroy(&net->netns_ids) occurs in cleanup_net(). + */ + if (atomic_read(&net->count) == 0) { + id = NETNSA_NSID_NOT_ASSIGNED; + goto unlock; + } + /* + * When peer is obtained from RCU lists, we may race with + * its cleanup. Check whether it's alive, and this guarantees + * we never hash a peer back to net->netns_ids, after it has + * just been idr_remove()'d from there in cleanup_net(). + */ + if (maybe_get_net(peer)) + alive = alloc = true; id = __peernet2id_alloc(net, peer, &alloc); +unlock: spin_unlock_bh(&net->nsid_lock); if (alloc && id >= 0) rtnl_net_notifyid(net, RTM_NEWNSID, id); + if (alive) + put_net(peer); return id; } EXPORT_SYMBOL_GPL(peernet2id_alloc);