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netns: protect netns ID lookups with RCU

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__peernet2id() can be protected by RCU as it only calls idr_for_each(),
which is RCU-safe, and never modifies the nsid table.

rtnl_net_dumpid() can also do lockless lookups. It does two nested
idr_for_each() calls on nsid tables (one direct call and one indirect
call because of rtnl_net_dumpid_one() calling __peernet2id()). The
netnsid tables are never updated. Therefore it is safe to not take the
nsid_lock and run within an RCU-critical section instead.

Signed-off-by: Guillaume Nault <gnault@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Guillaume Nault 2020-01-13 22:39:22 +01:00 committed by David S. Miller
parent 4905294162
commit 2dce224f46
1 changed files with 7 additions and 15 deletions
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22
net/core/net_namespace.c
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@ -211,7 +211,7 @@ static int net_eq_idr(int id, void *net, void *peer)
return 0;
}
/* Should be called with nsid_lock held. */
/* Must be called from RCU-critical section or with nsid_lock held */
static int __peernet2id(const struct net *net, struct net *peer)
{
int id = idr_for_each(&net->netns_ids, net_eq_idr, peer);
@ -272,9 +272,10 @@ int peernet2id(struct net *net, struct net *peer)
{
int id;
spin_lock_bh(&net->nsid_lock);
rcu_read_lock();
id = __peernet2id(net, peer);
spin_unlock_bh(&net->nsid_lock);
rcu_read_unlock();
return id;
}
EXPORT_SYMBOL(peernet2id);
@ -941,6 +942,7 @@ struct rtnl_net_dump_cb {
int s_idx;
};
/* Runs in RCU-critical section. */
static int rtnl_net_dumpid_one(int id, void *peer, void *data)
{
struct rtnl_net_dump_cb *net_cb = (struct rtnl_net_dump_cb *)data;
@ -1025,19 +1027,9 @@ static int rtnl_net_dumpid(struct sk_buff *skb, struct netlink_callback *cb)
goto end;
}
spin_lock_bh(&net_cb.tgt_net->nsid_lock);
if (net_cb.fillargs.add_ref &&
!net_eq(net_cb.ref_net, net_cb.tgt_net) &&
!spin_trylock_bh(&net_cb.ref_net->nsid_lock)) {
spin_unlock_bh(&net_cb.tgt_net->nsid_lock);
err = -EAGAIN;
goto end;
}
rcu_read_lock();
idr_for_each(&net_cb.tgt_net->netns_ids, rtnl_net_dumpid_one, &net_cb);
if (net_cb.fillargs.add_ref &&
!net_eq(net_cb.ref_net, net_cb.tgt_net))
spin_unlock_bh(&net_cb.ref_net->nsid_lock);
spin_unlock_bh(&net_cb.tgt_net->nsid_lock);
rcu_read_unlock();
cb->args[0] = net_cb.idx;
end: