[PATCH nf,v2] netfilter: nf_nat: unregister and release hooks on error

[Pablo Neira Ayuso <pablo@netfilter.org>]

After the base nat hooks are registered, the first nested nat hook is
added through nf_hook_entries_insert_raw() and ->users is bumped.

However, sashiko reports that nf_hook_entries_insert_raw() fails, then
->users count remains at zero and nf_nat_unregister_fn() could hit
WARN_ON() since base nat hooks with no users is unexpected in the
unregistration path.

Postpone setting nat_proto_net->nat_hook_ops when the hooks are
registered to simplify the error path to decide whether the nat hooks
need unwinding.

Fixes: 1cd472bf036c ("netfilter: nf_nat: add nat hook register functions to nf_nat")
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
---
v2: - move common error path handling under goto label
    - postpone setting nat_proto_net->nat_hook_ops to decide what to
      do in the error path.

 net/netfilter/nf_nat_core.c | 43 ++++++++++++++++++++++++-------------
 1 file changed, 28 insertions(+), 15 deletions(-)

diff --git a/net/netfilter/nf_nat_core.c b/net/netfilter/nf_nat_core.c
index 8ac326e1eb5b..de1fa53912c2 100644
--- a/net/netfilter/nf_nat_core.c
+++ b/net/netfilter/nf_nat_core.c
@@ -1224,31 +1224,44 @@ int nf_nat_register_fn(struct net *net, u8 pf, const struct nf_hook_ops *ops,
 		}
 
 		ret = nf_register_net_hooks(net, nat_ops, ops_count);
-		if (ret < 0) {
-			mutex_unlock(&nf_nat_proto_mutex);
-			for (i = 0; i < ops_count; i++) {
-				priv = nat_ops[i].priv;
-				kfree_rcu(priv, rcu_head);
-			}
-			kfree_rcu(nat_ops, rcu);
-			return ret;
-		}
-
-		nat_proto_net->nat_hook_ops = nat_ops;
+		if (ret < 0)
+			goto err_free_hooks;
 	}
 
 	nat_ops = nat_proto_net->nat_hook_ops;
 	priv = nat_ops[hooknum].priv;
 	if (WARN_ON_ONCE(!priv)) {
-		mutex_unlock(&nf_nat_proto_mutex);
-		return -EOPNOTSUPP;
+		ret = -EOPNOTSUPP;
+		goto err_unregister_hooks;
 	}
 
 	ret = nf_hook_entries_insert_raw(&priv->entries, ops);
-	if (ret == 0)
-		nat_proto_net->users++;
+	if (ret)
+		goto err_unregister_hooks;
+
+	if (!nat_proto_net->nat_hook_ops)
+		nat_proto_net->nat_hook_ops = nat_ops;
+
+	nat_proto_net->users++;
 
 	mutex_unlock(&nf_nat_proto_mutex);
+
+	return 0;
+
+err_unregister_hooks:
+	if (nat_proto_net->nat_hook_ops) {
+		mutex_unlock(&nf_nat_proto_mutex);
+		return ret;
+	}
+	nf_unregister_net_hooks(net, nat_ops, ops_count);
+err_free_hooks:
+	mutex_unlock(&nf_nat_proto_mutex);
+	for (i = 0; i < ops_count; i++) {
+		priv = nat_ops[i].priv;
+		kfree_rcu(priv, rcu_head);
+	}
+	kfree_rcu(nat_ops, rcu);
+
 	return ret;
 }
 
-- 
2.47.3