netfilter: ctnetlink: fix reliable event delivery if message building fails

This patch fixes a bug that allows to lose events when reliable
event delivery mode is used, ie. if NETLINK_BROADCAST_SEND_ERROR
and NETLINK_RECV_NO_ENOBUFS socket options are set.
Signed-off-by: NPablo Neira Ayuso <pablo@netfilter.org>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

include/linux/netfilter/nfnetlink.h

@@ -76,7 +76,7 @@ extern int nfnetlink_subsys_unregister(const struct nfnetlink_subsystem *n);
 extern int nfnetlink_has_listeners(struct net *net, unsigned int group);
 extern int nfnetlink_send(struct sk_buff *skb, struct net *net, u32 pid, unsigned group,
 			  int echo, gfp_t flags);
-extern void nfnetlink_set_err(struct net *net, u32 pid, u32 group, int error);
+extern int nfnetlink_set_err(struct net *net, u32 pid, u32 group, int error);
 extern int nfnetlink_unicast(struct sk_buff *skb, struct net *net, u_int32_t pid, int flags);
 
 extern void nfnl_lock(void);

net/netfilter/nf_conntrack_netlink.c

@@ -582,7 +582,9 @@ ctnetlink_conntrack_event(unsigned int events, struct nf_ct_event *item)
 nlmsg_failure:
 	kfree_skb(skb);
 errout:
-	nfnetlink_set_err(net, 0, group, -ENOBUFS);
+	if (nfnetlink_set_err(net, 0, group, -ENOBUFS) > 0)
+		return -ENOBUFS;
+
 	return 0;
 }
 #endif /* CONFIG_NF_CONNTRACK_EVENTS */

net/netfilter/nfnetlink.c

@@ -113,9 +113,9 @@ int nfnetlink_send(struct sk_buff *skb, struct net *net, u32 pid,
 }
 EXPORT_SYMBOL_GPL(nfnetlink_send);
 
-void nfnetlink_set_err(struct net *net, u32 pid, u32 group, int error)
+int nfnetlink_set_err(struct net *net, u32 pid, u32 group, int error)
 {
-	netlink_set_err(net->nfnl, pid, group, error);
+	return netlink_set_err(net->nfnl, pid, group, error);
 }
 EXPORT_SYMBOL_GPL(nfnetlink_set_err);