nefilter: nfnetlink: add nfnetlink_set_err and use it in ctnetlink

This patch adds nfnetlink_set_err() to propagate the error to netlink
broadcast listener in case of memory allocation errors in the
message building.
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
Signed-off-by: Patrick McHardy <kaber@trash.net>

include/linux/netfilter/nfnetlink.h

@@ -76,6 +76,7 @@ extern int nfnetlink_subsys_unregister(const struct nfnetlink_subsystem *n);
 extern int nfnetlink_has_listeners(unsigned int group);
 extern int nfnetlink_send(struct sk_buff *skb, u32 pid, unsigned group, 
 			  int echo);
+extern void nfnetlink_set_err(u32 pid, u32 group, int error);
 extern int nfnetlink_unicast(struct sk_buff *skb, u_int32_t pid, int flags);
 
 extern void nfnl_lock(void);

net/netfilter/nf_conntrack_netlink.c

@@ -518,6 +518,7 @@ static int ctnetlink_conntrack_event(struct notifier_block *this,
 nla_put_failure:
 	rcu_read_unlock();
 nlmsg_failure:
+	nfnetlink_set_err(0, group, -ENOBUFS);
 	kfree_skb(skb);
 	return NOTIFY_DONE;
 }
@@ -1514,6 +1515,7 @@ static int ctnetlink_expect_event(struct notifier_block *this,
 nla_put_failure:
 	rcu_read_unlock();
 nlmsg_failure:
+	nfnetlink_set_err(0, 0, -ENOBUFS);
 	kfree_skb(skb);
 	return NOTIFY_DONE;
 }

net/netfilter/nfnetlink.c

@@ -113,6 +113,12 @@ int nfnetlink_send(struct sk_buff *skb, u32 pid, unsigned group, int echo)
 }
 EXPORT_SYMBOL_GPL(nfnetlink_send);
 
+void nfnetlink_set_err(u32 pid, u32 group, int error)
+{
+	netlink_set_err(nfnl, pid, group, error);
+}
+EXPORT_SYMBOL_GPL(nfnetlink_set_err);
+
 int nfnetlink_unicast(struct sk_buff *skb, u_int32_t pid, int flags)
 {
 	return netlink_unicast(nfnl, skb, pid, flags);

net/netlink/af_netlink.c

@@ -1106,6 +1106,7 @@ void netlink_set_err(struct sock *ssk, u32 pid, u32 group, int code)
 
 	read_unlock(&nl_table_lock);
 }
+EXPORT_SYMBOL(netlink_set_err);
 
 /* must be called with netlink table grabbed */
 static void netlink_update_socket_mc(struct netlink_sock *nlk,