netlink: fix NETLINK_RECV_NO_ENOBUFS in netlink_set_err()

Currently, ENOBUFS errors are reported to the socket via
netlink_set_err() even if NETLINK_RECV_NO_ENOBUFS is set. However,
that should not happen. This fixes this problem and it changes the
prototype of netlink_set_err() to return the number of sockets that
have set the NETLINK_RECV_NO_ENOBUFS socket option. This return
value is used in the next patch in these bugfix series.

Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
---
 include/linux/netlink.h  |    2 +-
 net/netlink/af_netlink.c |   17 ++++++++++++++---
 2 files changed, 15 insertions(+), 4 deletions(-)

diff --git a/include/linux/netlink.h b/include/linux/netlink.h
index fde27c0..6eaca5e 100644
--- a/include/linux/netlink.h
+++ b/include/linux/netlink.h
@@ -188,7 +188,7 @@ extern int netlink_has_listeners(struct sock *sk, unsigned int group);
 extern int netlink_unicast(struct sock *ssk, struct sk_buff *skb, __u32 pid, int nonblock);
 extern int netlink_broadcast(struct sock *ssk, struct sk_buff *skb, __u32 pid,
 			     __u32 group, gfp_t allocation);
-extern void netlink_set_err(struct sock *ssk, __u32 pid, __u32 group, int code);
+extern int netlink_set_err(struct sock *ssk, __u32 pid, __u32 group, int code);
 extern int netlink_register_notifier(struct notifier_block *nb);
 extern int netlink_unregister_notifier(struct notifier_block *nb);
 
diff --git a/net/netlink/af_netlink.c b/net/netlink/af_netlink.c
index 4c5972b..0052d3c 100644
--- a/net/netlink/af_netlink.c
+++ b/net/netlink/af_netlink.c
@@ -1093,6 +1093,7 @@ static inline int do_one_set_err(struct sock *sk,
 				 struct netlink_set_err_data *p)
 {
 	struct netlink_sock *nlk = nlk_sk(sk);
+	int ret = 0;
 
 	if (sk == p->exclude_sk)
 		goto out;
@@ -1104,10 +1105,15 @@ static inline int do_one_set_err(struct sock *sk,
 	    !test_bit(p->group - 1, nlk->groups))
 		goto out;
 
+	if (p->code == ENOBUFS && nlk->flags & NETLINK_RECV_NO_ENOBUFS) {
+		ret = 1;
+		goto out;
+	}
+
 	sk->sk_err = p->code;
 	sk->sk_error_report(sk);
 out:
-	return 0;
+	return ret;
 }
 
 /**
@@ -1116,12 +1122,16 @@ out:
  * @pid: the PID of a process that we want to skip (if any)
  * @groups: the broadcast group that will notice the error
  * @code: error code, must be negative (as usual in kernelspace)
+ *
+ * This function returns the number of broadcast listeners that have set the
+ * NETLINK_RECV_NO_ENOBUFS socket option.
  */
-void netlink_set_err(struct sock *ssk, u32 pid, u32 group, int code)
+int netlink_set_err(struct sock *ssk, u32 pid, u32 group, int code)
 {
 	struct netlink_set_err_data info;
 	struct hlist_node *node;
 	struct sock *sk;
+	int ret = 0;
 
 	info.exclude_sk = ssk;
 	info.pid = pid;
@@ -1132,9 +1142,10 @@ void netlink_set_err(struct sock *ssk, u32 pid, u32 group, int code)
 	read_lock(&nl_table_lock);
 
 	sk_for_each_bound(sk, node, &nl_table[ssk->sk_protocol].mc_list)
-		do_one_set_err(sk, &info);
+		ret += do_one_set_err(sk, &info);
 
 	read_unlock(&nl_table_lock);
+	return ret;
 }
 EXPORT_SYMBOL(netlink_set_err);