net: add sock_bindtoindex

Add a helper to directly set the SO_BINDTOIFINDEX sockopt from kernel
space without going through a fake uaccess.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/net/sock.h

@@ -2688,6 +2688,7 @@ static inline bool sk_dev_equal_l3scope(struct sock *sk, int dif)
 
 void sock_def_readable(struct sock *sk);
 
+int sock_bindtoindex(struct sock *sk, int ifindex);
 void sock_no_linger(struct sock *sk);
 void sock_set_priority(struct sock *sk, u32 priority);
 void sock_set_reuseaddr(struct sock *sk);

net/core/sock.c

@@ -566,7 +566,7 @@ struct dst_entry *sk_dst_check(struct sock *sk, u32 cookie)
 }
 EXPORT_SYMBOL(sk_dst_check);
 
-static int sock_setbindtodevice_locked(struct sock *sk, int ifindex)
+static int sock_bindtoindex_locked(struct sock *sk, int ifindex)
 {
 	int ret = -ENOPROTOOPT;
 #ifdef CONFIG_NETDEVICES
@@ -594,6 +594,18 @@ static int sock_setbindtodevice_locked(struct sock *sk, int ifindex)
 	return ret;
 }
 
+int sock_bindtoindex(struct sock *sk, int ifindex)
+{
+	int ret;
+
+	lock_sock(sk);
+	ret = sock_bindtoindex_locked(sk, ifindex);
+	release_sock(sk);
+
+	return ret;
+}
+EXPORT_SYMBOL(sock_bindtoindex);
+
 static int sock_setbindtodevice(struct sock *sk, char __user *optval,
 				int optlen)
 {
@@ -634,10 +646,7 @@ static int sock_setbindtodevice(struct sock *sk, char __user *optval,
 			goto out;
 	}
 
-	lock_sock(sk);
-	ret = sock_setbindtodevice_locked(sk, index);
-	release_sock(sk);
-
+	return sock_bindtoindex(sk, index);
 out:
 #endif
 
@@ -1216,7 +1225,7 @@ int sock_setsockopt(struct socket *sock, int level, int optname,
 		break;
 
 	case SO_BINDTOIFINDEX:
-		ret = sock_setbindtodevice_locked(sk, val);
+		ret = sock_bindtoindex_locked(sk, val);
 		break;
 
 	default:

net/ipv4/udp_tunnel.c

@@ -22,9 +22,7 @@ int udp_sock_create4(struct net *net, struct udp_port_cfg *cfg,
 		goto error;
 
 	if (cfg->bind_ifindex) {
-		err = kernel_setsockopt(sock, SOL_SOCKET, SO_BINDTOIFINDEX,
-					(void *)&cfg->bind_ifindex,
-					sizeof(cfg->bind_ifindex));
+		err = sock_bindtoindex(sock->sk, cfg->bind_ifindex);
 		if (err < 0)
 			goto error;
 	}

net/ipv6/ip6_udp_tunnel.c

@@ -33,9 +33,7 @@ int udp_sock_create6(struct net *net, struct udp_port_cfg *cfg,
 			goto error;
 	}
 	if (cfg->bind_ifindex) {
-		err = kernel_setsockopt(sock, SOL_SOCKET, SO_BINDTOIFINDEX,
-					(void *)&cfg->bind_ifindex,
-					sizeof(cfg->bind_ifindex));
+		err = sock_bindtoindex(sock->sk, cfg->bind_ifindex);
 		if (err < 0)
 			goto error;
 	}