ipv4: add ip_sock_set_freebind

Add a helper to directly set the IP_FREEBIND 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>

drivers/target/iscsi/iscsi_target_login.c

@@ -15,6 +15,7 @@
 #include <linux/sched/signal.h>
 #include <linux/idr.h>
 #include <linux/tcp.h>        /* TCP_NODELAY */
+#include <net/ip.h>
 #include <net/ipv6.h>         /* ipv6_addr_v4mapped() */
 #include <scsi/iscsi_proto.h>
 #include <target/target_core_base.h>
@@ -855,7 +856,7 @@ int iscsit_setup_np(
 	struct sockaddr_storage *sockaddr)
 {
 	struct socket *sock = NULL;
-	int backlog = ISCSIT_TCP_BACKLOG, ret, opt = 0, len;
+	int backlog = ISCSIT_TCP_BACKLOG, ret, len;
 
 	switch (np->np_network_transport) {
 	case ISCSI_TCP:
@@ -900,15 +901,7 @@ int iscsit_setup_np(
 	if (np->np_network_transport == ISCSI_TCP)
 		tcp_sock_set_nodelay(sock->sk);
 	sock_set_reuseaddr(sock->sk);
-
-	opt = 1;
-	ret = kernel_setsockopt(sock, IPPROTO_IP, IP_FREEBIND,
-			(char *)&opt, sizeof(opt));
-	if (ret < 0) {
-		pr_err("kernel_setsockopt() for IP_FREEBIND"
-			" failed\n");
-		goto fail;
-	}
+	ip_sock_set_freebind(sock->sk);
 
 	ret = kernel_bind(sock, (struct sockaddr *)&np->np_sockaddr, len);
 	if (ret < 0) {

include/net/ip.h

@@ -765,6 +765,7 @@ static inline bool inetdev_valid_mtu(unsigned int mtu)
 	return likely(mtu >= IPV4_MIN_MTU);
 }
 
+void ip_sock_set_freebind(struct sock *sk);
 void ip_sock_set_tos(struct sock *sk, int val);
 
 #endif	/* _IP_H */

net/ipv4/ip_sockglue.c

@@ -581,6 +581,14 @@ void ip_sock_set_tos(struct sock *sk, int val)
 }
 EXPORT_SYMBOL(ip_sock_set_tos);
 
+void ip_sock_set_freebind(struct sock *sk)
+{
+	lock_sock(sk);
+	inet_sk(sk)->freebind = true;
+	release_sock(sk);
+}
+EXPORT_SYMBOL(ip_sock_set_freebind);
+
 /*
  *	Socket option code for IP. This is the end of the line after any
  *	TCP,UDP etc options on an IP socket.