ipv4: add ip_sock_set_pktinfo

Add a helper to directly set the IP_PKTINFO 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/ip.h

@@ -767,6 +767,7 @@ static inline bool inetdev_valid_mtu(unsigned int mtu)
 
 void ip_sock_set_freebind(struct sock *sk);
 int ip_sock_set_mtu_discover(struct sock *sk, int val);
+void ip_sock_set_pktinfo(struct sock *sk);
 void ip_sock_set_recverr(struct sock *sk);
 void ip_sock_set_tos(struct sock *sk, int val);
 

net/ipv4/ip_sockglue.c

@@ -608,6 +608,14 @@ int ip_sock_set_mtu_discover(struct sock *sk, int val)
 }
 EXPORT_SYMBOL(ip_sock_set_mtu_discover);
 
+void ip_sock_set_pktinfo(struct sock *sk)
+{
+	lock_sock(sk);
+	inet_sk(sk)->cmsg_flags |= IP_CMSG_PKTINFO;
+	release_sock(sk);
+}
+EXPORT_SYMBOL(ip_sock_set_pktinfo);
+
 /*
  *	Socket option code for IP. This is the end of the line after any
  *	TCP,UDP etc options on an IP socket.

net/sunrpc/svcsock.c

@@ -616,9 +616,8 @@ static void svc_udp_init(struct svc_sock *svsk, struct svc_serv *serv)
 	/* make sure we get destination address info */
 	switch (svsk->sk_sk->sk_family) {
 	case AF_INET:
-		level = SOL_IP;
-		optname = IP_PKTINFO;
-		break;
+		ip_sock_set_pktinfo(svsk->sk_sock->sk);
+		return;
 	case AF_INET6:
 		level = SOL_IPV6;
 		optname = IPV6_RECVPKTINFO;