net: inet_diag: export IPV6_V6ONLY sockopt

For AF_INET6 sockets, the value of struct ipv6_pinfo.ipv6only is
exported to userspace. It indicates whether a socket bound to in6addr_any
listens on IPv4 as well as IPv6. Since the socket is natively IPv6, it is not
listed by e.g. 'ss -l -4'.

This patch is accompanied by an appropriate one for iproute2 to enable
the additional information in 'ss -e'.
Signed-off-by: Phil Sutter <phil@nwl.cc>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/uapi/linux/inet_diag.h

@@ -112,9 +112,10 @@ enum {
 	INET_DIAG_SHUTDOWN,
 	INET_DIAG_DCTCPINFO,
 	INET_DIAG_PROTOCOL,  /* response attribute only */
+	INET_DIAG_SKV6ONLY,
 };
 
-#define INET_DIAG_MAX INET_DIAG_PROTOCOL
+#define INET_DIAG_MAX INET_DIAG_SKV6ONLY
 
 /* INET_DIAG_MEM */
 

net/ipv4/inet_diag.c

@@ -151,6 +151,10 @@ int inet_sk_diag_fill(struct sock *sk, struct inet_connection_sock *icsk,
 			if (nla_put_u8(skb, INET_DIAG_TCLASS,
 				       inet6_sk(sk)->tclass) < 0)
 				goto errout;
+
+		if (ipv6_only_sock(sk) &&
+		    nla_put_u8(skb, INET_DIAG_SKV6ONLY, 1))
+			goto errout;
 	}
 #endif