sock_diag: specify info_size per inet protocol

Previously, there was no clear distinction between the inet protocols
that used struct tcp_info to report information and those that didn't.
This change adds a specific size attribute to the inet_diag_handler
struct which defines these interfaces.  This will make dispatching
sock_diag get_info requests identical for all inet protocols in a
following patch.

Tested: ss -au
Tested: ss -at
Signed-off-by: Craig Gallek <kraig@google.com>
Acked-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/linux/inet_diag.h

@@ -24,6 +24,7 @@ struct inet_diag_handler {
 					  struct inet_diag_msg *r,
 					  void *info);
 	__u16		idiag_type;
+	__u16		idiag_info_size;
 };
 
 struct inet_connection_sock;

net/dccp/diag.c

@@ -66,6 +66,7 @@ static const struct inet_diag_handler dccp_diag_handler = {
 	.dump_one	 = dccp_diag_dump_one,
 	.idiag_get_info	 = dccp_diag_get_info,
 	.idiag_type	 = IPPROTO_DCCP,
+	.idiag_info_size = sizeof(struct tcp_info),
 };
 
 static int __init dccp_diag_init(void)

net/ipv4/inet_diag.c

@@ -200,9 +200,9 @@ int inet_sk_diag_fill(struct sock *sk, struct inet_connection_sock *icsk,
 	}
 #undef EXPIRES_IN_MS
 
-	if (ext & (1 << (INET_DIAG_INFO - 1))) {
+	if ((ext & (1 << (INET_DIAG_INFO - 1))) && handler->idiag_info_size) {
 		attr = nla_reserve(skb, INET_DIAG_INFO,
-				   sizeof(struct tcp_info));
+				   handler->idiag_info_size);
 		if (!attr)
 			goto errout;
 

net/ipv4/tcp_diag.c

@@ -50,6 +50,7 @@ static const struct inet_diag_handler tcp_diag_handler = {
 	.dump_one	 = tcp_diag_dump_one,
 	.idiag_get_info	 = tcp_diag_get_info,
 	.idiag_type	 = IPPROTO_TCP,
+	.idiag_info_size = sizeof(struct tcp_info),
 };
 
 static int __init tcp_diag_init(void)

net/ipv4/udp_diag.c

@@ -170,6 +170,7 @@ static const struct inet_diag_handler udp_diag_handler = {
 	.dump_one	 = udp_diag_dump_one,
 	.idiag_get_info  = udp_diag_get_info,
 	.idiag_type	 = IPPROTO_UDP,
+	.idiag_info_size = 0,
 };
 
 static void udplite_diag_dump(struct sk_buff *skb, struct netlink_callback *cb,
@@ -190,6 +191,7 @@ static const struct inet_diag_handler udplite_diag_handler = {
 	.dump_one	 = udplite_diag_dump_one,
 	.idiag_get_info  = udp_diag_get_info,
 	.idiag_type	 = IPPROTO_UDPLITE,
+	.idiag_info_size = 0,
 };
 
 static int __init udp_diag_init(void)