inet_diag: return classid for all socket types

In commit 1ec17dbd90 ("inet_diag: fix reporting cgroup classid and
fallback to priority") croup classid reporting was fixed. But this works
only for TCP sockets because for other socket types icsk parameter can
be NULL and classid code path is skipped. This change moves classid
handling to inet_diag_msg_attrs_fill() function.

Also inet_diag_msg_attrs_size() helper was added and addends in
nlmsg_new() were reordered to save order from inet_sk_diag_fill().

Fixes: 1ec17dbd90 ("inet_diag: fix reporting cgroup classid and fallback to priority")
Signed-off-by: Dmitry Yakunin <zeil@yandex-team.ru>
Reviewed-by: Konstantin Khlebnikov <khlebnikov@yandex-team.ru>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/linux/inet_diag.h

@@ -2,15 +2,10 @@
 #ifndef _INET_DIAG_H_
 #define _INET_DIAG_H_ 1
 
+#include <net/netlink.h>
 #include <uapi/linux/inet_diag.h>
 
-struct net;
-struct sock;
 struct inet_hashinfo;
-struct nlattr;
-struct nlmsghdr;
-struct sk_buff;
-struct netlink_callback;
 
 struct inet_diag_handler {
 	void		(*dump)(struct sk_buff *skb,
@@ -62,6 +57,17 @@ int inet_diag_bc_sk(const struct nlattr *_bc, struct sock *sk);
 
 void inet_diag_msg_common_fill(struct inet_diag_msg *r, struct sock *sk);
 
+static inline size_t inet_diag_msg_attrs_size(void)
+{
+	return	  nla_total_size(1)  /* INET_DIAG_SHUTDOWN */
+		+ nla_total_size(1)  /* INET_DIAG_TOS */
+#if IS_ENABLED(CONFIG_IPV6)
+		+ nla_total_size(1)  /* INET_DIAG_TCLASS */
+		+ nla_total_size(1)  /* INET_DIAG_SKV6ONLY */
+#endif
+		+ nla_total_size(4)  /* INET_DIAG_MARK */
+		+ nla_total_size(4); /* INET_DIAG_CLASS_ID */
+}
 int inet_diag_msg_attrs_fill(struct sock *sk, struct sk_buff *skb,
 			     struct inet_diag_msg *r, int ext,
 			     struct user_namespace *user_ns, bool net_admin);