sock: break up sock_cmsg_snd into __sock_cmsg_snd and loop

To process cmsg's of the SOL_SOCKET level in addition to
cmsgs of another level, protocols can call sock_cmsg_send().
This causes a double walk on the cmsghdr list, one for SOL_SOCKET
and one for the other level.

Extract the inner demultiplex logic from the loop that walks the list,
to allow having this called directly from a walker in the protocol
specific code.
Signed-off-by: Willem de Bruijn <willemb@google.com>
Signed-off-by: Soheil Hassas Yeganeh <soheil@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/net/sock.h

@@ -1420,6 +1420,8 @@ struct sockcm_cookie {
 	u32 mark;
 };
 
+int __sock_cmsg_send(struct sock *sk, struct msghdr *msg, struct cmsghdr *cmsg,
+		     struct sockcm_cookie *sockc);
 int sock_cmsg_send(struct sock *sk, struct msghdr *msg,
 		   struct sockcm_cookie *sockc);
 

net/core/sock.c

@@ -1866,16 +1866,9 @@ struct sk_buff *sock_alloc_send_skb(struct sock *sk, unsigned long size,
 }
 EXPORT_SYMBOL(sock_alloc_send_skb);
 
-int sock_cmsg_send(struct sock *sk, struct msghdr *msg,
+int __sock_cmsg_send(struct sock *sk, struct msghdr *msg, struct cmsghdr *cmsg,
 		     struct sockcm_cookie *sockc)
 {
-	struct cmsghdr *cmsg;
-
-	for_each_cmsghdr(cmsg, msg) {
-		if (!CMSG_OK(msg, cmsg))
-			return -EINVAL;
-		if (cmsg->cmsg_level != SOL_SOCKET)
-			continue;
 	switch (cmsg->cmsg_type) {
 	case SO_MARK:
 		if (!ns_capable(sock_net(sk)->user_ns, CAP_NET_ADMIN))
@@ -1887,6 +1880,24 @@ int sock_cmsg_send(struct sock *sk, struct msghdr *msg,
 	default:
 		return -EINVAL;
 	}
+	return 0;
+}
+EXPORT_SYMBOL(__sock_cmsg_send);
+
+int sock_cmsg_send(struct sock *sk, struct msghdr *msg,
+		   struct sockcm_cookie *sockc)
+{
+	struct cmsghdr *cmsg;
+	int ret;
+
+	for_each_cmsghdr(cmsg, msg) {
+		if (!CMSG_OK(msg, cmsg))
+			return -EINVAL;
+		if (cmsg->cmsg_level != SOL_SOCKET)
+			continue;
+		ret = __sock_cmsg_send(sk, msg, cmsg, sockc);
+		if (ret)
+			return ret;
 	}
 	return 0;
 }