net: port < inet_prot_sock(net) --> inet_port_requires_bind_service(net, port)

Note that the sysctl write accessor functions guarantee that:
  net->ipv4.sysctl_ip_prot_sock <= net->ipv4.ip_local_ports.range[0]
invariant is maintained, and as such the max() in selinux hooks is actually spurious.

ie. even though
  if (snum < max(inet_prot_sock(sock_net(sk)), low) || snum > high) {
per logic is the same as
  if ((snum < inet_prot_sock(sock_net(sk)) && snum < low) || snum > high) {
it is actually functionally equivalent to:
  if (snum < low || snum > high) {
which is equivalent to:
  if (snum < inet_prot_sock(sock_net(sk)) || snum < low || snum > high) {
even though the first clause is spurious.

But we want to hold on to it in case we ever want to change what what
inet_port_requires_bind_service() means (for example by changing
it from a, by default, [0..1024) range to some sort of set).

Test: builds, git 'grep inet_prot_sock' finds no other references
Cc: Eric Dumazet <edumazet@google.com>
Signed-off-by: Maciej Żenczykowski <maze@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/net/ip.h

@@ -351,9 +351,9 @@ static inline bool sysctl_dev_name_is_allowed(const char *name)
 	return strcmp(name, "default") != 0  && strcmp(name, "all") != 0;
 }
 
-static inline int inet_prot_sock(struct net *net)
+static inline bool inet_port_requires_bind_service(struct net *net, unsigned short port)
 {
-	return net->ipv4.sysctl_ip_prot_sock;
+	return port < net->ipv4.sysctl_ip_prot_sock;
 }
 
 #else
@@ -362,9 +362,9 @@ static inline bool inet_is_local_reserved_port(struct net *net, int port)
 	return false;
 }
 
-static inline int inet_prot_sock(struct net *net)
+static inline bool inet_port_requires_bind_service(struct net *net, unsigned short port)
 {
-	return PROT_SOCK;
+	return port < PROT_SOCK;
 }
 #endif
 

net/ipv4/af_inet.c

@@ -495,7 +495,7 @@ int __inet_bind(struct sock *sk, struct sockaddr *uaddr, int addr_len,
 
 	snum = ntohs(addr->sin_port);
 	err = -EACCES;
-	if (snum && snum < inet_prot_sock(net) &&
+	if (snum && inet_port_requires_bind_service(net, snum) &&
 	    !ns_capable(net->user_ns, CAP_NET_BIND_SERVICE))
 		goto out;
 

net/ipv6/af_inet6.c

@@ -292,7 +292,7 @@ static int __inet6_bind(struct sock *sk, struct sockaddr *uaddr, int addr_len,
 		return -EINVAL;
 
 	snum = ntohs(addr->sin6_port);
-	if (snum && snum < inet_prot_sock(net) &&
+	if (snum && inet_port_requires_bind_service(net, snum) &&
 	    !ns_capable(net->user_ns, CAP_NET_BIND_SERVICE))
 		return -EACCES;
 

net/netfilter/ipvs/ip_vs_ctl.c

@@ -423,7 +423,7 @@ ip_vs_service_find(struct netns_ipvs *ipvs, int af, __u32 fwmark, __u16 protocol
 
 	if (!svc && protocol == IPPROTO_TCP &&
 	    atomic_read(&ipvs->ftpsvc_counter) &&
-	    (vport == FTPDATA || ntohs(vport) >= inet_prot_sock(ipvs->net))) {
+	    (vport == FTPDATA || !inet_port_requires_bind_service(ipvs->net, ntohs(vport)))) {
 		/*
 		 * Check if ftp service entry exists, the packet
 		 * might belong to FTP data connections.

net/sctp/socket.c

@@ -384,7 +384,7 @@ static int sctp_do_bind(struct sock *sk, union sctp_addr *addr, int len)
 		}
 	}
 
-	if (snum && snum < inet_prot_sock(net) &&
+	if (snum && inet_port_requires_bind_service(net, snum) &&
 	    !ns_capable(net->user_ns, CAP_NET_BIND_SERVICE))
 		return -EACCES;
 
@@ -1061,7 +1061,7 @@ static int sctp_connect_new_asoc(struct sctp_endpoint *ep,
 		if (sctp_autobind(sk))
 			return -EAGAIN;
 	} else {
-		if (ep->base.bind_addr.port < inet_prot_sock(net) &&
+		if (inet_port_requires_bind_service(net, ep->base.bind_addr.port) &&
 		    !ns_capable(net->user_ns, CAP_NET_BIND_SERVICE))
 			return -EACCES;
 	}

security/selinux/hooks.c

@@ -4623,8 +4623,8 @@ static int selinux_socket_bind(struct socket *sock, struct sockaddr *address, in
 
 			inet_get_local_port_range(sock_net(sk), &low, &high);
 
-			if (snum < max(inet_prot_sock(sock_net(sk)), low) ||
-			    snum > high) {
+			if (inet_port_requires_bind_service(sock_net(sk), snum) ||
+			    snum < low || snum > high) {
 				err = sel_netport_sid(sk->sk_protocol,
 						      snum, &sid);
 				if (err)