ip: Fix data-races around sysctl_ip_prot_sock.

sysctl_ip_prot_sock is accessed concurrently, and there is always a chance
of data-race.  So, all readers and writers need some basic protection to
avoid load/store-tearing.

Fixes: 4548b683 ("Introduce a sysctl that modifies the value of PROT_SOCK.")
Signed-off-by: Kuniyuki Iwashima <kuniyu@amazon.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/net/ip.h

@@ -357,7 +357,7 @@ static inline bool sysctl_dev_name_is_allowed(const char *name)
 
 static inline bool inet_port_requires_bind_service(struct net *net, unsigned short port)
 {
-	return port < net->ipv4.sysctl_ip_prot_sock;
+	return port < READ_ONCE(net->ipv4.sysctl_ip_prot_sock);
 }
 
 #else

net/ipv4/sysctl_net_ipv4.c

@@ -84,7 +84,7 @@ static int ipv4_local_port_range(struct ctl_table *table, int write,
 		 * port limit.
 		 */
 		if ((range[1] < range[0]) ||
-		    (range[0] < net->ipv4.sysctl_ip_prot_sock))
+		    (range[0] < READ_ONCE(net->ipv4.sysctl_ip_prot_sock)))
 			ret = -EINVAL;
 		else
 			set_local_port_range(net, range);
@@ -110,7 +110,7 @@ static int ipv4_privileged_ports(struct ctl_table *table, int write,
 		.extra2 = &ip_privileged_port_max,
 	};
 
-	pports = net->ipv4.sysctl_ip_prot_sock;
+	pports = READ_ONCE(net->ipv4.sysctl_ip_prot_sock);
 
 	ret = proc_dointvec_minmax(&tmp, write, buffer, lenp, ppos);
 
@@ -122,7 +122,7 @@ static int ipv4_privileged_ports(struct ctl_table *table, int write,
 		if (range[0] < pports)
 			ret = -EINVAL;
 		else
-			net->ipv4.sysctl_ip_prot_sock = pports;
+			WRITE_ONCE(net->ipv4.sysctl_ip_prot_sock, pports);
 	}
 
 	return ret;