Use READ/WRITE_ONCE() for IP local_port_range.

Commit 227b60f510 added a seqlock to ensure that the low and high
port numbers were always updated together.
This is overkill because the two 16bit port numbers can be held in
a u32 and read/written in a single instruction.

More recently 91d0b78c51 added support for finer per-socket limits.
The user-supplied value is 'high << 16 | low' but they are held
separately and the socket options protected by the socket lock.

Use a u32 containing 'high << 16 | low' for both the 'net' and 'sk'
fields and use READ_ONCE()/WRITE_ONCE() to ensure both values are
always updated together.

Change (the now trival) inet_get_local_port_range() to a static inline
to optimise the calling code.
(In particular avoiding returning integers by reference.)

Signed-off-by: David Laight <david.laight@aculab.com>
Reviewed-by: Eric Dumazet <edumazet@google.com>
Reviewed-by: David Ahern <dsahern@kernel.org>
Acked-by: Mat Martineau <martineau@kernel.org>
Reviewed-by: Kuniyuki Iwashima <kuniyu@amazon.com>
Link: https://lore.kernel.org/r/4e505d4198e946a8be03fb1b4c3072b0@AcuMS.aculab.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

include/net/inet_sock.h

@@ -234,10 +234,7 @@ struct inet_sock {
 	int			uc_index;
 	int			mc_index;
 	__be32			mc_addr;
-	struct {
-		__u16 lo;
-		__u16 hi;
-	}			local_port_range;
+	u32			local_port_range;	/* high << 16 | low */
 
 	struct ip_mc_socklist __rcu	*mc_list;
 	struct inet_cork_full	cork;

include/net/ip.h

@@ -349,7 +349,13 @@ static inline u64 snmp_fold_field64(void __percpu *mib, int offt, size_t syncp_o
 	} \
 }
 
-void inet_get_local_port_range(const struct net *net, int *low, int *high);
+static inline void inet_get_local_port_range(const struct net *net, int *low, int *high)
+{
+	u32 range = READ_ONCE(net->ipv4.ip_local_ports.range);
+
+	*low = range & 0xffff;
+	*high = range >> 16;
+}
 void inet_sk_get_local_port_range(const struct sock *sk, int *low, int *high);
 
 #ifdef CONFIG_SYSCTL

include/net/netns/ipv4.h

@@ -19,8 +19,7 @@ struct hlist_head;
 struct fib_table;
 struct sock;
 struct local_ports {
-	seqlock_t	lock;
-	int		range[2];
+	u32		range;	/* high << 16 | low */
 	bool		warned;
 };
 

net/ipv4/af_inet.c

@@ -1847,9 +1847,7 @@ static __net_init int inet_init_net(struct net *net)
 	/*
 	 * Set defaults for local port range
 	 */
-	seqlock_init(&net->ipv4.ip_local_ports.lock);
-	net->ipv4.ip_local_ports.range[0] =  32768;
-	net->ipv4.ip_local_ports.range[1] =  60999;
+	net->ipv4.ip_local_ports.range = 60999u << 16 | 32768u;
 
 	seqlock_init(&net->ipv4.ping_group_range.lock);
 	/*

net/ipv4/inet_connection_sock.c

@@ -117,34 +117,25 @@ bool inet_rcv_saddr_any(const struct sock *sk)
 	return !sk->sk_rcv_saddr;
 }
 
-void inet_get_local_port_range(const struct net *net, int *low, int *high)
-{
-	unsigned int seq;
-
-	do {
-		seq = read_seqbegin(&net->ipv4.ip_local_ports.lock);
-
-		*low = net->ipv4.ip_local_ports.range[0];
-		*high = net->ipv4.ip_local_ports.range[1];
-	} while (read_seqretry(&net->ipv4.ip_local_ports.lock, seq));
-}
-EXPORT_SYMBOL(inet_get_local_port_range);
-
 void inet_sk_get_local_port_range(const struct sock *sk, int *low, int *high)
 {
 	const struct inet_sock *inet = inet_sk(sk);
 	const struct net *net = sock_net(sk);
 	int lo, hi, sk_lo, sk_hi;
+	u32 sk_range;
 
 	inet_get_local_port_range(net, &lo, &hi);
 
-	sk_lo = inet->local_port_range.lo;
-	sk_hi = inet->local_port_range.hi;
+	sk_range = READ_ONCE(inet->local_port_range);
+	if (unlikely(sk_range)) {
+		sk_lo = sk_range & 0xffff;
+		sk_hi = sk_range >> 16;
 
-	if (unlikely(lo <= sk_lo && sk_lo <= hi))
-		lo = sk_lo;
-	if (unlikely(lo <= sk_hi && sk_hi <= hi))
-		hi = sk_hi;
+		if (lo <= sk_lo && sk_lo <= hi)
+			lo = sk_lo;
+		if (lo <= sk_hi && sk_hi <= hi)
+			hi = sk_hi;
+	}
 
 	*low = lo;
 	*high = hi;

net/ipv4/ip_sockglue.c

@@ -1055,6 +1055,19 @@ int do_ip_setsockopt(struct sock *sk, int level, int optname,
 	case IP_TOS:	/* This sets both TOS and Precedence */
 		ip_sock_set_tos(sk, val);
 		return 0;
+	case IP_LOCAL_PORT_RANGE:
+	{
+		u16 lo = val;
+		u16 hi = val >> 16;
+
+		if (optlen != sizeof(u32))
+			return -EINVAL;
+		if (lo != 0 && hi != 0 && lo > hi)
+			return -EINVAL;
+
+		WRITE_ONCE(inet->local_port_range, val);
+		return 0;
+	}
 	}
 
 	err = 0;
@@ -1332,20 +1345,6 @@ int do_ip_setsockopt(struct sock *sk, int level, int optname,
 		err = xfrm_user_policy(sk, optname, optval, optlen);
 		break;
 
-	case IP_LOCAL_PORT_RANGE:
-	{
-		const __u16 lo = val;
-		const __u16 hi = val >> 16;
-
-		if (optlen != sizeof(__u32))
-			goto e_inval;
-		if (lo != 0 && hi != 0 && lo > hi)
-			goto e_inval;
-
-		inet->local_port_range.lo = lo;
-		inet->local_port_range.hi = hi;
-		break;
-	}
 	default:
 		err = -ENOPROTOOPT;
 		break;
@@ -1692,6 +1691,9 @@ int do_ip_getsockopt(struct sock *sk, int level, int optname,
 			return -EFAULT;
 		return 0;
 	}
+	case IP_LOCAL_PORT_RANGE:
+		val = READ_ONCE(inet->local_port_range);
+		goto copyval;
 	}
 
 	if (needs_rtnl)
@@ -1721,9 +1723,6 @@ int do_ip_getsockopt(struct sock *sk, int level, int optname,
 		else
 			err = ip_get_mcast_msfilter(sk, optval, optlen, len);
 		goto out;
-	case IP_LOCAL_PORT_RANGE:
-		val = inet->local_port_range.hi << 16 | inet->local_port_range.lo;
-		break;
 	case IP_PROTOCOL:
 		val = inet_sk(sk)->inet_num;
 		break;

net/ipv4/sysctl_net_ipv4.c

@@ -50,26 +50,22 @@ static int tcp_plb_max_cong_thresh = 256;
 static int sysctl_tcp_low_latency __read_mostly;
 
 /* Update system visible IP port range */
-static void set_local_port_range(struct net *net, int range[2])
+static void set_local_port_range(struct net *net, unsigned int low, unsigned int high)
 {
-	bool same_parity = !((range[0] ^ range[1]) & 1);
+	bool same_parity = !((low ^ high) & 1);
 
-	write_seqlock_bh(&net->ipv4.ip_local_ports.lock);
 	if (same_parity && !net->ipv4.ip_local_ports.warned) {
 		net->ipv4.ip_local_ports.warned = true;
 		pr_err_ratelimited("ip_local_port_range: prefer different parity for start/end values.\n");
 	}
-	net->ipv4.ip_local_ports.range[0] = range[0];
-	net->ipv4.ip_local_ports.range[1] = range[1];
-	write_sequnlock_bh(&net->ipv4.ip_local_ports.lock);
+	WRITE_ONCE(net->ipv4.ip_local_ports.range, high << 16 | low);
 }
 
 /* Validate changes from /proc interface. */
 static int ipv4_local_port_range(struct ctl_table *table, int write,
 				 void *buffer, size_t *lenp, loff_t *ppos)
 {
-	struct net *net =
-		container_of(table->data, struct net, ipv4.ip_local_ports.range);
+	struct net *net = table->data;
 	int ret;
 	int range[2];
 	struct ctl_table tmp = {
@@ -93,7 +89,7 @@ static int ipv4_local_port_range(struct ctl_table *table, int write,
 		    (range[0] < READ_ONCE(net->ipv4.sysctl_ip_prot_sock)))
 			ret = -EINVAL;
 		else
-			set_local_port_range(net, range);
+			set_local_port_range(net, range[0], range[1]);
 	}
 
 	return ret;
@@ -733,8 +729,8 @@ static struct ctl_table ipv4_net_table[] = {
 	},
 	{
 		.procname	= "ip_local_port_range",
-		.maxlen		= sizeof(init_net.ipv4.ip_local_ports.range),
-		.data		= &init_net.ipv4.ip_local_ports.range,
+		.maxlen		= 0,
+		.data		= &init_net,
 		.mode		= 0644,
 		.proc_handler	= ipv4_local_port_range,
 	},