netdev - [PATCH v4 net-next 4/5] net: Add net.ipv4.ip_autobind

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Date:   Mon, 9 Mar 2020 03:16:14 +0900
From:   Kuniyuki Iwashima <kuniyu@...zon.co.jp>
To:     <davem@...emloft.net>, <kuznet@....inr.ac.ru>,
        <yoshfuji@...ux-ipv6.org>, <edumazet@...gle.com>
CC:     <kuniyu@...zon.co.jp>, <kuni1840@...il.com>,
        <netdev@...r.kernel.org>, <osa-contribution-log@...zon.com>
Subject: [PATCH v4 net-next 4/5] net: Add net.ipv4.ip_autobind_reuse option.

The two commits("tcp: bind(addr, 0) remove the SO_REUSEADDR restriction
when ephemeral ports are exhausted" and "tcp: Forbid to automatically bind
more than one sockets haveing SO_REUSEADDR and SO_REUSEPORT per EUID")
introduced the new feature to reuse ports with SO_REUSEADDR when all
ephemeral pors are exhausted. They allow connect() and listen() to share
ports in the following way.

  1. setsockopt(sk1, SO_REUSEADDR)
  2. setsockopt(sk2, SO_REUSEADDR)
  3. bind(sk1, saddr, 0)
  4. bind(sk2, saddr, 0)
  5. connect(sk1, daddr)
  6. listen(sk2)

In this situation, new socket cannot be bound to the port, but sharing
port between connect() and listen() may break some applications. The
ip_autobind_reuse option is false (0) by default and disables the feature.
If it is set true, we can fully utilize the 4-tuples.

Signed-off-by: Kuniyuki Iwashima <kuniyu@...zon.co.jp>
---
 Documentation/networking/ip-sysctl.txt | 7 +++++++
 include/net/netns/ipv4.h               | 1 +
 net/ipv4/inet_connection_sock.c        | 2 +-
 net/ipv4/sysctl_net_ipv4.c             | 7 +++++++
 4 files changed, 16 insertions(+), 1 deletion(-)

diff --git a/Documentation/networking/ip-sysctl.txt b/Documentation/networking/ip-sysctl.txt
index 5f53faff4e25..9506a67a33c4 100644
--- a/Documentation/networking/ip-sysctl.txt
+++ b/Documentation/networking/ip-sysctl.txt
@@ -958,6 +958,13 @@ ip_nonlocal_bind - BOOLEAN
 	which can be quite useful - but may break some applications.
 	Default: 0
 
+ip_autobind_reuse - BOOLEAN
+	By default, bind() does not select the ports automatically even if
+	the new socket and all sockets bound to the port have SO_REUSEADDR.
+	ip_autobind_reuse allows bind() to reuse the port and this is useful
+	when you use bind()+connect(), but may break some applications.
+	Default: 0
+
 ip_dynaddr - BOOLEAN
 	If set non-zero, enables support for dynamic addresses.
 	If set to a non-zero value larger than 1, a kernel log
diff --git a/include/net/netns/ipv4.h b/include/net/netns/ipv4.h
index 08b98414d94e..154b8f01499b 100644
--- a/include/net/netns/ipv4.h
+++ b/include/net/netns/ipv4.h
@@ -101,6 +101,7 @@ struct netns_ipv4 {
 	int sysctl_ip_fwd_use_pmtu;
 	int sysctl_ip_fwd_update_priority;
 	int sysctl_ip_nonlocal_bind;
+	int sysctl_ip_autobind_reuse;
 	/* Shall we try to damage output packets if routing dev changes? */
 	int sysctl_ip_dynaddr;
 	int sysctl_ip_early_demux;
diff --git a/net/ipv4/inet_connection_sock.c b/net/ipv4/inet_connection_sock.c
index d27ed5fe7147..3b4f81790e3e 100644
--- a/net/ipv4/inet_connection_sock.c
+++ b/net/ipv4/inet_connection_sock.c
@@ -246,7 +246,7 @@ inet_csk_find_open_port(struct sock *sk, struct inet_bind_bucket **tb_ret, int *
 		goto other_half_scan;
 	}
 
-	if (!relax) {
+	if (net->ipv4.sysctl_ip_autobind_reuse && !relax) {
 		/* We still have a chance to connect to different destinations */
 		relax = true;
 		goto ports_exhausted;
diff --git a/net/ipv4/sysctl_net_ipv4.c b/net/ipv4/sysctl_net_ipv4.c
index 9684af02e0a5..3b191764718b 100644
--- a/net/ipv4/sysctl_net_ipv4.c
+++ b/net/ipv4/sysctl_net_ipv4.c
@@ -775,6 +775,13 @@ static struct ctl_table ipv4_net_table[] = {
 		.mode		= 0644,
 		.proc_handler	= proc_dointvec
 	},
+	{
+		.procname	= "ip_autobind_reuse",
+		.data		= &init_net.ipv4.sysctl_ip_autobind_reuse,
+		.maxlen		= sizeof(int),
+		.mode		= 0644,
+		.proc_handler	= proc_dointvec
+	},
 	{
 		.procname	= "fwmark_reflect",
 		.data		= &init_net.ipv4.sysctl_fwmark_reflect,
-- 
2.17.2 (Apple Git-113)