netdev - [PATCH v1 net 13/15] tcp: Fix a data-race around sysctl_tcp_ecn

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Date:   Mon, 11 Jul 2022 17:15:31 -0700
From:   Kuniyuki Iwashima <kuniyu@...zon.com>
To:     "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        David Ahern <dsahern@...nel.org>,
        Luis Chamberlain <mcgrof@...nel.org>,
        Kees Cook <keescook@...omium.org>,
        Iurii Zaikin <yzaikin@...gle.com>
CC:     Kuniyuki Iwashima <kuniyu@...zon.com>,
        Kuniyuki Iwashima <kuni1840@...il.com>,
        <netdev@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Florian Westphal <fw@...len.de>,
        Mirja Kühlewind 
        <mirja.kuehlewind@....ee.ethz.ch>,
        Brian Trammell <trammell@....ee.ethz.ch>
Subject: [PATCH v1 net 13/15] tcp: Fix a data-race around sysctl_tcp_ecn_fallback.

While reading sysctl_tcp_ecn_fallback, it can be changed concurrently.
Thus, we need to add READ_ONCE() to its reader.

Fixes: 492135557dc0 ("tcp: add rfc3168, section 6.1.1.1. fallback")
Signed-off-by: Kuniyuki Iwashima <kuniyu@...zon.com>
---
CC: Daniel Borkmann <daniel@...earbox.net>
CC: Florian Westphal <fw@...len.de>
CC: Mirja Kühlewind <mirja.kuehlewind@....ee.ethz.ch>
CC: Brian Trammell <trammell@....ee.ethz.ch>
---
 net/ipv4/sysctl_net_ipv4.c | 2 ++
 net/ipv4/tcp_output.c      | 2 +-
 2 files changed, 3 insertions(+), 1 deletion(-)

diff --git a/net/ipv4/sysctl_net_ipv4.c b/net/ipv4/sysctl_net_ipv4.c
index 5e308c1715af..108fd86f2718 100644
--- a/net/ipv4/sysctl_net_ipv4.c
+++ b/net/ipv4/sysctl_net_ipv4.c
@@ -685,6 +685,8 @@ static struct ctl_table ipv4_net_table[] = {
 		.maxlen		= sizeof(u8),
 		.mode		= 0644,
 		.proc_handler	= proc_dou8vec_minmax,
+		.extra1		= SYSCTL_ZERO,
+		.extra2		= SYSCTL_ONE,
 	},
 	{
 		.procname	= "ip_dynaddr",
diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c
index 3dc17551ce25..11aa0ab10bba 100644
--- a/net/ipv4/tcp_output.c
+++ b/net/ipv4/tcp_output.c
@@ -346,7 +346,7 @@ static void tcp_ecn_send_syn(struct sock *sk, struct sk_buff *skb)
 
 static void tcp_ecn_clear_syn(struct sock *sk, struct sk_buff *skb)
 {
-	if (sock_net(sk)->ipv4.sysctl_tcp_ecn_fallback)
+	if (READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_ecn_fallback))
 		/* tp->ecn_flags are cleared at a later point in time when
 		 * SYN ACK is ultimatively being received.
 		 */
-- 
2.30.2