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From:   Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To:     linux-kernel@vger.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        stable@vger.kernel.org, Kuniyuki Iwashima <kuniyu@amazon.com>,
        "David S. Miller" <davem@davemloft.net>,
        Sasha Levin <sashal@kernel.org>
Subject: [PATCH 5.4 24/87] tcp: Fix a data-race around sysctl_tcp_mtu_probe_floor.
Date:   Wed, 27 Jul 2022 18:10:17 +0200
Message-Id: <20220727161010.006453319@linuxfoundation.org>
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From: Kuniyuki Iwashima <kuniyu@amazon.com>

[ Upstream commit 8e92d4423615a5257d0d871fc067aa561f597deb ]

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

Fixes: c04b79b6cfd7 ("tcp: add new tcp_mtu_probe_floor sysctl")
Signed-off-by: Kuniyuki Iwashima <kuniyu@amazon.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 net/ipv4/tcp_timer.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/ipv4/tcp_timer.c b/net/ipv4/tcp_timer.c
index 0460c5deee3f..c48aeaef3ec7 100644
--- a/net/ipv4/tcp_timer.c
+++ b/net/ipv4/tcp_timer.c
@@ -172,7 +172,7 @@ static void tcp_mtu_probing(struct inet_connection_sock *icsk, struct sock *sk)
 	} else {
 		mss = tcp_mtu_to_mss(sk, icsk->icsk_mtup.search_low) >> 1;
 		mss = min(READ_ONCE(net->ipv4.sysctl_tcp_base_mss), mss);
-		mss = max(mss, net->ipv4.sysctl_tcp_mtu_probe_floor);
+		mss = max(mss, READ_ONCE(net->ipv4.sysctl_tcp_mtu_probe_floor));
 		mss = max(mss, READ_ONCE(net->ipv4.sysctl_tcp_min_snd_mss));
 		icsk->icsk_mtup.search_low = tcp_mss_to_mtu(sk, mss);
 	}
-- 
2.35.1