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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 5.10 054/105] tcp: Fix data-races around sysctl_max_syn_backlog.
Date:   Wed, 27 Jul 2022 18:10:40 +0200
Message-Id: <20220727161014.250317229@linuxfoundation.org>
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From: Kuniyuki Iwashima <kuniyu@amazon.com>

[ Upstream commit 79539f34743d3e14cc1fa6577d326a82cc64d62f ]

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

Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
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_input.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index 070e7015e9c9..5cbabe0e42c9 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -6847,10 +6847,12 @@ int tcp_conn_request(struct request_sock_ops *rsk_ops,
 		goto drop_and_free;
 
 	if (!want_cookie && !isn) {
+		int max_syn_backlog = READ_ONCE(net->ipv4.sysctl_max_syn_backlog);
+
 		/* Kill the following clause, if you dislike this way. */
 		if (!syncookies &&
-		    (net->ipv4.sysctl_max_syn_backlog - inet_csk_reqsk_queue_len(sk) <
-		     (net->ipv4.sysctl_max_syn_backlog >> 2)) &&
+		    (max_syn_backlog - inet_csk_reqsk_queue_len(sk) <
+		     (max_syn_backlog >> 2)) &&
 		    !tcp_peer_is_proven(req, dst)) {
 			/* Without syncookies last quarter of
 			 * backlog is filled with destinations,
-- 
2.35.1