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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 32/87] tcp: Fix data-races around sysctl_tcp_syncookies.
Date:   Wed, 27 Jul 2022 18:10:25 +0200
Message-Id: <20220727161010.353268949@linuxfoundation.org>
In-Reply-To: <20220727161008.993711844@linuxfoundation.org>
References: <20220727161008.993711844@linuxfoundation.org>
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From: Kuniyuki Iwashima <kuniyu@amazon.com>

[ Upstream commit f2e383b5bb6bbc60a0b94b87b3e49a2b1aefd11e ]

While reading sysctl_tcp_syncookies, 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/core/filter.c     |  4 ++--
 net/ipv4/syncookies.c |  3 ++-
 net/ipv4/tcp_input.c  | 20 ++++++++++++--------
 net/ipv6/syncookies.c |  3 ++-
 4 files changed, 18 insertions(+), 12 deletions(-)

diff --git a/net/core/filter.c b/net/core/filter.c
index 75f53b5e6389..72bf78032f45 100644
--- a/net/core/filter.c
+++ b/net/core/filter.c
@@ -5839,7 +5839,7 @@ BPF_CALL_5(bpf_tcp_check_syncookie, struct sock *, sk, void *, iph, u32, iph_len
 	if (sk->sk_protocol != IPPROTO_TCP || sk->sk_state != TCP_LISTEN)
 		return -EINVAL;
 
-	if (!sock_net(sk)->ipv4.sysctl_tcp_syncookies)
+	if (!READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_syncookies))
 		return -EINVAL;
 
 	if (!th->ack || th->rst || th->syn)
@@ -5914,7 +5914,7 @@ BPF_CALL_5(bpf_tcp_gen_syncookie, struct sock *, sk, void *, iph, u32, iph_len,
 	if (sk->sk_protocol != IPPROTO_TCP || sk->sk_state != TCP_LISTEN)
 		return -EINVAL;
 
-	if (!sock_net(sk)->ipv4.sysctl_tcp_syncookies)
+	if (!READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_syncookies))
 		return -ENOENT;
 
 	if (!th->syn || th->ack || th->fin || th->rst)
diff --git a/net/ipv4/syncookies.c b/net/ipv4/syncookies.c
index 6811174ad518..f1cbf8911844 100644
--- a/net/ipv4/syncookies.c
+++ b/net/ipv4/syncookies.c
@@ -297,7 +297,8 @@ struct sock *cookie_v4_check(struct sock *sk, struct sk_buff *skb)
 	struct flowi4 fl4;
 	u32 tsoff = 0;
 
-	if (!sock_net(sk)->ipv4.sysctl_tcp_syncookies || !th->ack || th->rst)
+	if (!READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_syncookies) ||
+	    !th->ack || th->rst)
 		goto out;
 
 	if (tcp_synq_no_recent_overflow(sk))
diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index 0808110451a0..85204903b2fa 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -6530,11 +6530,14 @@ static bool tcp_syn_flood_action(const struct sock *sk, const char *proto)
 {
 	struct request_sock_queue *queue = &inet_csk(sk)->icsk_accept_queue;
 	const char *msg = "Dropping request";
-	bool want_cookie = false;
 	struct net *net = sock_net(sk);
+	bool want_cookie = false;
+	u8 syncookies;
+
+	syncookies = READ_ONCE(net->ipv4.sysctl_tcp_syncookies);
 
 #ifdef CONFIG_SYN_COOKIES
-	if (net->ipv4.sysctl_tcp_syncookies) {
+	if (syncookies) {
 		msg = "Sending cookies";
 		want_cookie = true;
 		__NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPREQQFULLDOCOOKIES);
@@ -6542,8 +6545,7 @@ static bool tcp_syn_flood_action(const struct sock *sk, const char *proto)
 #endif
 		__NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPREQQFULLDROP);
 
-	if (!queue->synflood_warned &&
-	    net->ipv4.sysctl_tcp_syncookies != 2 &&
+	if (!queue->synflood_warned && syncookies != 2 &&
 	    xchg(&queue->synflood_warned, 1) == 0)
 		net_info_ratelimited("%s: Possible SYN flooding on port %d. %s.  Check SNMP counters.\n",
 				     proto, sk->sk_num, msg);
@@ -6578,7 +6580,7 @@ u16 tcp_get_syncookie_mss(struct request_sock_ops *rsk_ops,
 	struct tcp_sock *tp = tcp_sk(sk);
 	u16 mss;
 
-	if (sock_net(sk)->ipv4.sysctl_tcp_syncookies != 2 &&
+	if (READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_syncookies) != 2 &&
 	    !inet_csk_reqsk_queue_is_full(sk))
 		return 0;
 
@@ -6612,13 +6614,15 @@ int tcp_conn_request(struct request_sock_ops *rsk_ops,
 	bool want_cookie = false;
 	struct dst_entry *dst;
 	struct flowi fl;
+	u8 syncookies;
+
+	syncookies = READ_ONCE(net->ipv4.sysctl_tcp_syncookies);
 
 	/* TW buckets are converted to open requests without
 	 * limitations, they conserve resources and peer is
 	 * evidently real one.
 	 */
-	if ((net->ipv4.sysctl_tcp_syncookies == 2 ||
-	     inet_csk_reqsk_queue_is_full(sk)) && !isn) {
+	if ((syncookies == 2 || inet_csk_reqsk_queue_is_full(sk)) && !isn) {
 		want_cookie = tcp_syn_flood_action(sk, rsk_ops->slab_name);
 		if (!want_cookie)
 			goto drop;
@@ -6669,7 +6673,7 @@ int tcp_conn_request(struct request_sock_ops *rsk_ops,
 
 	if (!want_cookie && !isn) {
 		/* Kill the following clause, if you dislike this way. */
-		if (!net->ipv4.sysctl_tcp_syncookies &&
+		if (!syncookies &&
 		    (net->ipv4.sysctl_max_syn_backlog - inet_csk_reqsk_queue_len(sk) <
 		     (net->ipv4.sysctl_max_syn_backlog >> 2)) &&
 		    !tcp_peer_is_proven(req, dst)) {
diff --git a/net/ipv6/syncookies.c b/net/ipv6/syncookies.c
index 37ab254f7b92..7e5550546594 100644
--- a/net/ipv6/syncookies.c
+++ b/net/ipv6/syncookies.c
@@ -141,7 +141,8 @@ struct sock *cookie_v6_check(struct sock *sk, struct sk_buff *skb)
 	__u8 rcv_wscale;
 	u32 tsoff = 0;
 
-	if (!sock_net(sk)->ipv4.sysctl_tcp_syncookies || !th->ack || th->rst)
+	if (!READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_syncookies) ||
+	    !th->ack || th->rst)
 		goto out;
 
 	if (tcp_synq_no_recent_overflow(sk))
-- 
2.35.1