linux-kernel - [PATCH 4.9 22/60] tcp: annotate data races around tp->mtu

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Date:   Mon, 26 Jul 2021 17:38:36 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Eric Dumazet <edumazet@...gle.com>,
        "David S. Miller" <davem@...emloft.net>
Subject: [PATCH 4.9 22/60] tcp: annotate data races around tp->mtu_info

From: Eric Dumazet <edumazet@...gle.com>

commit 561022acb1ce62e50f7a8258687a21b84282a4cb upstream.

While tp->mtu_info is read while socket is owned, the write
sides happen from err handlers (tcp_v[46]_mtu_reduced)
which only own the socket spinlock.

Fixes: 563d34d05786 ("tcp: dont drop MTU reduction indications")
Signed-off-by: Eric Dumazet <edumazet@...gle.com>
Signed-off-by: David S. Miller <davem@...emloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 net/ipv4/tcp_ipv4.c |    4 ++--
 net/ipv6/tcp_ipv6.c |    4 ++--
 2 files changed, 4 insertions(+), 4 deletions(-)

--- a/net/ipv4/tcp_ipv4.c
+++ b/net/ipv4/tcp_ipv4.c
@@ -275,7 +275,7 @@ void tcp_v4_mtu_reduced(struct sock *sk)
 
 	if ((1 << sk->sk_state) & (TCPF_LISTEN | TCPF_CLOSE))
 		return;
-	mtu = tcp_sk(sk)->mtu_info;
+	mtu = READ_ONCE(tcp_sk(sk)->mtu_info);
 	dst = inet_csk_update_pmtu(sk, mtu);
 	if (!dst)
 		return;
@@ -442,7 +442,7 @@ void tcp_v4_err(struct sk_buff *icmp_skb
 			if (sk->sk_state == TCP_LISTEN)
 				goto out;
 
-			tp->mtu_info = info;
+			WRITE_ONCE(tp->mtu_info, info);
 			if (!sock_owned_by_user(sk)) {
 				tcp_v4_mtu_reduced(sk);
 			} else {
--- a/net/ipv6/tcp_ipv6.c
+++ b/net/ipv6/tcp_ipv6.c
@@ -311,7 +311,7 @@ static void tcp_v6_mtu_reduced(struct so
 	if ((1 << sk->sk_state) & (TCPF_LISTEN | TCPF_CLOSE))
 		return;
 
-	dst = inet6_csk_update_pmtu(sk, tcp_sk(sk)->mtu_info);
+	dst = inet6_csk_update_pmtu(sk, READ_ONCE(tcp_sk(sk)->mtu_info));
 	if (!dst)
 		return;
 
@@ -400,7 +400,7 @@ static void tcp_v6_err(struct sk_buff *s
 		if (!ip6_sk_accept_pmtu(sk))
 			goto out;
 
-		tp->mtu_info = ntohl(info);
+		WRITE_ONCE(tp->mtu_info, ntohl(info));
 		if (!sock_owned_by_user(sk))
 			tcp_v6_mtu_reduced(sk);
 		else if (!test_and_set_bit(TCP_MTU_REDUCED_DEFERRED,