netdev - [PATCH net-next 5/6] mptcp: annotate lockless accesses to sk->sk

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Message-ID: <20230315205746.3801038-6-edumazet@google.com>
Date:   Wed, 15 Mar 2023 20:57:45 +0000
From:   Eric Dumazet <edumazet@...gle.com>
To:     "David S . Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>
Cc:     netdev@...r.kernel.org, eric.dumazet@...il.com,
        Eric Dumazet <edumazet@...gle.com>
Subject: [PATCH net-next 5/6] mptcp: annotate lockless accesses to sk->sk_err

mptcp_poll() reads sk->sk_err without socket lock held/owned.

Add READ_ONCE() and WRITE_ONCE() to avoid load/store tearing.

Signed-off-by: Eric Dumazet <edumazet@...gle.com>
---
 net/mptcp/pm_netlink.c | 2 +-
 net/mptcp/protocol.c   | 8 ++++----
 net/mptcp/subflow.c    | 4 ++--
 3 files changed, 7 insertions(+), 7 deletions(-)

diff --git a/net/mptcp/pm_netlink.c b/net/mptcp/pm_netlink.c
index 56628b52d1001a967eb2e504bdbeac0c4cd17acc..cbaa1b49f7fe949b9de8f4be0cf74cea6cecc106 100644
--- a/net/mptcp/pm_netlink.c
+++ b/net/mptcp/pm_netlink.c
@@ -2019,7 +2019,7 @@ static int mptcp_event_put_token_and_ssk(struct sk_buff *skb,
 	    nla_put_s32(skb, MPTCP_ATTR_IF_IDX, ssk->sk_bound_dev_if))
 		return -EMSGSIZE;
 
-	sk_err = ssk->sk_err;
+	sk_err = READ_ONCE(ssk->sk_err);
 	if (sk_err && sk->sk_state == TCP_ESTABLISHED &&
 	    nla_put_u8(skb, MPTCP_ATTR_ERROR, sk_err))
 		return -EMSGSIZE;
diff --git a/net/mptcp/protocol.c b/net/mptcp/protocol.c
index 3ad9c46202fc63a5b3a870bf2ba994a8d9148264..3005a5adf715e8d147c119b0b4c13fcc58fe99f6 100644
--- a/net/mptcp/protocol.c
+++ b/net/mptcp/protocol.c
@@ -2463,15 +2463,15 @@ static void mptcp_check_fastclose(struct mptcp_sock *msk)
 	/* Mirror the tcp_reset() error propagation */
 	switch (sk->sk_state) {
 	case TCP_SYN_SENT:
-		sk->sk_err = ECONNREFUSED;
+		WRITE_ONCE(sk->sk_err, ECONNREFUSED);
 		break;
 	case TCP_CLOSE_WAIT:
-		sk->sk_err = EPIPE;
+		WRITE_ONCE(sk->sk_err, EPIPE);
 		break;
 	case TCP_CLOSE:
 		return;
 	default:
-		sk->sk_err = ECONNRESET;
+		WRITE_ONCE(sk->sk_err, ECONNRESET);
 	}
 
 	inet_sk_state_store(sk, TCP_CLOSE);
@@ -3791,7 +3791,7 @@ static __poll_t mptcp_poll(struct file *file, struct socket *sock,
 
 	/* This barrier is coupled with smp_wmb() in __mptcp_error_report() */
 	smp_rmb();
-	if (sk->sk_err)
+	if (READ_ONCE(sk->sk_err))
 		mask |= EPOLLERR;
 
 	return mask;
diff --git a/net/mptcp/subflow.c b/net/mptcp/subflow.c
index 4ae1a7304cf0da1840a1d236969549d18cf8ff97..01874059a16865ecb4ec464443f68a30c814f565 100644
--- a/net/mptcp/subflow.c
+++ b/net/mptcp/subflow.c
@@ -1335,7 +1335,7 @@ static bool subflow_check_data_avail(struct sock *ssk)
 			subflow->reset_reason = MPTCP_RST_EMPTCP;
 
 reset:
-			ssk->sk_err = EBADMSG;
+			WRITE_ONCE(ssk->sk_err, EBADMSG);
 			tcp_set_state(ssk, TCP_CLOSE);
 			while ((skb = skb_peek(&ssk->sk_receive_queue)))
 				sk_eat_skb(ssk, skb);
@@ -1419,7 +1419,7 @@ void __mptcp_error_report(struct sock *sk)
 		ssk_state = inet_sk_state_load(ssk);
 		if (ssk_state == TCP_CLOSE && !sock_flag(sk, SOCK_DEAD))
 			inet_sk_state_store(sk, ssk_state);
-		sk->sk_err = -err;
+		WRITE_ONCE(sk->sk_err, -err);
 
 		/* This barrier is coupled with smp_rmb() in mptcp_poll() */
 		smp_wmb();
-- 
2.40.0.rc2.332.ga46443480c-goog