linux-kernel - [PATCH 5.15 061/201] tcp: sk->sk_bound_dev_if once in inet_request_bound_dev

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Date:   Wed, 27 Jul 2022 18:09:25 +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>,
        Sasha Levin <sashal@...nel.org>
Subject: [PATCH 5.15 061/201] tcp: sk->sk_bound_dev_if once in inet_request_bound_dev_if()

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

[ Upstream commit fdb5fd7f736ec7ae9fb36d2842ea6d9ebc4e7269 ]

inet_request_bound_dev_if() reads sk->sk_bound_dev_if twice
while listener socket is not locked.

Another cpu could change this field under us.

Signed-off-by: Eric Dumazet <edumazet@...gle.com>
Signed-off-by: David S. Miller <davem@...emloft.net>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 include/net/inet_sock.h | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/include/net/inet_sock.h b/include/net/inet_sock.h
index 33344d54ad65..e71827aa2dfb 100644
--- a/include/net/inet_sock.h
+++ b/include/net/inet_sock.h
@@ -117,14 +117,15 @@ static inline u32 inet_request_mark(const struct sock *sk, struct sk_buff *skb)
 static inline int inet_request_bound_dev_if(const struct sock *sk,
 					    struct sk_buff *skb)
 {
+	int bound_dev_if = READ_ONCE(sk->sk_bound_dev_if);
 #ifdef CONFIG_NET_L3_MASTER_DEV
 	struct net *net = sock_net(sk);
 
-	if (!sk->sk_bound_dev_if && net->ipv4.sysctl_tcp_l3mdev_accept)
+	if (!bound_dev_if && net->ipv4.sysctl_tcp_l3mdev_accept)
 		return l3mdev_master_ifindex_by_index(net, skb->skb_iif);
 #endif
 
-	return sk->sk_bound_dev_if;
+	return bound_dev_if;
 }
 
 static inline int inet_sk_bound_l3mdev(const struct sock *sk)
-- 
2.35.1