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Date:   Fri, 13 May 2022 11:55:42 -0700
From:   Eric Dumazet <eric.dumazet@...il.com>
To:     "David S . Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>
Cc:     netdev <netdev@...r.kernel.org>,
        Eric Dumazet <edumazet@...gle.com>,
        Eric Dumazet <eric.dumazet@...il.com>,
        Neil Horman <nhorman@...driver.com>,
        Vlad Yasevich <vyasevich@...il.com>,
        Marcelo Ricardo Leitner <marcelo.leitner@...il.com>
Subject: [PATCH v2 net-next 02/10] sctp: read sk->sk_bound_dev_if once in sctp_rcv()

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

sctp_rcv() reads sk->sk_bound_dev_if twice while the socket
is not locked. Another cpu could change this field under us.

Fixes: 0fd9a65a76e8 ("[SCTP] Support SO_BINDTODEVICE socket option on incoming packets.")
Signed-off-by: Eric Dumazet <edumazet@...gle.com>
Cc: Neil Horman <nhorman@...driver.com>
Cc: Vlad Yasevich <vyasevich@...il.com>
Cc: Marcelo Ricardo Leitner <marcelo.leitner@...il.com>
---
 net/sctp/input.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/net/sctp/input.c b/net/sctp/input.c
index 90e12bafdd4894624b3a63d625ed21c85b60a4f0..4f43afa8678f9febf2f02c2ce1a840ce3ab6a07d 100644
--- a/net/sctp/input.c
+++ b/net/sctp/input.c
@@ -92,6 +92,7 @@ int sctp_rcv(struct sk_buff *skb)
 	struct sctp_chunk *chunk;
 	union sctp_addr src;
 	union sctp_addr dest;
+	int bound_dev_if;
 	int family;
 	struct sctp_af *af;
 	struct net *net = dev_net(skb->dev);
@@ -169,7 +170,8 @@ int sctp_rcv(struct sk_buff *skb)
 	 * If a frame arrives on an interface and the receiving socket is
 	 * bound to another interface, via SO_BINDTODEVICE, treat it as OOTB
 	 */
-	if (sk->sk_bound_dev_if && (sk->sk_bound_dev_if != af->skb_iif(skb))) {
+	bound_dev_if = READ_ONCE(sk->sk_bound_dev_if);
+	if (bound_dev_if && (bound_dev_if != af->skb_iif(skb))) {
 		if (transport) {
 			sctp_transport_put(transport);
 			asoc = NULL;
-- 
2.36.0.550.gb090851708-goog

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