[PATCH 4.14 077/218] sctp: read sk->sk_bound_dev_if once in sctp_rcv()

[Greg Kroah-Hartman]

From: Eric Dumazet <edumazet@xxxxxxxxxx>

[ Upstream commit a20ea298071f46effa3aaf965bf9bb34c901db3f ]

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@xxxxxxxxxx>
Cc: Neil Horman <nhorman@xxxxxxxxxxxxx>
Cc: Vlad Yasevich <vyasevich@xxxxxxxxx>
Cc: Marcelo Ricardo Leitner <marcelo.leitner@xxxxxxxxx>
Acked-by: Marcelo Ricardo Leitner <marcelo.leitner@xxxxxxxxx>
Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
 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 b20a1fbea8bf..3305e11035fd 100644
--- a/net/sctp/input.c
+++ b/net/sctp/input.c
@@ -103,6 +103,7 @@ 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);
@@ -180,7 +181,8 @@ 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;
-- 
2.35.1