smc_vlan_by_tcpsk() fetches sk_dst_get(sk)->dev before RTNL and
passes it to netdev_walk_all_lower_dev(), which is illegal.

Also, smc_vlan_by_tcpsk_walk() does not require RTNL at all.

Let's use __sk_dst_get(), dst_dev_rcu(), and
netdev_walk_all_lower_dev_rcu().

Note that the returned value of smc_vlan_by_tcpsk() is not used
in the caller.

Fixes: 0cfdd8f92cac ("smc: connection and link group creation")
Signed-off-by: Kuniyuki Iwashima <kuniyu@google.com>
---
Cc: "D. Wythe" <alibuda@linux.alibaba.com>
Cc: Dust Li <dust.li@linux.alibaba.com>
Cc: Sidraya Jayagond <sidraya@linux.ibm.com>
Cc: Wenjia Zhang <wenjia@linux.ibm.com>
Cc: Mahanta Jambigi <mjambigi@linux.ibm.com>
Cc: Tony Lu <tonylu@linux.alibaba.com>
Cc: Wen Gu <guwen@linux.alibaba.com>
Cc: Ursula Braun <ubraun@linux.vnet.ibm.com>
---
 net/smc/smc_core.c | 27 ++++++++++++---------------
 1 file changed, 12 insertions(+), 15 deletions(-)

diff --git a/net/smc/smc_core.c b/net/smc/smc_core.c
index 262746e304dd..2a559a98541c 100644
--- a/net/smc/smc_core.c
+++ b/net/smc/smc_core.c
@@ -1883,35 +1883,32 @@ static int smc_vlan_by_tcpsk_walk(struct net_device *lower_dev,
 /* Determine vlan of internal TCP socket. */
 int smc_vlan_by_tcpsk(struct socket *clcsock, struct smc_init_info *ini)
 {
-	struct dst_entry *dst = sk_dst_get(clcsock->sk);
 	struct netdev_nested_priv priv;
 	struct net_device *ndev;
+	struct dst_entry *dst;
 	int rc = 0;
 
 	ini->vlan_id = 0;
-	if (!dst) {
-		rc = -ENOTCONN;
-		goto out;
-	}
-	if (!dst->dev) {
+
+	rcu_read_lock();
+
+	dst = __sk_dst_get(clcsock->sk);
+	ndev = dst ? dst_dev_rcu(dst) : NULL;
+	if (!ndev) {
 		rc = -ENODEV;
-		goto out_rel;
+		goto out;
 	}
 
-	ndev = dst->dev;
 	if (is_vlan_dev(ndev)) {
 		ini->vlan_id = vlan_dev_vlan_id(ndev);
-		goto out_rel;
+		goto out;
 	}
 
 	priv.data = (void *)&ini->vlan_id;
-	rtnl_lock();
-	netdev_walk_all_lower_dev(ndev, smc_vlan_by_tcpsk_walk, &priv);
-	rtnl_unlock();
-
-out_rel:
-	dst_release(dst);
+	netdev_walk_all_lower_dev_rcu(ndev, smc_vlan_by_tcpsk_walk, &priv);
 out:
+	rcu_read_unlock();
+
 	return rc;
 }
 
-- 
2.51.0.384.g4c02a37b29-goog