net: use dst_dev_rcu() in sk_setup_caps()

Use RCU to protect accesses to dst->dev from sk_setup_caps()
and sk_dst_gso_max_size().

Also use dst_dev_rcu() in ip6_dst_mtu_maybe_forward(),
and ip_dst_mtu_maybe_forward().

ip4_dst_hoplimit() can use dst_dev_net_rcu().

Fixes: 4a6ce2b6f2ec ("net: introduce a new function dst_dev_put()")
Signed-off-by: Eric Dumazet <[e-mail]>
Reviewed-by: David Ahern <[e-mail]>
Link: https://patch.msgid.link/[e-mail]
Signed-off-by: Jakub Kicinski <[e-mail]>

include/net/ip.h

···
 						    bool forwarding)
 {
 	const struct rtable *rt = dst_rtable(dst);
+	const struct net_device *dev;
 	unsigned int mtu, res;
 	struct net *net;
 
 	rcu_read_lock();
 
-	net = dev_net_rcu(dst_dev(dst));
+	dev = dst_dev_rcu(dst);
+	net = dev_net_rcu(dev);
 	if (READ_ONCE(net->ipv4.sysctl_ip_fwd_use_pmtu) ||
 	    ip_mtu_locked(dst) ||
 	    !forwarding) {
···
 	if (mtu)
 		goto out;
 
-	mtu = READ_ONCE(dst_dev(dst)->mtu);
+	mtu = READ_ONCE(dev->mtu);
 
 	if (unlikely(ip_mtu_locked(dst))) {
 		if (rt->rt_uses_gateway && mtu > 576)

include/net/ip6_route.h

···
 
 	mtu = IPV6_MIN_MTU;
 	rcu_read_lock();
-	idev = __in6_dev_get(dst_dev(dst));
+	idev = __in6_dev_get(dst_dev_rcu(dst));
 	if (idev)
 		mtu = READ_ONCE(idev->cnf.mtu6);
 	rcu_read_unlock();

include/net/route.h

···
 		const struct net *net;
 
 		rcu_read_lock();
-		net = dev_net_rcu(dst_dev(dst));
+		net = dst_dev_net_rcu(dst);
 		hoplimit = READ_ONCE(net->ipv4.sysctl_ip_default_ttl);
 		rcu_read_unlock();
 	}

net/core/sock.c

···
 }
 EXPORT_SYMBOL_GPL(sk_clone_lock);
 
-static u32 sk_dst_gso_max_size(struct sock *sk, struct dst_entry *dst)
+static u32 sk_dst_gso_max_size(struct sock *sk, const struct net_device *dev)
 {
 	bool is_ipv6 = false;
 	u32 max_size;
···
 		   !ipv6_addr_v4mapped(&sk->sk_v6_rcv_saddr));
 #endif
 	/* pairs with the WRITE_ONCE() in netif_set_gso(_ipv4)_max_size() */
-	max_size = is_ipv6 ? READ_ONCE(dst_dev(dst)->gso_max_size) :
-			READ_ONCE(dst_dev(dst)->gso_ipv4_max_size);
+	max_size = is_ipv6 ? READ_ONCE(dev->gso_max_size) :
+			READ_ONCE(dev->gso_ipv4_max_size);
 	if (max_size > GSO_LEGACY_MAX_SIZE && !sk_is_tcp(sk))
 		max_size = GSO_LEGACY_MAX_SIZE;
 
···
 
 void sk_setup_caps(struct sock *sk, struct dst_entry *dst)
 {
+	const struct net_device *dev;
 	u32 max_segs = 1;
 
-	sk->sk_route_caps = dst_dev(dst)->features;
+	rcu_read_lock();
+	dev = dst_dev_rcu(dst);
+	sk->sk_route_caps = dev->features;
 	if (sk_is_tcp(sk)) {
 		struct inet_connection_sock *icsk = inet_csk(sk);
 
···
 			sk->sk_route_caps &= ~NETIF_F_GSO_MASK;
 		} else {
 			sk->sk_route_caps |= NETIF_F_SG | NETIF_F_HW_CSUM;
-			sk->sk_gso_max_size = sk_dst_gso_max_size(sk, dst);
+			sk->sk_gso_max_size = sk_dst_gso_max_size(sk, dev);
 			/* pairs with the WRITE_ONCE() in netif_set_gso_max_segs() */
-			max_segs = max_t(u32, READ_ONCE(dst_dev(dst)->gso_max_segs), 1);
+			max_segs = max_t(u32, READ_ONCE(dev->gso_max_segs), 1);
 		}
 	}
 	sk->sk_gso_max_segs = max_segs;
 	sk_dst_set(sk, dst);
+	rcu_read_unlock();
 }
 EXPORT_SYMBOL_GPL(sk_setup_caps);