net: Add Software fallback infrastructure for socket dependent offloads

With socket dependent offloads we rely on the netdev to transform
the transmitted packets before sending them to the wire.
When a packet from an offloaded socket is rerouted to a different
device we need to detect it and do the transformation in software.

Signed-off-by: Ilya Lesokhin <[email protected]>
Signed-off-by: Boris Pismenny <[email protected]>
Signed-off-by: David S. Miller <[email protected]>

Author: Ilya Lesokhin

include/net/sock.h

@@ -481,6 +481,11 @@ struct sock {
 	void			(*sk_error_report)(struct sock *sk);
 	int			(*sk_backlog_rcv)(struct sock *sk,
 						  struct sk_buff *skb);
+#ifdef CONFIG_SOCK_VALIDATE_XMIT
+	struct sk_buff*		(*sk_validate_xmit_skb)(struct sock *sk,
+							struct net_device *dev,
+							struct sk_buff *skb);
+#endif
 	void                    (*sk_destruct)(struct sock *sk);
 	struct sock_reuseport __rcu	*sk_reuseport_cb;
 	struct rcu_head		sk_rcu;
@@ -2332,6 +2337,22 @@ static inline bool sk_fullsock(const struct sock *sk)
 	return (1 << sk->sk_state) & ~(TCPF_TIME_WAIT | TCPF_NEW_SYN_RECV);
 }
 
+/* Checks if this SKB belongs to an HW offloaded socket
+ * and whether any SW fallbacks are required based on dev.
+ */
+static inline struct sk_buff *sk_validate_xmit_skb(struct sk_buff *skb,
+						   struct net_device *dev)
+{
+#ifdef CONFIG_SOCK_VALIDATE_XMIT
+	struct sock *sk = skb->sk;
+
+	if (sk && sk_fullsock(sk) && sk->sk_validate_xmit_skb)
+		skb = sk->sk_validate_xmit_skb(sk, dev, skb);
+#endif
+
+	return skb;
+}
+
 /* This helper checks if a socket is a LISTEN or NEW_SYN_RECV
  * SYNACK messages can be attached to either ones (depending on SYNCOOKIE)
  */

net/Kconfig

@@ -407,6 +407,9 @@ config GRO_CELLS
 	bool
 	default n
 
+config SOCK_VALIDATE_XMIT
+	bool
+
 config NET_DEVLINK
 	tristate "Network physical/parent device Netlink interface"
 	help

net/core/dev.c

@@ -3112,6 +3112,10 @@ static struct sk_buff *validate_xmit_skb(struct sk_buff *skb, struct net_device
 	if (unlikely(!skb))
 		goto out_null;
 
+	skb = sk_validate_xmit_skb(skb, dev);
+	if (unlikely(!skb))
+		goto out_null;
+
 	if (netif_needs_gso(skb, features)) {
 		struct sk_buff *segs;