xfrm: Fix double ESP trailer insertion in IPsec crypto offload.

During IPsec performance testing, we see bad ICMP checksum. The error packet
has duplicated ESP trailer due to double validate_xmit_xfrm calls. The first call
is from ip_output, but the packet cannot be sent because
netif_xmit_frozen_or_stopped is true and the packet gets dev_requeue_skb. The second
call is from NET_TX softirq. However after the first call, the packet already
has the ESP trailer.

Fix by marking the skb with XFRM_XMIT bit after the packet is handled by
validate_xmit_xfrm to avoid duplicate ESP trailer insertion.

Fixes: f6e2711 ("net: Add a xfrm validate function to validate_xmit_skb")
Signed-off-by: Huy Nguyen <huyn@mellanox.com>
Reviewed-by: Boris Pismenny <borisp@mellanox.com>
Reviewed-by: Raed Salem <raeds@mellanox.com>
Reviewed-by: Saeed Mahameed <saeedm@mellanox.com>
Signed-off-by: Steffen Klassert <steffen.klassert@secunet.com>

include/net/xfrm.h

@@ -1008,6 +1008,7 @@ struct xfrm_offload {
 #define	XFRM_GRO		32
 #define	XFRM_ESP_NO_TRAILER	64
 #define	XFRM_DEV_RESUME		128
+#define	XFRM_XMIT		256
 
 	__u32			status;
 #define CRYPTO_SUCCESS				1

net/xfrm/xfrm_device.c

@@ -108,7 +108,7 @@ struct sk_buff *validate_xmit_xfrm(struct sk_buff *skb, netdev_features_t featur
 	struct xfrm_offload *xo = xfrm_offload(skb);
 	struct sec_path *sp;
 
-	if (!xo)
+	if (!xo || (xo->flags & XFRM_XMIT))
 		return skb;
 
 	if (!(features & NETIF_F_HW_ESP))
@@ -129,6 +129,8 @@ struct sk_buff *validate_xmit_xfrm(struct sk_buff *skb, netdev_features_t featur
 		return skb;
 	}
 
+	xo->flags |= XFRM_XMIT;
+
 	if (skb_is_gso(skb)) {
 		struct net_device *dev = skb->dev;