xfrm: add prep for esp beet mode offload

Like __xfrm_transport/mode_tunnel_prep(), this patch is to add
__xfrm_mode_beet_prep() to fix the transport_header for gso
segments, and reset skb mac_len, and pull skb data to the
proto inside esp.

This patch also fixes a panic, reported by ltp:

  # modprobe esp4_offload
  # runltp -f net_stress.ipsec_tcp

  [ 2452.780511] kernel BUG at net/core/skbuff.c:109!
  [ 2452.799851] Call Trace:
  [ 2452.800298]  <IRQ>
  [ 2452.800705]  skb_push.cold.98+0x14/0x20
  [ 2452.801396]  esp_xmit+0x17b/0x270 [esp4_offload]
  [ 2452.802799]  validate_xmit_xfrm+0x22f/0x2e0
  [ 2452.804285]  __dev_queue_xmit+0x589/0x910
  [ 2452.806264]  __neigh_update+0x3d7/0xa50
  [ 2452.806958]  arp_process+0x259/0x810
  [ 2452.807589]  arp_rcv+0x18a/0x1c

It was caused by the skb going to esp_xmit with a wrong transport
header.

Signed-off-by: Xin Long <lucien.xin@gmail.com>
Signed-off-by: Steffen Klassert <steffen.klassert@secunet.com>

net/xfrm/xfrm_device.c

@@ -46,6 +46,25 @@ static void __xfrm_mode_tunnel_prep(struct xfrm_state *x, struct sk_buff *skb,
 	pskb_pull(skb, skb->mac_len + x->props.header_len);
 }
 
+static void __xfrm_mode_beet_prep(struct xfrm_state *x, struct sk_buff *skb,
+				  unsigned int hsize)
+{
+	struct xfrm_offload *xo = xfrm_offload(skb);
+	int phlen = 0;
+
+	if (xo->flags & XFRM_GSO_SEGMENT)
+		skb->transport_header = skb->network_header + hsize;
+
+	skb_reset_mac_len(skb);
+	if (x->sel.family != AF_INET6) {
+		phlen = IPV4_BEET_PHMAXLEN;
+		if (x->outer_mode.family == AF_INET6)
+			phlen += sizeof(struct ipv6hdr) - sizeof(struct iphdr);
+	}
+
+	pskb_pull(skb, skb->mac_len + hsize + (x->props.header_len - phlen));
+}
+
 /* Adjust pointers into the packet when IPsec is done at layer2 */
 static void xfrm_outer_mode_prep(struct xfrm_state *x, struct sk_buff *skb)
 {
@@ -66,9 +85,16 @@ static void xfrm_outer_mode_prep(struct xfrm_state *x, struct sk_buff *skb)
 			return __xfrm_transport_prep(x, skb,
 						     sizeof(struct ipv6hdr));
 		break;
+	case XFRM_MODE_BEET:
+		if (x->outer_mode.family == AF_INET)
+			return __xfrm_mode_beet_prep(x, skb,
+						     sizeof(struct iphdr));
+		if (x->outer_mode.family == AF_INET6)
+			return __xfrm_mode_beet_prep(x, skb,
+						     sizeof(struct ipv6hdr));
+		break;
 	case XFRM_MODE_ROUTEOPTIMIZATION:
 	case XFRM_MODE_IN_TRIGGER:
-	case XFRM_MODE_BEET:
 		break;
 	}
 }