datapath: Fix kernel panic for uninitialized tun_dst of ovs_gso_cb.

The variable tun_dst in struct ovs_gso_cb isn't necessarily all-zeros which
came from the Netlink layer. When delete a netdev port and immediately add
a vxlan port, they maybe use the same port_no. So the variable tun_dst of
struct ovs_gso_cb hasn't be set, when the skb sent to the vxlan port. And
the panic will be triggered.

	BUG: unable to handle kernel NULL pointer dereference at 0000000000000052
	IP: [<ffffffffa07954f4>] rpl_vxlan_xmit+0x34/0x60 [openvswitch]
	PGD 1f9f374067 PUD 1f9f375067 PMD 0
	Oops: 0000 [openvswitch#1] SMP
	RIP: 0010:[<ffffffffa07954f4>]  [<ffffffffa07954f4>] rpl_vxlan_xmit+0x34/0x60 [openvswitch]
	RSP: 0018:ffff881fff483898  EFLAGS: 00010202
	RAX: 0000000000000040 RBX: ffff881ff2d59f00 RCX: ffff881f742016b0
	RDX: 0000000000000001 RSI: ffff881f9f5f0000 RDI: ffff881ff2d59f00
	RBP: ffff881fff483898 R08: 000000000000002e R09: 0000000000000000
	R10: 0000000000000000 R11: ffff881fff483a50 R12: ffff881f74201680
	R13: 000000000000ffbe R14: 0000000000000000 R15: ffff881ff2d59f00
	FS:  00007f8b6f7fe700(0000) GS:ffff881fff480000(0000) knlGS:0000000000000000
	CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
	CR2: 0000000000000052 CR3: 0000001f9f373000 CR4: 00000000000027e0
	DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
	DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000400
	Call Trace:
	 <IRQ>
	[<ffffffffa0786480>] ovs_vport_send+0xa0/0x180 [openvswitch]
	[<ffffffffa077414e>] do_output+0x4e/0xf0 [openvswitch]
	[<ffffffffa07758ae>] do_execute_actions+0xa6e/0xa90 [openvswitch]
	[<ffffffff815b654f>] ? netlink_unicast+0x16f/0x1b0
	[<ffffffff815732bb>] ? skb_zerocopy+0x1fb/0x380
	[<ffffffffa07847ca>] ? flow_lookup.isra.8+0x4a/0xc0 [openvswitch]
	[<ffffffffa0775b2d>] ovs_execute_actions+0x4d/0x140 [openvswitch]
	[<ffffffffa077c604>] ovs_dp_process_packet+0x94/0x140 [openvswitch]
	[<ffffffffa07762c4>] ? ovs_ct_update_key+0xc4/0x150 [openvswitch]
	[<ffffffffa078637b>] ovs_vport_receive+0x7b/0xe0 [openvswitch]
	[<ffffffffa077c604>] ? ovs_dp_process_packet+0x94/0x140 [openvswitch]
	[<ffffffff816062d6>] ? __fib_validate_source.isra.13+0x2b6/0x400
	[<ffffffff8158da15>] ? dst_init+0xe5/0xf0
	[<ffffffffa021a2af>] ? generic_packet+0x1f/0x30 [nf_conntrack]
	[<ffffffffa02160d0>] ? nf_conntrack_in+0x350/0x5f0 [nf_conntrack]
	[<ffffffffa0787047>] netdev_port_receive+0xa7/0x100 [openvswitch]
	[<ffffffffa07870be>] netdev_frame_hook+0x1e/0x30 [openvswitch]
	[<ffffffff81581a52>] __netif_receive_skb_core+0x1e2/0x800
	[<ffffffff81582088>] __netif_receive_skb+0x18/0x60
	[<ffffffff81582110>] netif_receive_skb_internal+0x40/0xc0
	[<ffffffff81583228>] napi_gro_receive+0xd8/0x130
	[<ffffffffa04ef634>] ixgbe_clean_rx_irq+0x7c4/0xa60 [ixgbe]
	[<ffffffffa04f0930>] ixgbe_poll+0x2e0/0x6c0 [ixgbe]
	[<ffffffff815828b0>] net_rx_action+0x170/0x380
	[<ffffffff81090b0f>] __do_softirq+0xef/0x280
	[<ffffffff816ac15c>] call_softirq+0x1c/0x30
	[<ffffffff8102e47d>] do_softirq+0x5d/0xb0
	[<ffffffff81090ebd>] irq_exit+0x12d/0x140
	[<ffffffff816accf8>] do_IRQ+0x58/0xf0
	[<ffffffff816a1ced>] common_interrupt+0x6d/0x6d
	<EOI>

Signed-off-by: Yunjian Wang <[email protected]>
Signed-off-by: Ben Pfaff <[email protected]>
Tested-by: Greg Rose <[email protected]>
Reviewed-by: Greg Rose <[email protected]>

datapath/linux/compat/gso.h

@@ -34,11 +34,16 @@ struct ovs_gso_cb {
 static inline void skb_clear_ovs_gso_cb(struct sk_buff *skb)
 {
 	OVS_GSO_CB(skb)->fix_segment = NULL;
+#ifndef USE_UPSTREAM_TUNNEL
+	OVS_GSO_CB(skb)->tun_dst = NULL;
+#endif
 }
 #else
 static inline void skb_clear_ovs_gso_cb(struct sk_buff *skb)
 {
-
+#ifndef USE_UPSTREAM_TUNNEL
+	OVS_GSO_CB(skb)->tun_dst = NULL;
+#endif
 }
 #endif