If the vxlan interface is created without explicit group definition,
there are corner cases which may cause kernel panic.

For instance, in the following scenario:

node A:
$ ip link add dev vxlan42  address 2c:c2:60:00:10:20 type vxlan id 42
$ ip addr add dev vxlan42 10.0.0.1/24
$ ip link set up dev vxlan42
$ arp -i vxlan42 -s 10.0.0.2 2c:c2:60:00:01:02
$ bridge fdb add dev vxlan42 to 2c:c2:60:00:01:02 dst <IPv4 address>
$ ping 10.0.0.2

node B:
$ ip link add dev vxlan42 address 2c:c2:60:00:01:02 type vxlan id 42
$ ip addr add dev vxlan42 10.0.0.2/24
$ ip link set up dev vxlan42
$ arp -i vxlan42 -s 10.0.0.1 2c:c2:60:00:10:20

node B crashes:

 vxlan42: 2c:c2:60:00:10:20 migrated from 4011:eca4:c0a8:6466:c0a8:6415:8e09:2118 to (invalid address)
 vxlan42: 2c:c2:60:00:10:20 migrated from 4011:eca4:c0a8:6466:c0a8:6415:8e09:2118 to (invalid address)
 BUG: unable to handle kernel NULL pointer dereference at 0000000000000046
 IP: [<ffffffff8143c459>] ip6_route_output+0x58/0x82
 PGD 7bd89067 PUD 7bd4e067 PMD 0
 Oops: 0000 [#1] SMP
 Modules linked in:
 CPU: 1 PID: 0 Comm: swapper/1 Not tainted 3.14.0-rc8-hvx-xen-00019-g97a5221f-dirty #154
 Hardware name: Bochs Bochs, BIOS Bochs 01/01/2011
 task: ffff88007c774f50 ti: ffff88007c79c000 task.ti: ffff88007c79c000
 RIP: 0010:[<ffffffff8143c459>]  [<ffffffff8143c459>] ip6_route_output+0x58/0x82
 RSP: 0018:ffff88007fd03668  EFLAGS: 00010282
 RAX: 0000000000000000 RBX: ffffffff8186a000 RCX: 0000000000000040
 RDX: 0000000000000000 RSI: ffff88007b0e4a80 RDI: ffff88007fd03754
 RBP: ffff88007fd03688 R08: ffff88007b0e4a80 R09: 0000000000000000
 R10: 0200000a0100000a R11: 0001002200000000 R12: ffff88007fd03740
 R13: ffff88007b0e4a80 R14: ffff88007b0e4a80 R15: ffff88007bba0c50
 FS:  0000000000000000(0000) GS:ffff88007fd00000(0000) knlGS:0000000000000000
 CS:  0010 DS: 0000 ES: 0000 CR0: 000000008005003b
 CR2: 0000000000000046 CR3: 000000007bb60000 CR4: 00000000000006e0
 Stack:
  0000000000000000 ffff88007fd037a0 ffffffff8186a000 ffff88007fd03740
  ffff88007fd036c8 ffffffff814320bb 0000000000006e49 ffff88007b8b7360
  ffff88007bdbf200 ffff88007bcbc000 ffff88007b8b7000 ffff88007b8b7360
 Call Trace:
  <IRQ>
  [<ffffffff814320bb>] ip6_dst_lookup_tail+0x2d/0xa4
  [<ffffffff814322a5>] ip6_dst_lookup+0x10/0x12
  [<ffffffff81323b4e>] vxlan_xmit_one+0x32a/0x68c
  [<ffffffff814a325a>] ? _raw_spin_unlock_irqrestore+0x12/0x14
  [<ffffffff8104c551>] ? lock_timer_base.isra.23+0x26/0x4b
  [<ffffffff8132451a>] vxlan_xmit+0x66a/0x6a8
  [<ffffffff8141a365>] ? ipt_do_table+0x35f/0x37e
  [<ffffffff81204ba2>] ? selinux_ip_postroute+0x41/0x26e
  [<ffffffff8139d0c1>] dev_hard_start_xmit+0x2ce/0x3ce
  [<ffffffff8139d491>] __dev_queue_xmit+0x2d0/0x392
  [<ffffffff813b380f>] ? eth_header+0x28/0xb5
  [<ffffffff8139d569>] dev_queue_xmit+0xb/0xd
  [<ffffffff813a5aa6>] neigh_resolve_output+0x134/0x152
  [<ffffffff813db741>] ip_finish_output2+0x236/0x299
  [<ffffffff813dc074>] ip_finish_output+0x98/0x9d
  [<ffffffff813dc749>] ip_output+0x62/0x67
  [<ffffffff813da9f2>] dst_output+0xf/0x11
  [<ffffffff813dc11c>] ip_local_out+0x1b/0x1f
  [<ffffffff813dcf1b>] ip_send_skb+0x11/0x37
  [<ffffffff813dcf70>] ip_push_pending_frames+0x2f/0x33
  [<ffffffff813ff732>] icmp_push_reply+0x106/0x115
  [<ffffffff813ff9e4>] icmp_reply+0x142/0x164
  [<ffffffff813ffb3b>] icmp_echo.part.16+0x46/0x48
  [<ffffffff813c1d30>] ? nf_iterate+0x43/0x80
  [<ffffffff813d8037>] ? xfrm4_policy_check.constprop.11+0x52/0x52
  [<ffffffff813ffb62>] icmp_echo+0x25/0x27
  [<ffffffff814005f7>] icmp_rcv+0x1d2/0x20a
  [<ffffffff813d8037>] ? xfrm4_policy_check.constprop.11+0x52/0x52
  [<ffffffff813d810d>] ip_local_deliver_finish+0xd6/0x14f
  [<ffffffff813d8037>] ? xfrm4_policy_check.constprop.11+0x52/0x52
  [<ffffffff813d7fde>] NF_HOOK.constprop.10+0x4c/0x53
  [<ffffffff813d82bf>] ip_local_deliver+0x4a/0x4f
  [<ffffffff813d7f7b>] ip_rcv_finish+0x253/0x26a
  [<ffffffff813d7d28>] ? inet_add_protocol+0x3e/0x3e
  [<ffffffff813d7fde>] NF_HOOK.constprop.10+0x4c/0x53
  [<ffffffff813d856a>] ip_rcv+0x2a6/0x2ec
  [<ffffffff8139a9a0>] __netif_receive_skb_core+0x43e/0x478
  [<ffffffff812a346f>] ? virtqueue_poll+0x16/0x27
  [<ffffffff8139aa2f>] __netif_receive_skb+0x55/0x5a
  [<ffffffff8139aaaa>] process_backlog+0x76/0x12f
  [<ffffffff8139add8>] net_rx_action+0xa2/0x1ab
  [<ffffffff81047847>] __do_softirq+0xca/0x1d1
  [<ffffffff81047ace>] irq_exit+0x3e/0x85
  [<ffffffff8100b98b>] do_IRQ+0xa9/0xc4
  [<ffffffff814a37ad>] common_interrupt+0x6d/0x6d
  <EOI>
  [<ffffffff810378db>] ? native_safe_halt+0x6/0x8
  [<ffffffff810110c7>] default_idle+0x9/0xd
  [<ffffffff81011694>] arch_cpu_idle+0x13/0x1c
  [<ffffffff8107480d>] cpu_startup_entry+0xbc/0x137
  [<ffffffff8102e741>] start_secondary+0x1a0/0x1a5
 Code: 24 14 e8 f1 e5 01 00 31 d2 a8 32 0f 95 c2 49 8b 44 24 2c 49 0b 44 24 24 74 05 83 ca 04 eb 1c 4d 85 ed 74 17 49 8b 85 a8 02 00 00 <66> 8b 40 46 66 c1 e8 07 83 e0 07 c1 e0 03 09 c2 4c 89 e6 48 89
 RIP  [<ffffffff8143c459>] ip6_route_output+0x58/0x82
  RSP <ffff88007fd03668>
 CR2: 0000000000000046
 ---[ end trace 4612329caab37efd ]---

When vxlan interface is created without explicit group definition, the
default_dst protocol family is initialiazed to AF_UNSPEC and the driver
assumes IPv4 configuration. On the other side, the default_dst protocol
family is used to differentiate between IPv4 and IPv6 cases and, since,
AF_UNSPEC != AF_INET, the processing takes the IPv6 path.

Making the IPv4 assumption explicit by settting default_dst protocol
family to AF_INET4 and preventing mixing of IPv4 and IPv6 addresses in
snooped fdb entries fixes the corner case crashes.
Signed-off-by: Mike Rapoport <mike.rapoport@ravellosystems.com>
Signed-off-by: David S. Miller <davem@davemloft.net>