RHEL 7.4+ kernel crash with a NULL pointer dereference in vxlan_dellink+0xaa

Issue

• A system running kernel-3.10.0-693.el7 or higher experiences a kernel panic with a backtrace similar to the following:

  PID: 2134   TASK: ffff94fd28908000  CPU: 46  COMMAND: "ovs-vswitchd"
   #0 [ffff94e4fc32f578] machine_kexec at ffffffff822629da
   #1 [ffff94e4fc32f5d8] __crash_kexec at ffffffff82316692
   #2 [ffff94e4fc32f6a8] crash_kexec at ffffffff82316780
   #3 [ffff94e4fc32f6c0] oops_end at ffffffff8291d728
   #4 [ffff94e4fc32f6e8] no_context at ffffffff8290c6cd
   #5 [ffff94e4fc32f738] __bad_area_nosemaphore at ffffffff8290c764
   #6 [ffff94e4fc32f788] bad_area_nosemaphore at ffffffff8290c8d5
   #7 [ffff94e4fc32f798] __do_page_fault at ffffffff829206e0
   #8 [ffff94e4fc32f800] do_page_fault at ffffffff829208d5
   #9 [ffff94e4fc32f830] page_fault at ffffffff8291c758
      [exception RIP: vxlan_dellink+170]
      RIP: ffffffffc0ca692a  RSP: ffff94e4fc32f8e8  RFLAGS: 00010246
      RAX: 0000000000000000  RBX: 0000000000000001  RCX: 0000000000000000
      RDX: 0000000000000000  RSI: ffffe114dc788300  RDI: ffff94e4de20cb00
      RBP: ffff94e4fc32f910   R8: ffff94e4de20e200   R9: 000000018040003c
      R10: 00000000de20d801  R11: ffffe114dc788300  R12: ffff94fe65b60000
      R13: ffffffff82f42160  R14: ffff94e4fc32f920  R15: ffffc61dbc611da0
      ORIG_RAX: ffffffffffffffff  CS: 0010  SS: 0018
  #10 [ffff94e4fc32f918] rtnl_delete_link at ffffffff82802c76
  #11 [ffff94e4fc32f948] ovs_netdev_tunnel_destroy at ffffffffc09eff79 [openvswitch]
  #12 [ffff94e4fc32f960] ovs_vport_del at ffffffffc09eed6c [openvswitch]
  #13 [ffff94e4fc32f978] ovs_dp_detach_port at ffffffffc09e5130 [openvswitch]
  #14 [ffff94e4fc32f988] ovs_vport_cmd_del at ffffffffc09e5263 [openvswitch]
  #15 [ffff94e4fc32f9d0] genl_family_rcv_msg at ffffffff8282bdd8
  #16 [ffff94e4fc32fa98] genl_rcv_msg at ffffffff8282c05b
  #17 [ffff94e4fc32fac8] netlink_rcv_skb at ffffffff8282a06b
  #18 [ffff94e4fc32faf0] genl_rcv at ffffffff8282a5a8
  #19 [ffff94e4fc32fb08] netlink_unicast at ffffffff828299f0
  #20 [ffff94e4fc32fb50] netlink_sendmsg at ffffffff82829d98
  #21 [ffff94e4fc32fbd8] sock_sendmsg at ffffffff827d1396
  #22 [ffff94e4fc32fd40] ___sys_sendmsg at ffffffff827d21a9
  #23 [ffff94e4fc32fed0] __sys_sendmsg at ffffffff827d37b1
  #24 [ffff94e4fc32ff40] sys_sendmsg at ffffffff827d3802
  #25 [ffff94e4fc32ff50] system_call_fastpath at ffffffff8292579b
      RIP: 00007f5048e89d0d  RSP: 00007fffa9e67650  RFLAGS: 00000293
      RAX: 000000000000002e  RBX: 00007fffa9e67398  RCX: ffffffffffffffff
      RDX: 0000000000000000  RSI: 00007fffa9e66690  RDI: 000000000000039b
      RBP: 0000000000000001   R8: 0000000000000000   R9: 0000000000000001
      R10: 0000000000000040  R11: 0000000000000293  R12: 00007f5040004af0
      R13: 00007fffa9e66b20  R14: 0000000000001244  R15: 00007fffa9e66690
      ORIG_RAX: 000000000000002e  CS: 0033  SS: 002b