• Daniel Lenski's avatar
    Add support for GlobalProtect ESP tunnel · 1ad22fc3
    Daniel Lenski authored
    Most of the existing ESP support code (written for Juniper/nc) can be reused
    for GlobalProtect ESP. The ESP algorithms, SPIs, and keys are sent as part of the
    getconfig XML response.
    
    GlobalProtect requires a fairly awkward "tap dance" between the TCP mainloop and
    the UDP mainloop in order to support ESP:
    
    * Prior to the getconfig XML request, the HTTPS tunnel will not work (even though
      the authcookie is already known from the login response) and the ESP tunnel
      also will not work (because the ESP keys are not known).
    * After the getconfig XML request, either the ESP tunnel or the HTTPS tunnel can
      be connected, but not both.  As soon as the HTTPS tunnel is disconnected,
      the ESP keys are invalidated.  On the other hand, if the ESP tunnel stops
      responding due to some firewall that interferes with UDP, the HTTPS tunnel
      can still be connected.
    * Therefore, in order to allow the ESP tunnel to start, the TCP mainloop must
      refrain from actually connecting to the HTTPS tunnel unless the ESP tunnel
      is disabled or has failed to connect... but it can't wait *too* long
      because then the HTTPS keepalive connection may be dropped, and the user
      will wonder why no traffic is flowing even though the VPN has allegedly
      started.  The wait time is currently hard-coded at 5 seconds (half the DPD
      interval used by the official clients).
    
    Another quirk of the GlobalProtect ESP support: it uses specially
    constructed ICMP request/reply ("ping") packets as the probes for ESP
    initiation and DPD.
    
    * These packets must contain a "magic payload" in order to work.
    * In most GlobalProtect VPNs, the packets are addressed to the public, external IPv4
      address of the VPN gateway server even though they are sent over the ESP
      tunnel (???), but in some cases they must be addressed to a different address
      which is misleading described as <gw-address> in the getconfig XML response.
    
    Don't blame me. I didn't design this.
    
    GlobalProtect also has the strange quirk that incoming (server → client) ESP
    sequence numbers start at 1, not 0, but this just causes a one-time offset
    for the replay protection checker.
    Signed-off-by: default avatarDaniel Lenski <dlenski@gmail.com>
    Signed-off-by: default avatarDavid Woodhouse <dwmw2@infradead.org>
    1ad22fc3
mainloop.c 9.78 KB