Libreswan-xfrm-kernel-support

Here are gory details for Linux kernel support that you may run into. One recurring theme when Linux Kernel IPsec get a new feature usually the default is "N". And the distributions take that. However, when librewan start using the new feature we or someone often need to chase the various distributions get this feature enabled. The challenge of this model, as far as I see, is the libreswan, a userland application, has no easy way to require a kernel config option to be enabled or disabled.

Linux XFRM support

basic set =

== 4.19

Mobike CONFIG_XFRM_MIGRATE

Linux kernel support mobike for ages possibly since 2.x. However many distributions has CONFIG_XFRM_MIGRATE set to no. One could argue mobike is securtiy risk hence it should be disabled. However, it would affect a small set of users. And those users are possibly tweaking the kernel to their needs.

= Mobike possible security issue

A possible security issue - some one create a IPsec connection to a LAN while physically(or wifi) connected to an administratively allowed network. Say special project allows VPN only when you present at a site. When MOBIKE is administratively allowed in kernel and libreswan, one could move this IPsec/VPN to their 3G connection and take the IPsec/VPN connection outside the permitted LAN, say home. Now this VPN keeps connection from any where.

= CONFIG_XFRM_STATISTICS 3.28

Some distributions, as of may 2019, #CONFIG_XFRM_STATISTICS is not set. This cause a run time error with libreswan "No XFRM kernel interface detected". You need a couple of patches or enable this in kernel. This is specific to libreswan 3.28. 3.29 has fixes for this issue. However, it is really good idea to enable