Revert "nixos/firewall: fix reverse path check failures with IPsec"

The inclusion of the "meta ipsec" rule in the default reverse path
filtering breaks systems not built with specific XFRM kernel config
options.  Specifically CONFIG_XFRM must be set, which gets selected
by CONFIG_NFT_XFRM, which is hidden behind CONFIG_XFRM_USER.

These options are not selected by default in most defconfig's provided
by the kernel with the exception of some device-specific defconfigs.

These options are not set by the nix kernel common_config, and I would
argue that IPSec support does not belong in a minimal kernel as that
elevates its support status above other in-kernel VPN interfaces.

The contributor of this feature does not seem interested in working
towards a solution that does not break systems running kernels built
with "autoModules = false" while supporting this feature, and as this
silently breaks firewalls into an insecure state and poses an immediate
security issue I propose this be reverted until a solution that does not
break such systems is proposed.
https://github.com/NixOS/nixpkgs/pull/310857#discussion_r1742834970

Devices used as firewalls, if they do not have the required kernel
config, will fail to load the new firewall rules and will upon boot pass
traffic without any filtering into the internal network.

Devices exposed directly to the internet, after reboot, will boot
without filtering potentially exposing services not intended to be
exposed to the internet, such as databases.

The following platforms in nixpkgs appear to be impacted:
 - pc_simplekernel
 - pogoplug4
 - sheevaplug
 - zero-gravitas
 - zero-sugar
 - utilite
 - guruplug
 - beaglebone
 - fuloong2f_n32

References to hardware without autoModules can be found in
nixos-hardware, as well as in active third-party repos on github.

I suspect there are other users impacted that do not have their configurations
public, as autoModules = true leads to long compile times when targeting
kernels to less standard hardware or hardware with quirks that require
patches that cannot be upstreamed.

This reverts commit 3c12ef3f219c1a0f458d72e7b460782287974bbd.

0 files changed, 0 insertions, 0 deletions