When SElinux is enabled with a targeted policy, network labels can be configured on the VPN tunnel to restrict the security context that is allowed to pass via the VPN tunnel.

This basically looks like:

# /etc/ipsec.conf

config setup
    protostack=netkey
    # Use the private use number 32001. Older openswan versions use the squatted value of 10.
    secctx-attr-type=32001

conn ipsec_selinux_tunnel
    # Labeled IPsec is currently only supported for IKEv1
    # IKEv2 is work in progress, see: https://tools.ietf.org/html/draft-ietf-ipsecme-labeled-ipsec-03
    ikev2=never
    leftid=@west
    left=1.2.3.4
    leftrsasigkey=0sAQ[...]
    rightid=@east
    right=5.6.7.8
    rightrsasigkey=0sAQ[...]
    authby=rsasig
    auto=start
    # Enable Labelled IPsec with the policy you want to allow across the VPN
    policy-label=system_u:object_r:ipsec_spd_t:s0

Note that some seliux-policy versions are missing one policy and you might need to add the following selinux module:

module local 1.0;

require {
    type unconfined_t;
    type ipsec_spd_t;
    type ipsec_t;
    class association setcontext;
}

#============= ipsec_t ==============
allow ipsec_t ipsec_spd_t:association setcontext;

# Required if you run as a basic user.
allow ipsec_t unconfined_t:association setcontext;

You can see the labels in the ip xfrm state output, for example:

# ip xfrm state
src 1.2.3.4 dst 5.6.7.8
    proto esp spi 0x436be694 reqid 16389 mode tunnel
    replay-window 32 flag af-unspec
    auth-trunc hmac(sha1) 0x4c7d6ff6a191951fc69d9c3def070db3e0d59ae5 96 enc cbc(aes) 0x3c624b14b79e6f2dd632d26d36d90ff7
    security context unconfined_u:unconfined_r:netserver_t:s0-s0:c0.c1023
src 5.6.7.8 dst 1.2.3.4
    proto esp spi 0x3ad8e7fa reqid 16389 mode tunnel
    replay-window 32 flag af-unspec
    auth-trunc hmac(sha1) 0x91a06a54d2fd1899229129489bd1d766b8f00990 96 enc cbc(aes) 0x77a17777f44378970ffa25cdd2a8bd34
    security context unconfined_u:unconfined_r:netserver_t:s0-s0:c0.c1023