Description of problem:
use mkosi boot to enter a system with --network-veth, enable+start systemd-networkd both on the host and in the container, observe AVC denial
SELinux is preventing systemd-network from 'create' accesses on the netlink_netfilter_socket labeled systemd_networkd_t.

*****  Plugin catchall (100. confidence) suggests   **************************

If you believe that systemd-network should be allowed create access on netlink_netfilter_socket labeled systemd_networkd_t by default.
Then you should report this as a bug.
You can generate a local policy module to allow this access.
Do
allow this access for now by executing:
# ausearch -c 'systemd-network' --raw | audit2allow -M my-systemdnetwork
# semodule -X 300 -i my-systemdnetwork.pp

Additional Information:
Source Context                system_u:system_r:systemd_networkd_t:s0
Target Context                system_u:system_r:systemd_networkd_t:s0
Target Objects                Unknown [ netlink_netfilter_socket ]
Source                        systemd-network
Source Path                   systemd-network
Port                          <Unknown>
Host                          (removed)
Source RPM Packages           
Target RPM Packages           
SELinux Policy RPM            selinux-policy-targeted-35.13-1.fc35.noarch
Local Policy RPM              selinux-policy-targeted-35.13-1.fc35.noarch
Selinux Enabled               True
Policy Type                   targeted
Enforcing Mode                Enforcing
Host Name                     (removed)
Platform                      Linux (removed) 5.16.5-200.fc35.x86_64 #1 SMP
                              PREEMPT Tue Feb 1 21:37:11 UTC 2022 x86_64 x86_64
Alert Count                   1
First Seen                    2022-02-13 14:28:10 PST
Last Seen                     2022-02-13 14:28:10 PST
Local ID                      6af6023a-536b-437a-8586-f2f03ff6aa42

Raw Audit Messages
type=AVC msg=audit(1644791290.677:934): avc:  denied  { create } for  pid=160398 comm="systemd-network" scontext=system_u:system_r:systemd_networkd_t:s0 tcontext=system_u:system_r:systemd_networkd_t:s0 tclass=netlink_netfilter_socket permissive=0


Hash: systemd-network,systemd_networkd_t,systemd_networkd_t,netlink_netfilter_socket,create

Version-Release number of selected component:
selinux-policy-targeted-35.13-1.fc35.noarch

Additional info:
component:      selinux-policy
reporter:       libreport-2.15.2
hashmarkername: setroubleshoot
kernel:         5.16.5-200.fc35.x86_64
type:           libreport