Removing module fails - cannot find port type, but it's there?

Question

I have a SELinux module that, among other things, allows Apache to connect via TCP to a specific port:

cat <<EOF > sgtest.te
module sgtest 1.0.0;

require {
   attribute port_type;
   type httpd_t;
   class tcp_socket name_socket;
}

type my_port_t, port_type;

allow httpd_t my_port_t:tcp_socket name_socket;
EOF

echo > sgtest.fc

checkmodule -M -m -o sgtest.mod sgtest.te
semodule_package -o sgtest.pp -m sgtest.mod -f sgtest.fc
semodule -i sgtest.pp

semanage port -a -t my_port_t -p tcp 2002

This installs okay and the rules appear to work.

The port is definitely installed:

$ semanage port -l | grep my_port_t
my_port_t                      tcp      2002

However, I can't remove the module:

$ semodule -r sgtest
libsemanage.semanage_direct_remove_key: Removing last sgtest module (no other sgtest module exists at another priority).
libsepol.context_from_record: type my_port_t is not defined (No such file or directory).
libsepol.context_from_record: could not create context structure (Invalid argument).
libsepol.port_from_record: could not create port structure for range 2002:2002 (tcp) (Invalid argument).
libsepol.sepol_port_modify: could not load port range 2002 - 2002 (tcp) (Invalid argument).
libsemanage.dbase_policydb_modify: could not modify record value (Invalid argument).
libsemanage.semanage_base_merge_components: could not merge local modifications into policy (Invalid argument).
semodule:  Failed!

This is on CentOS 7.4.1708.

What have I done wrong?

Answer 1

I don't understand how this works, or how it relates to the error message, but I've found that I can get out of the situation if I remove the port first:

semanage port -d -p tcp 2002
semodule -r sgtest