irmd: Specify peer authentication contract

OAP accepted requests and responses without a certificate even when
the peer was expected to authenticate. An on-path attacker could
strip the certificate and signature from a flow allocation response
and substitute its own key exchange, silently downgrading the
handshake to unauthenticated.

Add an auth=required|optional policy to enc.conf, enforced per role: a
client config requires the server to present a valid certificate, a
server config requires the same from the client. Default is required
for client side (https), optional server side. The client side default
can be changed via OAP_CLIENT_AUTH_DEFAULT for testing.

Replace the bare 'none' keyword with encryption=none, which disables
encryption only: the digest and the authentication policy are kept, so
authenticated but unencrypted flows can be configured. Configs using
bare 'none' are now rejected.

Signed-off-by: Dimitri Staessens <dimitri@ouroboros.rocks>
Signed-off-by: Sander Vrijders <sander@ouroboros.rocks>

1 files changed, 8 insertions, 0 deletions

diff --git a/src/irmd/oap/srv.c b/src/irmd/oap/srv.c
index 587a8f9f..08b4d9d2 100644
--- a/src/irmd/oap/srv.c
+++ b/src/irmd/oap/srv.c
@@ -73,6 +73,9 @@ int load_srv_kex_config(const struct name_info * info,
         assert(info != NULL);
         assert(cfg != NULL);
 
+        memset(cfg, 0, sizeof(*cfg));
+
+        /* Client auth stays opt-in (mTLS); enable with auth=required */
         return load_kex_config(info->name, info->s.enc, cfg);
 }
 
@@ -441,6 +444,11 @@ int oap_srv_process(const struct name_info * info,
                 goto fail_auth;
         }
 
+        if (kcfg.req_auth && peer_hdr.crt.len == 0) {
+                log_err_id(id, "Client did not provide a certificate.");
+                goto fail_auth;
+        }
+
         if (do_server_kex(info, &peer_hdr, &kcfg, &local_hdr.kex, sk) < 0)
                 goto fail_kex;