Based on tb@'s feedback below, you can find a suggestion for
implementing this function properly with correct error handling.

Unknown fd types and imsgs without an fd are now treated as errors
instead of being silently ignored.

As an improvement no orphan cert is created when the relay is unknown.

BTW the old code loves to trust imsg_get_fd blindly.

Feedback, OK?

>> config.c:1219:36: warning: 'cert' may be used uninitialized [-Wmaybe-uninitialized]
>>  1219 |                 cert->cert_ocsp_fd = imsg_get_fd(imsg);
>>       |                 ~~~~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~
>> config.c:1186:34: note: 'cert' was declared here
>>  1186 |         struct relay_cert       *cert;
>>       |                                  ^~~~
>
>Maybe we should just ignore these warnings... Adding kludges to badly
>written code to appease a dumb compiler isn't making the world better
>place.


diff --git a/config.c b/config.c
index d1f8f8c..4690ae9 100644
--- a/config.c
+++ b/config.c
@@ -31,6 +31,9 @@
 #include "relayd.h"
 #include "log.h"
 
+static struct relay_cert *config_getcert(struct relayd *,
+		    struct ctl_relayfd *);
+
 int
 config_init(struct relayd *env)
 {
@@ -1178,55 +1181,70 @@ config_getrelaytable(struct relayd *env, struct imsg *imsg)
 	return (-1);
 }
 
+static struct relay_cert *
+config_getcert(struct relayd *env, struct ctl_relayfd *crfd)
+{
+	struct relay_cert	*cert;
+
+	if ((cert = cert_find(env, crfd->id)) == NULL) {
+		if ((cert = cert_add(env, crfd->id)) == NULL)
+			return (NULL);
+		cert->cert_relayid = crfd->relayid;
+	}
+	return (cert);
+}
+
 int
 config_getrelayfd(struct relayd *env, struct imsg *imsg)
 {
 	struct ctl_relayfd	 crfd;
-	struct relay		*rlay = NULL;
+	struct relay		*rlay;
 	struct relay_cert	*cert;
+	int			 fd;
 
 	if (imsg_get_data(imsg, &crfd, sizeof(crfd)) == -1) {
 		log_warn("%s: imsg_get_data", __func__);
 		return (-1);
 	}
 
-	switch (crfd.type) {
-	case RELAY_FD_CERT:
-	case RELAY_FD_KEY:
-	case RELAY_FD_OCSP:
-		if ((cert = cert_find(env, crfd.id)) == NULL) {
-			if ((cert = cert_add(env, crfd.id)) == NULL)
-				return (-1);
-			cert->cert_relayid = crfd.relayid;
-		}
-		/* FALLTHROUGH */
-	default:
-		if ((rlay = relay_find(env, crfd.relayid)) == NULL) {
-			log_debug("%s: unknown relay", __func__);
-			return (-1);
-		}
-		break;
+	if ((rlay = relay_find(env, crfd.relayid)) == NULL) {
+		log_debug("%s: unknown relay", __func__);
+		return (-1);
+	}
+
+	if ((fd = imsg_get_fd(imsg)) == -1) {
+		log_warnx("%s: no fd for type %d", __func__, crfd.type);
+		return (-1);
 	}
 
 	switch (crfd.type) {
 	case RELAY_FD_CERT:
-		cert->cert_fd = imsg_get_fd(imsg);
+		if ((cert = config_getcert(env, &crfd)) == NULL)
+			goto fail;
+		cert->cert_fd = fd;
 		break;
 	case RELAY_FD_KEY:
-		cert->cert_key_fd = imsg_get_fd(imsg);
+		if ((cert = config_getcert(env, &crfd)) == NULL)
+			goto fail;
+		cert->cert_key_fd = fd;
 		break;
 	case RELAY_FD_OCSP:
-		cert->cert_ocsp_fd = imsg_get_fd(imsg);
+		if ((cert = config_getcert(env, &crfd)) == NULL)
+			goto fail;
+		cert->cert_ocsp_fd = fd;
 		break;
 	case RELAY_FD_CACERT:
-		rlay->rl_tls_ca_fd = imsg_get_fd(imsg);
+		rlay->rl_tls_ca_fd = fd;
 		break;
 	case RELAY_FD_CAFILE:
-		rlay->rl_tls_cacert_fd = imsg_get_fd(imsg);
+		rlay->rl_tls_cacert_fd = fd;
 		break;
 	case RELAY_FD_CLIENTCACERT:
-		rlay->rl_tls_client_ca_fd = imsg_get_fd(imsg);
+		rlay->rl_tls_client_ca_fd = fd;
 		break;
+	default:
+		log_warnx("%s: unknown type %d", __func__, crfd.type);
+		goto fail;
 	}
 
 	log_debug("%s: %s %d received relay type %d for relay %s", __func__,
@@ -1234,4 +1252,8 @@ config_getrelayfd(struct relayd *env, struct imsg *imsg)
 	    crfd.type, rlay->rl_conf.name);
 
 	return (0);
+
+ fail:
+	close(fd);
+	return (-1);
 }