lxd/util: Check cloud-init configuration tag

This helps to avoid parsing an invalid conifiguration that lacks `#cloud-config` and also helps us check if the configuration is in a suported format.

Signed-off-by: hamistao <[email protected]>

lxd/util/config.go

@@ -109,6 +109,12 @@ type cloudInitUserSSHKeys struct {
 // In the case where we were not able to parse the cloud config, return the original, unchanged config and
 // the error.
 func MergeSSHKeyCloudConfig(instanceConfig map[string]string, cloudConfig string) (string, error) {
+	// Check if cloudConfig is in a supported format.
+	// A YAML cloud config without #cloud-config is invalid.
+	if cloudConfig != "" && !shared.ValueInSlice("#cloud-config", shared.SplitNTrimSpace(cloudConfig, "\n", 3, false)) {
+		return cloudConfig, errors.New(`Parsing configuration is not supported as it is not "#cloud-config"`)
+	}
+
 	// Use a pointer to cloudInitUserSSHKeys so we can append to its fields.
 	users := make(map[string]*cloudInitUserSSHKeys)