control/controlclient: report Synology "distro" + its version to control

cmd/tailscaled/depaware.txt

@@ -84,7 +84,7 @@ tailscale.com/cmd/tailscaled dependencies: (generated by github.com/tailscale/de
         tailscale.com/util/lineread                                  from tailscale.com/control/controlclient+
         tailscale.com/util/pidowner                                  from tailscale.com/ipn/ipnserver
         tailscale.com/version                                        from tailscale.com/control/controlclient+
-        tailscale.com/version/distro                                 from tailscale.com/wgengine+
+        tailscale.com/version/distro                                 from tailscale.com/control/controlclient+
         tailscale.com/wgengine                                       from tailscale.com/cmd/tailscaled+
         tailscale.com/wgengine/filter                                from tailscale.com/control/controlclient+
         tailscale.com/wgengine/magicsock                             from tailscale.com/cmd/tailscaled+

control/controlclient/hostinfo_linux.go

@@ -16,6 +16,7 @@ import (
 
 	"go4.org/mem"
 	"tailscale.com/util/lineread"
+	"tailscale.com/version/distro"
 )
 
 func init() {
@@ -23,8 +24,14 @@ func init() {
 }
 
 func osVersionLinux() string {
+	dist := distro.Get()
+	propFile := "/etc/os-release"
+	if dist == distro.Synology {
+		propFile = "/etc.defaults/VERSION"
+	}
+
 	m := map[string]string{}
-	lineread.File("/etc/os-release", func(line []byte) error {
+	lineread.File(propFile, func(line []byte) error {
 		eq := bytes.IndexByte(line, '=')
 		if eq == -1 {
 			return nil
@@ -71,6 +78,9 @@ func osVersionLinux() string {
 			return fmt.Sprintf("%s%s", v, attr)
 		}
 	}
+	if dist == distro.Synology {
+		return fmt.Sprintf("Synology %s%s", m["productversion"], attr)
+	}
 	return fmt.Sprintf("Other%s", attr)
 }