tailscaled.service: Harden systemd unit somewhat (#1062)

While not a full capability lockdown of the systemd unit, this still
improves sandboxing and security of the running process a good deal.

Signed-off-by: Frederik “Freso” S. Olesen <freso.dk@gmail.com>

cmd/tailscaled/tailscaled.service

@@ -20,5 +20,16 @@ CacheDirectory=tailscale
 CacheDirectoryMode=0750
 Type=notify
 
+LockPersonality=true
+MemoryDenyWriteExecute=true
+PrivateTmp=true
+ProtectControlGroups=true
+ProtectHome=true
+ProtectKernelTunables=true
+ProtectSystem=strict
+ReadWritePaths=/etc/
+RestrictSUIDSGID=true
+SystemCallArchitectures=native
+
 [Install]
 WantedBy=multi-user.target