What you do is split the file I/O from the rendering. Drop privs on the renderer, and feed it data from another process that handles the file access, setup, and

What you do is split the file I/O from the rendering. Drop privs on the renderer, and feed it data from another process that handles the file access, setup, and other privileged operations. You can open your X11 socket (or whatever your GUI uses) in the I/O process and hand it off to the renderer before dropping privileges, and hand it off without any loss of performance. Another thought -- although I don't generally touch 3d rendering, or know enough to know if it's possible off the top of my head -- is something like cross-process pbuffers: you render into one, and composite the result to the screen from another process. Since your OS already does this sort of thing (X11 compositors, for example, do this sort of cross-process compositing), this can't be too expensive. You might need to use the XACE extension to restrict the renderer to just the rendering output window in case it gets exploited, so that you don't have access to the rest of the UI. The places where vulnerabilities can do damage are when communicating with the rest of the OS: File I/O allows you to get user data, permanently install malware, and delete things. The window system allows you to snoop keystroke/mouse data, synthesize input, and watch what the user does. Drop privs on those, and your app is fairly effectively sandboxed.