Fork of Lua 5.1 to encourage end-user programming
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Kartik K. Agaram e4c0b0a3e7 sandbox: more scenarios 6 months ago
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README.md sandbox: more scenarios 6 months ago
includes stop futzing around and start sandboxing 6 months ago
system_includes stop futzing around and start sandboxing 6 months ago
unique_system_includes stop futzing around and start sandboxing 6 months ago

README.md

This directory includes some working notes to audit the entire Teliva codebase for side-effects that should be gated/sandboxed.

Founding principle for this approach: Side-effects come from the OS. There can be no effects visible outside a Unix process (regardless of language) if it doesn't invoke any OS syscalls.

Top down

Things to secure:

  • screen? Keep apps from drawing over standard Teliva UI elements.

    • Teliva currently doesn't stop apps from overwriting the menu, if they're clever. However, it always redraws its UI elements before accepting any input from the keyboard.
  • code? There are currently no protections against .tlv files clobbering existing definitions. I'm hoping that disallowing native code keeps this safe. Apps can only affect themselves.

  • files opened (for read/write) on file system

    • io_open
    • io_lines
  • destinations opened (for read/write) on network

    • inet_tryconnect // socket_connect
    • inet_tryaccept // socket_accept

It seems more difficult to control what is written to a file or socket once it's opened. For starters let's just focus on the interfaces that convert a string path or url to a file descriptor.

Scenarios:

  • (1) app reads system files
  • (1) app sends data to a remote server
  • (1) app should never be allowed to open Teliva's system files:
    • teliva_editor_state
    • app-specific sandboxing policies
  • (2) app can read from a remote server but not write (POST)
  • (1) app permissions are saved across restart
  • (1) permissions the owner grants to one app are not automatically granted to another
  • (2) downloading a second app with identical name doesn't receive its predecessors permissions
  • app gains access to a remote server for a legitimate purpose, reads sensitive data from the local system file for legitimate purpose. Now there's nothing preventing it from exfiltrating the sensitive data to the remote server.
    • (2) solution: make it obvious in the UI that granting both permissions allows an app to do anything. Educate people to separate apps that read sensitive data from apps that access remote servers.
    • (2) solution: map phases within an app to distinct permission sets
  • app A legitimately needs to read sensitive data. It saves a copy to file X. app B seems to legitimately needs to access the network, but also asks to read file X. If the owner forgets who wrote file X and what it contains, sensitive data could be exfiltrated.
  • (3) app wants access to system() or exec() or popen()

Difficulty levels

  1. I have some sense of how to enforce this.
  2. Seems vaguely doable.
  3. Seems unlikely to be doable.

UX:

  • distinguish what Teliva can do, what the app can do, and Teliva's ability to police the app.
  • easily visualize Teliva's ability to police an app.
    • maybe show a lock in halves; left half = file system, right half = network. One half unlocked = orange. Both unlocked = red.

Bottom up

  • includes: all #includes throughout the codebase. I assume that C the language itself can't invoke any syscalls without at least triggering warnings from the compiler.
    cd src
    grep '#include' * */* > ../sandboxing/includes
    
  • system_includes: all #include <...>s throughout the codebase. I assume side-effects require going outside the codebase. #includes could smuggle out of the codebase using relative paths (../) but I assume it's easy to protect against this using code review.
    grep '<' sandboxing/includes > sandboxing/system_includes
    
  • unique_system_includes: deduped
    sed 's/.*<\|>.*//g' sandboxing/system_includes |sort |uniq > sandboxing/unique_system_includes