Allow running bubblewrap in container

[cho-m]

Experimenting to see if it is possible to run bubblewrap inside container.

Currently, Homebrew/core always disables sandbox on Linux as container lacks necessary privileges to run bubblewrap. This means sandbox feature, deny_network_access!, etc don't actually work yet.

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[cho-m]

Looks like --privileged is needed to provide write access to /sys path so bubblewrap can handle Ubuntu 24.04+ AppArmor defaults. Maybe a non-user-namespace-based sandbox could work better, e.g. Lacklock API, but relatively new and would need to find another tool as Bubblewrap doesn't support it.

Not sure how much --privileged container matters within GitHub actions runners. At least should be similar to a containerless run. I guess it depends on whether there is anything security-specific we wanted from container isolation or if mainly for a fixed/reproducible environment.

[SMillerDev]

Any way we can build it with this configuration instead?

[MikeMcQuaid]

This makes sense, let's do it!

[MikeMcQuaid]

Thanks @cho-m!

[Copilot]

Pull request overview

This PR experiments with enabling Bubblewrap-based sandboxing when Homebrew runs inside Linux containers by (a) tightening sandbox availability checks and (b) configuring GitHub Actions container execution to run with elevated privileges when needed.

Changes:

• Add Sandbox.ensure_sandbox_available! and use it from sandbox execution paths.
• Make test-bot on GitHub Actions raise (for Homebrew-owned repos) when sandbox configuration fails, instead of silently disabling sandboxing.
• Update GitHub Actions runner/container configuration to add --privileged for container-based Linux test-bot runs.

Reviewed changes

Copilot reviewed 7 out of 7 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
Library/Homebrew/sandbox.rb	Adds ensure_sandbox_available! and reuses it in run_command.
Library/Homebrew/test_bot.rb	Enforces sandbox availability for Homebrew-owned repos on GitHub Actions before disabling sandboxing.
Library/Homebrew/github_runner_matrix.rb	Adds conditional --privileged container options when Linux sandboxing is enabled.
.github/workflows/tests.yml	Refactors test-bot job container config to include options (intended for --privileged).
Library/Homebrew/extend/os/linux/dev-cmd/tests.rb	Switches to Sandbox.ensure_sandbox_available! during environment checks.
Library/Homebrew/test/dev-cmd/tests_spec.rb	Updates expectation to match the new exception type from sandbox availability checks.
Library/Homebrew/test/test_bot_spec.rb	Splits behavior between Homebrew-owned vs external repos and updates sandbox setup expectations.

Comments suppressed due to low confidence (1)

Library/Homebrew/test/test_bot_spec.rb:226

• Similar to the previous example: prefer with_env over stubbing ENV[] to avoid interfering with unrelated environment lookups and keep the test isolated.

      allow(described_class).to receive(:configure_sandbox!).and_return(false)
      allow(ENV).to receive(:[]).with("GITHUB_REPOSITORY_OWNER").and_return("foo")

      described_class.setup_github_actions_sandbox!

      expect(ENV.fetch("HOMEBREW_NO_SANDBOX_LINUX")).to eq("1")

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[cho-m]

Will take a look at Copilot comments to see if we need any.

EDIT: Don't think any are required. Test change could be cleaner to scope module-under-test boundary.