Module: SafeImage::Sandbox

Defined in:
lib/safe_image/sandbox.rb

Constant Summary collapse

DEFAULT_RLIMITS = 
{
  cpu_seconds: 30,
  memory_bytes: 2 * 1024 * 1024 * 1024,
  file_size_bytes: 1024 * 1024 * 1024,
  open_files: 256
}.freeze
OPERATIONS = 
%w[
  probe thumbnail type size dimensions info orientation dominant_color optimize resize crop downsize convert convert_to_jpeg fix_orientation
  convert_favicon_to_png frame_count animated? letter_avatar optimize_image!
  sanitize_svg!
].freeze

Class Method Summary collapse

Class Method Details

.available? ⇒ Boolean

Returns:

  • (Boolean) 


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# File 'lib/safe_image/sandbox.rb', line 24

def available?
  require "landlock"
  Landlock::SafeExec.supported?
rescue LoadError
  false
end

.capture_command!(argv, read:, write:, timeout: Runner::DEFAULT_TIMEOUT, env: nil, rlimits: DEFAULT_RLIMITS) ⇒ Object 



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# File 'lib/safe_image/sandbox.rb', line 31

def capture_command!(argv, read:, write:, timeout: Runner::DEFAULT_TIMEOUT, env: nil, rlimits: DEFAULT_RLIMITS)
  require "landlock"
  env ||= Runner.command_env(Dir.tmpdir)

  result = Landlock::SafeExec.capture!(
    *argv.map(&:to_s),
    read: existing_paths([*Landlock::SafeExec.default_read_paths, *runtime_read_paths, *read]),
    write: existing_paths(write),
    execute: existing_paths([*Landlock::SafeExec.default_execute_paths, File.dirname(RbConfig.ruby)]),
    env: env.merge("SAFE_IMAGE_SANDBOX_CHILD" => "1"),
    inherit_env: false,
    timeout: timeout,
    rlimits: rlimits,
    seccomp_deny_network: true,
    max_output_bytes: 512 * 1024,
    truncate_output: false
  )
  [result.stdout, result.stderr]
rescue LoadError
  raise Error, "landlock sandbox requested but the landlock gem is unavailable"
rescue Landlock::SafeExec::CommandError => e
  raise CommandError.new(
    "sandboxed command failed: #{failure_detail(e)}",
    command: argv,
    status: e.status&.exitstatus,
    stdout: e.stdout,
    stderr: e.stderr
  )
end

.existing_paths(paths) ⇒ Object 



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# File 'lib/safe_image/sandbox.rb', line 245

def existing_paths(paths)
  paths.flatten.compact.map(&:to_s).reject(&:empty?).select { |path| File.exist?(path) }.uniq
end

.failure_detail(error) ⇒ Object

Sandbox failures often happen before the child can run any Ruby (e.g. a denied shared-library read kills it at dynamic-link time); without the child’s stderr in the message they are undiagnosable from a CI log.



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# File 'lib/safe_image/sandbox.rb', line 252

def failure_detail(error)
  detail = error.stderr.to_s.strip
  detail = "exit status #{error.status&.exitstatus.inspect}" if detail.empty?
  detail[0, 2000]
end

.looks_like_path?(value) ⇒ Boolean

Returns:

  • (Boolean) 


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# File 'lib/safe_image/sandbox.rb', line 218

def looks_like_path?(value)
  value.start_with?("/", "./", "../") || File.extname(value) != ""
end

.public_call!(operation, args:, kwargs:) ⇒ Object

Raises:

  • (ArgumentError) 


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# File 'lib/safe_image/sandbox.rb', line 61

def public_call!(operation, args:, kwargs:)
  operation = operation.to_s
  raise ArgumentError, "unsupported sandbox operation: #{operation}" unless OPERATIONS.include?(operation)
  result = run_worker!(operation, { args: args, kwargs: kwargs })
  operation == "type" && result ? result.to_sym : result
end

.run_worker!(operation, request) ⇒ Object 



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# File 'lib/safe_image/sandbox.rb', line 68

def run_worker!(operation, request)
  operation = operation.to_s
  raise ArgumentError, "unsupported sandbox operation: #{operation}" unless OPERATIONS.include?(operation)

  require "landlock"
  config = SafeImage.config
  payload = JSON.dump(
    {
      operation: operation,
      request: request,
      # The worker is a fresh process and must be configured like the
      # parent — minus landlock, since it already runs inside the sandbox.
      config: { backend: config.backend, max_pixels: config.max_pixels }
    }
  )
  code = <<~'RUBY'
    require "json"
    require "safe_image"

    def deep_symbolize(value)
      case value
      when Hash
        value.each_with_object({}) { |(k, v), h| h[k.to_sym] = deep_symbolize(v) }
      when Array
        value.map { |v| deep_symbolize(v) }
      else
        value
      end
    end

    payload = JSON.parse(ARGV.fetch(0), symbolize_names: true)
    operation = payload.fetch(:operation).to_s
    allowed_operations = %w[
      probe thumbnail type size dimensions info orientation dominant_color optimize resize crop downsize convert convert_to_jpeg fix_orientation
      convert_favicon_to_png frame_count animated? letter_avatar optimize_image! sanitize_svg!
    ]
    raise ArgumentError, "unsupported sandbox operation: #{operation}" unless allowed_operations.include?(operation)

    request = payload.fetch(:request)
    args = request[:args] || []
    kwargs = deep_symbolize(request[:kwargs] || {})

    config = payload.fetch(:config)
    SafeImage.configure!(
      backend: config.fetch(:backend).to_sym,
      landlock: false,
      max_pixels: config.fetch(:max_pixels)
    )

    result = SafeImage.__send__(operation, *args, **kwargs)

    if defined?(SafeImage::Result) && result.is_a?(SafeImage::Result)
      puts JSON.dump({ __type: "Result", data: result.to_h })
    elsif defined?(SafeImage::Info) && result.is_a?(SafeImage::Info)
      puts JSON.dump({ __type: "Info", data: result.to_h })
    else
      puts JSON.dump({ __type: "Value", data: result })
    end
  RUBY

  paths = sandbox_paths(request, operation)
  Dir.mktmpdir("safe-image-worker-") do |tmpdir|
    worker_env = Runner.command_env(tmpdir).merge(
      "SAFE_IMAGE_SANDBOX_CHILD" => "1",
      "GEM_HOME" => ENV["GEM_HOME"].to_s,
      "GEM_PATH" => ENV["GEM_PATH"].to_s,
      "RUBYLIB" => $LOAD_PATH.select { |p| p && File.directory?(p) }.join(File::PATH_SEPARATOR)
    )

    stdout, = Landlock::SafeExec.capture!(
      RbConfig.ruby,
      "-I#{File.expand_path("../../", __dir__)}",
      "-rjson",
      "-e",
      code,
      payload,
      read: existing_paths([*Landlock::SafeExec.default_read_paths, *runtime_read_paths, *paths.fetch(:read), tmpdir]),
      write: existing_paths([*paths.fetch(:write), tmpdir]),
      execute: existing_paths([*Landlock::SafeExec.default_execute_paths, File.dirname(RbConfig.ruby)]),
      env: worker_env,
      inherit_env: false,
      timeout: Runner::DEFAULT_TIMEOUT,
      rlimits: DEFAULT_RLIMITS,
      seccomp_deny_network: true,
      max_output_bytes: 512 * 1024,
      truncate_output: false
    )
    response = JSON.parse(stdout, symbolize_names: true)
    if response[:__type] == "Result"
      data = response.fetch(:data)
      Result.new(**data)
    elsif response[:__type] == "Info"
      data = response.fetch(:data)
      Info.new(**data)
    else
      response[:data]
    end
  end
rescue LoadError
  raise Error, "landlock sandbox requested but the landlock gem is unavailable"
rescue Landlock::SafeExec::CommandError => e
  raise CommandError.new(
    "sandboxed worker failed: #{failure_detail(e)}",
    command: [RbConfig.ruby, "-e", "..."],
    status: e.status&.exitstatus,
    stdout: e.stdout,
    stderr: e.stderr
  )
end

.runtime_read_paths ⇒ Object 



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# File 'lib/safe_image/sandbox.rb', line 222

def runtime_read_paths
  paths = []
  paths.concat(Gem.path) if defined?(Gem)
  paths.concat($LOAD_PATH.select { |path| path && path != "." })
  paths << RbConfig::CONFIG["rubylibdir"]
  paths << RbConfig::CONFIG["rubyarchdir"]
  paths << RbConfig::CONFIG["sitearchdir"]
  paths << RbConfig::CONFIG["vendorarchdir"]
  # An --enable-shared Ruby installed outside the default read roots
  # (e.g. GitHub Actions' /opt/hostedtoolcache builds) keeps libruby in
  # libdir; without read access the worker dies at dynamic-link time
  # before any Ruby code runs.
  paths << RbConfig::CONFIG["libdir"]
  paths << File.dirname(RbConfig.ruby)
  # Pango/fontconfig need the font directories and configs for the native
  # letter_avatar text rendering inside the worker.
  paths << "/etc/fonts"
  paths << "/usr/share/fonts"
  paths << "/usr/local/share/fonts"
  paths << "/var/cache/fontconfig"
  paths
end

.sandbox_paths(request, operation) ⇒ Object 



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# File 'lib/safe_image/sandbox.rb', line 178

def sandbox_paths(request, operation)
  read = []
  write = []

  values = []
  values.concat(Array(request[:args]))
  values.concat(Array(request.dig(:kwargs)&.values))
  values.flatten.compact.each do |value|
    next unless value.is_a?(String)
    next if value.empty? || value.include?("\0")

    expanded = File.expand_path(value) rescue next
    if File.exist?(expanded)
      read << expanded
    elsif looks_like_path?(value)
      write << File.dirname(expanded)
    end
  end

  # Common keyword names for generated outputs. Include the containing dir
  # even when a stale file already exists, because operations may replace it.
  kwargs = request[:kwargs] || {}
  %i[output to path].each do |key|
    next unless kwargs[key].is_a?(String)
    write << File.dirname(File.expand_path(kwargs[key]))
  end

  # In-place mutators need write permission for an existing input path too.
  if %w[optimize optimize_image! sanitize_svg! fix_orientation].include?(operation.to_s)
    first = Array(request[:args]).first
    if first.is_a?(String) && File.exist?(first)
      expanded = File.expand_path(first)
      write << expanded
      write << File.dirname(expanded)
    end
  end

  { read: read.uniq, write: write.uniq }
end

.symbolize(hash) ⇒ Object 



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# File 'lib/safe_image/sandbox.rb', line 258

def symbolize(hash)
  hash.transform_keys(&:to_sym)
end