Restrict direct url installs to the file:// scheme

Library/Homebrew/cask/cask_loader.rb

@@ -12,6 +12,9 @@ module Cask
   module CaskLoader
     extend Context
 
+    ALLOWED_URL_SCHEMES = %w[file].freeze
+    private_constant :ALLOWED_URL_SCHEMES
+
     module ILoader
       extend T::Helpers
       interface!
@@ -171,17 +174,25 @@ def self.try_new(ref, warn: false)
         new(uri)
       end
 
-      attr_reader :url
+      attr_reader :url, :name
 
       sig { params(url: T.any(URI::Generic, String)).void }
       def initialize(url)
         @url = URI(url)
-        super Cache.path/File.basename(T.must(@url.path))
+        @name = File.basename(T.must(@url.path))
+        super Cache.path/name
       end
 
       def load(config:)
         path.dirname.mkpath
 
+        if ALLOWED_URL_SCHEMES.exclude?(url.scheme)
+          raise UnsupportedInstallationMethod,
+                "Non-checksummed download of #{name} formula file from an arbitrary URL is unsupported! " \
+                "`brew extract` or `brew create` and `brew tap-new` to create a formula file in a tap " \
+                "on GitHub instead."
+        end
+
         begin
           ohai "Downloading #{url}"
           ::Utils::Curl.curl_download url, to: path

Library/Homebrew/formulary.rb

@@ -17,8 +17,8 @@ module Formulary
   extend Context
   extend Cachable
 
-  URL_START_REGEX = %r{(https?|ftp|file)://}
-  private_constant :URL_START_REGEX
+  ALLOWED_URL_SCHEMES = %w[file].freeze
+  private_constant :ALLOWED_URL_SCHEMES
 
   # `:codesign` and custom requirement classes are not supported.
   API_SUPPORTED_REQUIREMENTS = [:arch, :linux, :macos, :maximum_macos, :xcode].freeze
@@ -696,7 +696,7 @@ class FromURILoader < FormulaLoader
     def self.try_new(ref, from: T.unsafe(nil), warn: false)
       ref = ref.to_s
 
-      new(ref, from:) if URL_START_REGEX.match?(ref)
+      new(ref, from:) if URI(ref).scheme.present?
     end
 
     attr_reader :url
@@ -713,12 +713,8 @@ def initialize(url, from: nil)
     end
 
     def load_file(flags:, ignore_errors:)
-      match = url.match(%r{githubusercontent.com/[\w-]+/[\w-]+/[a-f0-9]{40}(?:/Formula)?/(?<name>[\w+-.@]+).rb})
-      if match
-        raise UnsupportedInstallationMethod,
-              "Installation of #{match[:name]} from a GitHub commit URL is unsupported! " \
-              "`brew extract #{match[:name]}` to a stable tap on GitHub instead."
-      elsif url.match?(%r{^(https?|ftp)://})
+      url_scheme = URI(url).scheme
+      if ALLOWED_URL_SCHEMES.exclude?(url_scheme)
         raise UnsupportedInstallationMethod,
               "Non-checksummed download of #{name} formula file from an arbitrary URL is unsupported! " \
               "`brew extract` or `brew create` and `brew tap-new` to create a formula file in a tap " \

Library/Homebrew/test/cask/cask_loader/from_uri_loader_spec.rb

@@ -18,4 +18,34 @@
       RUBY
     end
   end
+
+  describe "::load" do
+    it "raises an error when given an https URL" do
+      loader = described_class.new("https://brew.sh/foo.rb")
+      expect do
+        loader.load(config: nil)
+      end.to raise_error(UnsupportedInstallationMethod)
+    end
+
+    it "raises an error when given an ftp URL" do
+      loader = described_class.new("ftp://brew.sh/foo.rb")
+      expect do
+        loader.load(config: nil)
+      end.to raise_error(UnsupportedInstallationMethod)
+    end
+
+    it "raises an error when given an sftp URL" do
+      loader = described_class.new("sftp://brew.sh/foo.rb")
+      expect do
+        loader.load(config: nil)
+      end.to raise_error(UnsupportedInstallationMethod)
+    end
+
+    it "does not raise an error when given a file URL" do
+      loader = described_class.new("file://#{TEST_FIXTURE_DIR}/cask/Casks/local-caffeine.rb")
+      expect do
+        loader.load(config: nil)
+      end.not_to raise_error(UnsupportedInstallationMethod)
+    end
+  end
 end

Library/Homebrew/test/formulary_spec.rb

@@ -523,6 +523,38 @@ def formula_json_contents(extra_items = {})
         end
       end
     end
+
+    context "when passed a URL" do
+      it "raises an error when given an https URL" do
+        expect do
+          described_class.factory("https://brew.sh/foo.rb")
+        end.to raise_error(UnsupportedInstallationMethod)
+      end
+
+      it "raises an error when given a bottle URL" do
+        expect do
+          described_class.factory("https://brew.sh/foo-1.0.arm64_catalina.bottle.tar.gz")
+        end.to raise_error(UnsupportedInstallationMethod)
+      end
+
+      it "raises an error when given an ftp URL" do
+        expect do
+          described_class.factory("ftp://brew.sh/foo.rb")
+        end.to raise_error(UnsupportedInstallationMethod)
+      end
+
+      it "raises an error when given an sftp URL" do
+        expect do
+          described_class.factory("sftp://brew.sh/foo.rb")
+        end.to raise_error(UnsupportedInstallationMethod)
+      end
+
+      it "does not raise an error when given a file URL" do
+        expect do
+          described_class.factory("file://#{TEST_FIXTURE_DIR}/testball.rb")
+        end.not_to raise_error(UnsupportedInstallationMethod)
+      end
+    end
   end
 
   specify "::from_contents" do