[RubyGemsGemInstaller] Validate checksums from the compact index

2 files changed, 29 insertions, 1 deletions

diff --git a/lib/bundler/rubygems_gem_installer.rb b/lib/bundler/rubygems_gem_installer.rb
index e18f46268b..cccd28e294 100644
--- a/lib/bundler/rubygems_gem_installer.rb
+++ b/lib/bundler/rubygems_gem_installer.rb
@@ -12,5 +12,32 @@ module Bundler
     def check_executable_overwrite(filename)
       # Bundler needs to install gems regardless of binstub overwriting
     end
+
+    def pre_install_checks
+      super && validate_bundler_checksum(options[:bundler_expected_checksum])
+    end
+
+  private
+
+    def validate_bundler_checksum(checksum)
+      return true unless checksum
+      return true unless source = @package.instance_variable_get(:@gem)
+      return true unless source.respond_to?(:with_read_io)
+      digest = source.with_read_io do |io|
+        digest = Digest::SHA256.new
+        digest << io.read(16_384) until io.eof?
+        io.rewind
+        digest.base64digest!
+      end
+      unless digest == checksum
+        raise SecurityError,
+          "The checksum for the downloaded `#{spec.full_name}.gem` did not match " \
+          "the checksum given by the API. This means that the contents of the " \
+          "gem appear to be different from what was uploaded, and could be an indicator of a security issue.\n" \
+          "(The expected SHA256 checksum was #{checksum.inspect}, but the checksum for the downloaded gem was #{digest.inspect}.)\n" \
+          "Bundler cannot continue installing #{spec.name} (#{spec.version})."
+      end
+      true
+    end
   end
 end
diff --git a/lib/bundler/source/rubygems.rb b/lib/bundler/source/rubygems.rb
index aedad7086d..89f7673eb8 100644
--- a/lib/bundler/source/rubygems.rb
+++ b/lib/bundler/source/rubygems.rb
@@ -140,7 +140,8 @@ module Bundler
               :bin_dir             => bin_path.to_s,
               :ignore_dependencies => true,
               :wrappers            => true,
-              :env_shebang         => true
+              :env_shebang         => true,
+              :bundler_expected_checksum => spec.respond_to?(:checksum) && spec.checksum
             ).install
           end
           spec.full_gem_path = installed_spec.full_gem_path