Allow reading private sandbox temporary files

Library/Homebrew/sandbox.rb

@@ -902,6 +902,7 @@ def home_write_paths = []
 
   sig { params(tmpdir: String).returns(T::Hash[String, String]) }
   def sandbox_environment(tmpdir)
+    allow_read path: tmpdir, type: :subpath
     allow_write_path(tmpdir)
     allow_network path: tmpdir, type: :subpath
     { "HOMEBREW_TEMP" => tmpdir, "TMPDIR" => tmpdir, "TEMP" => tmpdir, "TMP" => tmpdir }

Library/Homebrew/test/sandbox_shared_spec.rb

@@ -269,6 +269,26 @@
       allow(described_class).to receive(:isolate_operation?).and_call_original
     end
 
+    it "allows reading only its private temporary directory under a denied parent" do
+      temporary_directory = mktmpdir
+      outside = temporary_directory/"outside"
+      outside.write("secret")
+      sandbox.deny_read_path temporary_directory
+      result = sandbox.capture(RbConfig.ruby, temporary_directory:, args: ["-e", <<~RUBY, outside])
+        file = File.join(ENV.fetch("TMPDIR"), "archive")
+        File.write(file, "contents")
+        puts File.read(file)
+        begin
+          File.read(ARGV.fetch(0))
+          abort "Read escaped the sandbox"
+        rescue Errno::EPERM, Errno::EACCES
+          nil
+        end
+      RUBY
+
+      expect(result.stdout).to eq("contents\n")
+    end
+
     it "allows its output directory and denies writes through an escaping symlink" do
       directory = mktmpdir
       output = directory/"output"