From 9e05a54e679086460972ecf0c9bb755658ec03b4 Mon Sep 17 00:00:00 2001
From: Mike McQuaid <mike@mikemcquaid.com>
Date: Sat, 24 Oct 2026 17:28:47 +0100
Subject: [PATCH] Allow reading private sandbox temporary files

- Let archive tools read files in the sandbox's temporary directory
  without granting read access to its parent.
- Exercise temporary-file reads and denied parent access in the sandbox.

Fixes #24348
---
 Library/Homebrew/sandbox.rb                  |  1 +
 Library/Homebrew/test/sandbox_shared_spec.rb | 20 ++++++++++++++++++++
 2 files changed, 21 insertions(+)

diff --git a/Library/Homebrew/sandbox.rb b/Library/Homebrew/sandbox.rb
index 7f35f724257d9..2c0c308eceff2 100644
--- a/Library/Homebrew/sandbox.rb
+++ b/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 }
diff --git a/Library/Homebrew/test/sandbox_shared_spec.rb b/Library/Homebrew/test/sandbox_shared_spec.rb
index 30ac240c92764..ba2b1bb82cf2a 100644
--- a/Library/Homebrew/test/sandbox_shared_spec.rb
+++ b/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"