Initial implementation of the Mac Bootstrap Sandbox.

sandbox/mac/bootstrap_sandbox.h

+// Copyright 2014 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef SANDBOX_MAC_BOOTSTRAP_SANDBOX_H_
+#define SANDBOX_MAC_BOOTSTRAP_SANDBOX_H_
+
+#include <mach/mach.h>
+
+#include <map>
+#include <string>
+
+#include "base/mac/scoped_mach_port.h"
+#include "base/memory/scoped_ptr.h"
+#include "base/process/process_handle.h"
+#include "base/synchronization/lock.h"
+#include "sandbox/mac/policy.h"
+
+namespace sandbox {
+
+class LaunchdInterceptionServer;
+
+// The BootstrapSandbox is a second-layer sandbox for Mac. It is used to limit
+// the bootstrap namespace attack surface of child processes. The parent
+// process creates an instance of this class and registers policies that it
+// can enforce on its children.
+//
+// With this sandbox, the bootstrap port of the parent process is replaced, so
+// that child processes is taken over by the sandbox. Bootstrap messages from
+// the parent are forwarded to launchd. Requests from the child that would
+// normally go to launchd are filtered based on the specified per-process
+// policies. If a request is permitted by the policy, it is forwarded on to
+// launchd for servicing. If it is not, then the sandbox will reply with a
+// primitive that does not grant additional capabilities to the receiver.
+//
+// Clients that which to use the sandbox must inform it of the creation and
+// death of child processes for which the sandbox should be enforced. The
+// client of the sandbox is intended to be an unsandboxed parent process that
+// fork()s sandboxed (and other unsandboxed) child processes.
+//
+// When the parent is ready to fork a new child process with this sandbox
+// being enforced, it should use the pair of methods PrepareToForkWithPolicy()
+// and FinishedFork(), and call fork() between them. The first method will
+// set the policy for the new process, and the second will finialize the
+// association between the process ID and sandbox policy ID.
+//
+// All methods of this class may be called from any thread, but
+// PrepareToForkWithPolicy() and FinishedFork() must be non-nested and balanced.
+class BootstrapSandbox {
+ public:
+  // Creates a new sandbox manager. Returns NULL on failure.
+  static scoped_ptr<BootstrapSandbox> Create();
+
+  ~BootstrapSandbox();
+
+  // Registers a bootstrap policy associated it with an identifier. The
+  // |sandbox_policy_id| must be greater than 0.
+  void RegisterSandboxPolicy(int sandbox_policy_id,
+                             const BootstrapSandboxPolicy& policy);
+
+  // Called in the parent prior to fork()ing a child. The policy registered
+  // to |sandbox_policy_id| will be enforced on the new child. Returns true
+  // on success and false if the policy does not exist.
+  void PrepareToForkWithPolicy(int sandbox_policy_id);

[Avi (use Gerrit), 2014/05/09 21:02:06]

The comment talks about returning a bool, but this function returns nothing.

[Robert Sesek, 2014/05/09 22:04:03]

Done.

+
+  // Called in the parent after fork()ing a child. It records the |handle|
+  // and associates it with the specified-above |sandbox_policy_id|.
+  // If fork() failed and a new child was not created, pass kNullProcessHandle.

[Mark Mentovai, 2014/05/09 20:11:19]

Do you want to leave a TODO somewhere (.cc file?) about being able to handle
this without a long-lived lock and threadiness restriction if a better process
launchy thing was available?

[Robert Sesek, 2014/05/09 22:04:03]

Sure, but I feel like it'll be a long-time coming.

+  void FinishedFork(base::ProcessHandle handle);
+
+  // Called in the parent when a process has died. It cleans up the references
+  // to the process.
+  void ChildDied(base::ProcessHandle handle);
+
+  // Looks up the policy for a given process ID. If no policy is associated
+  // with the |pid|, this returns NULL.
+  const BootstrapSandboxPolicy* PolicyForProcess(pid_t pid) const;
+
+  mach_port_t real_bootstrap_port() const { return real_bootstrap_port_; }
+
+ private:
+  BootstrapSandbox();
+
+  // A Mach IPC message server that is used to intercept and filter bootstrap
+  // requests.
+  scoped_ptr<LaunchdInterceptionServer> server_;
+
+  // The original bootstrap port of the process, which is connected to the
+  // real launchd server.
+  base::mac::ScopedMachPort real_bootstrap_port_;
+
+  // The |lock_| protects all the following variables.
+  mutable base::Lock lock_;
+
+  // The sandbox_policy_id that will be enforced for the new child.
+  int effective_policy_id_;
+
+  // All the policies that have been registered with this sandbox manager.
+  std::map<int, const BootstrapSandboxPolicy> policies_;
+
+  // The association between process ID and sandbox policy ID.
+  std::map<base::ProcessHandle, int> sandboxed_processes_;
+};
+
+}  // namespace sandbox
+
+#endif  // SANDBOX_MAC_BOOTSTRAP_SANDBOX_H_