Start all children in their own PID namespace.

sandbox/linux/services/credentials.h

 // Copyright (c) 2013 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_LINUX_SERVICES_CREDENTIALS_H_
 #define SANDBOX_LINUX_SERVICES_CREDENTIALS_H_
 
 #include "build/build_config.h"
 // Link errors are tedious to track, raise a compile-time error instead.
 #if defined(OS_ANDROID)
 #error "Android is not supported."
 #endif  // defined(OS_ANDROID).
 
 #include <string>
 #include <vector>
 
 #include "base/basictypes.h"
 #include "base/compiler_specific.h"
 #include "base/memory/scoped_ptr.h"
 #include "sandbox/linux/system_headers/capability.h"
 #include "sandbox/sandbox_export.h"
 
 namespace sandbox {
 
-// For brevity, we only expose enums for the subset of capabilities we use.
-// This can be expanded as the need arises.
-enum class LinuxCapability {
-  kCapSysChroot,
-  kCapSysAdmin,
-};
-
 // This class should be used to manipulate the current process' credentials.
 // It is currently a stub used to manipulate POSIX.1e capabilities as
 // implemented by the Linux kernel.
 class SANDBOX_EXPORT Credentials {
  public:
+  // For brevity, we only expose enums for the subset of capabilities we use.
+  // This can be expanded as the need arises.
+  enum class Capability {
+    kCapSysChroot,

[jln (very slow on Chromium), 2015/03/26 22:01:33]

Nit: you could drop the "Cap", now that it's qualified with ..::Capability::k..

Up to you.

[mdempsky, 2015/03/27 20:32:11]

Also, Chromium style is to use SHOUTY_CASE for enums. :(

[rickyz (no longer on Chrome), 2015/03/27 21:08:02]

Oop, missed that, changed it as well, but let me know if you'd prefer that to
happen in another CL.

+    kCapSysAdmin,
+  };
+
   // Drop all capabilities in the effective, inheritable and permitted sets for
   // the current thread. For security reasons, since capabilities are
   // per-thread, the caller is responsible for ensuring it is single-threaded
   // when calling this API.
   // |proc_fd| must be a file descriptor to /proc/ and remains owned by
   // the caller.
   static bool DropAllCapabilities(int proc_fd) WARN_UNUSED_RESULT;
   // A similar API which assumes that it can open /proc/self/ by itself.
   static bool DropAllCapabilities() WARN_UNUSED_RESULT;
   // Sets the effective and permitted capability sets for the current thread to
   // the list of capabiltiies in |caps|. All other capability flags are cleared.
   static bool SetCapabilities(int proc_fd,
-                              const std::vector<LinuxCapability>& caps)
+                              const std::vector<Capability>& caps)
       WARN_UNUSED_RESULT;
 
+  // Versions of the above functions which do not check that the process is
+  // single-threaded. After calling these functions, capabilities of other
+  // threads will not be changed.

[jln (very slow on Chromium), 2015/03/26 22:01:33]

Maybe add something along the lines "This is dangerous, do not use unless you
know what you are doing"?

[rickyz (no longer on Chrome), 2015/03/27 21:08:02]

Heh, sure, done

+  static bool DropAllCapabilitiesOnCurrentThread() WARN_UNUSED_RESULT;
+  static bool SetCapabilitiesOnCurrentThread(
+      const std::vector<Capability>& caps) WARN_UNUSED_RESULT;
+
   // Returns true if the current thread has either the effective, permitted, or
   // inheritable flag set for the given capability.
-  static bool HasCapability(LinuxCapability cap);
+  static bool HasCapability(Capability cap);
 
   // Return true iff there is any capability in any of the capabilities sets
   // of the current thread.
   static bool HasAnyCapability();
 
   // Returns whether the kernel supports CLONE_NEWUSER and whether it would be
   // possible to immediately move to a new user namespace. There is no point
   // in using this method right before calling MoveToNewUserNS(), simply call
   // MoveToNewUserNS() immediately. This method is only useful to test the
   // ability to move to a user namespace ahead of time.
@@ skipping 22 matching lines @@
   //   - DropAllCapabilities() must be called to prevent escapes.
   static bool DropFileSystemAccess(int proc_fd) WARN_UNUSED_RESULT;
 
  private:
   DISALLOW_IMPLICIT_CONSTRUCTORS(Credentials);
 };
 
 }  // namespace sandbox.
 
 #endif  // SANDBOX_LINUX_SERVICES_CREDENTIALS_H_