Add utility functions for forking new PID namespaces.

sandbox/linux/services/namespace_sandbox.h

 // Copyright 2015 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_NAMESPACE_SANDBOX_H_
 #define SANDBOX_LINUX_SERVICES_NAMESPACE_SANDBOX_H_
 
+#include <sys/types.h>
+
 #include <string>
 #include <vector>
 
 #include "base/command_line.h"
 #include "base/macros.h"
 #include "base/process/launch.h"
 #include "base/process/process.h"
 #include "sandbox/sandbox_export.h"
 
 namespace sandbox {
@@ skipping 10 matching lines @@
 //    not have an explicit signal handler registered.
 //    If B dies, all the processes in the namespace will die.
 //    B can fork() and the parent can assume the role of init(1), by using
 //    CreateInitProcessReaper().
 // 4. B chroots using Credentials::MoveToNewUserNS() and
 //    Credentials::DropFileSystemAccess()
 // 5. B drops capabilities gained by entering the new user namespace with
 //    Credentials::DropAllCapabilities().
 class SANDBOX_EXPORT NamespaceSandbox {
  public:
+  static const int kDefaultExitCode = 1;
+
   // Launch a new process inside its own user/PID/network namespaces (depending
   // on kernel support). Requires at a minimum that user namespaces are
   // supported (use Credentials::CanCreateProcessInNewUserNS to check this).
   //
   // pre_exec_delegate and clone_flags fields of LaunchOptions should be nullptr
   // and 0, respectively, since this function makes a copy of options and
   // overrides them.
   static base::Process LaunchProcess(const base::CommandLine& cmdline,
                                      const base::LaunchOptions& options);
   static base::Process LaunchProcess(const std::vector<std::string>& argv,
                                      const base::LaunchOptions& options);
 
+  // Forks a process in its own PID namespace. The child process is the init
+  // process inside of the PID namespace, so if the child needs to fork further,
+  // it should call CreateInitProcessReaper, which turns the init process into a
+  // reaper process.
+  //
+  // Otherwise, the child should setup handlers for signals which should
+  // terminate the process using InstallDefaultTerminationSignalHandlers or
+  // InstallTerminationSignalHandler. This works around the fact that init
+  // processes ignore such signals unless they have an explicit handler set.
+  //
+  // This function requries CAP_SYS_ADMIN. If |drop_capabilities_in_child| is
+  // true, then capabilities are dropped in the child.
+  static pid_t ForkInNewPidNamespace(bool drop_capabilities_in_child);
+
+  // Installs a signal handler for:
+  //
+  // SIGHUP, SIGINT, SIGABRT, SIGQUIT, SIGPIPE, SIGTERM, SIGUSR1, SIGUSR2
+  //
+  // that exits with kDefaultExitCode. These are signals whose default action is
+  // to terminate the program (apart from SIGILL, SIGFPE, and SIGSEGV, which
+  // will still terminate the process if e.g. an illegal instruction is
+  // encountered, etc.).
+  //
+  // If any of these already had a signal handler installed, this function will
+  // not override them.
+  static void InstallDefaultTerminationSignalHandlers();
+
+  // Installs a signal handler for |sig| which exits with |exit_code|. If a
+  // signal handler was already present for |sig|, does nothing and returns
+  // false.
+  static bool InstallTerminationSignalHandler(int sig, int exit_code);
+
   // Returns whether the namespace sandbox created a new user, PID, and network
   // namespace. In particular, InNewUserNamespace should return true iff the
   // process was started via this class.
   static bool InNewUserNamespace();
   static bool InNewPidNamespace();
   static bool InNewNetNamespace();
 
  private:
   DISALLOW_IMPLICIT_CONSTRUCTORS(NamespaceSandbox);
 };
 
 }  // namespace sandbox
 
 #endif  // SANDBOX_LINUX_SERVICES_NAMESPACE_SANDBOX_H_