Start all children in their own PID namespace.

sandbox/linux/services/namespace_sandbox.h

Index: sandbox/linux/services/namespace_sandbox.h
diff --git a/sandbox/linux/services/namespace_sandbox.h b/sandbox/linux/services/namespace_sandbox.h
index b92f5818f1bee1b4afb3cc32e260113dd6caa48b..a784360ac3335db466bd578c4b4ecbe37fbaefae 100644
--- a/sandbox/linux/services/namespace_sandbox.h
+++ b/sandbox/linux/services/namespace_sandbox.h
@@ -5,6 +5,8 @@
 #ifndef SANDBOX_LINUX_SERVICES_NAMESPACE_SANDBOX_H_
 #define SANDBOX_LINUX_SERVICES_NAMESPACE_SANDBOX_H_
 
+#include <sys/types.h>
+
 #include <string>
 #include <vector>
 
@@ -47,6 +49,38 @@ class SANDBOX_EXPORT NamespaceSandbox {
   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.)
+  static void InstallDefaultTerminationSignalHandlers();

[jln (very slow on Chromium), 2015/03/27 21:24:35]

Add to the doc that if a signal handler already exists, it won't get overridden.

[rickyz (no longer on Chrome), 2015/03/27 21:48:59]

Done.

+
+  // Installs a signal handler for |sig| which exits with |exit_code|. Existing
+  // signal handlers are overridden if |override_existing_handler| is true.
+  // Returns false if |override_existing_handler| is false and a signal handler
+  // was already set.
+  static bool InstallTerminationSignalHandler(int sig,
+                                              int exit_code,
+                                              bool override_existing_handler);

[jln (very slow on Chromium), 2015/03/26 22:01:34]

I don't think we need |override_existing_handler|, do we?

I don't really see a case where we would want to override an existing handler.
If an existing handler exists: great, the "init" oddity doesn't exist, nothing
to fix.

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

The use case I was thinking of was that a user might want to call
InstallDefaultTerminationSignalHandlers and then override the exit code for
specific signals with InstallTerminationSignalHandler. What do you think?

[jln (very slow on Chromium), 2015/03/27 21:24:36]

Well, in that case, one could simply install the specific handler with
InstallTerminationSignalHandler and then
InstallDefaultTerminationSignalHandlers. So I think we can get rid of the
parameter.

[rickyz (no longer on Chrome), 2015/03/27 21:48:59]

Ah, good point, removed.

+
   // 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.
@@ -54,6 +88,8 @@ class SANDBOX_EXPORT NamespaceSandbox {
   static bool InNewPidNamespace();
   static bool InNewNetNamespace();
 
+  static const int kDefaultExitCode = 1;

[jln (very slow on Chromium), 2015/03/26 22:01:34]

Style: static const members should go to top of the class.

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

Done.

+
  private:
   DISALLOW_IMPLICIT_CONSTRUCTORS(NamespaceSandbox);
 };