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..dfe41bef2a8ffa6b738089ec81c5150769a6cd72 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 +49,30 @@ 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.
+  //
+  // If the child does not call CreateInitProcessReaper, then there are some
+  // special considerations to be made for the fact that it is an init process
+  // in a PID namespace.
+  //
+  // Aside from SIGKILL and SIGSTOP, the init process in a PID namespace ignores
+  // signals for which it does not have an explicit signal handler. The child
+  // may call InstallTerminationSignalHandler to setup handlers for these
+  // signals that exit with a specific exit code. For most purposes, handlers
+  // should be installed for at least these signals:
+  //
+  // SIGHUP, SIGINT, SIGABRT, SIGQUIT, SIGPIPE, SIGTERM, SIGUSR1, SIGUSR2
+  //
+  // 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 |sig| which exits with |exit_code|.
+  static void InstallTerminationSignalHandler(int sig, int exit_code);

[jln (very slow on Chromium), 2015/03/26 00:49:47]

I think that's the last remaining nit for this CL.

[rickyz (no longer on Chrome), 2015/03/26 05:36:35]

I added a InstallDefaultTerminationSignalHandlers.

Eventually, we might want to make two version of ForkInNewPidNamespace: One that
calls InstallDefaultTerminationSignalHandlers and one that calls
CreateInitProcessReaper, but I honestly couldn't think of a great name that
conveys all the weird gotchas of both, so I just made the lower level pieces for
now.

+
   // 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.