Enable one PID namespace per process for NaCl processes.

components/nacl/loader/nacl_helper_linux.cc

 // Copyright 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.
 
 // A mini-zygote specifically for Native Client.
 
 #include "components/nacl/loader/nacl_helper_linux.h"
 
 #include <errno.h>
 #include <fcntl.h>
@@ skipping 23 matching lines @@
 #include "components/nacl/common/nacl_switches.h"
 #include "components/nacl/loader/nacl_listener.h"
 #include "components/nacl/loader/nonsfi/nonsfi_listener.h"
 #include "components/nacl/loader/sandbox_linux/nacl_sandbox_linux.h"
 #include "content/public/common/content_descriptors.h"
 #include "content/public/common/send_zygote_child_ping_linux.h"
 #include "content/public/common/zygote_fork_delegate_linux.h"
 #include "crypto/nss_util.h"
 #include "ipc/ipc_descriptors.h"
 #include "ipc/ipc_switches.h"
+#include "sandbox/linux/services/credentials.h"
 #include "sandbox/linux/services/libc_urandom_override.h"
+#include "sandbox/linux/services/namespace_sandbox.h"
 
 #if defined(OS_NACL_NONSFI)
 #include "native_client/src/public/nonsfi/irt_exception_handling.h"
 #else
 #include <link.h>
 #include "components/nacl/loader/nonsfi/irt_exception_handling.h"
 #endif
 
 namespace {
 
@@ skipping 128 matching lines @@
     return false;
   }
 
   if (content::ZygoteForkDelegate::kNumPassedFDs != child_fds.size()) {
     LOG(ERROR) << "nacl_helper: unexpected number of fds, got "
         << child_fds.size();
     return false;
   }
 
   VLOG(1) << "nacl_helper: forking";
-  pid_t child_pid = fork();
+  pid_t child_pid;
+  if (sandbox::NamespaceSandbox::InNewUserNamespace()) {
+    child_pid = sandbox::NamespaceSandbox::ForkInNewPidNamespace(
+        /*drop_capabilities_in_child=*/true);
+  } else {
+    child_pid = sandbox::Credentials::ForkAndDropCapabilitiesInChild();
+  }
+
   if (child_pid < 0) {
     PLOG(ERROR) << "*** fork() failed.";
   }
 
   if (child_pid == 0) {
+    // Install termiantion signal handlers for nonsfi NaCl. The SFI NaCl runtime
+    // will install signal handlers for SIGINT, SIGTERM, etc. so we do not need
+    // to install termination signal handlers ourselves (in fact, it will crash
+    // if signal handlers for these are present).
+    if (uses_nonsfi_mode && getpid() == 1) {
+      // Note that nonsfi NaCl may override some of these signal handlers, which
+      // is fine.
+      sandbox::NamespaceSandbox::InstallDefaultTerminationSignalHandlers();
+    }
     ChildNaClLoaderInit(child_fds.Pass(),
                         system_info,
                         uses_nonsfi_mode,
                         nacl_sandbox,
                         channel_id);
     NOTREACHED();
   }
 
   // I am the parent.
   // First, close the dummy_fd so the sandbox won't find me when
@@ skipping 268 matching lines @@
   // Now handle requests from the Zygote.
   while (true) {
     bool request_handled = HandleZygoteRequest(
         kNaClZygoteDescriptor, system_info, nacl_sandbox.get());
     // Do not turn this into a CHECK() without thinking about robustness
     // against malicious IPC requests.
     DCHECK(request_handled);
   }
   NOTREACHED();
 }