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 !defined(OS_NACL_NONSFI)
+  if (sandbox::NamespaceSandbox::InNewUserNamespace()) {

[jln (very slow on Chromium), 2015/05/28 09:02:33]

Hidehiko, Mark, what's missing for this to compile in OS_NACL_NONSFI?

One PID per NS is very desirable for NONSFI.

[hidehiko, 2015/05/29 05:46:58]

base::ForkWithFlags in base/process/launch_posix.cc.
It is not built in libbase_nacl_nonsfi.a now.

Supporting ForkWithFlags *only* would not be much difficult, IIUC.
Though, other code in the file would hit problems if we build with PNaCl
toolchain, especially around signals, so I just dropped the file at all, as we
didn't need it.

Also, in ForkInNewPidNamespace, we need to use LINUX_SIGCHLD instead of SIGCHLD
for the workaround of signal ABI problem.

[hidehiko, 2015/05/29 06:14:52]

FYI: Like this https://codereview.chromium.org/1161933003/

[rickyz (no longer on Chrome), 2015/05/29 23:16:39]

Thanks for the comments, Hidehiko - it sounds like there might be a little extra
work involved for nonsfi, so I'll start working on that in a separate CL.

+    // The NaCl runtime will install signal handlers for SIGINT, SIGTERM, etc.
+    // so we do not need to install termination signal handlers ourselves.
+    child_pid = sandbox::NamespaceSandbox::ForkInNewPidNamespace(
+        /*drop_capabilities_in_child=*/true);
+  } else {
+#endif
+    child_pid = fork();

[jln (very slow on Chromium), 2015/05/28 09:02:33]

We never drop all capabilities in this codepath!

[rickyz (no longer on Chrome), 2015/05/29 23:16:39]

The combination of keeping CAP_SYS_ADMIN and hitting this codepath is probably
impossible, but agreed, the separation of responsibility is really unclear :-(
What do you think about this change? I added a helper that forks and drops
capabilities, and call that instead of fork().

+#if !defined(OS_NACL_NONSFI)

[mdempsky, 2015/05/28 21:23:23]

nit: Having an #if block just for a } is kind of ugly.  I'd suggest either
reshuffling the "} else { #endif" to "} else #endif {" so you can have the close
brace unconditionally, or the more intrusive option of something like

    namespace {
    #if defined(OS_NACL_NONSFI)
    pid_t ForkChild() {
      return sandbox::NamespaceSandbox::ForkInNewPidNamespace(...);
    }
    #else
    pid_t ForkChild() {
      return fork();
    }
    #endif
    }  // namespace

Your call.

[rickyz (no longer on Chrome), 2015/05/29 23:16:39]

Done.

+  }
+#endif
+
   if (child_pid < 0) {
     PLOG(ERROR) << "*** fork() failed.";
   }
 
   if (child_pid == 0) {
     ChildNaClLoaderInit(child_fds.Pass(),
                         system_info,
                         uses_nonsfi_mode,
                         nacl_sandbox,
                         channel_id);
@@ skipping 273 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();
 }