Update from https://crrev.com/318214

sandbox/linux/services/credentials.cc

 // Copyright (c) 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.
 
 #include "sandbox/linux/services/credentials.h"
 
 #include <errno.h>
 #include <signal.h>
 #include <stdio.h>
 #include <sys/capability.h>
 #include <sys/syscall.h>
 #include <sys/types.h>
 #include <sys/wait.h>
 #include <unistd.h>
 
 #include "base/basictypes.h"
 #include "base/bind.h"
 #include "base/files/file_path.h"
 #include "base/files/file_util.h"
 #include "base/logging.h"
 #include "base/posix/eintr_wrapper.h"
 #include "base/process/launch.h"
 #include "base/template_util.h"
 #include "base/third_party/valgrind/valgrind.h"
+#include "build/build_config.h"
 #include "sandbox/linux/services/namespace_utils.h"
+#include "sandbox/linux/services/proc_util.h"
 #include "sandbox/linux/services/syscall_wrappers.h"
+#include "sandbox/linux/services/thread_helpers.h"
 
 namespace sandbox {
 
 namespace {
 
 bool IsRunningOnValgrind() { return RUNNING_ON_VALGRIND; }
 
 struct CapFreeDeleter {
   inline void operator()(cap_t cap) const {
     int ret = cap_free(cap);
@@ skipping 85 matching lines @@
 void CheckCloneNewUserErrno(int error) {
   // EPERM can happen if already in a chroot. EUSERS if too many nested
   // namespaces are used. EINVAL for kernels that don't support the feature.
   // Valgrind will ENOSYS unshare().
   PCHECK(error == EPERM || error == EUSERS || error == EINVAL ||
          error == ENOSYS);
 }
 
 }  // namespace.
 
-bool Credentials::DropAllCapabilities() {
+bool Credentials::DropAllCapabilities(int proc_fd) {
+  DCHECK_LE(0, proc_fd);
+#if !defined(THREAD_SANITIZER)
+  // With TSAN, accept to break the security model as it is a testing
+  // configuration.
+  CHECK(ThreadHelpers::IsSingleThreaded(proc_fd));
+#endif
+
   ScopedCap cap(cap_init());
   CHECK(cap);
   PCHECK(0 == cap_set_proc(cap.get()));
   CHECK(!HasAnyCapability());
   // We never let this function fail.
   return true;
 }
 
+bool Credentials::DropAllCapabilities() {
+  base::ScopedFD proc_fd(ProcUtil::OpenProc());
+  return Credentials::DropAllCapabilities(proc_fd.get());
+}
+
 bool Credentials::HasAnyCapability() {
   ScopedCap current_cap(cap_get_proc());
   CHECK(current_cap);
   ScopedCap empty_cap(cap_init());
   CHECK(empty_cap);
   return cap_compare(current_cap.get(), empty_cap.get()) != 0;
 }
 
 scoped_ptr<std::string> Credentials::GetCurrentCapString() {
   ScopedCap current_cap(cap_get_proc());
   CHECK(current_cap);
   ScopedCapText cap_text(cap_to_text(current_cap.get(), NULL));
   CHECK(cap_text);
   return scoped_ptr<std::string> (new std::string(cap_text.get()));
 }
 
 // static
 bool Credentials::CanCreateProcessInNewUserNS() {
   // Valgrind will let clone(2) pass-through, but doesn't support unshare(),
   // so always consider UserNS unsupported there.
   if (IsRunningOnValgrind()) {
     return false;
   }
 
+#if defined(THREAD_SANITIZER)
+  // With TSAN, processes will always have threads running and can never
+  // enter a new user namespace with MoveToNewUserNS().
+  return false;
+#endif
+
   // This is roughly a fork().
   const pid_t pid = sys_clone(CLONE_NEWUSER | SIGCHLD, 0, 0, 0, 0);
 
   if (pid == -1) {
     CheckCloneNewUserErrno(errno);
     return false;
   }
 
   // The parent process could have had threads. In the child, these threads
   // have disappeared. Make sure to not do anything in the child, as this is a
@@ skipping 38 matching lines @@
   // /proc/sys/kernel/overflowuid). Setup the uid and gid maps.
   DCHECK(GetRESIds(NULL, NULL));
   const char kGidMapFile[] = "/proc/self/gid_map";
   const char kUidMapFile[] = "/proc/self/uid_map";
   PCHECK(NamespaceUtils::WriteToIdMapFile(kGidMapFile, gid));
   PCHECK(NamespaceUtils::WriteToIdMapFile(kUidMapFile, uid));
   DCHECK(GetRESIds(NULL, NULL));
   return true;
 }
 
-bool Credentials::DropFileSystemAccess() {
+bool Credentials::DropFileSystemAccess(int proc_fd) {
+  CHECK_LE(0, proc_fd);
+
   CHECK(ChrootToSafeEmptyDir());
   CHECK(!base::DirectoryExists(base::FilePath("/proc")));
+  CHECK(!ProcUtil::HasOpenDirectory(proc_fd));
   // We never let this function fail.
   return true;
 }
 
 }  // namespace sandbox.