Add check for file system access to the sandbox.

sandbox/linux/services/credentials_unittest.cc

 // Copyright (c) 2012 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 <fcntl.h>
 #include <limits.h>
 #include <pthread.h>
@@ skipping 131 matching lines @@
   PCHECK(0 == chdir("/"));
   CHECK(WorkingDirectoryIsRoot());
 }
 
 // Disabled on ASAN because of crbug.com/451603.
 SANDBOX_TEST(Credentials, DISABLE_ON_ASAN(DropFileSystemAccessIsSafe)) {
   CHECK(Credentials::DropAllCapabilities());
   // Probably missing kernel support.
   if (!Credentials::MoveToNewUserNS()) return;
   CHECK(Credentials::DropFileSystemAccess(ProcUtil::OpenProc().get()));
   CHECK(!base::DirectoryExists(base::FilePath("/proc")));

[rickyz (no longer on Chrome), 2016/09/23 23:40:20]

Would be fine with replacing this line rather than adding a separate test

[Greg K, 2016/09/26 20:22:12]

Done.

   CHECK(WorkingDirectoryIsRoot());
   CHECK(base::IsDirectoryEmpty(base::FilePath("/")));
   // We want the chroot to never have a subdirectory. A subdirectory
   // could allow a chroot escape.
   CHECK_NE(0, mkdir("/test", 0700));
 }
 
+// Check that callers can reliably test if file system access exists.
+SANDBOX_TEST(Credentials, DISABLE_ON_ASAN(HasFileSystemAccess)) {
+  CHECK(Credentials::HasFileSystemAccess());
+  CHECK(Credentials::DropAllCapabilities());
+  // Probably missing kernel support.
+  if (!Credentials::MoveToNewUserNS()) return;
+  CHECK(Credentials::DropFileSystemAccess(ProcUtil::OpenProc().get()));
+  CHECK(!Credentials::HasFileSystemAccess());
+}
+
 // Check that after dropping filesystem access and dropping privileges
 // it is not possible to regain capabilities.
 SANDBOX_TEST(Credentials, DISABLE_ON_ASAN(CannotRegainPrivileges)) {
   base::ScopedFD proc_fd(ProcUtil::OpenProc());
   CHECK(Credentials::DropAllCapabilities(proc_fd.get()));
   // Probably missing kernel support.
   if (!Credentials::MoveToNewUserNS()) return;
   CHECK(Credentials::DropFileSystemAccess(proc_fd.get()));
   CHECK(Credentials::DropAllCapabilities(proc_fd.get()));
 
@@ skipping 91 matching lines @@
   action.sa_handler = &SignalHandler;
   PCHECK(sigaction(SIGUSR1, &action, nullptr) == 0);
 
   PCHECK(raise(SIGUSR1) == 0);
   CHECK_EQ(1, signal_handler_called);
 }
 
 }  // namespace.
 
 }  // namespace sandbox.