Intercept file Open/Close

base/files/protect_file_posix.cc

+// Copyright 2014 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 "base/containers/hash_tables.h"
+#include "base/files/file.h"
+#include "base/lazy_instance.h"
+#include "base/logging.h"
+#include "base/posix/eintr_wrapper.h"
+#include "base/synchronization/lock.h"
+
+// These hooks provided for base::File perform additional sanity checks when
+// files are closed. These extra checks are hard to understand and maintain,
+// hence they are temporary. TODO(pasko): Remove these extra checks as soon as
+// crbug.com/424562 is fixed.
+//
+// Background:
+//   1. The browser process crashes if a call to close() provided by the C
+//      library (i.e. close(3)) fails. This is done for security purposes. See
+//      base/files/scoped_file.cc. When a crash like this happens, there is not
+//      enough context in the minidump to triage the problem.
+//   2. base::File provides a good abstraction to prevent closing incorrect
+//      file descriptors or double-closing. Closing non-owned file descriptors
+//      would more likely happen from outside base::File and base::ScopedFD.
+//
+// These hooks intercept base::File operations to 'protect' file handles /
+// descriptors from accidental close(3) by other portions of the code being
+// linked into the browser. Also, this file provides an interceptor for the
+// close(3) itself, and requires to be linked with cooperation of
+// --Wl,--wrap=close (i.e. linker wrapping).
+//
+// Wrapping close(3) on all libraries can lead to confusion, particularly for
+// the libraries that do not use ::base (I am also looking at you,
+// crazy_linker). Instead two hooks are added to base::File, which are
+// implemented as no-op by default. This file should be linked into the Chrome
+// native binary(-ies) for a whitelist of targets where "file descriptor
+// protection" is useful.
+
+// With compilers other than GCC/Clang the wrapper is trivial. This is to avoid
+// overexercising mechanisms for overriding weak symbols.
+#if !defined(COMPILER_GCC)
+extern "C" {
+
+int __real_close(int fd);
+
+BASE_EXPORT int __wrap_close(int fd) {
+  return __real_close(fd);
+}
+
+}  // extern "C"
+
+#else  // defined(COMPILER_GCC)
+
+namespace {
+
+// Protects the |g_protected_fd_set|.
+base::LazyInstance<base::Lock>::Leaky g_lock = LAZY_INSTANCE_INITIALIZER;
+
+// Holds the set of all 'protected' file descriptors.
+base::LazyInstance<base::hash_set<int> >::Leaky g_protected_fd_set =
+    LAZY_INSTANCE_INITIALIZER;
+
+bool IsFileDescriptorProtected(int fd) {
+  base::AutoLock lock(*g_lock.Pointer());
+  return g_protected_fd_set.Get().count(fd) != 0;
+}
+
+}  // namespace
+
+namespace base {
+
+BASE_EXPORT void ProtectFileDescriptor(int fd) {
+  base::AutoLock lock(g_lock.Get());
+  CHECK(!g_protected_fd_set.Get().count(fd)) << "fd: " << fd;
+  g_protected_fd_set.Get().insert(fd);
+}
+
+BASE_EXPORT void UnprotectFileDescriptor(int fd) {
+  base::AutoLock lock(*g_lock.Pointer());
+  CHECK(g_protected_fd_set.Get().erase(fd)) << "fd: " << fd;
+}
+
+}  // namespace base
+
+extern "C" {
+
+int __real_close(int fd);
+
+BASE_EXPORT int __wrap_close(int fd) {
+  // The crash happens here if a protected file descriptor was attempted to be
+  // closed without first being unprotected. Unprotection happens only in
+  // base::File. In other words this is an "early crash" as compared to the one
+  // happening in scoped_file.cc.
+  //
+  // Getting an earlier crash provides a more useful stack trace (minidump)
+  // allowing to debug deeper into the thread that freed the wrong resource.
+  CHECK(!IsFileDescriptorProtected(fd)) << "fd: " << fd;
+
+  // Crash by the same reason as in scoped_file.cc.
+  PCHECK(0 == IGNORE_EINTR(__real_close(fd)));
+  return 0;
+}
+
+}  // extern "C"
+
+#endif  // defined(COMPILER_GCC)