Add memory corruption checking to base::File().

base/files/file.h

 // 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.
 
 #ifndef BASE_FILES_FILE_H_
 #define BASE_FILES_FILE_H_
 
 #include "build/build_config.h"
 #if defined(OS_WIN)
 #include <windows.h>
 #endif
 
 #if defined(OS_POSIX)
 #include <sys/stat.h>
 #endif
 
 #include <string>
 
 #include "base/base_export.h"
 #include "base/basictypes.h"
 #include "base/files/scoped_file.h"
+#include "base/gtest_prod_util.h"
 #include "base/move.h"
 #include "base/time/time.h"
 
 #if defined(OS_WIN)
 #include "base/win/scoped_handle.h"
 #endif
 
+FORWARD_DECLARE_TEST(FileTest, MemoryCorruption);
+
 namespace base {
 
 class FilePath;
 
 #if defined(OS_WIN)
 typedef HANDLE PlatformFile;
 #elif defined(OS_POSIX)
 typedef int PlatformFile;
 
 #if defined(OS_BSD) || defined(OS_MACOSX) || defined(OS_NACL)
@@ skipping 250 matching lines @@
 #if defined(OS_WIN)
   static Error OSErrorToFileError(DWORD last_error);
 #elif defined(OS_POSIX)
   static Error OSErrorToFileError(int saved_errno);
 #endif
 
   // Converts an error value to a human-readable form. Used for logging.
   static std::string ErrorToString(Error error);
 
  private:
+  FRIEND_TEST_ALL_PREFIXES(::FileTest, MemoryCorruption);
+
+#if defined(OS_POSIX)
+  // Encloses a single ScopedFD, saving a cheap tamper resistent memory checksum
+  // alongside it. This checksum is validated at every access, allowing early
+  // detection of memory corruption.
+  class MemoryCheckingScopedFD {
+   public:
+    MemoryCheckingScopedFD();
+    MemoryCheckingScopedFD(int fd);
+    ~MemoryCheckingScopedFD();
+
+    bool is_valid() const { Check(); return file_.is_valid(); }
+    int get() const { Check(); return file_.get(); }
+
+    void reset() { Check(); file_.reset(); UpdateChecksum(); }
+    void reset(int fd) { Check(); file_.reset(fd); UpdateChecksum(); }
+    int release() {
+      Check();
+      int fd = file_.release();
+      UpdateChecksum();
+      return fd;
+    }
+
+   private:
+    FRIEND_TEST_ALL_PREFIXES(::FileTest, MemoryCorruption);
+
+    // Computes the checksum for the current value of |file_|. Returns via an
+    // out parameter to guard against implicit conversions of unsigned integral
+    // types.
+    void ComputeMemoryChecksum(unsigned int* out_checksum) const;
+
+    // Confirms that the current |file_| and |file_memory_checksum_| agree,
+    // failing a CHECK if they do not.
+    void Check() const;
+
+    void UpdateChecksum();
+
+    ScopedFD file_;
+    unsigned int file_memory_checksum_;
+  };
+#endif
+
   void SetPlatformFile(PlatformFile file);
 
 #if defined(OS_WIN)
   win::ScopedHandle file_;
 #elif defined(OS_POSIX)
-  ScopedFD file_;
+  MemoryCheckingScopedFD file_;
 #endif
 
   Error error_details_;
   bool created_;
   bool async_;
 };
 
 }  // namespace base
 
 #endif  // BASE_FILES_FILE_H_