Fix the potential integer overflow from 'offset+size' in extension.h and fpdfview.cpp

core/src/fxcrt/extension.h

 // Copyright 2014 PDFium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 // Original code copyright 2014 Foxit Software Inc. http://www.foxitsoftware.com
 
 #ifndef _FXCRT_EXTENSION_IMP_
 #define _FXCRT_EXTENSION_IMP_
 
 #include "../../../third_party/numerics/safe_math.h"
@@ skipping 50 matching lines @@
     virtual FX_FILESIZE                 GetPosition()
     {
         FX_FILESIZE pos = m_pFile->GetPosition();
         if (m_bUseRange) {
             pos -= m_nOffset;
         }
         return pos;
     }
     virtual FX_BOOL                             SetRange(FX_FILESIZE offset, FX_FILESIZE size)
     {
-        if (offset < 0 || offset + size > m_pFile->GetSize()) {
+        base::CheckedNumeric<FX_FILESIZE> pos = size;

[palmer, 2014/07/25 00:40:14]

Putting something like this:

    typedef base::CheckedNumeric<FX_FILESIZE> FileSizeT;

at the top of the file might make the code look a little cleaner. (And then you
could also use the typedef in other files that #include this one.)

[jun_fang, 2014/07/25 01:04:00]

Good idea.

+        pos += offset;
+
+        if (!pos.IsValid() || offset < 0 || size < 0 || pos.ValueOrDie() >= m_pFile->GetSize()) {
             return FALSE;
         }
+
         m_nOffset = offset, m_nSize = size;
         m_bUseRange = TRUE;
         m_pFile->SetPosition(m_nOffset);
         return TRUE;
     }
     virtual void                                ClearRange()
     {
         m_bUseRange = FALSE;
     }
     virtual FX_BOOL                             ReadBlock(void* buffer, FX_FILESIZE offset, size_t size)
     {
+        base::CheckedNumeric<FX_FILESIZE> pos = offset;
+
         if (m_bUseRange) {
-            if (offset + size > (size_t)GetSize()) {
+            pos += m_nOffset;
+            if (!pos.IsValid() || pos.ValueOrDie() >= (size_t)GetSize()) {
                 return FALSE;
             }
-            offset += m_nOffset;
         }
-        return (FX_BOOL)m_pFile->ReadPos(buffer, size, offset);
+        return (FX_BOOL)m_pFile->ReadPos(buffer, size, pos.ValueOrDie());
     }
     virtual size_t                              ReadBlock(void* buffer, size_t size)
     {
         if (m_bUseRange) {
             FX_FILESIZE availSize = m_nOffset + m_nSize - m_pFile->GetPosition();
             if ((size_t)availSize < size) {
                 size -= size - (size_t)availSize;
             }
         }
         return m_pFile->Read(buffer, size);
@@ skipping 76 matching lines @@
     {
         FX_FILESIZE pos = (FX_FILESIZE)m_nCurPos;
         if (m_bUseRange) {
             pos -= (FX_FILESIZE)m_nOffset;
         }
         return pos;
     }
     virtual FX_BOOL                             SetRange(FX_FILESIZE offset, FX_FILESIZE size)
     {
         base::CheckedNumeric<FX_FILESIZE> range = size;
-        range += size;
- 
-        if (!range.IsValid() || offset <= 0 || size <= 0 || range.ValueOrDie() > m_nCurSize) {
+        range += offset;
+        if (!range.IsValid() || offset <= 0 || size <= 0 || range.ValueOrDie() >= m_nCurSize) {
             return FALSE;
         }
         
         m_nOffset = (size_t)offset, m_nSize = (size_t)size;
         m_bUseRange = TRUE;
         m_nCurPos = m_nOffset;
         return TRUE;
     }
     virtual void                                ClearRange()
     {
@@ skipping 11 matching lines @@
         }
          
         if (!safeOffset.IsValid()) {
             return FALSE;
         }
 
         offset = safeOffset.ValueOrDie();
 
         base::CheckedNumeric<size_t> newPos = size;
         newPos += offset;
-        if (!newPos.IsValid() || newPos.ValueOrDefault(0) == 0 || newPos.ValueOrDie() > m_nCurSize) {
+        if (!newPos.IsValid() || newPos.ValueOrDefault(0) == 0 || newPos.ValueOrDie() >= m_nCurSize) {
             return FALSE;
         }
 
         m_nCurPos = newPos.ValueOrDie();
         if (m_dwFlags & FX_MEMSTREAM_Consecutive) {
             FXSYS_memcpy32(buffer, (FX_LPBYTE)m_Blocks[0] + (size_t)offset, size);
             return TRUE;
         }
         size_t nStartBlock = (size_t)offset / m_nGrowSize;
         offset -= (FX_FILESIZE)(nStartBlock * m_nGrowSize);
@@ skipping 186 matching lines @@
     FX_DWORD mt[MT_N];
 } FX_MTRANDOMCONTEXT, * FX_LPMTRANDOMCONTEXT;
 typedef FX_MTRANDOMCONTEXT const * FX_LPCMTRANDOMCONTEXT;
 #if _FXM_PLATFORM_ == _FXM_PLATFORM_WINDOWS_
 FX_BOOL FX_GenerateCryptoRandom(FX_LPDWORD pBuffer, FX_INT32 iCount);
 #endif
 #ifdef __cplusplus
 }
 #endif
 #endif