Andrey Karpov

Apr 24 2014

Tags:

#Cpp

A Check of the Open-Source Project WinSCP Developed in Embarcadero C++ Builder

• WinSCP
• Analysis
• Analysis results
  • Memset() function's arguments mixed up
  • Using a nonexistent object
  • Garbage in a dialog
  • A duplicated line
  • Failed check
  • A dangerous way to use the fprintf() function
  • Something wrong with the 'err' variable
• Conclusion

We regularly check open-source C/C++ projects, but what we check are mostly projects developed in the Visual Studio IDE. For some reason, we haven't paid much attention to the Embarcadero C++ Builder IDE. In order to improve this situation, we are going to discuss the WinSCP project I have checked recently.

WinSCP

WinSCP is a free and open-source SFTP, SCP and FTP client for Microsoft Windows. Its main function is secure file transfer between a local and a remote computer. Beyond this, WinSCP offers basic file manager and file synchronization functionality. Since July 16, 2003, it is licensed under the GNU GPL and hosted on SourceForge.net.

The official website: http://winscp.net

You need Embarcadero C++ Builder XE2 to build the project.

Analysis

Analysis was done with the PVS-Studio static analyzer. The tool currently supports the following IDEs:

• Visual Studio 2013 C, C++, C++11, C++/CX (WinRT)
• Visual Studio 2012 C, C++, C++11, C++/CX (WinRT)
• Visual Studio 2010 C, C++, C++0x
• Visual Studio 2008 C, C++
• Visual Studio 2005 C, C++
• Embarcadero RAD Studio XE5 C, C++, C++11, 64-bit compiler included
• Embarcadero RAD Studio XE4 C, C++, C++11, 64-bit compiler included
• Embarcadero RAD Studio XE3 Update 1 C, C++, C++11, 64-bit compiler included
• Embarcadero RAD Studio XE2 C, C++, C++0x
• Embarcadero RAD Studio XE C, C++
• Embarcadero RAD Studio 2010 C, C++
• Embarcadero RAD Studio 2009 C, C++
• MinGW C, C++, C++11

Besides, you can also work in PVS-Studio Standalone. It allows checking *.i files prepared in advance and monitoring the project build process in order to collect all the necessary information for a check. To find out more about it, see the article "PVS-Studio Now Supports Any Build System under Windows and Any Compiler".

Analysis results

There are not many errors in the project - but still enough to write an article to attract Embarcadero RAD Studio users' attention.

Memset() function's arguments mixed up

TForm * __fastcall TMessageForm::Create(....)
{
  ....
  LOGFONT AFont;
  ....   
  memset(&AFont, sizeof(AFont), 0);
  ....
}

PVS-Studio's diagnostic message: V575 The 'memset' function processes '0' elements. Inspect the third argument. messagedlg.cpp 786

The memset() function receives an array size as the third argument. It's an ordinary but very unpleasant typo resulting in the structure remaining uninitialized.

There is a similar typo a bit farther in the code: messagedlg.cpp 796

Using a nonexistent object

void __fastcall TCustomScpExplorerForm::EditorAutoConfig()
{
  ....
  else
  {
    ....
    TEditorList EditorList;
    EditorList = *WinConfiguration->EditorList;
    EditorList.Insert(0, new TEditorPreferences(EditorData));
    WinConfiguration->EditorList = &EditorList;
  }
  ....
}

PVS-Studio's diagnostic message: V506 Pointer to local variable 'EditorList' is stored outside the scope of this variable. Such a pointer will become invalid. customscpexplorer.cpp 2633

The 'EditorList' object will be destroyed immediately after leaving the scope. However, the programmer saves a pointer to this object and uses it after that. It leads to undefined behavior.

Garbage in a dialog

bool __fastcall RecursiveDeleteFile(....)
{
  SHFILEOPSTRUCT Data;
  memset(&Data, 0, sizeof(Data));
  ....
  Data.pTo = L"";
  ....
}

PVS-Studio's diagnostic message: V540 Member 'pTo' should point to string terminated by two 0 characters. common.cpp 1659

Notice the following line in the pTo parameter's description in MSDN: "Note This string must be double-null terminated".

Because of the error, the file-handling dialog will contain garbage - or it will not. It all depends on how lucky you are. But the code is incorrect anyway.

A duplicated line

int CFileZillaApi::Init(....)
{
  ....
  m_pMainThread->m_hOwnerWnd=m_hOwnerWnd;
  m_pMainThread->m_hOwnerWnd=m_hOwnerWnd;
  ....
}

PVS-Studio's diagnostic message: V519 The 'm_pMainThread->m_hOwnerWnd' variable is assigned values twice successively. Perhaps this is a mistake. Check lines: 88, 89. filezillaapi.cpp 89

Perhaps there is no error here - just one extra line written by mistake.

Failed check

STDMETHODIMP CShellExtClassFactory::CreateInstance(....)
{
  ....
  CShellExt* ShellExt = new CShellExt();
  if (NULL == ShellExt)
  {
    return E_OUTOFMEMORY;
  }
  ....
}

PVS-Studio's diagnostic message: V668 There is no sense in testing the 'ShellExt' pointer against null, as the memory was allocated using the 'new' operator. The exception will be generated in the case of memory allocation error. dragext.cpp 554

The check "if (NULL == ShellExt)" is meaningless as the 'new' operator will throw the std::bad_alloc exception if it fails to allocate memory.

A dangerous way to use the fprintf() function

bool CAsyncSslSocketLayer::CreateSslCertificate(....)
{
  ....
  char buffer[1001];
  int len;
  while ((len = pBIO_read(bio, buffer, 1000)) > 0)
  {
    buffer[len] = 0;
    fprintf(file, buffer);
  }
  ....
}

V618 It's dangerous to call the 'fprintf' function in such a manner, as the line being passed could contain format specification. The example of the safe code: printf("%s", str); asyncsslsocketlayer.cpp 2247

If the buffer contains control specifiers while data are being written into the file, it will lead to an unpredictable result. The safe way of using the function is as follows:

fprintf(file, "%s", buffer);

This error can also be treated as a potential vulnerability.

Something wrong with the 'err' variable

static error_t
client_send_propfind_request(....)
{
  ....
  error_t err = 0;
  int code = 0;

  apr_hash_t * props = NULL;
  const char * target = path_uri_encode(remote_path, pool);
  char * url_path = apr_pstrdup(pool, target);

  WEBDAV_ERR(neon_get_props(&props, ras, url_path,
    NEON_DEPTH_ZERO, starting_props,
    false, pool));

  if (err && (err == WEBDAV_ERR_DAV_REQUEST_FAILED))
  ....
}

PVS-Studio's diagnostic message: V560 A part of conditional expression is always false: (err == 1003). webdavfilesystem.cpp 10990

Conclusion

Where are you, Embarcadero RAD Studio users? Hey! According to our statistics, they are very few. Well, come and try the PVS-Studio static analyzer!

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