Where to put common writable application files?

By : dennisV
Source: Stackoverflow.com
Question!

I thought that CSIDL_COMMON_APPDATA\company\product should be the place to put files that are common for all users of the application and that the application can modify, however, on Vista this is a read-only location, unless modified by the installer (as per MSDN - http://msdn.microsoft.com/en-us/library/ms995853.aspx), so... what's best? Modify the location's security settings to allow writing or use CSIDL_COMMON_DOCUMENTS\company\product instead? Maybe there's a third option?

Also, is there an "official" Microsoft recommendation on this somewhere?

By : dennisV


Answers

Here's a simple example showing how to create files and folders with Read/Write permission for all users in the Common App Data folder (CSIDL_COMMON_APPDATA). Any user can run this code to give all other users permission to write to the files & folders:

#include <windows.h>

#include <shlobj.h>
#pragma comment(lib, "shell32.lib")

// for PathAppend
#include <Shlwapi.h>
#pragma comment(lib, "Shlwapi.lib")

#include <stdio.h>
#include <aclapi.h>
#include <tchar.h>
#pragma comment(lib, "advapi32.lib")    

#include <iostream>
#include <fstream>
using namespace std;

int _tmain(int argc, _TCHAR* argv[])
{
    DWORD dwRes, dwDisposition;
    PSID pEveryoneSID = NULL;
    PACL pACL = NULL;
    PSECURITY_DESCRIPTOR pSD = NULL;
    EXPLICIT_ACCESS ea;
    SID_IDENTIFIER_AUTHORITY SIDAuthWorld = SECURITY_WORLD_SID_AUTHORITY;
    SID_IDENTIFIER_AUTHORITY SIDAuthNT = SECURITY_NT_AUTHORITY;
    SECURITY_ATTRIBUTES sa;

    // Create a well-known SID for the Everyone group.
    if (!AllocateAndInitializeSid(&SIDAuthWorld, 1,
                     SECURITY_WORLD_RID, 0, 0, 0, 0, 0, 0, 0,
                     &pEveryoneSID))
    {
        _tprintf(_T("AllocateAndInitializeSid Error %u\n"), GetLastError());
        goto Cleanup;
    }

    // Initialize an EXPLICIT_ACCESS structure for an ACE.
    // The ACE will allow Everyone access to files & folders you create.
    ZeroMemory(&ea, sizeof(EXPLICIT_ACCESS));
    ea.grfAccessPermissions = 0xFFFFFFFF;
    ea.grfAccessMode = SET_ACCESS;

    // both folders & files will inherit this ACE
    ea.grfInheritance= CONTAINER_INHERIT_ACE|OBJECT_INHERIT_ACE;
    ea.Trustee.TrusteeForm = TRUSTEE_IS_SID;
    ea.Trustee.TrusteeType = TRUSTEE_IS_WELL_KNOWN_GROUP;
    ea.Trustee.ptstrName  = (LPTSTR) pEveryoneSID;

    // Create a new ACL that contains the new ACEs.
    dwRes = SetEntriesInAcl(1, &ea, NULL, &pACL);
    if (ERROR_SUCCESS != dwRes)
    {
        _tprintf(_T("SetEntriesInAcl Error %u\n"), GetLastError());
        goto Cleanup;
    }

    // Initialize a security descriptor.
    pSD = (PSECURITY_DESCRIPTOR) LocalAlloc(LPTR, SECURITY_DESCRIPTOR_MIN_LENGTH);
    if (NULL == pSD)
    {
        _tprintf(_T("LocalAlloc Error %u\n"), GetLastError());
        goto Cleanup;
    }

    if (!InitializeSecurityDescriptor(pSD, SECURITY_DESCRIPTOR_REVISION))
    {
        _tprintf(_T("InitializeSecurityDescriptor Error %u\n"), GetLastError());
        goto Cleanup;
    }

    // Add the ACL to the security descriptor.
    if (!SetSecurityDescriptorDacl(pSD,
            TRUE,     // bDaclPresent flag
            pACL,
            FALSE))   // not a default DACL
    {
        _tprintf(_T("SetSecurityDescriptorDacl Error %u\n"), GetLastError());
        goto Cleanup;
    }

    // Initialize a security attributes structure.
    sa.nLength = sizeof(SECURITY_ATTRIBUTES);
    sa.lpSecurityDescriptor = pSD;
    sa.bInheritHandle = FALSE;



    TCHAR szPath[MAX_PATH];

    if (SUCCEEDED(SHGetFolderPath(NULL, CSIDL_COMMON_APPDATA|CSIDL_FLAG_CREATE, NULL, 0, szPath))) 
    {
        PathAppend(szPath, TEXT("Your Shared Folder"));

        if (!CreateDirectory(szPath, &sa)
            && GetLastError() != ERROR_ALREADY_EXISTS) 
        {
            goto Cleanup;
        }

        PathAppend(szPath, TEXT("textitup.txt"));

        HANDLE hFile = CreateFile(szPath, GENERIC_READ | GENERIC_WRITE, 0, &sa, CREATE_ALWAYS, 0, 0);
        if (hFile == INVALID_HANDLE_VALUE)
            goto Cleanup;
        else
            CloseHandle(hFile);

        //TODO: do the writing
        ofstream fsOut;
        fsOut.exceptions(ios::eofbit | ios::failbit | ios::badbit);
        fsOut.open(szPath, ios::out | ios::binary | ios::trunc);

        fsOut << "Hello world!\n";
        fsOut.close();
    }

Cleanup:

    if (pEveryoneSID) 
        FreeSid(pEveryoneSID);
    if (pACL) 
        LocalFree(pACL);
    if (pSD) 
        LocalFree(pSD);

    return 0;
}


Guidelines for Vista/UAC can be found here. Search that page for "CSIDL" and you'll find some "official" answers.



Modify just the security on a specific sub-directory of the AppData directory (this is from the link you provided):

CSIDL_COMMON_APPDATA This folder should be used for application data that is not user specific. For example, an application may store a spell check dictionary, a database of clip-art or a log file in the CSIDL_COMMON_APPDATA folder. This information will not roam and is available to anyone using the computer. By default, this location is read-only for normal (non-admin, non-power) Users. If an application requires normal Users to have write access to an application specific subdirectory of CSIDL_COMMON_APPDATA, then the application must explicitly modify the security on that sub-directory during application setup. The modified security must be documented in the Vendor Questionnaire.



This video can help you solving your question :)
By: admin