c++ - 使用两个 LPTSTR 时发生堆损坏

Question

我一直在使用一个从过滤器驱动程序接收消息的应用程序。驱动程序运行良好，但我的内存管理有问题，可能是 LPTSTRs user & domain。

在调试时，我收到有关堆损坏的消息，它们通常指向两个 free 或第二个 LookupAccountSid 调用。我在这里做错了什么？

#include "stdafx.h"
#include "myapp-service.h"
#include <Windows.h>
#include <fltUser.h>
#include <string>
#include <sddl.h>

BOOL
getUser(
_In_ WCHAR* sidstr,
_Inout_ LPTSTR* AcctName,
_Inout_ LPTSTR* DomainName
)
{
    PSID sid;
    DWORD dwAcctName = 1;
    DWORD dwDomainName = 1;
    SID_NAME_USE eUse = SidTypeUnknown;
    bool success;

    if (!ConvertStringSidToSidW(sidstr, &sid))
    {
        printf_s("ConvertStringSidToSid failed with 0x%08x\n", GetLastError);
        return false;
    }

    // Lookup!
    LookupAccountSid(
        NULL,
        sid,
        *AcctName,
        (LPDWORD)&dwAcctName,
        *DomainName,
        (LPDWORD)&dwDomainName,
        &eUse);

    *AcctName = (LPTSTR)GlobalAlloc(GMEM_FIXED, dwAcctName);
    *DomainName = (LPTSTR)GlobalAlloc(GMEM_FIXED, dwDomainName);

    success = LookupAccountSid(
        NULL,
        sid,
        *AcctName,
        (LPDWORD)&dwAcctName,
        *DomainName,
        (LPDWORD)&dwDomainName,
        &eUse);

    if (success) {
        _tprintf(TEXT("Username %s@%s\n"), *AcctName, *DomainName);
    }
    else {
        printf_s("LookupAccountSid failed with 0x%08x\n", GetLastError);
        return false;
    }

    return true;
}

int _tmain(int argc, _TCHAR* argv[])
{
    HRESULT status;
    HANDLE port;
    myapp_USER_MESSAGE msg;

    //
    //  Open a communication channel to the filter
    //

    printf("myapp-service: Connecting to the filter ...\n");

    status = FilterConnectCommunicationPort(myappPortName,
        0,
        NULL,
        0,
        NULL,
        &port);

    if (IS_ERROR(status)) {

        printf("ERROR: Connecting to filter port: 0x%08x\n", status);
        return 2;
    }

    //
    // Fetch messages & handle them
    //

    while (TRUE) {
        status = FilterGetMessage(port,
            &msg.MessageHeader,
            sizeof(msg),
            NULL
            );

        if (status == S_OK) {
            // Got a message successfully!

            // The problem is most likely with these two
            LPTSTR user = NULL;
            LPTSTR domain = NULL;

            if (getUser(msg.Message.Sid, &user, &domain)) {
                _tprintf(TEXT("Username %s@%s accessed %ls at %ls\n"), user, domain, &msg.Message.FileName, &msg.Message.TimeStamp);
            }
            else {
                printf("Unable to get user data!");
            };

            if (user) {
                GlobalFree(user);
            }
            if (domain) {
                GlobalFree(domain);
            }

        }
        else {
            printf("ERROR: GetMessage: 0x%08x\n", status);
        }

        printf("\n\n");
    }

    // 
    // Close the communication channel to the filter
    //

    printf("myapp-service: Closing connection ...\n");

    CloseHandle(&port);

    return 0;
}

Answer 1

LookupAccountSid的参数cchName和cchReferenceDomainName以 cch 为前缀(即 字符数)。在分配内存时你必须考虑到这一点，因为 GlobalAlloc取字节数:

*AcctName = (LPTSTR)GlobalAlloc(GMEM_FIXED, dwAcctName * sizeof(TCHAR));
*DomainName = (LPTSTR)GlobalAlloc(GMEM_FIXED, dwDomainName * sizeof(TCHAR));

您还应该在第一次调用之前对大小参数进行零初始化:

DWORD dwAcctName = 0x0;
DWORD dwDomainName = 0x0;

这在文档中有概述:

If the function fails because the buffer is too small or if cchName is zero, cchName receives the required buffer size, including the terminating null character.

---

顺便说一句:您的两个 printf_s 调用都将打印 GetLastError 的 地址，而不是它的返回值。您必须添加括号 ( GetLastError()) 才能调用函数。