堆内存破坏检测实战--附完整调试过程

首先解释一下，什么是堆内存？

堆是一种常见的内存管理器，应用程序通过堆来动态地分配和释放内存，通常使用堆的情况是无法预先知道所需要的内存大小，或者申请内存太大，无法通过栈内存来自动分配，下面让我们再来看一段英文解释。

A heap is a form of memory manager that an application can use when it needs to allocate and free memory dynamically. Common situations that call for the use of a heap are when the size of the memory needed is not known ahead of time and the size of the memory is too large to neatly fit on the stack (automatic memory).

常见的情况是由于效率或特殊需求一个进程中同时使用几个堆，如下图：

下面通过一个完整的demo来带大家调试一个对破坏问题，demo代码如下：

#define SZ_MAX_LEN  10

void __cdecl wmain (int argc, WCHAR* args[])
{
    if(argc==2)
    {
        wprintf(L"Press any key to start
");
        _getch();
        DupString(args[1]);
    }
    else
    {
        wprintf(L"Please enter a string");
    }
}
BOOL DupString(WCHAR* psz)
{
    BOOL bRet=FALSE;
    
    if(psz!=NULL)
    {
        pszCopy=(WCHAR*) HeapAlloc(GetProcessHeap(), 0, SZ_MAX_LEN*sizeof(WCHAR));
        if(pszCopy)
        {
            wcscpy(pszCopy, psz);
            wprintf(L"Copy of string: %s", pszCopy);
            HeapFree(GetProcessHeap(), 0, pszCopy);
            bRet=TRUE;
        }
    }
    return bRet;

在应用程序验证器下启用普通页堆，配置gflags, 运行build出来的代码，

输入参数为：SolidmangoSolidmangoSolidmango

得到如下输出：

CommandLine: C:WinXP.x86.chk6overrun.exe SolidmangoSolidmangoSolidmango
Executable search path is: 
ModLoad: 01000000 01005000   06overrun.exe
ModLoad: 7c900000 7c9b2000   ntdll.dll
AVRF: 06overrun.exe: pid 0x120C: flags 0x8044B026: application verifier enabled
ModLoad: 5ad10000 5ad59000   C:WINDOWSSystem32verifier.dll
ModLoad: 10000000 10029000   C:WINDOWSSystem32vrfcore.dll
ModLoad: 003a0000 003dc000   C:WINDOWSSystem32vfbasics.dll
ModLoad: 7c800000 7c8f6000   C:WINDOWSsystem32kernel32.dll
AVRF: verifier.dll provider initialized for 06overrun.exe with flags 0x8044B026 
ModLoad: 77c10000 77c68000   C:WINDOWSsystem32msvcrt.dll
(120c.1700): Break instruction exception - code 80000003 (first chance)
eax=00391ec4 ebx=7ffd8000 ecx=00000004 edx=00000010 esi=00391f98 edi=00391ec4
eip=7c90120e esp=0006fb20 ebp=0006fc94 iopl=0         nv up ei pl nz na po nc
cs=001b  ss=0023  ds=0023  es=0023  fs=003b  gs=0000             efl=00000202
ntdll!DbgBreakPoint:
7c90120e cc              int     3
0:000> g0:000> g

我们会看到一个访问违例, 继续运行得到如下输出，说明应用程序验证器验证成功：

=======================================
VERIFIER STOP 00000008: pid 0x120C: Corrupted heap block. 

    00081000 : Heap handle used in the call.
    001E2B60 : Heap block involved in the operation.
    00000014 : Size of the heap block.
    00000000 : Reserved
=======================================
This verifier stop is not continuable. Process will be terminated 
when you use the `go' debugger command.
=======================================
(120c.1700): Break instruction exception - code 80000003 (first chance)
eax=1000e848 ebx=1000cd44 ecx=00000001 edx=0006f939 esi=00000000 edi=1000e848
eip=7c90120e esp=0006f9cc ebp=0006fbd0 iopl=0         nv up ei pl nz na po nc
cs=001b  ss=0023  ds=0023  es=0023  fs=003b  gs=0000             efl=00000202
ntdll!DbgBreakPoint:
7c90120e cc              int     3

继续调试，此时我们已经找到了出问题的堆快，注意观察上面的输出中有这样一条语句：

001E2B60 : Heap block involved in the operation，好的，让我们看看这个堆块里面是什么东西，

0:000> dt _DPH_BLOCK_INFORMATION 001E2B60-0x20
ntdll!_DPH_BLOCK_INFORMATION
   +0x000 StartStamp       : 0xabcdaaaa
   +0x004 Heap             : 0x80081000 Void
   +0x008 RequestedSize    : 0x14
   +0x00c ActualSize       : 0x3c
   +0x010 FreeQueue        : _LIST_ENTRY [ 0x1e - 0x0 ]
   +0x010 TraceIndex       : 0x1e
   +0x018 StackTrace       : 0x00286c3c Void
   +0x01c EndStamp         : 0xdcbaaaaa
0:000> dds 0x00286c3c //callstack
00286c3c  abcdaaaa
00286c40  00000001
00286c44  00000007
00286c48  00000001
00286c4c  00000014
00286c50  00081000
00286c54  00000000
00286c58  00286c5c
00286c5c  7c94b244 ntdll!RtlAllocateHeapSlowly+0x44
00286c60  7c919c0c ntdll!RtlAllocateHeap+0xe64
00286c64  003afd2c vfbasics!AVrfpRtlAllocateHeap+0xb1
00286c68  010012f4 06overrun!DupString+0x24 [c:awdchapter6overrunoverrun.cpp @ 41]
00286c6c  010012ab 06overrun!wmain+0x2b [c:awdchapter6overrunoverrun.cpp @ 28]
00286c70  010014b8 06overrun!__wmainCRTStartup+0x102 [d:vistartmasecrtscrtw32dllstuffcrtexe.c @ 711]
00286c74  7c817077 kernel32!BaseProcessStart+0x23
00286c78  00000000

我们找到了出问题的callstack:
0:000> kb
ChildEBP RetAddr  Args to Child              
0006f9c8 10003b68 10062cb0 00000008 001e2b60 ntdll!DbgBreakPoint
0006fbd0 100078c9 1000c540 00000008 00081000 vrfcore!VerifierStopMessageEx+0x4d1
0006fbf4 7c96c06e 00000008 7c96c314 00081000 vrfcore!VfCoreRedirectedStopMessage+0x81
0006fc70 7c96d147 00081000 00000004 001e2b60 ntdll!RtlpDphReportCorruptedBlock+0x17c
0006fc94 7c96d34a 00081000 01000002 00000010 ntdll!RtlpDphNormalHeapFree+0x2e
0006fce4 7c9703eb 00080000 01000002 001e2b60 ntdll!RtlpDebugPageHeapFree+0x79
0006fd58 7c94bafc 00080000 01000002 001e2b60 ntdll!RtlDebugFreeHeap+0x2c
0006fe40 7c91a1ba 00080000 01000002 001e2b60 ntdll!RtlFreeHeapSlowly+0x37
0006ff10 003afe9c 00080000 00000000 001e2b60 ntdll!RtlFreeHeap+0xf9
0006ff58 01001340 00080000 00000000 00000014 vfbasics!AVrfpRtlFreeHeap+0xf8
0006ff70 010012ab 00a64692 0006ffc0 010014b8 06overrun!DupString+0x70 [c:awdchapter6overrunoverrun.cpp @ 47]
0006ff7c 010014b8 00000002 00a64648 00a66e98 06overrun!wmain+0x2b [c:awdchapter6overrunoverrun.cpp @ 28]
0006ffc0 7c817077 00daf6ee 00daf784 7ffd8000 06overrun!__wmainCRTStartup+0x102 [d:vistartmasecrtscrtw32dllstuffcrtexe.c @ 711]
0006fff0 00000000 010015f6 00000000 78746341 kernel32!BaseProcessStart+0x23
0:000> du 00a64692 
00a64692  "SolidmangoSolidmangoSolidmango"

总结：

原来是我们的参数破坏了了堆内存，终于找到了根源，我们代码中定义的堆的大小为10，而我们使用的时候，由于堆块越界，破坏了堆块的完整性，从而导致了crash的发生..

注：本文的附图和代码灵感源自网络，具体出处不详，其他内容为原创..