blast · 2016/05/30 18:14
0x00 简介
事情得从一个报告说起，有人说网页map.yahoo.co.jp，在IE中进行打印预览时，使用倍率666%会让IE崩溃（至少2016-5-28为止还是这样），为什么IE中会出现这么6的问题呢？从打印预览这个功能看起吧。
0x01 打印预览（Web）
从网页的角度来看，负责打印预览的相关内容位于res://ieframe.dll/preview.dlg与res://ieframe.dll/preview.js。IE自5.5开始引入了打印预览以及自定义的打印预览功能。而微软的早期文档内容十分丰富，可以参考到很多有用信息。
在雅虎网站造成IE的崩溃中，一步不可缺少的操作是——设置缩放比例。所以，我们的关注点可以集中到缩放比率上。
在MSDN介绍自定义打印预览模板时，微软提到：“推荐使用一个DIV作为主容器”。在preview.dlg的LN253-256，可以看到MasterContainer，是一个DIV，这也与微软的推荐做法一致。
#!html
<div id="MasterContainer" tabindex="0" style="width:100%; position:absolute;" ><!-- Pages go here --><div id="EmptyPage" class="divPage" style="position:absolute; left:0px; top:0px; display:none;"><div class="page"> </div></div>
</div>
复制代码另外，还“推荐使用CSS的zoom属性来为主容器设置百分比的缩放”，这在preview.js中得到了良好的体现：
#!js
function PositionPages(nDispPage) {
……MasterContainer.style.zoom = g_nZoomLevel + "%";
……
复制代码与：
#!js
function ChangeZoom() {MasterContainer.style.zoom = g_nZoomLevel + "%";PositionPages(g_nDispPage);return g_nZoomLevel;
}
复制代码在了解了缩放功能进行缩放的方法之后，让我们再看一看页面是如何被转入预览中的。
在preview.js的CPrintDoc_AddPage()函数中，可以看到如下的代码注入到了MasterContainer的beforeEnd处。
#!js
newHTM = "<DIV class=divPage><IE:DeviceRect media=\"print\" class=page id=mDiv" + this._nStatus + this._strDoc + "p" + aPage.length + ">";
newHTM += "<IE:LAYOUTRECT id=mRect" + this._nStatus + this._strDoc + "p" + aRect.length;
newHTM += " class='" + classLayoutRect + "' nextRect=mRect" + this._nStatus + this._strDoc + "p" + (aRect.length + 1);
newHTM += " onlayoutcomplete=\"OnRectComplete('" + this._strDoc + "', " + g_ObsoleteBar + ")\"";
newHTM += " tabindex=-1 onbeforefocusenter='event.returnValue=false;' ";
newHTM += " />";
newHTM += "<DIV class='" + classHeader + "' id=header>";
newHTM += HeadFoot.HtmlHead;
newHTM += "</DIV>";
newHTM += "<DIV class='" + classFooter + "' id=footer>";
newHTM += HeadFoot.HtmlFoot;
newHTM += "</DIV>";
newHTM += "</IE:DeviceRect></DIV>";
MasterContainer.insertAdjacentHTML("beforeEnd", newHTM);
复制代码在上面的代码中可以看到一些特殊的元素。比如IE:DEVICERECT和IE:LAYOUTRECT。DeviceRect、LayoutRect两个元素用来组合展示页面。每个DeviceRect代表一个页面，
LayoutRect为DeviceRect的子元素，IE在它里面显示页面预览。因为preview.dlg指定了XML Namespace（<HTML XMLNS:IE>）所以元素前带有IE:前缀。
与其他元素不同的是，LayoutRect似乎并没有innerHTML属性。IE只是在里面展示页面的预览，页面并不能操作它。那么问题来了，IE怎么产生的预览？
0x02 打印预览窗口的创建
要知道这个，让我们先完整地跟踪整个流程。首先，因为打印预览是在res: protocol下的，之前的文章我们介绍了CResProtocol是处理Res Protocol的类，在DoParseAndBind上下断点可以观察到此处完整的调用（无关的栈已经删除）：
#!bash
0:058> bp MSHTML!CResProtocol::DoParseAndBind
0:牌058> g
Breakpoint 0 hit
eax=14061280 ebx=140611fc ecx=08101bd4 edx=1406127c esi=76c2f1fc edi=120ae270
eip=6474f8dd esp=120ae258 ebp=120ae290 iopl=0 nv up ei pl zr na pe nc
cs=0023 ss=002b ds=002b es=002b fs=0053 gs=002b efl=00000246
MSHTML!CResProtocol::DoParseAndBind:
6474f8dd 8bff mov edi,edi
0:058> kvn# ChildEBP RetAddr Args to Child
00 120ae254 647504d6 14061280 14061284 14061274 MSHTML!CResProtocol::DoParseAndBind (FPO: [4,163,4])
01 120ae268 64750495 120ae2b0 64750410 140611e0 MSHTML!CResProtocol::ParseAndBind+0x26 (FPO: [0,0,0])
02 120ae290 76c63067 140611fc 06e8c9f0 08109f38 MSHTML!CResProtocol::Start+0x88 (FPO: [6,5,4])
…………………………
10 120aeeb4 6467517a 120aeed0 00000000 00000000 MSHTML!CMarkup::Load+0x228 (FPO: [1,71,4])
11 120af26c 6479f0a1 120af2a0 00000000 00000000 MSHTML!CMarkup::LoadFromInfo+0xb07 (FPO: [Non-Fpo])
12 120af3b0 6479ebf4 120af3d8 00000000 120af490 MSHTML!CDoc::LoadFromInfo+0x48d (FPO: [Non-Fpo])
13 120af474 65075c07 03ea5400 00000001 081d4de0 MSHTML!CDoc::Load+0xd7 (FPO: [5,41,4])
14 120af5ec 650772d6 120af678 120af668 080940c8 MSHTML!CHTMLDlg::Create+0x869 (FPO: [Non-Fpo])
15 120af65c 6507e39d 00000000 10908ed0 00000000 MSHTML!InternalShowModalDialog+0x1c1 (FPO: [Non-Fpo])
16 120af718 6507e54d 120af770 6629d470 0000000b MSHTML!ModelessThreadInit+0x12f (FPO: [Non-Fpo])
……………………
复制代码根据15层栈可以知道该窗口是一个Modeless Window，那么这个调用是谁发起的呢？观察其他线程，可以发现下列调用栈（无关栈已经删除）：
#!bash
43 Id: 5404.3b18 Suspend: 1 Teb: 7ef7e000 Unfrozen
# ChildEBP
…………………………
06 10908f58 6507a498 1449d3c0 054b8f94 081a995c MSHTML!InternalModelessDialog+0x431 (FPO: [Non-Fpo])
07 10908fe8 6655f9b0 00a62528 081d4de0 000003e0 MSHTML!ShowHTMLDialogEx+0xa8 (FPO: [6,32,0])
08 109095b4 6649aafe 10909728 00000000 00000001 IEFRAME!CDocHostUIHandler::DoTemplatePrinting+0x31d (FPO: [Non-Fpo])
09 10909688 650587fb 08260e7c 6464d428 00000007 IEFRAME!`Microsoft::WRL::Module<1,Microsoft::WRL::Details::DefaultModule<1> >::Create'::`2'::`dynamic atexit destructor for 'module''+0x64146
0a 10909b94 648662de 0a4d2b40 00000000 00000000 MSHTML!CDoc::PrintHandler+0x73a (FPO: [Non-Fpo])
0b 1090a7a8 6464dea1 00000000 663d9884 000007d3 MSHTML!`CBackgroundInfo::Property<CBackgroundImage>'::`7'::`dynamic atexit destructor for 'fieldDefaultValue''+0xbdfbd
0c 1090a7c8 66562101 03ea3f00 663d9884 000007d3 MSHTML!CDoc::Exec+0x21 (FPO: [6,0,0])
0d 1090ba08 66568f04 080fd650 00000000 1090ba70 IEFRAME!CDocHostUIHandler::ShowContextMenu+0x98d (FPO: [5,1157,4])
0e 1090ba3c 64f4aaac 004bc898 00000000 1090ba70 IEFRAME!CDocObjectHost::ShowContextMenu+0xd4 (FPO: [Non-Fpo])
0f 1090ba80 64f7ed1f 00000123 000000d7 00000000 MSHTML!CDoc::ShowContextMenu+0x137 (FPO: [4,7,4])
10 1090ba9c 64f7dbe6 00000123 000000d7 00000000 MSHTML!CElement::ShowContextMenu+0x1f (FPO: [Non-Fpo])
11 1090bc00 64eb5e79 1090bd78 00000000 64647180 MSHTML!CElement::OnContextMenu+0x17b (FPO: [2,81,4])
12 1090bc50 64bb244c 0a58da40 1090bd78 1090bd78 MSHTML!`CBackgroundInfo::Property<CBackgroundImage>'::`7'::`dynamic atexit destructor for 'fieldDefaultValue''+0xb62fa
13 1090bc70 645c789e 0a58da40 1090bd78 03ea3f00 MSHTML!CElement::HandleMessage+0xc2 (FPO: [Non-Fpo])
14 1090bc90 645c7430 14054840 0000007b 03ea3f00 MSHTML!CElement::HandleWindowMessage+0x6b (FPO: [Non-Fpo])
15 1090bd1c 647e7558 1090bd78 14054840 00000000 MSHTML!CDoc::PumpMessage+0x638 (FPO: [3,29,4])
16 1090be94 64cee296 0000007b 00a62528 00d70123 MSHTML!CDoc::OnMouseMessage+0x2b4 (FPO: [7,85,4])
…………………………
复制代码可以发现
- MSHTML!CDoc::PrintHandler处理了相关的打印请求；
- 最终页面启动了一个新IE窗口用来加载res://ieframe.dll/preview.dlg（IEFRAME!CDocHostUIHandler::DoTemplatePrinting → MSHTML!ShowHTMLDialogEx）。
0x03 CDoc::PrintHandler
有了之前的结论之后，首先来观察MSHTML!CDoc::PrintHandler。在IDA中打开MSHTML.DLL，定位到CDoc::PrintHandler后查看伪代码（下为Win7+IE11的结果）。
首先CDoc::PrintHandler检查指定的CLSID是否被支持。下伪代码实际含义pCommandTarget->Exec(&CGID_DocHostCommandHandler, a10（即：guid）, a7, &varIn （即：v73）, &varOut （即：v67）); 。
#!cpp
if ( pCommandTarget && a7 != 2 && !(*(_DWORD *)(v10 + 3584) & 0x400000) )
{hr = (*(int (__stdcall **)(int, const GUID *, int, int, int, int *))(*(_DWORD *)pCommandTarget + 16))(pCommandTarget,&CGID_DocHostCommandHandler,(a10 != 0) + 6,a7,v73,v67);v11 = hr;if ( hr != OLECMDERR_E_NOTSUPPORTED && hr != OLECMDERR_E_UNKNOWNGROUP && hr != OLECMDERR_E_DISABLED)goto Cleanup;v12 = v72;
}
复制代码接着，程序寻找是否有alternative print source，也即由<link>元素的REL=alternate MEDIA=print指定的其他可选打印源。如果没有，做一些简单的字符串处理工作：
#!cpp
if ( !CDoc::GetAlternatePrintDoc((const unsigned __int16 *)v71, v12, (unsigned __int16 *)&v78, v12) ){v16 = &v78;do{v17 = *(_WORD *)v16;v16 += 2;}while ( v17 != (_WORD)v69 ); //wcslenif ( (signed int)(v16 - (char *)&v79) >> 1 ){v15 = (int)&v78;v71 = (int)&v78;
LABEL_14:if ( !RatingEnabledQuery() ){v11 = 0x80004005u;goto Cleanup;}goto LABEL_16;}}
复制代码再接下来是一个比较长的函数段。首先程序判断是否有可打印的plugin site。例如acrobat pdf都算是这种。然后发送“Print”请求。MSDN解释是“用默认模版或自定义模版”来打印（msdn.microsoft.com/en-us/libra…）。
#!cpp
v73 = 0;
if( !CDoc::GetPlugInSiteForPrinting(v72, &v73) )
{v18 = v73;if ( a10 ){v11 = -2147467259;}else{memset(&v50, 0, 0x20u);v69 = 0;Cookie = 0;//发送IDM_PRINT请求v11 = (*(int (__stdcall **)(int, GUID *, wchar_t **, signed int, LCID, ULONG_PTR *))(*(_DWORD *)v73 + 20))(v73,&GUID_NULL,&off_6449DFC0, //"Print"1,g_lcidUserDefault,&Cookie);if ( v11 ){FreeEXCEPINFO(v46);goto LABEL_70;}VariantInit(&pvarg);v55 = 0;v53 = 0;v54 = 0;//v11 = (*(int (__stdcall **)(int, ULONG_PTR, GUID *, LCID, signed int, char *, VARIANTARG *, char *, int *))(*(_DWORD *)v18 + 24))(v18,Cookie,&GUID_NULL,g_lcidUserDefault,1,&v52,&pvarg,&v50,&v69);VariantClear(&pvarg);FreeEXCEPINFO(v46);}
LABEL_69:ReleaseInterface((struct IUnknown *)v46);goto LABEL_70;
}
复制代码然后，可以看到PrintHandler将当前页面保存到了临时目录下。
#!cpp
CDoc::PrintHandler(CDocument *,ushort const *,ushort const *,ulong,tagSAFEARRAY *,ulong,tagVARIANT *,tagVARIANT *,int)
{......if ( !v71 ){CDoc::SetTempFileTracking(1);Cookie = CDoc::HasTextSelection(v10);CDoc::SaveToTempFileForPrint(v72,&v78,260u,Cookie != 0 ? (int)&v77 : 0,Cookie != 0 ? 0x104 : 0,Cookie != 0 ? (int)&v77 : 0);CDoc::TransferTempFileList(&v56);CDoc::SetTempFileTracking(0);v71 = (int)&v78;}......
复制代码随后，SetPrintCommandParameters、SetPrintManagerCommandParameters用来设置打印参数，先跳过不看，之后有一个关键操作CreateHTMLDocSource，则是负责弹出打印窗口的主人公。
#!cpp
v11 = CreateHTMLDocSource(v61, v39, v40, v38, (struct IInspectable **)v48, v49);
复制代码0x04 CreateHTMLDocSource
CreateHTMLDocSource代码简单明了，列举如下：
#!cpp
HRESULT __fastcall CreateHTMLDocSource(int a1, int a2, int a3, struct IWebPlatformHostSecurityManagerFactory *a4, struct IInspectable **a5, bool a6)
{HRESULT v6; // [email protected]int v8; // [sp+4h] [bp-4h]@1v8 = 0;v6 = HTMLDocumentSource::Create((int)&v8, a1, a2, (char)a4);if ( v6 >= 0 )v6 = HTMLDocumentSource::QueryInterface(v8, &_GUID_af86e2e0_b12d_4c6a_9c5a_d7aa65101e90, a3);TSmartPointer<HTMLDocumentSource>::_TSmartPointer<HTMLDocumentSource>(&v8);return v6;
}
复制代码调用HTMLDocumentSource::Create并QueryInterface并返回在参数a3中。查看HTMLDocumentSource::Create的代码，也是一个短小的函数：
#!cpp
HRESULT __fastcall HTMLDocumentSource::Create(int a1, int a2, int a3, char a4)
{int v4; // [email protected]int v5; // [email protected]LPVOID v6; // [email protected]int v7; // [email protected]HRESULT v8; // [email protected]int v10; // [sp+Ch] [bp-4h]@4v4 = a2;v5 = a1;v6 = HeapAlloc(g_hProcessHeap, 0, 0x60u);if ( v6 )v7 = HTMLDocumentSource::HTMLDocumentSource(v6);elsev7 = 0;v10 = v7;if ( v7 ){v8 = HTMLDocumentSource::_Initialize((void *)v7, v4, a3, a4);if ( v8 >= 0 ){v10 = 0;*(_DWORD *)v5 = v7;}}else{v8 = -2147024882;}TSmartPointer<HTMLDocumentSource>::_TSmartPointer<HTMLDocumentSource>(&v10);return v8;
}
复制代码函数创建HTMLDocumentSource类，并调用_Initialize函数进行初始化。构造函数的代码简单易懂，全部都是赋初值的，跳过不叙述了。接下来查看_Initialize。
_Initialize是一个较长的函数，但是逻辑较为清晰，我把所有IDA没有识别出的guid等全部以注释的形式标记了。该函数先获取了IHTMLEventObj2接口，然后识别环境并设置浏览模式为__IE_Immersive（Win8 Immersive Mode），若Immersive Mode生效，再设置成__IE_ShrinkToFit（Shrink to fit模式，该模式下浏览器自动将页面收缩成方便打印的大小）模式。
然后，调用PrintManagerOptions::Create。这个操作将创建一个PrintManagerOptions对象，并调用其_Initialize方法，干的事情也就是拿到它的IUnkonwn接口，所以这块我们也跳过。
接下来，IE试图打开“res://ieframe.dll/preview.dlg”，很熟悉的字眼。告知该处理程序临时文件位置等设置。
#!cpp
HRESULT __thiscall HTMLDocumentSource::_Initialize(void *this, int a2, int a3, char a4)
{int v4; // [email protected]LPVOID *v5; // [email protected]HRESULT v6; // [email protected]int v7; // [email protected]IUnknown *v8; // [email protected]LPUNKNOWN *v9; // [email protected]int v10; // [email protected]int v11; // [email protected]int v12; // [email protected]const WCHAR *v13; // [email protected]BSTR v14; // [email protected]LPMONIKER v15; // [email protected]struct IMonikerVtbl *v16; // [email protected]LONG v18; // [sp-4h] [bp-130h]@23struct HTMLDLGINFO *v19; // [sp+0h] [bp-12Ch]@24int v20; // [sp+4h] [bp-128h]@24int Dst; // [sp+10h] [bp-11Ch]@24LPMONIKER v22; // [sp+14h] [bp-118h]@24VARIANTARG *v23; // [sp+20h] [bp-10Ch]@24char v24; // [sp+28h] [bp-104h]@26int *v25; // [sp+2Ch] [bp-100h]@24int v26; // [sp+30h] [bp-FCh]@24char v27; // [sp+38h] [bp-F4h]@26int v28; // [sp+48h] [bp-E4h]@24int v29; // [sp+60h] [bp-CCh]@24int v30; // [sp+70h] [bp-BCh]@24int v31; // [sp+74h] [bp-B8h]@24int v32; // [sp+78h] [bp-B4h]@24int v33; // [sp+7Ch] [bp-B0h]@24BSTR v34; // [sp+80h] [bp-ACh]@24int v35; // [sp+84h] [bp-A8h]@24VARIANTARG pvargSrc; // [sp+88h] [bp-A4h]@14int v37; // [sp+98h] [bp-94h]@5int v38; // [sp+9Ch] [bp-90h]@5int v39; // [sp+A0h] [bp-8Ch]@5int v40; // [sp+A4h] [bp-88h]@5int v41; // [sp+A8h] [bp-84h]@14int v42; // [sp+ACh] [bp-80h]@14LPCWSTR szURL; // [sp+B0h] [bp-7Ch]@14int v44; // [sp+B4h] [bp-78h]@14int *v45; // [sp+B8h] [bp-74h]@13int v46; // [sp+BCh] [bp-70h]@1VARIANTARG pvarg; // [sp+C0h] [bp-6Ch]@8LPUNKNOWN punkOuter; // [sp+D4h] [bp-58h]@1void *v49; // [sp+D8h] [bp-54h]@1LPMONIKER ppmk; // [sp+DCh] [bp-50h]@21LONG v51; // [sp+E0h] [bp-4Ch]@4char v52; // [sp+E7h] [bp-45h]@5char v53; // [sp+E8h] [bp-44h]@14unsigned int v54; // [sp+124h] [bp-8h]@1int v55; // [sp+12Ch] [bp+0h]@1v54 = (unsigned int)&v55 ^ __security_cookie;punkOuter = 0;v4 = (int)this;v46 = a3;v49 = this;v5 = (LPVOID *)TSmartPointer<CDCompLayer>::operator_((char *)this + 52);v6 = CoCreateInstance(&CLSID_StdGlobalInterfaceTable, 0, 1u, &_GUID_00000146_0000_0000_c000_000000000046, v5); //guid of IGlobalInterfaceTableif ( v6 >= 0 ){v7 = TSmartPointer<CDCompLayer>::operator_(&punkOuter);v6 = HTMLDocumentSource::QueryInterface(v4, &_GUID_00000000_0000_0000_c000_000000000046, v7); //querying IID_IUnknownif ( v6 >= 0 ){v8 = punkOuter;v9 = (LPUNKNOWN *)TSmartPointer<CDCompLayer>::operator_(v4 + 56);v6 = CoCreateFreeThreadedMarshaler(v8, v9);if ( v6 >= 0 ){v51 = 0;v10 = TSmartPointer<IDispEffectConvolveMatrix>::operator_(&v51);v6 = (**(int (__stdcall ***)(int, GUID *, int))a2)(a2, &_GUID_3050f48b_98b5_11cf_bb82_00aa00bdce0b, v10); //getting IHTMLEventObj2if ( v6 >= 0 ){v52 = 1;v37 = 0;v38 = 0;v39 = 0;v40 = 0;if ( (*(int (__stdcall **)(LONG, _DWORD, _DWORD, int *))(*(_DWORD *)v51 + 32))(v51,L"__IE_Immersive",0,&v37) >= 0&& (_WORD)v37 == 11&& -1 == (_WORD)v39 ){*(_QWORD *)&pvarg.vt = 0i64;*(_QWORD *)&pvarg.lVal = 0i64;if ( (*(int (__stdcall **)(LONG, _DWORD, _DWORD, VARIANTARG *))(*(_DWORD *)v51 + 32))(v51,L"__IE_ShrinkToFit",0,&pvarg) < 0|| pvarg.vt != 11|| (v52 = 1, -1 != LOWORD(pvarg.lVal)) )v52 = 0;VariantClear(&pvarg);}v45 = (int *)((char *)v49 + 60);v11 = TSmartPointer<PrintManagerOptions>::operator_((char *)v49 + 60);LOBYTE(v12) = v52;v6 = PrintManagerOptions::Create(v12, v11);if ( v6 >= 0 ){v41 = 0;v42 = 0;szURL = 0;v44 = 0;memcpy(&v53, L"res://ieframe.dll/preview.dlg", 0x3Cu);*(_QWORD *)&pvargSrc.vt = 0i64;*(_QWORD *)&pvargSrc.lVal = 0i64;if ( (*(int (__stdcall **)(LONG, _DWORD, _DWORD, VARIANTARG *))(*(_DWORD *)v51 + 32))(v51,L"__IE_TemporaryFiles",0,&pvargSrc) >= 0&& pvargSrc.vt == 8200 )VariantCopy((VARIANTARG *)((char *)v49 + 72), &pvargSrc);if ( (*(int (__stdcall **)(_DWORD, _DWORD, _DWORD, int *))(*(_DWORD *)v51 + 32))(v51,L"__IE_TemplateUrl",0,&v41) < 0|| (_WORD)v41 != 8|| (v13 = szURL) == 0 )v13 = (const WCHAR *)&v53;ppmk = 0;v6 = CreateURLMonikerEx(0, v13, &ppmk, 1u);if ( v6 >= 0 ){*(_QWORD *)&pvarg.vt = 0i64;*(_QWORD *)&pvarg.lVal = 0i64;pvarg.vt = 13;v6 = PrintManagerOptions::QueryInterface(*v45,&_GUID_00000000_0000_0000_c000_000000000046,(int)&pvarg.lVal);if ( v6 >= 0 ){v18 = 0;v6 = (*(int (__stdcall **)(LONG, _DWORD, _DWORD, _DWORD, LONG, _DWORD, _DWORD))(*(_DWORD *)v51 + 28))(v51,L"__PE_PrintManagerOptions",*(_DWORD *)&pvarg,*(_DWORD *)&pvarg.wReserved2,pvarg.lVal,HIDWORD(pvarg.dblVal),0);if ( v6 >= 0 ){VariantClear(&pvarg);pvarg.vt = 13;pvarg.lVal = v51;v18 = v51;(*(void (__stdcall **)(LONG))(*(_DWORD *)v51 + 4))(v51);HTMLDLGINFO::HTMLDLGINFO(&Dst);v32 = 0;v33 = 0;v34 = 0;v35 = 0;LOWORD(v32) = 8;v14 = SysAllocString(0);Dst = 0;v29 = 0;v34 = v14;v22 = ppmk;v23 = &pvarg;v25 = &v32;v28 = 720;v26 = 1;v30 = 1;v31 = v46;v6 = InternalModelessDialog(v19, v20);if ( v6 >= 0 )*((_BYTE *)v49 + 88) = a4;VariantClear((VARIANTARG *)&v32);VariantClear((VARIANTARG *)&v27);CStr::_Free(&v24);}}VariantClear(&pvarg);}v15 = ppmk;ppmk = 0;if ( v15 ){v16 = v15->lpVtbl;v18 = (LONG)v15;v16->Release(v15);}VariantClear(&pvargSrc);VariantClear((VARIANTARG *)&v41);}VariantClear((VARIANTARG *)&v37);}TSmartPointer<IMFGetService>::_TSmartPointer<IMFGetService>(&v51);}}}TSmartPointer<IMFGetService>::_TSmartPointer<IMFGetService>(&punkOuter);return v6;
}
复制代码最后，通过InternalModelessDialog启动该窗口实现预览
#!cpp
HRESULT __usercall InternalModelessDialog<eax>(int a1<edx>, int a2<ecx>, HRESULT a3<esi>)
复制代码那么这个预览窗口中显示的文档和其他的到底有什么不同呢？根据MSDN文档的意思是：有点像禁止了Script的WebBrowser。代码将Layout当作一个容器来显示预览后的内容。在Modeless Window中，我们不能F12，不能呼出右键菜单，怎么办？我们有另一种方法——通过IE暴露的接口来取得整个窗口的DOM内容。
0x05 使用C++获取打印预览窗口的body.outerHTML
这个逻辑中，预览的窗口标题为“打印预览”。可以使用FindWindow找到对应的窗口并枚举出正确的Server窗口，或是使用Spy++找到窗口的HWND（因为这里我们并不是写一个通用的工具，所以怎么方便怎么来）。
注意目标窗口是Internet Explorer_Server而不是外层的Internet Explorer_TridentDlgFrame。这里使用的代码如下：
#!cpp
// prjFindPrintview.cpp : 定义控制台应用程序的入口点。
//#include "stdafx.h"
#include <Windows.h>
#include <mshtml.h>
#include <Exdisp.h>
#include <atlbase.h>
#include <SHLGUID.h>
#include <oleacc.h>
#include <comdef.h>
#include <tchar.h>
#pragma comment(lib, "Oleacc.lib")int _tmain(int argc, _TCHAR* argv[])
{::CoInitialize(NULL);HRESULT hr = S_OK;UINT nMsg = ::RegisterWindowMessage(_T("WM_HTML_GETOBJECT"));LRESULT lRes = 0;::SendMessageTimeout((HWND)0x000711FA, nMsg, 0L, 0L, SMTO_ABORTIFHUNG, 1000, (PDWORD)&lRes);CComPtr<IHTMLDocument2> spDoc;hr = ObjectFromLresult(lRes, IID_IHTMLDocument2, 0, (void**)&spDoc);if (FAILED(hr)) return -1;CComPtr<IHTMLElementCollection> spElementCollection;hr = spDoc->get_all(&spElementCollection);if (FAILED(hr)) return -2;long lElementCount;hr = spElementCollection->get_length(&lElementCount);if (FAILED(hr)) return -3;VARIANT vIndex; vIndex.vt = VT_I4;VARIANT vSubIndex; vSubIndex.vt = VT_I4; vSubIndex.lVal = 0;for (vIndex.lVal = 0; vIndex.lVal < lElementCount; vIndex.lVal++){CComPtr<IDispatch> spDispatchElement;if (FAILED(spElementCollection->item(vIndex, vSubIndex, &spDispatchElement)))continue;CComPtr<IHTMLElement> spElement;if (FAILED(spDispatchElement->QueryInterface(IID_IHTMLElement, (void**)&spElement)))continue;CComBSTR outerHTML;spElement->get_outerHTML(&outerHTML);OutputDebugStringW(outerHTML);}::CoUninitialize();return 0;
}
复制代码取得窗口的DOM如下：
将其输出到文件，自行添上</BODY></HTML>即为完整的内容。不过需要记得的是Layout等元素只在打印预览中有效，所以单独提取出来崩溃不了也不要太疑惑，这里只是为了方便了解预览中最终的DOM分布情况而已。
接下来，让我们复现崩溃吧。打开map.yahoo.co.jp，访问出现崩溃的代码，右键预览。只不过这次我们使用缓存文件的方式来精简代码。预览后，从%TEMP%下复制走所有新生成的HTM文件，然后调节打印预览的比例为666%。在确定仍然可以崩溃之后，让我们开始删除无用数据，记下异常偏移e9b102（在我的机器上是这个数字，因为有些崩溃在精简代码时可能变成其他的崩溃，所以最好记下偏移地址，以免中途不知道从什么位置产生了新问题）。多次精简之后，我们留下了下列代码：
#!html
<!DOCTYPE HTML>
<HTML><HEAD>
</HEAD>
<BODY>
<DIV style="left: -5000px; top: -5000px; width: 10000px; height: 10000px; text-align: justify; position: absolute; z-index: 0;"><svg
xmlns="http://www.w3.org/2000/svg" style="position: relative;" viewBox="0 0 10000 10000"
width="10000" height="10000" />
</DIV>
</BODY></HTML>
复制代码而且精简到这一步就可以发现，只要发起打印预览，IE就会直接崩溃。所以，为了让IE自动触发崩溃，我们手写一下调用print();即可。
#!html
<!DOCTYPE HTML>
<HTML><HEAD>
</HEAD>
<BODY>
<DIV style="left: -5000px; top: -5000px; width: 10000px; height: 10000px; text-align: justify; position: absolute; z-index: 0;"><svg
xmlns="http://www.w3.org/2000/svg" style="position: relative;" viewBox="0 0 10000 10000"
width="10000" height="10000" />
</DIV>
<script>print();</script>
</BODY></HTML>
复制代码跟随调试可以发现，崩溃位置维持不变：
#!bash
0:040> g
(24c8.2960): Access violation - code c0000005 (!!! second chance !!!)
eax=00000000 ebx=00000000 ecx=00000000 edx=00000000 esi=045c9220 edi=0a68eeac
eip=6537b102 esp=0a68eea4 ebp=0a68eeb8 iopl=0 nv up ei pl zr na pe nc
cs=0023 ss=002b ds=002b es=002b fs=0053 gs=002b efl=00010246
MSHTML!CDispParentNode::ComputeVisibleBoundsOnDirtySVGSubtree+0x16:
6537b102 8b33 mov esi,dword ptr [ebx] ds:002b:00000000=????????
复制代码接下来让我们看看打印预览窗口的DOM结构。因为DIV的STYLE属性是触发崩溃的关键条件之一，但是我们又想拿到预览窗口的DOM，所以我们得做一些改动，先手动删除部分STYLE，然后预览，这时，便可使用我们之前的程序抓出DOM。
篇幅考虑我就不扯淡再去看这个DOM了，直接以上述精简后的代码开始分析工作。
0x06 崩溃分析
在崩溃后查看崩溃栈如下：
#!bash
0:033> kvn# ChildEBP RetAddr Args to Child
00 0b2df530 64c7b6b7 0b2df75c 0b2df75c 64c7b63a MSHTML!CDispParentNode::ComputeVisibleBoundsOnDirtySVGSubtree+0x16 (FPO: [Non-Fpo])
01 0b2df774 645de05b 0b2df7bc 0b2df79a 0b2dfb3c MSHTML!`CBackgroundInfo::Property<CBackgroundImage>'::`7'::`dynamic atexit destructor for 'fieldDefaultValue''+0x2b2eb
02 0b2df860 64b4110c 0b2dfb3c 0b2dfb3c 0b2dfb3c MSHTML!Layout::FlowBoxBuilder::BuildBoxItem+0x89 (FPO: [1,51,4])
03 0b2df87c 64b410d7 0b2dfb3c 0d82d0e0 0b2df8e4 MSHTML!Layout::LayoutBuilder::BuildBoxItem+0x2e (FPO: [Non-Fpo])
04 0b2df88c 64b40193 0b2dfb3c 0b2df908 64e657d0 MSHTML!Layout::LayoutBuilder::Move+0x57 (FPO: [Non-Fpo])
05 0b2df8e4 65358d8d 0d83264c 00000000 0d83264c MSHTML!Layout::LayoutBuilderDriver::BuildElementLayout+0xce (FPO: [Non-Fpo])
06 0b2df974 65359137 ffffffff 00000001 04c29ab4 MSHTML!Layout::MultiFragmentBoxBuilder::BuildCrossFragmentPositionedElement+0x1c3 (FPO: [Non-Fpo])
07 0b2df9d4 64ec4753 0b2dfa24 0d82d020 0d82cff0 MSHTML!Layout::MultiFragmentBoxBuilder::PositionAndArrangeCrossFragmentAbsolutePositionedElement+0x17e (FPO: [Non-Fpo])
08 0b2dfa2c 645d06b0 0d7e8ba0 04c29ab4 0b2dfb3c MSHTML!`CBackgroundInfo::Property<CBackgroundImage>'::`7'::`dynamic atexit destructor for 'fieldDefaultValue''+0xce2e3
09 0b2dfb14 645d72b9 0b2dfb3c 0b2dfb48 645d6ae0 MSHTML!Layout::PageCollection::LayoutPagesCore+0x37e (FPO: [Non-Fpo])
0a 0b2dfb40 65340900 65340760 0b2dfb88 0d832648 MSHTML!Layout::PageCollection::LayoutPages+0xca (FPO: [Non-Fpo])
0b 0b2dfb7c 64a9ec7e 00100000 04c29500 00000000 MSHTML!Layout::PageCollection::DoLayout+0x1a0 (FPO: [1,9,4])
0c 0b2dfbcc 64592161 00100000 64a7d7f0 00000000 MSHTML!CView::ExecuteLayoutTasks+0x159 (FPO: [Non-Fpo])
0d 0b2dfc24 64a7d840 00000000 64a7d7f0 0b2dfc54 MSHTML!CView::EnsureView+0x3bb (FPO: [1,15,4])
0e 0b2dfc44 64585813 04c29b38 00000000 00000001 MSHTML!CView::EnsureViewCallback+0x50 (FPO: [Non-Fpo])
0f 0b2dfc8c 6456d52c 3f72ceb5 00000000 6456cc90 MSHTML!GlobalWndOnMethodCall+0x17b (FPO: [Non-Fpo])
10 0b2dfce0 769f62fa 000825e0 00008002 00000000 MSHTML!GlobalWndProc+0x103 (FPO: [Non-Fpo])
11 0b2dfd0c 769f6d3a 6456cc90 000825e0 00008002 USER32!InternalCallWinProc+0x23
12 0b2dfd84 769f77c4 0539315c 6456cc90 000825e0 USER32!UserCallWinProcCheckWow+0x109 (FPO: [Non-Fpo])
13 0b2dfde4 769f788a 6456cc90 00000000 0b2dfe40 USER32!DispatchMessageWorker+0x3bc (FPO: [Non-Fpo])
14 0b2dfdf4 6507e640 0b2dfe24 0b2dfe4c 6629d470 USER32!DispatchMessageW+0xf (FPO: [Non-Fpo])
15 0b2dfe40 6ed93a31 05c7ab90 00000000 00000000 MSHTML!ModelessThreadProc+0x1a0 (FPO: [1,13,4])
复制代码MSHTML!CDispParentNode::ComputeVisibleBoundsOnDirtySVGSubtree是一个Thiscall，代码十分简单，就是调用自己一个成员函数：
#!cpp
int __thiscall CDispParentNode::ComputeVisibleBoundsOnDirtySVGSubtree(void *this, int a2, int a3, int a4, float a5)
{return (*(int (__stdcall **)(_DWORD, int, _DWORD, _DWORD, _DWORD, _DWORD))(*(_DWORD *)this + 216))(0,a3,0,0,LODWORD(a5),0);
}
复制代码查看函数代码，很明显，this指针为null。
#!bash
0:033> uf .
MSHTML!CDispParentNode::ComputeVisibleBoundsOnDirtySVGSubtree:
6537b0ec 8bff mov edi,edi
6537b0ee 55 push ebp
6537b0ef 8bec mov ebp,esp
6537b0f1 d94514 fld dword ptr [ebp+14h]
6537b0f4 33c0 xor eax,eax
6537b0f6 53 push ebx
6537b0f7 56 push esi
6537b0f8 57 push edi
6537b0f9 8bfc mov edi,esp
6537b0fb 8bd9 mov ebx,ecx ; ebx = ecx = this
6537b0fd 50 push eax
6537b0fe 51 push ecx
6537b0ff d91c24 fstp dword ptr [esp]
6537b102 8b33 mov esi,dword ptr [ebx] ; esi = *ebx
复制代码查看上一层
#!bash
0:033> ub .
MSHTML!`CBackgroundInfo::Property<CBackgroundImage>'::`7'::`dynamic atexit destructor for 'fieldDefaultValue''+0x2b2d4:
64c7b6a0 83ec08 sub esp,8
64c7b6a3 d95c2404 fstp dword ptr [esp+4]
64c7b6a7 51 push ecx
64c7b6a8 51 push ecx
64c7b6a9 8b08 mov ecx,dword ptr [eax]
64c7b6ab e8307699ff call MSHTML!Layout::LayoutBox::GetDisplayNodeAsParent (64612ce0)
64c7b6b0 8bc8 mov ecx,eax
64c7b6b2 e835fa6f00 call MSHTML!CDispParentNode::ComputeVisibleBoundsOnDirtySVGSubtree (6537b0ec)
复制代码很明显MSHTML!Layout::LayoutBox::GetDisplayNodeAsParent返回了NULL。
#!cpp
int __thiscall Layout::LayoutBox::GetDisplayNodeAsParent(void *this)
{int pThisVar; // [email protected]int nResult; // [email protected]int v3; // [email protected]int v4; // [email protected]int v5; // [email protected]pThisVar = (*(int (**)(void))(*(_DWORD *)this + 788))();nResult = pThisVar;if ( !pThisVar )goto Cleanup;v3 = *(_DWORD *)(pThisVar + 28);v4 = pThisVar;if ( *(_BYTE *)(v3 + 56) & 1&& !*(_BYTE *)(*(_DWORD *)(__readfsdword(44) + 4 * LODWORD(_tls_index)) + 36)&& *(_DWORD *)(v3 + 4) != *(_DWORD *)(pThisVar + 8) ){v5 = *(_DWORD *)(pThisVar + 4);if ( !v5 )v5 = nResult;if ( v5 != nResult )v4 = v5;}if ( !(*(_BYTE *)(v4 + 21) & 0x20) ){
Cleanup:nResult = NULL;}return nResult;
}
复制代码可以简单跟踪一下代码看看到底是哪儿出现了问题。为了避免重复断到断点上（Layout的调用是十分频繁的），可以
bp MSHTML!ModelessThreadProc
复制代码触发后
bc 0
bp MSHTML!Layout::FlowBoxBuilder::BuildBoxItem
复制代码触发后
bc 0
bp MSHTML!Layout::LayoutBox::GetDisplayNodeAsParent
复制代码这样就没问题了
#!bash
0:031> g
Breakpoint 1 hit
eax=05618f80 ebx=0c07f060 ecx=0eebc4e0 edx=00000002 esi=0ee946e0 edi=0ee5ecb0
eip=64612ce0 esp=0c07f04c ebp=0c07f28c iopl=0 nv up ei pl nz ac po nc
cs=0023 ss=002b ds=002b es=002b fs=0053 gs=002b efl=00000212
MSHTML!Layout::LayoutBox::GetDisplayNodeAsParent:
64612ce0 8bff mov edi,edi
0:031> k
ChildEBP RetAddr
0c07f048 64c7b6b0 MSHTML!Layout::LayoutBox::GetDisplayNodeAsParent
0c07f28c 645de05b MSHTML!`CBackgroundInfo::Property<CBackgroundImage>'::`7'::`dynamic atexit destructor for 'fieldDefaultValue''+0x2b2e4
0c07f378 64b4110c MSHTML!Layout::FlowBoxBuilder::BuildBoxItem+0x89
0c07f394 64b410d7 MSHTML!Layout::LayoutBuilder::BuildBoxItem+0x2e
0c07f3a4 64b40193 MSHTML!Layout::LayoutBuilder::Move+0x57
0c07f3fc 65358d8d MSHTML!Layout::LayoutBuilderDriver::BuildElementLayout+0xce
复制代码再度跟踪可以发现是
#!cpp
pThisVar = (*(int (**)(void))(*(_DWORD *)this + 788))();// MSHTML!Layout::SvgBox::GetDisplayNode //returns null
nResult = pThisVar;
if ( !pThisVar )goto Cleanup; //return NULL(0);
复制代码查看GetDisplayNode，很明显，校验失败，返回了0.
#!cpp
int __thiscall Layout::SvgBox::GetDisplayNode(int this)
{int result; // [email protected]if ( !(*(_BYTE *)(this + 56) & 4) || *(_BYTE *)(*(_DWORD *)(__readfsdword(44) + 4 * LODWORD(_tls_index)) + 36) )result = *(_DWORD *)(this + 16);elseresult = 0;return result;
}
复制代码加上对内存的跟踪，我们可以断定这是一个空指针问题。不过这倒也给了一个提醒——是否一些在网页内不能触发的问题，通过打印预览就又可以做了呢？Fuzzer看来也可以加上这个策略，试一试打印预览是否健壮。