微软Windows FastFAT.sys FAT分区拒绝服务漏洞重现

还记得去年的MS14-063 FAT32驱动内核溢出漏洞么?今天出续集了,但是这一次是在FAT12分区。

演示视频

分析

– 受影响系统

从Windows NT到Windows 7 SP1

– 我测试的机型

* Windows XP SP3 x86  * Windows 7 SP1 x86/x64

BUG重现:创建FAT12分区并在0×16(Sectors per FAT)设置一个WORD,例如0×3000

注意:值不要超过0x3FFF

查阅Loopback Device资料建议,并且建议设置参数bs=512 count=32067

镜像可为空

细节:在FAT12引导扇区中“Sectors per FAT”字段中的值发生错误,导致在FAT1分区映射到缓存期间尝试读取未分配的内存区域。

错误的分区显示如下:

微软Windows FastFAT.sys FAT分区拒绝服务漏洞重现

崩溃

Windows 7 SP1 x86

kd> !analyze -v  *******************************************************************************  *                                                                             *  *                        Bugcheck Analysis                                    *  *                                                                             *  *******************************************************************************     PAGE_FAULT_IN_NONPAGED_AREA (50)  Invalid system memory was referenced.  This cannot be protected by try-except,  it must be protected by a Probe.  Typically the address is just plain bad or it  is pointing at freed memory.  Arguments:  Arg1: a3f00000, memory referenced.  Arg2: 00000000, value 0 = read operation, 1 = write operation.  Arg3: 82a6a05e, If non-zero, the instruction address which referenced the bad memory      address.  Arg4: 00000000, (reserved)     Debugging Details:  ------------------        READ_ADDRESS:  a3f00000     FAULTING_IP:  nt!CcMapData+ae  82a6a05e 8a0e            mov     cl,byte ptr [esi]     MM_INTERNAL_CODE:  0  DEFAULT_BUCKET_ID:  WIN7_DRIVER_FAULT  BUGCHECK_STR:  0x50  PROCESS_NAME:  explorer.exe  CURRENT_IRQL:  2     TRAP_FRAME:  a2447414 -- (.trap 0xffffffffa2447414)  ErrCode = 00000000  eax=000006e2 ebx=86eb8b98 ecx=a2447400 edx=00000011 esi=a3f00000 edi=0000000f  eip=82a6a05e esp=a2447488 ebp=a24474c8 iopl=0         nv up ei pl nz ac po nc  cs=0008  ss=0010  ds=0023  es=0023  fs=0030  gs=0000             efl=00010212  nt!CcMapData+0xae:  82a6a05e 8a0e            mov     cl,byte ptr [esi]          ds:0023:a3f00000=??  Resetting default scope     LAST_CONTROL_TRANSFER:  from 82916d5f to 828b27b8     STACK_TEXT:   a2446f64 82916d5f 00000003 6641e18b 00000065 nt!RtlpBreakWithStatusInstruction  a2446fb4 8291785d 00000003 00000000 00082982 nt!KiBugCheckDebugBreak+0x1c  a2447378 828c5879 00000050 a3f00000 00000000 nt!KeBugCheck2+0x68b  a24473fc 82878aa8 00000000 a3f00000 00000000 nt!MmAccessFault+0x104  a24473fc 82a6a05e 00000000 a3f00000 00000000 nt!KiTrap0E+0xdc  a24474c8 975dbb32 86e819c0 004474ec 00721e00 nt!CcMapData+0xae  a24474f4 975d9e1d a2b52fb8 85dad920 00001000 fastfat!FatReadVolumeFile+0x3a  a2447580 975da534 a2b52fb8 a2447524 00000002 fastfat!FatExamineFatEntries+0x11f  a24475e8 975ecd64 a2b52fb8 85dad920 3519a638 fastfat!FatSetupAllocationSupport+0x38a  a2447774 975ee3cf a2b52fb8 8a9b0da8 a3392fa8 fastfat!FatMountVolume+0x418  a2447794 975ee478 a2b52fb8 93528e90 3519a6ac fastfat!FatCommonFileSystemControl+0x3f  a24477e0 82b696c3 82275620 93528e90 93528e90 fastfat!FatFsdFileSystemControl+0x82  a2447804 8286ebd5 00000001 93528ff4 82275620 nt!IovCallDriver+0x258  a2447818 85499a56 270d61d5 8229bde8 93528e90 nt!IofCallDriver+0x1b  a2447878 85499c5b 8229bde8 93528e90 86f2c678 fltmgr!FltpFsControlMountVolume+0x180  a24478a8 82b696c3 8229bde8 93528e90 93528e90 fltmgr!FltpFsControl+0x5b  a24478cc 8286ebd5 00000001 8296fb88 8229bde8 nt!IovCallDriver+0x258  a24478e0 829d1dd9 82804870 8a9b0da8 82804900 nt!IofCallDriver+0x1b  a2447944 828df92e 8a9b0da8 85dac000 00000000 nt!IopMountVolume+0x1d8  a244797c 82a7ddfb 85dac008 a2447aa8 a2447a40 nt!IopCheckVpbMounted+0x64  a2447a60 82a5dd1e 8a9b0da8 851cfde8 85d66750 nt!IopParseDevice+0x7db  a2447adc 82a6e147 00000000 a2447b30 00000040 nt!ObpLookupObjectName+0x4fa  a2447b38 82a64c25 02effc44 851cfde8 828b1d01 nt!ObOpenObjectByName+0x165  a2447bb4 82a884a4 02effca0 00100081 02effc44 nt!IopCreateFile+0x673  a2447c00 828758c6 02effca0 00100081 02effc44 nt!NtCreateFile+0x34  a2447c00 776170f4 02effca0 00100081 02effc44 nt!KiSystemServicePostCall  02effc00 77615614 7573a9d9 02effca0 00100081 ntdll!KiFastSystemCallRet  02effc04 7573a9d9 02effca0 00100081 02effc44 ntdll!ZwCreateFile+0xc  02effca8 772ce99f 00004000 00100081 00000007 KERNELBASE!CreateFileW+0x35e  02effcd4 761a2fc5 03cc0038 00000001 00000007 kernel32!CreateFileWImplementation+0x69  02effd38 761a2bc9 03cc0038 00000001 00000000 SHELL32!CLocalInterruptSource::v_CreateEvent+0x41  02effd5c 761aac0f 0368f598 00000000 02effd94 SHELL32!CFSInterruptSource::GetEvent+0x7b  02effd9c 761aa92a 02effdc0 00000000 006e7a90 SHELL32!CChangeNotify::_GetInterruptEvents+0x93  02effdc8 7611561b 00000000 00000000 00000067 SHELL32!CChangeNotify::_MessagePump+0x67  02effde0 75fd43c0 006e7a90 00000000 00000000 SHELL32!CChangeNotify::s_ThreadProc+0x4f  02effe68 772cee1c 0201ed74 02effeb4 776337eb SHLWAPI!WrapperThreadProc+0x1b5  02effe74 776337eb 0201ed74 758640f9 00000000 kernel32!BaseThreadInitThunk+0xe  02effeb4 776337be 75fd42ed 0201ed74 00000000 ntdll!__RtlUserThreadStart+0x70  02effecc 00000000 75fd42ed 0201ed74 00000000 ntdll!_RtlUserThreadStart+0x1b        STACK_COMMAND:  kb     FOLLOWUP_IP:  nt!CcMapData+ae  82a6a05e 8a0e            mov     cl,byte ptr [esi]     SYMBOL_STACK_INDEX:  5  SYMBOL_NAME:  nt!CcMapData+ae  FOLLOWUP_NAME:  MachineOwner  MODULE_NAME: nt  IMAGE_NAME:  ntkrpamp.exe  DEBUG_FLR_IMAGE_TIMESTAMP:  521e9cb6  FAILURE_BUCKET_ID:  0x50_VRF_nt!CcMapData+ae  BUCKET_ID:  0x50_VRF_nt!CcMapData+ae  Followup: MachineOwner  ---------

漏洞代码:

/wrk-v1.2/base/ntos/cache/pinsup.c

Line 72:  BOOLEAN  CcMapData (      __in PFILE_OBJECT FileObject,      __in PLARGE_INTEGER FileOffset,      __in ULONG Length,      __in ULONG Flags,      __out PVOID *Bcb,      __deref_out_bcount(Length) PVOID *Buffer      )  ...     Line 155:      ULONG PageCount = ADDRESS_AND_SIZE_TO_SPAN_PAGES((ULongToPtr(FileOffset->LowPart)), Length);      PETHREAD Thread = PsGetCurrentThread();      BOOLEAN ReturnStatus;         DebugTrace(+1, me, "CcMapData/n", 0 );         MmSavePageFaultReadAhead( Thread, &SavedState );         ReturnStatus = CcMapDataCommon( FileObject,                                      FileOffset,                                      Length,                                      Flags,                                      &TempBcb,                                      Buffer );  ...  Line 193              //              //  Loop to touch each page              //                 BaseAddress = *Buffer;                 while (PageCount != 0) {                     MmSetPageFaultReadAhead( Thread, PageCount - 1 );                     ch = *((volatile UCHAR *)(BaseAddress));   // <----------   CRASH!!!!                     BaseAddress = (PCHAR) BaseAddress + PAGE_SIZE;                  PageCount -= 1;              }

PageCount基于控制长度值进行计算,在这种情况下(读取FATx)包括:

Sectors per FAT * Bytes per sector

kd> . frame /c 5  kd> dd ebp+10 L1 //get Length value  f53e1510  00721e00  kd> ?00721e00 / 0x200(= Bytes per sector)  Evaluate expression: 14607 = 0000390f (= Sectors per FAT)

FileOffset也就等于:

kd> dt _LARGE_INTEGER poi(ebp+c)  nt!_LARGE_INTEGER   0x200     +0x000 LowPart          : 0x200     +0x004 HighPart         : 0     +0x000 u                : __unnamed     +0x000 QuadPart         : 512

调用PageCount计算的这些值:

Evaluate expression: 1826 = 00000722

while迭代循环,通过PAGE_SIZE增加BaseAddress指针。所以在这种情况下内存区域会被“覆盖”:

kd> ?(0x722 * 0x1000) / 0x400  ------------^-----------^----------^----  PageCount     PAGE_SIZE     1KB     Evaluate expression: 7304 = 00001c88  kd> ?00001c88 / 0x400  Evaluate expression: 7 = 00000007   ~   7MB

接下来检测一下我们能够缓存多少字节:

/wrk-v1.2/base/ntos/cache/pinsup.c

Line 241:  BOOLEAN  CcMapDataCommon (      IN PFILE_OBJECT FileObject,      IN PLARGE_INTEGER FileOffset,      IN ULONG Length,      IN ULONG Flags,      OUT PVOID *Bcb,      OUT PVOID *Buffer      )     ...  Line 350:      //      //  Get pointer to SharedCacheMap.      //         SharedCacheMap = FileObject->SectionObjectPointer->SharedCacheMap;         //      //  Call local routine to Map or Access the file data.  If we cannot map      //  the data because of a Wait condition, return FALSE.      //         if (FlagOn(Flags, MAP_WAIT)) {             *Buffer = CcGetVirtualAddress( SharedCacheMap,                                         *FileOffset,                                         (PVACB *)&TempBcb,                                         &ReceivedLength );             ASSERT( ReceivedLength >= Length ); // maybe convert it to IF ?         }

在CcGetVirtualAddress中检测ReceiveLength:

/wrk-v1.2/base/ntos/cache/vacbsup.c

Line 388:  ULONG VacbOffset = FileOffset.LowPart & (VACB_MAPPING_GRANULARITY - 1);  ...  Line  449:  *ReceivedLength = VACB_MAPPING_GRANULARITY - VacbOffset;

VACB_MAPPING_GRANULARITY的值是多少?

/wrk-v1.2/base/ntos/inc/cache.h

Line 31:  #define VACB_MAPPING_GRANULARITY         (0x40000)

从上面的代码片段中获知ReceiveLength应该是大于等于0×40000 bytes也就是256KB.

MSDN CcMapData

微软官方CcMapData文档[点我]

在缓存管理器中CcMapData无法通过视图边界映射数据,系统缓存管理器中的文件标准大小为256 KB(缓存管理器的视图的大小是通过系统定义常数VACB_MAPPING_GRANULARITY指定的,其大小在ntifs.h中设置为256 KB),映射区域不能超越256 KB。因此最大映射区域为256 KB,从文件中的偏移量从256 KB开始。

代码和文档都清晰的指出映射文件数据不能超过256 KB,在我们这个例子中内核大于有7M可用空间,迭代这个超过256 KB
会导致崩溃。

为何存在这个BUG

长度值缺少验证,会导致这个迭代无限循环

/wrk-v1.2/base/ntos/cache/pinsup.c

Line 198                 while (PageCount != 0) {                     MmSetPageFaultReadAhead( Thread, PageCount - 1 );                     ch = *((volatile UCHAR *)(BaseAddress));   // <----------   CRASH!!!!                     BaseAddress = (PCHAR) BaseAddress + PAGE_SIZE;                  PageCount -= 1;              }

超过可用映射/分配区域

并非每次都触发

在实验中我发现不是每一个Sectors per FAT的值都会超过0×0200从而导致崩溃,例如Sectors per FAT设置为0×4000就是一个例外!FatCommonRead:

堆栈跟踪:Sectors per FAT == 40 00

Windows XP SP3  ChildEBP RetAddr  Args to Child               bad46fc0 b7e0d505 86a69e50 bad46fec 804e24f1 Fastfat!FatExceptionFilter+0x5  bad46fcc 804e24f1 bad46ff4 00000000 bad46ff4 Fastfat!FatFsdRead+0x12b  bad46ff4 804db49a bad470d8 bad47518 bad47128 nt!_except_handler3+0x61  bad47018 804db46b bad470d8 bad47518 bad47128 nt!ExecuteHandler2+0x26  bad470c8 804dc6a1 bad470d8 bad47128 c000000d nt!ExecuteHandler+0x24  bad473fc b7e12fc4 c000000d 86a69e50 8667b888 nt!ExRaiseStatus+0xb5  bad474b8 b7e0d69a 86a69e50 8667b888 86a501e8 Fastfat!FatCommonRead+0x66b  bad47528 804e37f7 8686ba98 8667b888 00000000 Fastfat!FatFsdRead+0x13d  bad47538 804f95d8 00000000 86b01ad0 86b01ae0 nt!IopfCallDriver+0x31  bad4754c 804f95ff 8686ba98 86b01b08 86b01ae8 nt!IopPageReadInternal+0xf4  bad4756c 804f9264 86a501e8 86b01b08 86b01ae8 nt!IoPageRead+0x1b  bad475e0 804eba6a 0dead8c0 c7fc0000 c031ff00 nt!MiDispatchFault+0x274  bad47630 804e1718 00000000 c7fc0000 00000000 nt!MmAccessFault+0x5bc  bad47630 8056d716 00000000 c7fc0000 00000000 nt!KiTrap0E+0xcc  bad47708 b7e15b25 86a501e8 bad47734 00001000 nt!CcMapData+0xef  bad4773c b7e1e8b6 86a84e28 8698b3a8 00000000 Fastfat!FatReadDirectoryFile+0x92  bad47770 b7e137b7 86a84e28 8686bb90 bad47880 Fastfat!FatLocateVolumeLabel+0x7f  bad4790c b7e10a93 86a84e28 86b6a718 86bd3af0 Fastfat!FatMountVolume+0x49b  bad4792c b7e10a38 86a84e28 8690eaf0 8690ec78 Fastfat!FatCommonFileSystemControl+0x49  bad47978 804e37f7 86a2d928 8690eaf0 8690ec9c Fastfat!FatFsdFileSystemControl+0x85     EXCEPTION:  Fastfat!FatExceptionFilter+0x5:  b7e0d485 53              push    ebx  kd> .exr poi(poi(ebp+c))  ExceptionAddress: b7e12fc4 (Fastfat!FatCommonRead+0x0000066b)     ExceptionCode: c000000d  // STATUS_INVALID_PARAMETER     ExceptionFlags: 00000001  NumberParameters: 0

我并没有深入下去,当然也就无法指出在代码中哪个地方导致的这个例外。所以我猜测可能是已经存在一个长度验证,但是精准度还不够!

* 参考来源:Icewall,编译/FB小编鸢尾,转载请注明来自FreeBuf黑客与极客(FreeBuf.COM)

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