一：背景
1. 讲故事
最近收到了两起程序崩溃的dump，查了下都是经典的 double free 造成的，蛮有意思，这里就抽一篇出来分享一下经验供后面的学习者避坑吧。
二：WinDbg 分析
1. 崩溃点在哪里
windbg 带了一个自动化分析命令 !analyze -v 可以帮助我们找到崩溃时的程序指令地址以及崩溃的代码，这对我们分析问题非常有帮助。
0:090> !analyze -v
*******************************************************************************
* *
* Exception Analysis *
* *
*******************************************************************************
CONTEXT: (.ecxr)
rax=00007ffec265d6e0 rbx=00000000c0000374 rcx=00000053653fe4f0
rdx=00007ffec1d3e9a0 rsi=0000000000000001 rdi=00007ffed7b827f0
rip=00007ffed7b1b349 rsp=00000053653fed10 rbp=000001c14fd20000
r8=000001c11957d9a0 r9=0000000000000033 r10=000001c453dbc7f0
r11=00007ffeb94db004 r12=0000000000000001 r13=000001c12e8526d0
r14=0000000000000000 r15=000001ce25531c60
iopl=0 nv up ei pl nz na po nc
cs=0033 ss=002b ds=002b es=002b fs=0053 gs=002b efl=00000206
ntdll!RtlReportFatalFailure+0x9:
00007ffe`d7b1b349 eb00 jmp ntdll!RtlReportFatalFailure+0xb (00007ffe`d7b1b34b)
Resetting default scope
EXCEPTION_RECORD: (.exr -1)
ExceptionAddress: 00007ffed7b1b349 (ntdll!RtlReportFatalFailure+0x0000000000000009)
ExceptionCode: c0000374
ExceptionFlags: 00000001
NumberParameters: 1
Parameter[0]: 00007ffed7b827f0
PROCESS_NAME: w3wp.exe
...熟悉 windows ntheap 的朋友应该知道，ExceptionCode: c0000374 是经典的 堆破坏 状态码，那到底是谁破坏了呢？
2. 到底是谁破坏了NT堆
windows 给了 ntheap 强大的调试支持，默认开启了 Termination on corruption 破坏检测，也就是说当你使用 !heap -s 的时候会显示具体破坏的详情记录，输出如下：
0:090> !heap -s
************************************************************************************************************************
NT HEAP STATS BELOW
************************************************************************************************************************
**************************************************************
* *
* HEAP ERROR DETECTED *
* *
**************************************************************
Details:
Heap address: 000001c14fd20000
Error address: 000001ce25531c50
Error type: HEAP_FAILURE_BLOCK_NOT_BUSY
Details: The caller performed an operation (such as a free
or a size check) that is illegal on a free block.
Follow-up: Check the error's stack trace to find the culprit.
Stack trace:
Stack trace at 0x00007ffed7b82848
00007ffed7abe109: ntdll!RtlpLogHeapFailure+0x45
00007ffed7acbb0e: ntdll!RtlFreeHeap+0x9d3ce
00007ffeb093276f: OraOps12!ssmem_free+0xf
00007ffeb0943077: OraOps12!OpsMetFreeValCtx+0xd7
00007ffeb093cdd8: OraOps12!OpsDacDispose+0x2b8
00007ffe655e4374: +0x655e4374
LFH Key : 0x5baf44f8068da60f
Termination on corruption : ENABLED
Heap Flags Reserv Commit Virt Free List UCR Virt Lock Fast
(k) (k) (k) (k) length blocks cont. heap
-------------------------------------------------------------------------------------
000001c14fd20000 00000002 1021576 964388 1020020 19222 6063 166 2 82f LFH
000001c14fc70000 00008000 64 4 64 2 1 1 0 0
...上面的 Error type: HEAP_FAILURE_BLOCK_NOT_BUSY 表示是一个 double free，从 Stack trace 看是 OpsDacDispose 方法造成的，应该和 Oracle 相关，这就比较迷了。。。
3. 是托管层触发的吗
是不是托管层触发的呢？这就需要理解 Windows 独有的 SEH 异常处理机制，也就是说 Windows 的异常都会在 内核态 走一圈，画个图如下：
只要找到 t1 时刻的崩溃点，然后观察线程栈即可，代码如下：
0:090> .ecxr
rax=00007ffec265d6e0 rbx=00000000c0000374 rcx=00000053653fe4f0
rdx=00007ffec1d3e9a0 rsi=0000000000000001 rdi=00007ffed7b827f0
rip=00007ffed7b1b349 rsp=00000053653fed10 rbp=000001c14fd20000
r8=000001c11957d9a0 r9=0000000000000033 r10=000001c453dbc7f0
r11=00007ffeb94db004 r12=0000000000000001 r13=000001c12e8526d0
r14=0000000000000000 r15=000001ce25531c60
iopl=0 nv up ei pl nz na po nc
cs=0033 ss=002b ds=002b es=002b fs=0053 gs=002b efl=00000206
ntdll!RtlReportFatalFailure+0x9:
00007ffe`d7b1b349 eb00 jmp ntdll!RtlReportFatalFailure+0xb (00007ffe`d7b1b34b)
0:090> k
*** Stack trace for last set context - .thread/.cxr resets it
# Child-SP RetAddr Call Site
00 00000053`653fed10 00007ffe`d7b1b313 ntdll!RtlReportFatalFailure+0x9
01 00000053`653fed60 00007ffe`d7b23b9e ntdll!RtlReportCriticalFailure+0x97
02 00000053`653fee50 00007ffe`d7b23eaa ntdll!RtlpHeapHandleError+0x12
03 00000053`653fee80 00007ffe`d7abe109 ntdll!RtlpHpHeapHandleError+0x7a
04 00000053`653feeb0 00007ffe`d7acbb0e ntdll!RtlpLogHeapFailure+0x45
05 00000053`653feee0 00007ffe`b093276f ntdll!RtlFreeHeap+0x9d3ce
06 00000053`653fef80 00007ffe`b0943077 OraOps12!ssmem_free+0xf
07 00000053`653fefb0 00007ffe`b093cdd8 OraOps12!OpsMetFreeValCtx+0xd7
08 00000053`653fefe0 00007ffe`655e4374 OraOps12!OpsDacDispose+0x2b8
09 00000053`653ff060 00007ffe`655e31cf 0x00007ffe`655e4374
0a 00000053`653ff150 00007ffe`6a80969d 0x00007ffe`655e31cf
0b 00000053`653ff1f0 00007ffe`c4b96d06 0x00007ffe`6a80969d
0c 00000053`653ff220 00007ffe`c4c30e81 clr!FastCallFinalizeWorker+0x6
0d 00000053`653ff250 00007ffe`c4c30e09 clr!FastCallFinalize+0x55
0e 00000053`653ff2a0 00007ffe`c4c30d3a clr!MethodTable::CallFinalizer+0xb5
0f 00000053`653ff2f0 00007ffe`c4c30bf5 clr!CallFinalizer+0x5e
10 00000053`653ff330 00007ffe`c4c304dc clr!FinalizerThread::DoOneFinalization+0x95
11 00000053`653ff410 00007ffe`c4c31777 clr!FinalizerThread::FinalizeAllObjects+0xbf
12 00000053`653ff450 00007ffe`c4b97d01 clr!FinalizerThread::FinalizeAllObjects_Wrapper+0x18
13 00000053`653ff480 00007ffe`c4b97c70 clr!ManagedThreadBase_DispatchInner+0x39
14 00000053`653ff4c0 00007ffe`c4b97bad clr!ManagedThreadBase_DispatchMiddle+0x6c
15 00000053`653ff5c0 00007ffe`c4b9ac34 clr!ManagedThreadBase_DispatchOuter+0x75
16 00000053`653ff650 00007ffe`c4bf5271 clr!ManagedThreadBase_DispatchInCorrectAD+0x15
17 00000053`653ff680 00007ffe`c4b9ac72 clr!Thread::DoADCallBack+0x109
18 00000053`653ff830 00007ffe`c4c3172a clr!ManagedThreadBase_DispatchInner+0x82
19 00000053`653ff870 00007ffe`c4c304dc clr!FinalizerThread::DoOneFinalization+0x1f1
1a 00000053`653ff950 00007ffe`c4c3062b clr!FinalizerThread::FinalizeAllObjects+0xbf
1b 00000053`653ff990 00007ffe`c4b97d01 clr!FinalizerThread::FinalizerThreadWorker+0xbb
1c 00000053`653ff9d0 00007ffe`c4b97c70 clr!ManagedThreadBase_DispatchInner+0x39
1d 00000053`653ffa10 00007ffe`c4b97bad clr!ManagedThreadBase_DispatchMiddle+0x6c
1e 00000053`653ffb10 00007ffe`c4cf4d4a clr!ManagedThreadBase_DispatchOuter+0x75
1f 00000053`653ffba0 00007ffe`c4d5044f clr!FinalizerThread::FinalizerThreadStart+0x126
20 00000053`653ffc40 00007ffe`d6157e94 clr!Thread::intermediateThreadProc+0x86
21 00000053`653ffd00 00007ffe`d7a87ad1 kernel32!BaseThreadInitThunk+0x14
22 00000053`653ffd30 00000000`00000000 ntdll!RtlUserThreadStart+0x21
0:090> !clrstack
OS Thread Id: 0x5634 (90)
Child SP IP Call Site
00000053653ff0b8 00007ffed7abf0e4 [InlinedCallFrame: 00000053653ff0b8] Oracle.DataAccess.Client.OpsDac.Dispose(IntPtr, IntPtr, IntPtr, IntPtr ByRef, Oracle.DataAccess.Client.OpoMetValCtx*, Oracle.DataAccess.Client.OpoDacValCtx* ByRef, Oracle.DataAccess.Client.OpoSqlValCtx*, Int32, Int32)
00000053653ff0b8 00007ffe655e4374 [InlinedCallFrame: 00000053653ff0b8] Oracle.DataAccess.Client.OpsDac.Dispose(IntPtr, IntPtr, IntPtr, IntPtr ByRef, Oracle.DataAccess.Client.OpoMetValCtx*, Oracle.DataAccess.Client.OpoDacValCtx* ByRef, Oracle.DataAccess.Client.OpoSqlValCtx*, Int32, Int32)
00000053653ff060 00007ffe655e4374 DomainNeutralILStubClass.IL_STUB_PInvoke(IntPtr, IntPtr, IntPtr, IntPtr ByRef, Oracle.DataAccess.Client.OpoMetValCtx*, Oracle.DataAccess.Client.OpoDacValCtx* ByRef, Oracle.DataAccess.Client.OpoSqlValCtx*, Int32, Int32)
00000053653ff150 00007ffe655e31cf Oracle.DataAccess.Client.OracleDataReader.Dispose(Boolean)
00000053653ff1f0 00007ffe6a80969d Oracle.DataAccess.Client.OracleDataReader.Finalize()
00000053653ff608 00007ffec4b96d06 [DebuggerU2MCatchHandlerFrame: 00000053653ff608]
00000053653ff788 00007ffec4b96d06 [ContextTransitionFrame: 00000053653ff788]
00000053653ff8d0 00007ffec4b96d06 [GCFrame: 00000053653ff8d0]
00000053653ffb58 00007ffec4b96d06 [DebuggerU2MCatchHandlerFrame: 00000053653ffb58]从调用栈来看，原来是 终结器线程 在调用 OracleDataReader.Dispose() 方法的时候抛的异常，这个结果还是挺意外的，也就是说这个问题不是用户代码造成的，真的是 Oracle 这个 OraOps12.dll 造成的。。。
接下来用 lm 观察下这个 dll 的详情信息，输出如下：
0:090> lmDvmOraOps12
Browse full module list
start end module name
00007ffe`b0920000 00007ffe`b098c000 OraOps12 C (export symbols) OraOps12.dll
Loaded symbol image file: OraOps12.dll
Image path: C:\ODAC\xxxx\OraOps12.dll
Image name: OraOps12.dll
Browse all global symbols functions data
Timestamp: Sat Sep 26 23:16:56 2015 (5606B6E8)
CheckSum: 00000000
ImageSize: 0006C000
File version: 2.121.2.0
Product version: 2.121.2.0
File flags: 0 (Mask 3F)
File OS: 4 Unknown Win32
File type: 2.0 Dll
File date: 00000000.00000000
Translations: 0409.04b0
Information from resource tables:
CompanyName: Oracle Corporation
ProductName: Oracle Data Provider for .NET
InternalName: OraOps
OriginalFilename: OraOps12.dll
ProductVersion: 2.121.2.0 ODAC RELEASE 4
FileVersion: 2.121.2.0
FileDescription: Oracle Provider Services
LegalCopyright: Copyright © 2014虽然对 Oracle 不熟，但从 Timestamp: Sat Sep 26 23:16:56 2015 来看应该是一个比较老的 DLL 了，所以给到朋友的建议就是升级 OraOps12.dll 。
4. 是否有同行者
有时候直接让朋友升级dll有点缺少底气，最好就是找到一些同行者，经过一顿搜索，还真有同行者，又多了一份说服力，网址： https://techcommunity.microsoft.com/t5/iis-support-blog/w3wp-exe-crash-exception-code-0xc0000005/ba-p/334351 。
三：总结
在百加dump的分析旅程中，碰到和 Oracle SDK 相关的也有 3+ 起了，可能也许这些 SDK 在对接 .NET 上还不是特别稳健，大家在使用上尽量更新到最新版本吧，且用且珍惜！
