某些可执行文件的LD_PRELOAD和calloc（）插入问题

问题描述

关于以前的

我已成功插入 malloc ，但 calloc 更有问题。

这是与某些主机， calloc 陷入无限循环， code> calloc 调用 dlsym 。但是，基本测试主机不会显示此行为，但是我的系统的ls命令。

这是我的代码：

  // build with：g ++ -O2 -Wall -fPIC -ldl -o libnano.so -shared Main.cc 
 #include< stdio.h> 
 #include< dlfcn.h> 
 
 bool gNanoUp = false; // global 
 
 //函数类型
 typedef void *（* MallocFn）（size_t size）; 
 typedef void *（* CallocFn）（size_t elements，size_t size）; 
 
 struct MemoryFunctions {
 MallocFn mMalloc; 
 CallocFn mCalloc; 
}; 
 
 MemoryFunctions orgMemFuncs; 
 
 //保存原始方法。 
 void __attribute __（（constructor））__nano_init（void）{
 fprintf（stderr，NANO：init（）\\\
）; 
 
 //获取原始函数的地址
 orgMemFuncs.mMalloc =（MallocFn）dlsym（RTLD_NEXT，malloc）; 
 orgMemFuncs.mCalloc =（CallocFn）dlsym（RTLD_NEXT，calloc）; 
 
 fprintf（stderr，NANO：malloc（）found @％p\\\
，orgMemFuncs.mMalloc）; 
 fprintf（stderr，NANO：calloc（）found @％p \\\
，orgMemFuncs.mCalloc）; 
 
 gNanoUp = true; 
} 
 
 //替换函数
 externC{
 void * malloc（size_t size）{
 if（！gNanoUp）__nano_init ; 
 return orgMemFuncs.mMalloc（size）; 
} 
 
 void * calloc（size_t elements，size_t size）{
 if（！gNanoUp）__nano_init（）; 
 return orgMemFuncs.mCalloc（elements，size）; 
} 
} 
  

现在，当我执行以下操作时，无限循环后跟一个seg错误，例如：

 ％setenv LD_PRELOAD./libnano.so
％ls 
 ... 
 NANO：init（）
 NANO：init（）
 NANO：init（）
分段故障（内核转储）
  calloc 插件，它几乎 
似乎：
 ％setenv LD_PRELOAD./libnano.so
％ls 
 NANO：init（）
 NANO：init（）
 NANO：malloc（）找到@ 0x3b36274dc0 
 NANO：calloc（）found @ 0x3b362749e0 
 @ 0x3b36274dc0 
 NANO：calloc（）found @ 0x3b362749e0 
< directory content> 
 ... 
  
所以有些ls表示 init（）被调用两次。 
 
 
 
 EDIT 
请注意，以下主机程序可正常工作 -   init（）并且 calloc 已成功插入，如您从输出中可以看到的。 
  // build with：g ++ test.cc -o test 
 #include< stdio.h& 
 #include< stdlib.h> 
 
 int main（int argc，char * argv []）{
 
 void * p = malloc（123）; 
 printf（HOST p =％p\\\
，p）; 
 free（p）; 
 
 char * c = new char; 
 printf（HOST c =％p \\\
，c）; 
 delete c; 
 
 void * ca = calloc（10,10）; 
 printf（HOST ca =％p\\\
，ca）; 
 free（ca）; 
} 
 
％setenv LD_PRELOAD./libnano.so
％./test 
 NANO：init（）
 NANO：malloc @ 0x3b36274dc0 
 NANO：calloc（）found @ 0x3b362749e0 
 HOST p = 0x601010 
 HOST c = 0x601010 
 HOST ca = 0x601030 
  
 
 
解决方案
关于 __ nano_init（）你已经将函数声明为一个构造函数，因此在库加载时被调用，当你的 malloc（）和 calloc（）实现首先被调用。选择一个。
 
 
 
关于 calloc（） Interposer会崩溃您的应用程序：使用 dlsym（）和 fprintf（）可能正在尝试分配内存，调用插件函数。考虑后果，并据此采取行动。
 
Relating to a previous question of mine 
I've successfully interposed malloc, but calloc seems to be more problematic.
That is with certain hosts, calloc gets stuck in an infinite loop with a possible internal calloc call inside dlsym. However, a basic test host does not exhibit this behaviour, but my system's "ls" command does.
Here's my code:
// build with: g++ -O2 -Wall -fPIC -ldl -o libnano.so -shared Main.cc
#include <stdio.h>
#include <dlfcn.h>

bool gNanoUp = false;// global

// Function types
typedef void* (*MallocFn)(size_t size);
typedef void* (*CallocFn)(size_t elements, size_t size);

struct MemoryFunctions {
    MallocFn   mMalloc;
    CallocFn   mCalloc;
};

MemoryFunctions orgMemFuncs;

// Save original methods.
void __attribute__((constructor)) __nano_init(void) {
    fprintf(stderr, "NANO: init()\n");

    // Get address of original functions
    orgMemFuncs.mMalloc = (MallocFn)dlsym(RTLD_NEXT, "malloc");
    orgMemFuncs.mCalloc = (CallocFn)dlsym(RTLD_NEXT, "calloc");

    fprintf(stderr, "NANO: malloc() found @%p\n", orgMemFuncs.mMalloc);
    fprintf(stderr, "NANO: calloc() found @%p\n", orgMemFuncs.mCalloc);

    gNanoUp = true;
}

// replacement functions
extern "C" {
    void *malloc(size_t size) {
        if (!gNanoUp) __nano_init();
        return orgMemFuncs.mMalloc(size);
    }

    void* calloc(size_t elements, size_t size) {
        if (!gNanoUp) __nano_init();
        return orgMemFuncs.mCalloc(elements, size);
    }
}
Now, When I do the following, I get an infinite loop followed by a seg fault, eg:
% setenv LD_PRELOAD "./libnano.so"
% ls
...
NANO: init()
NANO: init()
NANO: init()
Segmentation fault (core dumped)
However if I comment out the calloc interposer, it almost seems to work:
% setenv LD_PRELOAD "./libnano.so"
% ls
NANO: init()
NANO: malloc() found @0x3b36274dc0
NANO: calloc() found @0x3b362749e0
NANO: init()
NANO: malloc() found @0x3b36274dc0
NANO: calloc() found @0x3b362749e0
<directory contents>
...
So somethings up with "ls" that means init() gets called twice. 
EDITNote that the following host program works correctly - init() is only called once, and calloc is successfully interposed, as you can see from the output. 
// build with: g++ test.cc -o test
#include <stdio.h>
#include <stdlib.h>

int main(int argc, char* argv[]) {

    void* p = malloc(123);
    printf("HOST p=%p\n", p);
    free(p);

    char* c = new char;
    printf("HOST c=%p\n", c);
    delete c;

    void* ca = calloc(10,10);
    printf("HOST ca=%p\n", ca);
    free(ca);
}

% setenv LD_PRELOAD "./libnano.so"
% ./test 
NANO: init()
NANO: malloc() found @0x3b36274dc0
NANO: calloc() found @0x3b362749e0
HOST p=0x601010
HOST c=0x601010
HOST ca=0x601030
 解决方案 
With regard to __nano_init() being called twice: You've declared the function as a constructor, so it's called when the library is loaded, and it's called a second time explicitly when your malloc() and calloc() implementations are first called. Pick one.
With regard to the calloc() interposer crashing your application: Some of the functions you're using, including dlsym() and fprintf(), may themselves be attempting to allocate memory, calling your interposer functions. Consider the consequences, and act accordingly.
                        
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