在使用OpenSSL的RSA加解密的时候，发现RSA_new()初始化和RSA_free()释放RSA结构体后依然会有内存泄漏。网上Baidu、Google之，发现这个相关信息很少（至少中文搜索结果是这样，不知是研究这个的人太少还是这个太基础了。。。），最后终于在某个E文论坛上找到了解决办法。在这里总结了一下，供大家参考。我的OpenSSL版本是0.9.8l。（by 月落上弦）

具体如下：
RSA * rsa = RSA_new();
RSA_free( rsa );

产生内存泄漏：

Debug for memory leaks 

Code highlighting produced by Actipro CodeHighlighter (freeware)http://www.CodeHighlighter.com/-->Detected memory leaks!
Dumping objects ->
{140} normal block at 0x003B97A0, 12 bytes long.
 Data: <  ;         > B8 96 3B 00 00 00 00 00 06 00 00 00 
{139} normal block at 0x003B9750, 16 bytes long.
 Data: <                > 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 
{138} normal block at 0x003B9700, 20 bytes long.
 Data: <    P ;         > 00 00 00 00 50 97 3B 00 00 00 00 00 04 00 00 00 
{137} normal block at 0x003B96B8, 12 bytes long.
 Data: <      ;     > 06 00 00 00 00 97 3B 00 00 00 00 00 
{136} normal block at 0x003B9638, 64 bytes long.
 Data: <                > 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 
{135} normal block at 0x003B9598, 96 bytes long.
 Data: <8 ;   A   A     > 38 96 3B 00 C0 FD 41 00 B0 FD 41 00 08 00 00 00 
Object dump complete.

View Code

解决方法很简单：

调用OpenSSL的crypto库，在退出前需要调用API "CRYPTO_cleanup_all_ex_data"，清除管理CRYPTO_EX_DATA的全局hash表中的数据，避免内存泄漏。如下：

RSA * rsa = RSA_new();
RSA_free( rsa );
CRYPTO_cleanup_all_ex_data(); 

这样就没有内存泄漏了。

需要注意的是，CRYPTO_cleanup_all_ex_data()不能在potential race-conditions条件在调用（不太懂这个术语，我理解的意思是当函数外部存在RSA结构体的时候，在函数内部执行CRYPTO_cleanup_all_ex_data()将导致函数外的RSA结构体也被清理掉），因此最好在程序结束的时候才调用。

关于CRYPTO_cleanup_all_ex_data()的注释说明和代码如下：

Code highlighting produced by Actipro CodeHighlighter (freeware)http://www.CodeHighlighter.com/-->/* Release all "ex_data" state to prevent memory leaks. This can't be made
 * thread-safe without overhauling a lot of stuff, and shouldn't really be
 * called under potential race-conditions anyway (it's for program shutdown
 * after all). */
void CRYPTO_cleanup_all_ex_data(void)
    {
    IMPL_CHECK
    EX_IMPL(cleanup)();
    }

同样，其他相应的模块也需要在使用后清理：

CONF_modules_unload(1);        //for conf
EVP_cleanup();                 //For EVP
ENGINE_cleanup();              //for engine
CRYPTO_cleanup_all_ex_data();  //generic 
ERR_remove_state(0);           //for ERR
ERR_free_strings();            //for ERR

　　// thread-local cleanup
    ERR_remove_state(0);
     
    // thread-safe cleanup
    ENGINE_cleanup();
    CONF_modules_unload(1);
 
    // global application exit cleanup (after all SSL activity is shutdown)
    ERR_free_strings();
    EVP_cleanup();
    CRYPTO_cleanup_all_ex_data();
  
        // 这个函数是网上找的，描述说内存泄漏现象是 _comp_method（不知道有没有记错）对象没释放
        // 额外添加的函数，用以释放资源（没有调用该函数，OpenSSL 会有内存泄漏(160字节)）
    SSL_free_comp_methods();

  http://www.cnblogs.com/moonset7/archive/2009/12/30/1635770.html 月落上弦