openssl代码学习记录-SSL

  通过Source Insight查看openssl的源代码，可发现SSL建立的来龙去脉。

      1.    先看SSL_NEW.

static int ssl_new(BIO *bi)
{
    BIO_SSL *bs;

    bs = (BIO_SSL *)OPENSSL_malloc(sizeof(BIO_SSL));
    if (bs == NULL) {
        BIOerr(BIO_F_SSL_NEW, ERR_R_MALLOC_FAILURE);
        return (0);
    }
    memset(bs, 0, sizeof(BIO_SSL));
    bi->init = 0;
    bi->ptr = (char *)bs;
    bi->flags = 0;
    return (1);
}

bs为BIO_SSL指针，指向OPENSSL_malloc的返回值，即地址，OPENSSL_malloc的作用是什么？再追踪：

# define OPENSSL_malloc(num)     CRYPTO_malloc((int)num,__FILE__,__LINE__)，原来是CRYPTO_malloc，再追踪：

void *CRYPTO_malloc(int num, const char *file, int line)
{
    void *ret = NULL;

    if (num <= 0)
        return NULL;

    if (allow_customize)
        allow_customize = 0;
    if (malloc_debug_func != NULL) {
        if (allow_customize_debug)
            allow_customize_debug = 0;
        malloc_debug_func(NULL, num, file, line, 0);
    }
    ret = malloc_ex_func(num, file, line);
#ifdef LEVITTE_DEBUG_MEM
    fprintf(stderr, "LEVITTE_DEBUG_MEM:         > 0x%p (%d)\n", ret, num);
#endif
    if (malloc_debug_func != NULL)
        malloc_debug_func(ret, num, file, line, 1);

#ifndef OPENSSL_CPUID_OBJ
    /*
     * Create a dependency on the value of 'cleanse_ctr' so our memory
     * sanitisation function can't be optimised out. NB: We only do this for
     * >2Kb so the overhead doesn't bother us.
     */
    if (ret && (num > 2048)) {
        extern unsigned char cleanse_ctr;
        ((unsigned char *)ret)[0] = cleanse_ctr;
    }
#endif

    return ret;
}

 实体函数出现了。关键代码就一句： ret = malloc_ex_func(num, file, line);

malloc_ex_func最终引向常用的malloc函数，但是openssl对内存管理提供了很方便的查询/管理接口，后话。

SSL-NEW的作用就是申请了一块存放  BIO_SSL的空间，并初始化bi；

2.  再看ssl_free。

static int ssl_free(BIO *a)
{
    BIO_SSL *bs;

    if (a == NULL)
        return (0);
    bs = (BIO_SSL *)a->ptr;
    if (bs->ssl != NULL)
        SSL_shutdown(bs->ssl);
    if (a->shutdown) {
        if (a->init && (bs->ssl != NULL))
            SSL_free(bs->ssl);
        a->init = 0;
        a->flags = 0;
    }
    if (a->ptr != NULL)
        OPENSSL_free(a->ptr);
    return (1);
}

这个函数应该是释放内存空间的，追踪验证一下。

int SSL_shutdown(SSL *s)
{
    /*
     * Note that this function behaves differently from what one might
     * expect.  Return values are 0 for no success (yet), 1 for success; but
     * calling it once is usually not enough, even if blocking I/O is used
     * (see ssl3_shutdown).
     */

    if (s->handshake_func == 0) {
        SSLerr(SSL_F_SSL_SHUTDOWN, SSL_R_UNINITIALIZED);
        return -1;
    }

    if ((s != NULL) && !SSL_in_init(s))
        return (s->method->ssl_shutdown(s));
    else
        return (1);
}

看代码，发现函数的目的与预想的很不同；有趣的是，这个函数需多个调用才能完成ssl链接的关闭。why? 再追踪，

到了int ssl3_shutdown(SSL *s)这里；目的是确保SSL链接确实结束。这个函数似乎没有回收内存的代码，只是关闭SSL链接。