3. 产生漏洞的主要原因比较OpenSSL 1.0.1g、OpenSSL 1.0.1f两个文件。在这两个文件的ssl文件夹中的d1_both.c、t1_lib.c两个文件中，都有一个tls1_process_heartbeat函数，它就是漏洞的关键。如下图：
图左比图右的代码，添加了两个判断，主要是针对length字段。再查看length的声明，如下图。
OpenSSL 1.0.1f处理过程代码:
#define n2s(c,s) ((s=(((unsigned int)(c[0]))<< 8)| \
(((unsigned int)(c[1])) )),c+=2)
int
dtls1_process_heartbeat(SSL *s)
{
unsigned char *p = &s->s3->rrec.data[0], *pl;
unsigned short hbtype;
unsigned int payload;
unsigned int padding = 16; /* Use minimum padding */
/* Read type and payload length first */
hbtype = *p++;
n2s(p, payload);
pl = p;
if (s->msg_callback)
s->msg_callback(0, s->version, TLS1_RT_HEARTBEAT,
&s->s3->rrec.data[0], s->s3->rrec.length,
s, s->msg_callback_arg);
if (hbtype == TLS1_HB_REQUEST)
{
unsigned char *buffer, *bp;
int r;
/* Allocate memory for the response, size is 1 byte
* message type, plus 2 bytes payload length, plus
* payload, plus padding
*/
buffer = OPENSSL_malloc(1 + 2 + payload + padding);
bp = buffer;
/* Enter response type, length and copy payload */
*bp++ = TLS1_HB_RESPONSE;
s2n(payload, bp);
memcpy(bp, pl, payload);
bp += payload;
/* Random padding */
RAND_pseudo_bytes(bp, padding);
r = dtls1_write_bytes(s, TLS1_RT_HEARTBEAT, buffer, 3 + payload + padding);
if (r >= 0 && s->msg_callback)
s->msg_callback(1, s->version, TLS1_RT_HEARTBEAT,
buffer, 3 + payload + padding,
s, s->msg_callback_arg);
OPENSSL_free(buffer);
if (r < 0)
return r;
}
else if (hbtype == TLS1_HB_RESPONSE)
{
unsigned int seq;
/* We only send sequence numbers (2 bytes unsigned int),
* and 16 random bytes, so we just try to read the
* sequence number */
n2s(pl, seq);
if (payload == 18 && seq == s->tlsext_hb_seq)
{
dtls1_stop_timer(s);
s->tlsext_hb_seq++;
s->tlsext_hb_pending = 0;
}
}
return 0;
}
处理过程：从数据中读取长度payload，并根据数据包长度直接申请内存，然后拷贝payload 大小的数据到申请的内存空间；由于没有验证length是否真是数据包的实际大小，所以如果让有心人伪造一个length字段（length字段比实际数据要大），就可以越界访问内存，从而导致内存泄漏。
而OpenSSL 1.0.1g 文件中，则对length字段进行了相关的验证。
