摘要：
它首先介绍了opendpi如何设置每个协议的处理，然后描述了如何处理每个包，最后是软件流程图。
先介绍opendpi如何设置各个协议的处理，然后介绍如何处理每一个包，最后是软件的流程图。
第一：首先看下要用到的重要的宏
View Code #define IPOQUE_SAVE_AS_BITMASK(bitmask,value) (bitmask)=(((IPOQUE_PROTOCOL_BITMASK)1)<<(value))
#define IPOQUE_BITMASK_COMPARE(a,b) ((a) & (b))
#define IPOQUE_BITMASK_MATCH(x,y) ((x) == (y))
#define IPOQUE_BITMASK_COMPARE(a,b) ((a) & (b))
#define IPOQUE_COMPARE_PROTOCOL_TO_BITMASK(bmask,value) IPOQUE_BITMASK_COMPARE(bmask,IPOQUE_CONVERT_PROTOCOL_TO_BITMASK(value))
#define IPOQUE_CONVERT_PROTOCOL_TO_BITMASK(p) ( ((IPOQUE_PROTOCOL_BITMASK)1) << (p) )
#define IPOQUE_ADD_PROTOCOL_TO_BITMASK(bmask,value) IPOQUE_BITMASK_ADD(bmask,IPOQUE_CONVERT_PROTOCOL_TO_BITMASK(value))
#define IPOQUE_BITMASK_ADD(a,b) (a)|=(b)
#define IPOQUE_BITMASK_SET(a,b) (a)=(b)
#define IPOQUE_DEL_PROTOCOL_FROM_BITMASK(bmask,value) IPOQUE_BITMASK_DEL(bmask,IPOQUE_CONVERT_PROTOCOL_TO_BITMASK(value))
#define IPOQUE_BITMASK_DEL(a,b) (a)=((a) & (~(b)))
#define IPOQUE_BITMASK_SET_ALL(a) (a) = ((IPOQUE_PROTOCOL_BITMASK)0xFFFFFFFFFFFFFFFFULL)
#define IPOQUE_BITMASK_RESET(a) (a) = 0
然后是标识协议掩码的数据结构：
#if IPOQUE_MAX_SUPPORTED_PROTOCOLS >= 128
typedef struct ipoque_protocol_bitmask_struct {
u64 bitmask[3];
} ipoque_protocol_bitmask_struct_t;
#define IPOQUE_PROTOCOL_BITMASK struct ipoque_protocol_bitmask_struct
#elif IPOQUE_MAX_SUPPORTED_PROTOCOLS >= 64
typedef struct ipoque_protocol_bitmask_struct {
u64 bitmask[2];
} ipoque_protocol_bitmask_struct_t;
#define IPOQUE_PROTOCOL_BITMASK struct ipoque_protocol_bitmask_struct
#if IPOQUE_MAX_SUPPORTED_PROTOCOLS >= 128
typedef struct ipoque_protocol_bitmask_struct {
u64 bitmask[3];
} ipoque_protocol_bitmask_struct_t;
#define IPOQUE_PROTOCOL_BITMASK struct ipoque_protocol_bitmask_struct
#elif IPOQUE_MAX_SUPPORTED_PROTOCOLS >= 64
typedef struct ipoque_protocol_bitmask_struct {
u64 bitmask[2];
} ipoque_protocol_bitmask_struct_t;
#define IPOQUE_PROTOCOL_BITMASK struct ipoque_protocol_bitmask_struct
#else
#define IPOQUE_PROTOCOL_BITMASK u64
#endif
#ifndef u64
#define u64 unsigned long long
#endif
#ifndef u32
#define u32 unsigned int
#endif
#ifndef u16
#define u16 unsigned short
#endif
#ifndef u8
#define u8 unsigned char
#endif
我开始的时候一直以为 IPOQUE_PROTOCOL_BITMASK是整型，没想到是个结构体。
在函数ipoque_set_protocol_detection_bitmask2中开启了对某个固定协议的处理，比如这样就开启了所有协议来检测包：
// enable all protocols
IPOQUE_BITMASK_SET_ALL(all);
ipoque_set_protocol_detection_bitmask2(ipoque_struct, &all);
在具体的一种协议的实现中是这样处理的，比如YAHOO：
View Code #ifdef IPOQUE_PROTOCOL_YAHOO
if (IPOQUE_COMPARE_PROTOCOL_TO_BITMASK(*detection_bitmask, IPOQUE_PROTOCOL_YAHOO) != 0) {
ipoque_struct->callback_buffer[a].func = ipoque_search_yahoo;
ipoque_struct->callback_buffer[a].ipq_selection_bitmask = IPQ_SELECTION_BITMASK_PROTOCOL_TCP_OR_UDP;
IPOQUE_SAVE_AS_BITMASK(ipoque_struct->callback_buffer[a].detection_bitmask, IPOQUE_PROTOCOL_UNKNOWN);
IPOQUE_ADD_PROTOCOL_TO_BITMASK(ipoque_struct->callback_buffer[a].detection_bitmask, IPOQUE_PROTOCOL_YAHOO);
IPOQUE_SAVE_AS_BITMASK(ipoque_struct->callback_buffer[a].excluded_protocol_bitmask, IPOQUE_PROTOCOL_YAHOO);
a++;
}
而函数ipoque_search_yahoo就是存在于目录protocol中，对于YAHOO的具体检查，实现如下：
View Code void ipoque_search_yahoo(struct ipoque_detection_module_struct *ipoque_struct)
{
struct ipoque_packet_struct *packet = &ipoque_struct->packet;
struct ipoque_flow_struct *flow = ipoque_struct->flow;
IPQ_LOG(IPOQUE_PROTOCOL_YAHOO, ipoque_struct, IPQ_LOG_DEBUG, "search yahoo\n");
if (packet->payload_packet_len > 0 && flow->yahoo_detection_finished == 0) {
if (packet->tcp != NULL && packet->tcp_retransmission == 0) {
#ifdef IPOQUE_PROTOCOL_HTTP
if (packet->detected_protocol == IPOQUE_PROTOCOL_UNKNOWN
|| packet->detected_protocol == IPOQUE_PROTOCOL_HTTP)
#else
if (packet->detected_protocol == IPOQUE_PROTOCOL_UNKNOWN)
#endif
{
ipoque_search_yahoo_tcp(ipoque_struct);
}
} else if (packet->udp != NULL) {
ipoque_search_yahoo_udp(ipoque_struct);
}
}
if (packet->payload_packet_len > 0 && flow->yahoo_detection_finished == 2) {
if (packet->tcp != NULL && packet->tcp_retransmission == 0) {
ipoque_search_yahoo_tcp(ipoque_struct);
}
}
}
这个函数检查了YAHOO是基于UDP还是TCP，还有没有payload长度是不是等于0.
这样就建立了一个匹配的模式数据库。
第二:对于每一个包，在这个函数中从pcap文件中获得：
// executed for each packet in the pcap file
static void pcap_packet_callback(u_char * args, const struct pcap_pkthdr *header, const u_char * packet)
// here the actual detection is performed
protocol = ipoque_detection_process_packet(ipoque_struct, ipq_flow, (uint8_t *) iph, ipsize, time, src, dst);
这是对每个包的具体处理，而返回值就是我们所想要知道的，这个包所属于的协议号。
在函数 ipoque_detection_process_packet中最重要的是如下的代码：
if (flow != NULL && ipoque_struct->packet.tcp != NULL) {
if (ipoque_struct->packet.payload_packet_len != 0) {
for (a = 0; a < ipoque_struct->callback_buffer_size_tcp_payload; a++) {
if ((ipoque_struct->callback_buffer_tcp_payload[a].ipq_selection_bitmask & ipq_selection_packet) ==
ipoque_struct->callback_buffer_tcp_payload[a].ipq_selection_bitmask
&& IPOQUE_BITMASK_COMPARE(ipoque_struct->flow->excluded_protocol_bitmask,
ipoque_struct->callback_buffer_tcp_payload[a].excluded_protocol_bitmask) == 0
&& IPOQUE_BITMASK_COMPARE(ipoque_struct->callback_buffer_tcp_payload[a].detection_bitmask,
detection_bitmask) != 0) {
ipoque_struct->callback_buffer_tcp_payload[a].func(ipoque_struct);
}
}
首先判断了payload，而ipq_selection_packet依赖于下面的这些判断：
View Code /* build ipq_selction packet bitmask */
ipq_selection_packet = IPQ_SELECTION_BITMASK_PROTOCOL_COMPLETE_TRAFFIC;
if (ipoque_struct->packet.iph != NULL) {
ipq_selection_packet |= IPQ_SELECTION_BITMASK_PROTOCOL_IP | IPQ_SELECTION_BITMASK_PROTOCOL_IPV4_OR_IPV6;
}
if (ipoque_struct->packet.tcp != NULL) {
ipq_selection_packet |=
(IPQ_SELECTION_BITMASK_PROTOCOL_INT_TCP | IPQ_SELECTION_BITMASK_PROTOCOL_INT_TCP_OR_UDP);
}
if (ipoque_struct->packet.udp != NULL) {
ipq_selection_packet |=
(IPQ_SELECTION_BITMASK_PROTOCOL_INT_UDP | IPQ_SELECTION_BITMASK_PROTOCOL_INT_TCP_OR_UDP);
}
if (ipoque_struct->packet.payload_packet_len != 0) {
ipq_selection_packet |= IPQ_SELECTION_BITMASK_PROTOCOL_HAS_PAYLOAD;
}
if (ipoque_struct->packet.tcp_retransmission == 0) {
ipq_selection_packet |= IPQ_SELECTION_BITMASK_PROTOCOL_NO_TCP_RETRANSMISSION;
}
excluded_protocol_bitmask是设置不需要检查的协议，我们上面已经设置为all。
detection_bitmask通过这样初始化：
View Code #define IPOQUE_CONVERT_PROTOCOL_TO_BITMASK(p) ( ((IPOQUE_PROTOCOL_BITMASK)1) << (p) )
IPOQUE_SAVE_AS_BITMASK(detection_bitmask, ipoque_struct->packet.detected_protocol);
通过gdb可以查看 detection_bitmask的值是：bitmask = {1, 0}。
这样就把每一个包放入已有的协议模式去匹配。
主要流程图：
也许有错误，希望指教。