opendpi 源码分析（二）

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

#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：

#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：

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 filestatic void pcap_packet_callback(u_char * args, const struct pcap_pkthdr *header, const u_char * packet)

然后在函数

 // 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：

 /* 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：

#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。