PF_RING使用BPF过滤器

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转载：http://blog.chinaunix.net/uid-10540984-id-3240755.html

PF_RING是支持BPF过滤器的，这个在PF_RING的UserGuide中也有相应的函数原型说明。

当编译创建配置的时候，也可以关闭BPF的支持。

./userland/lib/configure --disable-bpf

默认是支持开启BPF过滤器的，在./userland/lib/pfring_mod.c源码中,会有一个宏定义:

#ifdef ENABLE_BPF

#include <pcap/pcap.h>

#include <pcap/bpf.h>

#include <linux/filter.h>

#endif

所以默认没有关闭BPF支持的情况下gcc编译时需要加入pcap的动态库。

PF_RING自己也有过滤器，确实功能功能比较少，习惯了pcap的过滤器书写，当然能使用它的过滤器是再好不过了。

代码中使用了PF_RING过滤器方式和BPF过滤器方式，用gcc编译时加"-D PRINT_ARG"则捕捉arp包,否则捕捉tcp包(其中排除了ssh和samba)

#define _GNU_SOURCE
#include <stdio.h>
#include <stdlib.h>
#include <pfring.h>
#include <string.h>
#include <errno.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <linux/if_ether.h>
#include <linux/ip.h>
#include <linux/tcp.h>
#include <getopt.h>

#define SNAP_LEN 1518
#define MIN_LEN (sizeof(struct ethhdr) + sizeof(struct iphdr) \
                    + sizeof(struct tcphdr))

#ifdef ARP_SWICTH
    #define PRINT_ARG "arp"
#else
    #define PRINT_ARG "tcp and not (dst port (22 or 445) or src port (22 or 445))"
#endif

static pfring *pd;
static char *in_dev = NULL;
static struct option opts[] = {
    {.name = "interface", .has_arg = 1, .val = 'i'},
    {.name = "help", .has_arg = 0, .val = 'h'},
    {NULL}
};

static void printHelp(void) {
    printf("-h Print this help\n");
    printf("-i <device> Device name. Use device\n");
    exit(EXIT_FAILURE);
}

static int process_packet(const struct pfring_pkthdr *header,
                            const u_char *packet) {
    struct ethhdr *ethh;
    struct arphdr *arph;
    struct iphdr *iph;
    struct tcphdr *tcph;
    struct in_addr src, dst;

    /* 判断长度避免访问到空指针 */
    if (header->caplen < MIN_LEN) return; 

    ethh = (struct ethhdr *)packet;
    printf("Eth_type:");
    switch(ntohs(ethh->h_proto)) {
        case 0x0800:
            printf("IP | ");
            /* 打印IP协议的目的地址和源地址 */
            packet += sizeof(struct ethhdr);
            iph = (struct iphdr *)packet;
            src.s_addr = iph->saddr;
            dst.s_addr = iph->daddr;
            printf("%s->", inet_ntoa(src));
            printf("%s | ", inet_ntoa(dst));
            
            switch (iph->protocol) {
                case 6:
                    packet += sizeof(struct iphdr);
                    tcph = (struct tcphdr *)packet;
                    printf("Protocol:TCP sport:%d->", ntohs(tcph->source));
                    printf("dport:%d", ntohs(tcph->dest));
                    break;
                case 1:
                    printf("Protocol:ICMP");
                    break;
            }
            break;
        case 0x0806:
            printf("ARP_request ");
            struct in_addr *src_in_addr, *dst_in_addr;
            struct macaddr { 
                   u_char MAC[6];
            };
            struct macaddr *src_mac, *dst_mac;

            packet += sizeof(struct ethhdr) + 8;
            src_mac = (struct macaddr *)packet;
            
            packet += 6;
            src_in_addr = (struct in_addr *)packet;
            printf("%s", inet_ntoa(*src_in_addr));
            
            packet += 4;
            dst_mac = (struct macaddr *)packet;

            packet += 6;
            dst_in_addr = (struct in_addr *)packet;
            printf(" -> %s", inet_ntoa(*dst_in_addr));

            printf(" %02x:%02x:%02x:%02x:%02x:%02x",
                    src_mac->MAC[0], src_mac->MAC[1], src_mac->MAC[2],
                    src_mac->MAC[3], src_mac->MAC[4], src_mac->MAC[5]
            );
            printf(" -> %02x:%02x:%02x:%02x:%02x:%02x",
                    dst_mac->MAC[0], dst_mac->MAC[1], dst_mac->MAC[2],
                    dst_mac->MAC[3], dst_mac->MAC[4], dst_mac->MAC[5]
            );
            break;
        case 0x8035:
            printf("ARP_response ");
            break;
        }
    printf("\n");
}

int main(int argc, char *argv[]) {
    char c;
    while((c = getopt_long(argc, argv, "hi:", opts, NULL)) != -1) {
        switch(c) {
        case 'h':
            printHelp(); 
            break;
        case 'i':
            in_dev = strdup(optarg);
            break;
        }
    }

    if(in_dev == NULL) printHelp();

    printf("Capturing from %s\n", in_dev);

    /* 打开pf设备 */
    pd = pfring_open(in_dev, SNAP_LEN, PF_RING_PROMISC);
    if(pd == NULL) {
        printf("pfring_open %s error [%s]\n", in_dev, strerror(errno));
        exit(EXIT_FAILURE);
    } else {
        u_int32_t version;
        /* 获取版本号 */
        pfring_version(pd, &version);
        printf("Using PF_RING v%u.%u.%u\n",
            (version & 0xFFFF0000) >> 16, 
            (version & 0x0000FF00) >> 8,
            version & 0x000000FF);
    }

    /* 
    设定捕获方向
    rx_and_tx_direction 双向捕获
    rx_only_direction 只捕获接收
    tx_only_direction 只捕获发送
    */
    if (pfring_set_direction(pd, rx_only_direction) != 0) {
        printf("pfring_set_direction is failure error [%s]\n", strerror(errno));
        exit(EXIT_FAILURE);
    }

#if 0 /* PF_RING过滤器 */
    int rc;
    filtering_rule rule;
    memset(&rule, 0, sizeof(rule));
    rule.rule_id = 1; /* 设置规则运行优先级,数值越小优先级越高 */
    /* 匹配哪些情况 */
    rule.rule_action = forward_packet_and_stop_rule_evaluation;
// rule.core_fields.proto = 6 /* 设置需要过滤的传输层协议 6 TCP*/;
    rule.core_fields.dhost.v4 = inet_addr("8.8.8.8"); /* 过滤出的IP地址*/
    rule.core_fields.dhost_mask.v4= inet_addr("255.255.255.255"); /* 主机子网 */
    /* 编译规则 */
    if((rc = pfring_add_filtering_rule(pd, &rule)) < 0)
        fprintf(stderr, "pfring_add_filtering_rule(2) failed\n");
        exit(EXIT_FAILURE);
    else
        printf("Rule added successfully...\n");
    /* 开启过滤器,第二个参数0表示drop,非零则为accept*/
    pfring_toggle_filtering_policy(pd, 0); 
#endif

#if 1 /* 使用BPF过滤器 */
    /* 过滤掉目标端口为22或455的数据包,也可以在前面加协议 */
    char filter_buffer[] = {PRINT_ARG};
    if (pfring_set_bpf_filter(pd, filter_buffer) != 0) {
        printf("set_BPF is failure!\n");
        exit(EXIT_FAILURE);
    }
#endif

    /* 开启pfring */
    if (pfring_enable_ring(pd) != 0) {
        printf("pfring_enable is failure error [%s]\n", strerror(errno));
        exit(EXIT_FAILURE);
    }

    while(1) {
        struct pfring_pkthdr hdr;
        u_char *buffer;
        int rc;

        /* 接收处理数据报文,最后一个参数非0则为阻塞*/
        if((rc = pfring_recv(pd, &buffer, 0, &hdr, 1) > 0)) {
            /* 调用函数处理捕获的数据包 */
            process_packet(&hdr, buffer);
        } else{
            /* 稍等PF_RING就绪 */
            usleep(10);
        }
    }

    pfring_close(pd);

    return(0);
}

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