c++ - 'pcap_loop' 没有记录数据包，甚至没有运行

Question

我正在尝试使用 pcap 进行一些简单的数据包捕获，因此我创建了一个句柄来通过 eth0 进行监听。我的问题是代码末尾附近的 pcap_loop(handle, 10, myCallback, NULL); 行。我正在尝试使用 pcap_loop。预期的输出应该是:

eth0
Activated!
1
2
3
...
10
Done processing packets!

当前输出缺少增量:

eth0
Activated!
Done processing packets!

目前它只是直接跳到“完成数据包处理!”我不知道为什么。即使它没有进入回调，它仍应等待数据包，因为 ;count' 参数(请参阅 pcap_loop 的文档)设置为 10。

#include <iostream>
#include <pcap.h>
#include <stdlib.h>
#include <netinet/in.h> 
#include <arpa/inet.h>

void myCallback(u_char *useless, const struct pcap_pkthdr* hdr, const u_char*packet){
    static int count = 1;
    std::cout <<count<<std::endl;
    count ++;
}

int main(){
    char errbuf[PCAP_ERRBUF_SIZE];
    char * devName;
    char* net;
    char* mask;
    const u_char*packet;
    struct in_addr addr;
    struct pcap_pkthdr hdr;
    bpf_u_int32 netp;
    bpf_u_int32 maskp;

    pcap_if_t *devs;
    pcap_findalldevs(&devs, errbuf);
    devName = pcap_lookupdev(errbuf);
    std::cout <<devName<<std::endl;

    int success = pcap_lookupnet(devName, &netp, &maskp, errbuf);
    if(success<0){
        exit(EXIT_FAILURE);
    }
    pcap_freealldevs(devs);

    //Create a handle
    pcap_t *handle = pcap_create(devName, errbuf);
    pcap_set_promisc(handle, 1);
    pcap_can_set_rfmon(handle);

    //Activate the handle
    if(pcap_activate(handle)){
        std::cout <<"Activated!"<<std::endl;
    }
    else{
        exit(EXIT_FAILURE);
    }

    pcap_loop(handle, 10, myCallback, NULL);
    std::cout <<"Done processing packets!"<<std::endl;

    //close handle
    pcap_close(handle);
    }

Answer 1

pcap_findalldevs(&devs, errbuf);

该调用没有做任何有用的事情，因为除了释放它之外，您没有对 devs 做任何事情。 (您也不会检查它是成功还是失败。)您最好将其删除，除非您需要知道可以捕获的所有设备是什么。

pcap_can_set_rfmon(handle);

这一切都没有做任何有用的事情，因为您没有检查它的返回值。如果您在 Wi-Fi 设备上捕获，并且想在监控模式下捕获，则在创建后的句柄上调用 pcap_set_rfmon() - 而不是 pcap_can_set_rfmon()在激活 handle 之前。

//Activate the handle
if(pcap_activate(handle)){
    std::cout <<"Activated!"<<std::endl;
}
else{
    exit(EXIT_FAILURE);
}

引用 pcap_activate() 手册页:

RETURN VALUE
   pcap_activate()  returns  0  on  success  without  warnings, PCAP_WARN-
   ING_PROMISC_NOTSUP on success on a device that doesn't support  promis-
   cuous  mode  if promiscuous mode was requested, PCAP_WARNING on success
   with any other warning, PCAP_ERROR_ACTIVATED if the handle has  already
   been  activated, PCAP_ERROR_NO_SUCH_DEVICE if the capture source speci-
   fied when the handle was created doesn't exist,  PCAP_ERROR_PERM_DENIED
   if  the  process  doesn't  have  permission to open the capture source,
   PCAP_ERROR_RFMON_NOTSUP if monitor mode was specified but  the  capture
   source  doesn't  support  monitor  mode, PCAP_ERROR_IFACE_NOT_UP if the
   capture source is not up, and PCAP_ERROR if another error occurred.  If
   PCAP_WARNING  or PCAP_ERROR is returned, pcap_geterr() or pcap_perror()
   may be called with p as an argument  to  fetch  or  display  a  message
   describing  the  warning  or  error.   If  PCAP_WARNING_PROMISC_NOTSUP,
   PCAP_ERROR_NO_SUCH_DEVICE,  or  PCAP_ERROR_PERM_DENIED   is   returned,
   pcap_geterr()  or  pcap_perror() may be called with p as an argument to
   fetch or display an message giving additional details about the problem
   that might be useful for debugging the problem if it's unexpected.

这意味着上面的代码是 100% 错误的 - 如果 pcap_activate() 返回一个非零值，它可能失败，如果它返回 0，它成功了。

如果返回值为负数，则为错误值，失败。如果它非零但为正，则为警告值；它已成功，但是，例如，它可能没有打开混杂模式，因为操作系统或设备可能不允许设置混杂模式。

所以你想要的是:

//Activate the handle
int status;
status = pcap_activate(handle);
if(status >= 0){
    if(status == PCAP_WARNING){
        // warning
        std:cout << "Activated, with warning: " << pcap_geterror(handle) << std::endl;
    }
    else if (status != 0){
        // warning
        std:cout << "Activated, with warning: " << pcap_statustostr(status) << std::endl;
    }
    else{
        // no warning
        std::cout <<"Activated!"<<std::endl;
    }
}
else{
    if(status == PCAP_ERROR){
        std:cout << "Failed to activate: " << pcap_geterror(handle) << std::endl;
    }
    else{
        std:cout << "Failed to activate: " << pcap_statustostr(status) << std::endl;
    }
    exit(EXIT_FAILURE);
}