eBPF 数据包过滤器没有给我正确的数据

Question

所以我一直在尝试看看是否可以将 eBPF 数据包过滤器附加到网络接口 enp32s0np1。我正在尝试捕获所有传入的发件人 IP 地址。但是，运行下面的代码让我产生了奇怪的反应。我没有看到发件人 IP 地址，而是看到了一些随机数字。

代码如下：

from bcc import BPF

# Network interface to be monoitored
INTERFACE = "enp32s0np1"

bpf_text = """

#include <linux/bpf.h>
#include <linux/if_ether.h>
#include <linux/if_packet.h>
#include <linux/ip.h>
#include <net/sock.h>
#include <bcc/proto.h>
#include <uapi/linux/ptrace.h>

int skb_matching(struct __sk_buff *skb) {
u8 *cursor = 0;
u64 saddr =0;
void *data_end = (void*)(long)skb->data_end;
void *data = (void*)(long)skb->data;
struct ethhdr *eth = data;

u32 nh_off = 0;
nh_off = sizeof(*eth);

/* // Code here has been blocked because this part keeps giving me errors as well..
if (data + nh_off > data_end ) { 
    bpf_trace_printk("error");
}
*/
//bpf_trace_printk("%p", data);

struct ethernet_t *ethernet = cursor_advance(cursor, sizeof(*ethernet));
struct ip_t *ip = cursor_advance(cursor,sizeof(*ip));
saddr = ip -> dst;
bpf_trace_printk("sss = %d", saddr);

bpf_trace_printk("Incoming packet!\n");
return -1;
}

"""

from ctypes import *
import sys
import socket
import os
import struct

bpf = BPF(text=bpf_text)

function_skb_matching = bpf.load_func("skb_matching", BPF.SOCKET_FILTER)

BPF.attach_raw_socket(function_skb_matching, INTERFACE)

print("=========================packet monitor=============================\n")
bpf.trace_print()

结果如下：

   handler27-3403  [010] ..s1 135652.183626: 0: sss = -1062731519       handler27-3403  [010] ..s1 135652.183642: 0: Incoming packet!!
   handler27-3403  [010] ..s1 135652.183691: 0: sss = -1062731518       handler27-3403  [010] ..s1 135652.183695: 0: Incoming packet!!
      <idle>-0     [010] ..s. 135653.184712: 0: sss = -1062731519          <idle>-0     [010] ..s. 135653.184728: 0: Incoming packet!!
      <idle>-0     [010] ..s. 135653.184759: 0: sss = -1062731518          <idle>-0     [010] ..s. 135653.184760: 0: Incoming packet!!
      <idle>-0     [010] ..s. 135654.205715: 0: sss = -1062731519          <idle>-0     [010] ..s. 135654.205734: 0: Incoming packet!!
      <idle>-0     [010] ..s. 135654.205765: 0: sss = -1062731518          <idle>-0     [010] ..s. 135654.205766: 0: Incoming packet!!
      <idle>-0     [010] ..s. 135655.229752: 0: sss = -1062731519          <idle>-0     [010] ..s. 135655.229771: 0: Incoming packet!!
      <idle>-0     [010] ..s. 135655.229802: 0: sss = -1062731518          <idle>-0     [010] ..s. 135655.229802: 0: Incoming packet!!
      <idle>-0     [010] ..s. 135656.253777: 0: sss = -1062731519          <idle>-0     [010] ..s. 135656.253796: 0: Incoming packet!!
      <idle>-0     [010] ..s. 135656.253827: 0: sss = -1062731518          <idle>-0     [010] ..s. 135656.253828: 0: Incoming packet!!
      <idle>-0     [010] ..s. 135657.194068: 0: sss = 16842752          <idle>-0     [010] ..s. 135657.194084: 0: Incoming packet!!
   handler27-3403  [010] ..s1 135657.195105: 0: sss = 16908309       handler27-3403  [010] ..s1 135657.195111: 0: Incoming packet!!
      <idle>-0     [010] ..s. 135657.213711: 0: sss = 16908288          <idle>-0     [010] ..s. 135657.213727: 0: Incoming packet!!
      <idle>-0     [010] ..s. 135657.213741: 0: sss = 16842773          <idle>-0     [010] ..s. 135657.213742: 0: Incoming packet!!
      <idle>-0     [010] ..s. 135657.277815: 0: sss = -1062731519          <idle>-0     [010] ..s. 135657.277832: 0: Incoming packet!!
      <idle>-0     [010] ..s. 135657.277860: 0: sss = -1062731518          <idle>-0     [010] ..s. 135657.277861: 0: Incoming packet!!

Answer 1

这些数字是您的 IP 地址，采用十进制格式。 例如，如果我在一个终端中启动您的脚本，同时在另一个终端中 ping 8.8.8.8，我得到：

term1$ ping 8.8.8.8
PING 8.8.8.8 (8.8.8.8) 56(84) bytes of data.
64 bytes from 8.8.8.8: icmp_seq=1 ttl=52 time=9.80 ms
[...]

term2$ python test.py
[...]
            ping-6545  [004] ....  1876.984747: 0: sss = 134744072            ping-6545  [004] ....  1876.984763: 0: Incoming packet!
[...]

号码134744072对应IP8.8.8.8（可以使用在线decimal-to-IP or decimal-to-hex转换器查看）。

您可以将这些数字转换为通常的 IP 表示形式，例如 Python 侧的 IPAddress（参见 bcc 的示例 tunnel_monitor )，但你必须使用 perf 环形缓冲区或映射将数据从内核端传输到用户空间，Python 端。

eBPF 数据包过滤器没有给我正确的数据

eBPF packet filter not giving me correct data

bpf

ebpf

bcc-bpf