So I've been trying to see if I could attach a eBPF packet filter to a network interface, enp32s0np1. I'm trying to catch all the incoming sender IP addresses. However, running the below code gives me weird reaction. Instead of seeing the sender IP address, I see some random numbers filled in.
Here's the code :
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()
and here is the result :
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!!
Those numbers are your IP addresses, in decimal format. For example, if I launch your script in one terminal while I ping 8.8.8.8 in the other, I get:
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!
[...]
The number 134744072 corresponds to IP 8.8.8.8 (you can use online decimal-to-IP or decimal-to-hex converters to check that).
You can convert these numbers to the usual IP representation with e.g., IPAddress on the Python side (see bcc's example tunnel_monitor), but you'll have to use a perf ring buffer or a map to transmit data from the kernel side to the userspace, Python side.