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tcpdrop.py
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tcpdrop.py
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#!/usr/bin/python
# @lint-avoid-python-3-compatibility-imports
#
# tcpdrop Trace TCP kernel-dropped packets/segments.
# For Linux, uses BCC, eBPF. Embedded C.
#
# This provides information such as packet details, socket state, and kernel
# stack trace for packets/segments that were dropped via tcp_drop().
#
# USAGE: tcpdrop [-4 | -6] [-h]
#
# This uses dynamic tracing of kernel functions, and will need to be updated
# to match kernel changes.
#
# Copyright 2018 Netflix, Inc.
# Licensed under the Apache License, Version 2.0 (the "License")
#
# 30-May-2018 Brendan Gregg Created this.
from __future__ import print_function
from bcc import BPF
import argparse
from time import strftime
from socket import inet_ntop, AF_INET, AF_INET6
from struct import pack
from time import sleep
from bcc import tcp
# arguments
examples = """examples:
./tcpdrop # trace kernel TCP drops
./tcpdrop -4 # trace IPv4 family only
./tcpdrop -6 # trace IPv6 family only
"""
parser = argparse.ArgumentParser(
description="Trace TCP drops by the kernel",
formatter_class=argparse.RawDescriptionHelpFormatter,
epilog=examples)
group = parser.add_mutually_exclusive_group()
group.add_argument("-4", "--ipv4", action="store_true",
help="trace IPv4 family only")
group.add_argument("-6", "--ipv6", action="store_true",
help="trace IPv6 family only")
parser.add_argument("--ebpf", action="store_true",
help=argparse.SUPPRESS)
args = parser.parse_args()
debug = 0
# define BPF program
bpf_text = """
#include <uapi/linux/ptrace.h>
#include <uapi/linux/tcp.h>
#include <uapi/linux/ip.h>
#include <net/sock.h>
#include <bcc/proto.h>
BPF_STACK_TRACE(stack_traces, 1024);
// separate data structs for ipv4 and ipv6
struct ipv4_data_t {
u32 pid;
u64 ip;
u32 saddr;
u32 daddr;
u16 sport;
u16 dport;
u8 state;
u8 tcpflags;
u32 stack_id;
};
BPF_PERF_OUTPUT(ipv4_events);
struct ipv6_data_t {
u32 pid;
u64 ip;
unsigned __int128 saddr;
unsigned __int128 daddr;
u16 sport;
u16 dport;
u8 state;
u8 tcpflags;
u32 stack_id;
};
BPF_PERF_OUTPUT(ipv6_events);
static struct tcphdr *skb_to_tcphdr(const struct sk_buff *skb)
{
// unstable API. verify logic in tcp_hdr() -> skb_transport_header().
return (struct tcphdr *)(skb->head + skb->transport_header);
}
static inline struct iphdr *skb_to_iphdr(const struct sk_buff *skb)
{
// unstable API. verify logic in ip_hdr() -> skb_network_header().
return (struct iphdr *)(skb->head + skb->network_header);
}
// from include/net/tcp.h:
#ifndef tcp_flag_byte
#define tcp_flag_byte(th) (((u_int8_t *)th)[13])
#endif
int trace_tcp_drop(struct pt_regs *ctx, struct sock *sk, struct sk_buff *skb)
{
if (sk == NULL)
return 0;
u32 pid = bpf_get_current_pid_tgid() >> 32;
// pull in details from the packet headers and the sock struct
u16 family = sk->__sk_common.skc_family;
char state = sk->__sk_common.skc_state;
u16 sport = 0, dport = 0;
struct tcphdr *tcp = skb_to_tcphdr(skb);
struct iphdr *ip = skb_to_iphdr(skb);
u8 tcpflags = ((u_int8_t *)tcp)[13];
sport = tcp->source;
dport = tcp->dest;
sport = ntohs(sport);
dport = ntohs(dport);
FILTER_FAMILY
if (family == AF_INET) {
struct ipv4_data_t data4 = {};
data4.pid = pid;
data4.ip = 4;
data4.saddr = ip->saddr;
data4.daddr = ip->daddr;
data4.dport = dport;
data4.sport = sport;
data4.state = state;
data4.tcpflags = tcpflags;
data4.stack_id = stack_traces.get_stackid(ctx, 0);
ipv4_events.perf_submit(ctx, &data4, sizeof(data4));
} else if (family == AF_INET6) {
struct ipv6_data_t data6 = {};
data6.pid = pid;
data6.ip = 6;
// The remote address (skc_v6_daddr) was the source
bpf_probe_read_kernel(&data6.saddr, sizeof(data6.saddr),
sk->__sk_common.skc_v6_daddr.in6_u.u6_addr32);
// The local address (skc_v6_rcv_saddr) was the destination
bpf_probe_read_kernel(&data6.daddr, sizeof(data6.daddr),
sk->__sk_common.skc_v6_rcv_saddr.in6_u.u6_addr32);
data6.dport = dport;
data6.sport = sport;
data6.state = state;
data6.tcpflags = tcpflags;
data6.stack_id = stack_traces.get_stackid(ctx, 0);
ipv6_events.perf_submit(ctx, &data6, sizeof(data6));
}
// else drop
return 0;
}
"""
if debug or args.ebpf:
print(bpf_text)
if args.ebpf:
exit()
if args.ipv4:
bpf_text = bpf_text.replace('FILTER_FAMILY',
'if (family != AF_INET) { return 0; }')
elif args.ipv6:
bpf_text = bpf_text.replace('FILTER_FAMILY',
'if (family != AF_INET6) { return 0; }')
else:
bpf_text = bpf_text.replace('FILTER_FAMILY', '')
# process event
def print_ipv4_event(cpu, data, size):
event = b["ipv4_events"].event(data)
print("%-8s %-7d %-2d %-20s > %-20s %s (%s)" % (
strftime("%H:%M:%S"), event.pid, event.ip,
"%s:%d" % (inet_ntop(AF_INET, pack('I', event.saddr)), event.sport),
"%s:%s" % (inet_ntop(AF_INET, pack('I', event.daddr)), event.dport),
tcp.tcpstate[event.state], tcp.flags2str(event.tcpflags)))
for addr in stack_traces.walk(event.stack_id):
sym = b.ksym(addr, show_offset=True)
print("\t%s" % sym)
print("")
def print_ipv6_event(cpu, data, size):
event = b["ipv6_events"].event(data)
print("%-8s %-7d %-2d %-20s > %-20s %s (%s)" % (
strftime("%H:%M:%S"), event.pid, event.ip,
"%s:%d" % (inet_ntop(AF_INET6, event.saddr), event.sport),
"%s:%d" % (inet_ntop(AF_INET6, event.daddr), event.dport),
tcp.tcpstate[event.state], tcp.flags2str(event.tcpflags)))
for addr in stack_traces.walk(event.stack_id):
sym = b.ksym(addr, show_offset=True)
print("\t%s" % sym)
print("")
# initialize BPF
b = BPF(text=bpf_text)
if b.get_kprobe_functions(b"tcp_drop"):
b.attach_kprobe(event="tcp_drop", fn_name="trace_tcp_drop")
else:
print("ERROR: tcp_drop() kernel function not found or traceable. "
"Older kernel versions not supported.")
exit()
stack_traces = b.get_table("stack_traces")
# header
print("%-8s %-7s %-2s %-20s > %-20s %s (%s)" % ("TIME", "PID", "IP",
"SADDR:SPORT", "DADDR:DPORT", "STATE", "FLAGS"))
# read events
b["ipv4_events"].open_perf_buffer(print_ipv4_event)
b["ipv6_events"].open_perf_buffer(print_ipv6_event)
while 1:
try:
b.perf_buffer_poll()
except KeyboardInterrupt:
exit()