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// SPDX-License-Identifier: GPL-2.0
#include "vmlinux.h"
#include <bpf/bpf_helpers.h>
#include <bpf/bpf_endian.h>
/* 127.0.0.1 in host byte order */
#define SERVER_IP 0x7F000001
/* ::1 in host byte order (last 32-bit word) */
#define SERVER_IP6_LO 0x00000001
__u16 server_port = 0;
int unreach_type = 0;
int unreach_code = 0;
int kfunc_ret = -1;
int target_pid = -1;
unsigned int rec_count = 0;
int rec_kfunc_rets[] = { -1, -1 };
SEC("cgroup_skb/egress")
int egress(struct __sk_buff *skb)
{
void *data = (void *)(long)skb->data;
void *data_end = (void *)(long)skb->data_end;
struct iphdr *iph;
struct ipv6hdr *ip6h;
struct tcphdr *tcph;
__u8 version;
if (data + 1 > data_end)
return SK_PASS;
version = (*((__u8 *)data)) >> 4;
if (version == 4) {
iph = data;
if ((void *)(iph + 1) > data_end ||
iph->protocol != IPPROTO_TCP ||
iph->daddr != bpf_htonl(SERVER_IP))
return SK_PASS;
tcph = (void *)iph + iph->ihl * 4;
if ((void *)(tcph + 1) > data_end ||
tcph->dest != bpf_htons(server_port))
return SK_PASS;
} else if (version == 6) {
ip6h = data;
if ((void *)(ip6h + 1) > data_end ||
ip6h->nexthdr != IPPROTO_TCP)
return SK_PASS;
if (ip6h->daddr.in6_u.u6_addr32[0] != 0 ||
ip6h->daddr.in6_u.u6_addr32[1] != 0 ||
ip6h->daddr.in6_u.u6_addr32[2] != 0 ||
ip6h->daddr.in6_u.u6_addr32[3] != bpf_htonl(SERVER_IP6_LO))
return SK_PASS;
tcph = (void *)(ip6h + 1);
if ((void *)(tcph + 1) > data_end ||
tcph->dest != bpf_htons(server_port))
return SK_PASS;
} else {
return SK_PASS;
}
kfunc_ret = bpf_icmp_send(skb, unreach_type, unreach_code);
return SK_DROP;
}
SEC("cgroup_skb/egress")
int recursion(struct __sk_buff *skb)
{
void *data = (void *)(long)skb->data;
void *data_end = (void *)(long)skb->data_end;
struct icmphdr *icmph;
struct tcphdr *tcph;
struct iphdr *iph;
int ret;
if ((bpf_get_current_pid_tgid() >> 32) != target_pid)
return SK_PASS;
iph = data;
if ((void *)(iph + 1) > data_end || iph->version != 4)
return SK_PASS;
if (iph->daddr != bpf_htonl(SERVER_IP))
return SK_PASS;
if (iph->protocol == IPPROTO_TCP) {
tcph = (void *)iph + iph->ihl * 4;
if ((void *)(tcph + 1) > data_end ||
tcph->dest != bpf_htons(server_port))
return SK_PASS;
} else if (iph->protocol == IPPROTO_ICMP) {
icmph = (void *)iph + iph->ihl * 4;
if ((void *)(icmph + 1) > data_end ||
icmph->type != unreach_type || icmph->code != unreach_code)
return SK_PASS;
} else {
return SK_PASS;
}
/*
* This call will provoke a recursion: the ICMP packet generated by the
* kfunc will re-trigger this program since we are in the root cgroup in
* which the kernel ICMP socket belongs. However when re-entering the
* kfunc, it should return EBUSY.
*/
ret = bpf_icmp_send(skb, unreach_type, unreach_code);
rec_kfunc_rets[rec_count & 1] = ret;
__sync_fetch_and_add(&rec_count, 1);
/* Let the first ICMP error message pass */
if (iph->protocol == IPPROTO_ICMP)
return SK_PASS;
return SK_DROP;
}
char LICENSE[] SEC("license") = "Dual BSD/GPL";
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