1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 | // 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"; |