1// SPDX-License-Identifier: GPL-2.0-only
  2#include "vmlinux.h"
  3#include <bpf/bpf_helpers.h>
  4#include <bpf/bpf_endian.h>
  5#include "bpf_tracing_net.h"
  6
  7#define NF_DROP			0
  8#define NF_ACCEPT		1
  9#define ETH_P_IP		0x0800
 10#define ETH_P_IPV6		0x86DD
 11#define IP_MF			0x2000
 12#define IP_OFFSET		0x1FFF
 13#define NEXTHDR_FRAGMENT	44
 14
 15extern int bpf_dynptr_from_skb(struct sk_buff *skb, __u64 flags,
 16			      struct bpf_dynptr *ptr__uninit) __ksym;
 17extern void *bpf_dynptr_slice(const struct bpf_dynptr *ptr, uint32_t offset,
 18			      void *buffer, uint32_t buffer__sz) __ksym;
 19
 20volatile int shootdowns = 0;
 21
 22static bool is_frag_v4(struct iphdr *iph)
 23{
 24	int offset;
 25	int flags;
 26
 27	offset = bpf_ntohs(iph->frag_off);
 28	flags = offset & ~IP_OFFSET;
 29	offset &= IP_OFFSET;
 30	offset <<= 3;
 31
 32	return (flags & IP_MF) || offset;
 33}
 34
 35static bool is_frag_v6(struct ipv6hdr *ip6h)
 36{
 37	/* Simplifying assumption that there are no extension headers
 38	 * between fixed header and fragmentation header. This assumption
 39	 * is only valid in this test case. It saves us the hassle of
 40	 * searching all potential extension headers.
 41	 */
 42	return ip6h->nexthdr == NEXTHDR_FRAGMENT;
 43}
 44
 45static int handle_v4(struct sk_buff *skb)
 46{
 47	struct bpf_dynptr ptr;
 48	u8 iph_buf[20] = {};
 49	struct iphdr *iph;
 50
 51	if (bpf_dynptr_from_skb(skb, 0, &ptr))
 52		return NF_DROP;
 53
 54	iph = bpf_dynptr_slice(&ptr, 0, iph_buf, sizeof(iph_buf));
 55	if (!iph)
 56		return NF_DROP;
 57
 58	/* Shootdown any frags */
 59	if (is_frag_v4(iph)) {
 60		shootdowns++;
 61		return NF_DROP;
 62	}
 63
 64	return NF_ACCEPT;
 65}
 66
 67static int handle_v6(struct sk_buff *skb)
 68{
 69	struct bpf_dynptr ptr;
 70	struct ipv6hdr *ip6h;
 71	u8 ip6h_buf[40] = {};
 72
 73	if (bpf_dynptr_from_skb(skb, 0, &ptr))
 74		return NF_DROP;
 75
 76	ip6h = bpf_dynptr_slice(&ptr, 0, ip6h_buf, sizeof(ip6h_buf));
 77	if (!ip6h)
 78		return NF_DROP;
 79
 80	/* Shootdown any frags */
 81	if (is_frag_v6(ip6h)) {
 82		shootdowns++;
 83		return NF_DROP;
 84	}
 85
 86	return NF_ACCEPT;
 87}
 88
 89SEC("netfilter")
 90int defrag(struct bpf_nf_ctx *ctx)
 91{
 92	struct sk_buff *skb = ctx->skb;
 93
 94	switch (bpf_ntohs(skb->protocol)) {
 95	case ETH_P_IP:
 96		return handle_v4(skb);
 97	case ETH_P_IPV6:
 98		return handle_v6(skb);
 99	default:
100		return NF_ACCEPT;
101	}
102}
103
104char _license[] SEC("license") = "GPL";