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 
15 extern int bpf_dynptr_from_skb(struct sk_buff *skb, __u64 flags,
16 			      struct bpf_dynptr *ptr__uninit) __ksym;
17 extern void *bpf_dynptr_slice(const struct bpf_dynptr *ptr, uint32_t offset,
18 			      void *buffer, uint32_t buffer__sz) __ksym;
19 
20 volatile int shootdowns = 0;
21 
22 static 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 
35 static 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 
45 static 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 
67 static 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 
89 SEC("netfilter")
90 int 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 
104 char _license[] SEC("license") = "GPL";
105