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 = (struct __sk_buff *)ctx->skb;
93
94 switch (bpf_ntohs(ctx->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
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