105 lines
2.2 KiB
C
105 lines
2.2 KiB
C
// SPDX-License-Identifier: GPL-2.0-only
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#include "vmlinux.h"
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#include <bpf/bpf_helpers.h>
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#include <bpf/bpf_endian.h>
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#include "bpf_tracing_net.h"
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#define NF_DROP 0
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#define NF_ACCEPT 1
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#define ETH_P_IP 0x0800
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#define ETH_P_IPV6 0x86DD
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#define IP_MF 0x2000
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#define IP_OFFSET 0x1FFF
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#define NEXTHDR_FRAGMENT 44
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extern int bpf_dynptr_from_skb(struct __sk_buff *skb, __u64 flags,
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struct bpf_dynptr *ptr__uninit) __ksym;
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extern void *bpf_dynptr_slice(const struct bpf_dynptr *ptr, uint32_t offset,
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void *buffer, uint32_t buffer__sz) __ksym;
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volatile int shootdowns = 0;
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static bool is_frag_v4(struct iphdr *iph)
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{
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int offset;
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int flags;
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offset = bpf_ntohs(iph->frag_off);
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flags = offset & ~IP_OFFSET;
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offset &= IP_OFFSET;
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offset <<= 3;
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return (flags & IP_MF) || offset;
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}
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static bool is_frag_v6(struct ipv6hdr *ip6h)
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{
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/* Simplifying assumption that there are no extension headers
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* between fixed header and fragmentation header. This assumption
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* is only valid in this test case. It saves us the hassle of
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* searching all potential extension headers.
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*/
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return ip6h->nexthdr == NEXTHDR_FRAGMENT;
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}
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static int handle_v4(struct __sk_buff *skb)
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{
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struct bpf_dynptr ptr;
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u8 iph_buf[20] = {};
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struct iphdr *iph;
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if (bpf_dynptr_from_skb(skb, 0, &ptr))
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return NF_DROP;
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iph = bpf_dynptr_slice(&ptr, 0, iph_buf, sizeof(iph_buf));
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if (!iph)
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return NF_DROP;
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/* Shootdown any frags */
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if (is_frag_v4(iph)) {
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shootdowns++;
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return NF_DROP;
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}
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return NF_ACCEPT;
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}
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static int handle_v6(struct __sk_buff *skb)
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{
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struct bpf_dynptr ptr;
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struct ipv6hdr *ip6h;
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u8 ip6h_buf[40] = {};
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if (bpf_dynptr_from_skb(skb, 0, &ptr))
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return NF_DROP;
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ip6h = bpf_dynptr_slice(&ptr, 0, ip6h_buf, sizeof(ip6h_buf));
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if (!ip6h)
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return NF_DROP;
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/* Shootdown any frags */
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if (is_frag_v6(ip6h)) {
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shootdowns++;
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return NF_DROP;
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}
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return NF_ACCEPT;
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}
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SEC("netfilter")
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int defrag(struct bpf_nf_ctx *ctx)
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{
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struct __sk_buff *skb = (struct __sk_buff *)ctx->skb;
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switch (bpf_ntohs(ctx->skb->protocol)) {
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case ETH_P_IP:
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return handle_v4(skb);
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case ETH_P_IPV6:
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return handle_v6(skb);
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default:
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return NF_ACCEPT;
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}
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}
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char _license[] SEC("license") = "GPL";
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