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