Steven Polley
b318bcb3c1
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Thank you code aesthetic
75 lines
1.8 KiB
C
75 lines
1.8 KiB
C
/*
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Copyright © 2024 Steven Polley <himself@stevenpolley.net>
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*/
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//go:build ignore
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#include "vmlinux.h"
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#include "bpf_endian.h"
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#include <bpf/bpf_helpers.h>
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char __license[] SEC("license") = "BSD";
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// representation of knock data that gets sent to userspace
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struct knock_data {
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__u32 srcip; // 4 bytes
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__u16 dstport; // 2 bytes
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__u16 pad; // required padding - struct must be multiple of 4 bytes
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};
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// ring buffer used to send data to userspace
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struct {
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__uint(type, BPF_MAP_TYPE_RINGBUF);
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__uint(max_entries, 1 << 24);
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} rb SEC(".maps");
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// force emitting struct event into the ELF
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const struct knock_data *unused __attribute__((unused));
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// hook into xpress data path attach point
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SEC("xdp")
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int xdp_prog_func(struct xdp_md *ctx) {
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// xdp gives us the raw frame with no structures, it must be parsed
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void *data = (void *)(long)ctx->data;
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void *data_end = (void *)(long)ctx->data_end;
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// A knock should not contain any data
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if (data_end - data > 60) {
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return XDP_PASS;
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}
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// parse ethernet header
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struct ethhdr *eth = data;
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if ((void *)eth + sizeof(*eth) > data_end) {
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return XDP_PASS;
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}
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// parse IP header
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struct iphdr *ip = data + sizeof(*eth);
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if ((void *)ip + sizeof(*ip) > data_end) {
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return XDP_PASS;
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}
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// Ensure IP header protocol field is UDP (protocol 17)
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if (ip->protocol != IPPROTO_UDP) {
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return XDP_PASS;
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}
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// parse UDP header
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struct udphdr *udp = (void *)ip + sizeof(*ip);
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if ((void *)udp + sizeof(*udp) > data_end) {
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return XDP_PASS;
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}
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// pack into knock structure and send to userspace
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struct knock_data knock = {
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.srcip = bpf_ntohl(ip->saddr),
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.dstport = bpf_htons(udp->dest),
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.pad = 0
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};
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bpf_ringbuf_output(&rb, &knock, sizeof(knock), BPF_RB_FORCE_WAKEUP);
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// We send everything to XDP_PASS
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return XDP_PASS;
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}
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