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// SPDX-License-Identifier: GPL-2.0
/* This logic is lifted from a real-world use case of packet parsing, used in
* the open source library katran, a layer 4 load balancer.
*
* This test demonstrates how to parse packet contents using dynptrs. The
* original code (parsing without dynptrs) can be found in test_parse_tcp_hdr_opt.c
*/
#include <linux/bpf.h>
#include <bpf/bpf_helpers.h>
#include <linux/tcp.h>
#include <stdbool.h>
#include <linux/ipv6.h>
#include <linux/if_ether.h>
#include "test_tcp_hdr_options.h"
#include "bpf_kfuncs.h"
char _license[] SEC("license") = "GPL";
/* Kind number used for experiments */
const __u32 tcp_hdr_opt_kind_tpr = 0xFD;
/* Length of the tcp header option */
const __u32 tcp_hdr_opt_len_tpr = 6;
/* maximum number of header options to check to lookup server_id */
const __u32 tcp_hdr_opt_max_opt_checks = 15;
__u32 server_id;
static int parse_hdr_opt(struct bpf_dynptr *ptr, __u32 *off, __u8 *hdr_bytes_remaining,
__u32 *server_id)
{
__u8 kind, hdr_len;
__u8 buffer[sizeof(kind) + sizeof(hdr_len) + sizeof(*server_id)];
__u8 *data;
__builtin_memset(buffer, 0, sizeof(buffer));
data = bpf_dynptr_slice(ptr, *off, buffer, sizeof(buffer));
if (!data)
return -1;
kind = data[0];
if (kind == TCPOPT_EOL)
return -1;
if (kind == TCPOPT_NOP) {
*off += 1;
*hdr_bytes_remaining -= 1;
return 0;
}
if (*hdr_bytes_remaining < 2)
return -1;
hdr_len = data[1];
if (hdr_len > *hdr_bytes_remaining)
return -1;
if (kind == tcp_hdr_opt_kind_tpr) {
if (hdr_len != tcp_hdr_opt_len_tpr)
return -1;
__builtin_memcpy(server_id, (__u32 *)(data + 2), sizeof(*server_id));
return 1;
}
*off += hdr_len;
*hdr_bytes_remaining -= hdr_len;
return 0;
}
SEC("xdp")
int xdp_ingress_v6(struct xdp_md *xdp)
{
__u8 buffer[sizeof(struct tcphdr)] = {};
__u8 hdr_bytes_remaining;
struct tcphdr *tcp_hdr;
__u8 tcp_hdr_opt_len;
int err = 0;
__u32 off;
struct bpf_dynptr ptr;
bpf_dynptr_from_xdp(xdp, 0, &ptr);
off = sizeof(struct ethhdr) + sizeof(struct ipv6hdr);
tcp_hdr = bpf_dynptr_slice(&ptr, off, buffer, sizeof(buffer));
if (!tcp_hdr)
return XDP_DROP;
tcp_hdr_opt_len = (tcp_hdr->doff * 4) - sizeof(struct tcphdr);
if (tcp_hdr_opt_len < tcp_hdr_opt_len_tpr)
return XDP_DROP;
hdr_bytes_remaining = tcp_hdr_opt_len;
off += sizeof(struct tcphdr);
/* max number of bytes of options in tcp header is 40 bytes */
for (int i = 0; i < tcp_hdr_opt_max_opt_checks; i++) {
err = parse_hdr_opt(&ptr, &off, &hdr_bytes_remaining, &server_id);
if (err || !hdr_bytes_remaining)
break;
}
if (!server_id)
return XDP_DROP;
return XDP_PASS;
}
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