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// SPDX-License-Identifier: GPL-2.0
/* This parsing logic is taken from the open source library katran, a layer 4
* load balancer.
*
* This code logic using dynptrs can be found in test_parse_tcp_hdr_opt_dynptr.c
*
* https://github.com/facebookincubator/katran/blob/main/katran/lib/bpf/pckt_parsing.h
*/
#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"
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;
struct hdr_opt_state {
__u32 server_id;
__u8 byte_offset;
__u8 hdr_bytes_remaining;
};
static int parse_hdr_opt(const struct xdp_md *xdp, struct hdr_opt_state *state)
{
const void *data = (void *)(long)xdp->data;
const void *data_end = (void *)(long)xdp->data_end;
__u8 *tcp_opt, kind, hdr_len;
tcp_opt = (__u8 *)(data + state->byte_offset);
if (tcp_opt + 1 > data_end)
return -1;
kind = tcp_opt[0];
if (kind == TCPOPT_EOL)
return -1;
if (kind == TCPOPT_NOP) {
state->hdr_bytes_remaining--;
state->byte_offset++;
return 0;
}
if (state->hdr_bytes_remaining < 2 ||
tcp_opt + sizeof(__u8) + sizeof(__u8) > data_end)
return -1;
hdr_len = tcp_opt[1];
if (hdr_len > state->hdr_bytes_remaining)
return -1;
if (kind == tcp_hdr_opt_kind_tpr) {
if (hdr_len != tcp_hdr_opt_len_tpr)
return -1;
if (tcp_opt + tcp_hdr_opt_len_tpr > data_end)
return -1;
state->server_id = *(__u32 *)&tcp_opt[2];
return 1;
}
state->hdr_bytes_remaining -= hdr_len;
state->byte_offset += hdr_len;
return 0;
}
SEC("xdp")
int xdp_ingress_v6(struct xdp_md *xdp)
{
const void *data = (void *)(long)xdp->data;
const void *data_end = (void *)(long)xdp->data_end;
struct hdr_opt_state opt_state = {};
__u8 tcp_hdr_opt_len = 0;
struct tcphdr *tcp_hdr;
__u64 tcp_offset = 0;
int err;
tcp_offset = sizeof(struct ethhdr) + sizeof(struct ipv6hdr);
tcp_hdr = (struct tcphdr *)(data + tcp_offset);
if (tcp_hdr + 1 > data_end)
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;
opt_state.hdr_bytes_remaining = tcp_hdr_opt_len;
opt_state.byte_offset = sizeof(struct tcphdr) + tcp_offset;
/* 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(xdp, &opt_state);
if (err || !opt_state.hdr_bytes_remaining)
break;
}
if (!opt_state.server_id)
return XDP_DROP;
server_id = opt_state.server_id;
return XDP_PASS;
}
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