samples/bpf/tcp_tos_reflect_kern.c

0001 // SPDX-License-Identifier: GPL-2.0
0002 /*
0003  * Copyright (c) 2018 Facebook
0004  *
0005  * BPF program to automatically reflect TOS option from received syn packet
0006  *
0007  * Use "bpftool cgroup attach $cg sock_ops $prog" to load this BPF program.
0008  */
0009
0010 #include <uapi/linux/bpf.h>
0011 #include <uapi/linux/tcp.h>
0012 #include <uapi/linux/if_ether.h>
0013 #include <uapi/linux/if_packet.h>
0014 #include <uapi/linux/ip.h>
0015 #include <uapi/linux/ipv6.h>
0016 #include <uapi/linux/in.h>
0017 #include <linux/socket.h>
0018 #include <bpf/bpf_helpers.h>
0019 #include <bpf/bpf_endian.h>
0020
0021 #define DEBUG 1
0022
0023 SEC("sockops")
0024 int bpf_basertt(struct bpf_sock_ops *skops)
0025 {
0026     char header[sizeof(struct ipv6hdr)];
0027     struct ipv6hdr *hdr6;
0028     struct iphdr *hdr;
0029     int hdr_size = 0;
0030     int save_syn = 1;
0031     int tos = 0;
0032     int rv = 0;
0033     int op;
0034
0035     op = (int) skops->op;
0036
0037 #ifdef DEBUG
0038     bpf_printk("BPF command: %d\n", op);
0039 #endif
0040     switch (op) {
0041     case BPF_SOCK_OPS_TCP_LISTEN_CB:
0042         rv = bpf_setsockopt(skops, SOL_TCP, TCP_SAVE_SYN,
0043                    &save_syn, sizeof(save_syn));
0044         break;
0045     case BPF_SOCK_OPS_PASSIVE_ESTABLISHED_CB:
0046         if (skops->family == AF_INET)
0047             hdr_size = sizeof(struct iphdr);
0048         else
0049             hdr_size = sizeof(struct ipv6hdr);
0050         rv = bpf_getsockopt(skops, SOL_TCP, TCP_SAVED_SYN,
0051                     header, hdr_size);
0052         if (!rv) {
0053             if (skops->family == AF_INET) {
0054                 hdr = (struct iphdr *) header;
0055                 tos = hdr->tos;
0056                 if (tos != 0)
0057                     bpf_setsockopt(skops, SOL_IP, IP_TOS,
0058                                &tos, sizeof(tos));
0059             } else {
0060                 hdr6 = (struct ipv6hdr *) header;
0061                 tos = ((hdr6->priority) << 4 |
0062                        (hdr6->flow_lbl[0]) >>  4);
0063                 if (tos)
0064                     bpf_setsockopt(skops, SOL_IPV6,
0065                                IPV6_TCLASS,
0066                                &tos, sizeof(tos));
0067             }
0068             rv = 0;
0069         }
0070         break;
0071     default:
0072         rv = -1;
0073     }
0074 #ifdef DEBUG
0075     bpf_printk("Returning %d\n", rv);
0076 #endif
0077     skops->reply = rv;
0078     return 1;
0079 }
0080 char _license[] SEC("license") = "GPL";