samples/bpf/tcp_tos_reflect_kern.c

   1 // SPDX-License-Identifier: GPL-2.0
   2 /*
   3  * Copyright (c) 2018 Facebook
   4  *
   5  * BPF program to automatically reflect TOS option from received syn packet
   6  *
   7  * Use "bpftool cgroup attach $cg sock_ops $prog" to load this BPF program.
   8  */
   9
  10 #include <uapi/linux/bpf.h>
  11 #include <uapi/linux/tcp.h>
  12 #include <uapi/linux/if_ether.h>
  13 #include <uapi/linux/if_packet.h>
  14 #include <uapi/linux/ip.h>
  15 #include <uapi/linux/ipv6.h>
  16 #include <uapi/linux/in.h>
  17 #include <linux/socket.h>
  18 #include "bpf_helpers.h"
  19 #include "bpf_endian.h"
  20
  21 #define DEBUG 1
  22
  23 #define bpf_printk(fmt, ...)                                    \
  24 ({                                                              \
  25                char ____fmt[] = fmt;                            \
  26                bpf_trace_printk(____fmt, sizeof(____fmt),       \
  27                                 ##__VA_ARGS__);                 \
  28 })
  29
  30 SEC("sockops")
  31 int bpf_basertt(struct bpf_sock_ops *skops)
  32 {
  33         char header[sizeof(struct ipv6hdr)];
  34         struct ipv6hdr *hdr6;
  35         struct iphdr *hdr;
  36         int hdr_size = 0;
  37         int save_syn = 1;
  38         int tos = 0;
  39         int rv = 0;
  40         int op;
  41
  42         op = (int) skops->op;
  43
  44 #ifdef DEBUG
  45         bpf_printk("BPF command: %d\n", op);
  46 #endif
  47         switch (op) {
  48         case BPF_SOCK_OPS_TCP_LISTEN_CB:
  49                 rv = bpf_setsockopt(skops, SOL_TCP, TCP_SAVE_SYN,
  50                                    &save_syn, sizeof(save_syn));
  51                 break;
  52         case BPF_SOCK_OPS_PASSIVE_ESTABLISHED_CB:
  53                 if (skops->family == AF_INET)
  54                         hdr_size = sizeof(struct iphdr);
  55                 else
  56                         hdr_size = sizeof(struct ipv6hdr);
  57                 rv = bpf_getsockopt(skops, SOL_TCP, TCP_SAVED_SYN,
  58                                     header, hdr_size);
  59                 if (!rv) {
  60                         if (skops->family == AF_INET) {
  61                                 hdr = (struct iphdr *) header;
  62                                 tos = hdr->tos;
  63                                 if (tos != 0)
  64                                         bpf_setsockopt(skops, SOL_IP, IP_TOS,
  65                                                        &tos, sizeof(tos));
  66                         } else {
  67                                 hdr6 = (struct ipv6hdr *) header;
  68                                 tos = ((hdr6->priority) << 4 |
  69                                        (hdr6->flow_lbl[0]) >>  4);
  70                                 if (tos)
  71                                         bpf_setsockopt(skops, SOL_IPV6,
  72                                                        IPV6_TCLASS,
  73                                                        &tos, sizeof(tos));
  74                         }
  75                         rv = 0;
  76                 }
  77                 break;
  78         default:
  79                 rv = -1;
  80         }
  81 #ifdef DEBUG
  82         bpf_printk("Returning %d\n", rv);
  83 #endif
  84         skops->reply = rv;
  85         return 1;
  86 }
  87 char _license[] SEC("license") = "GPL";